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Survival and establishment of mangrove propagules at tidal elevations beyond the landward margin of their distribution underlie continued existence of mangroves in response to sea-level rise. Yet few studies have empirically examined mangrove performance at higher intertidal positions (novel sites) into which mangroves disperse. We compared propagule establishment and seedling growth at 2 intertidal elevations for black mangroves Avicennia germinans displaying landward expansion. Propagule survival, establishment success, and growth rate of seedlings were monitored for 158 d during a reciprocal transplant experiment targeting 2 tidal elevations: one within the current niche of the mangrove population (LOW) and one representing marginal habitat where mangroves have begun migration upland (MID). We introduced propagules to 4 treatments: (1) originating (site of parent tree) at LOW, stranding at MID; (2) originating at MID, stranding at LOW; (3) and (4) stranding and originating at the same position (MID or LOW). Resident and transplant propagules of MID origin were 22 times more likely to die during the first 33 d than propagules of LOW origin. Resident and transplant propagules in MID positions were 6.5 times more likely to die over the first 33 d than individuals in LOW positions. After seedling establishment, no mortality was observed in LOW or MID positions. Thus, environmental conditions of novel intertidal areas into which black mangroves migrate had a greater deleterious impact on propagules than on seedlings. Identifying processes underlying success of mangroves introduced into novel environments, such as those operating as sea level rises, will require increased attention to the fate of propagules.

Using aerial imagery and GIS techniques, a retrospective study conducted fine-scale (1.0 m2 resolution) seagrass mapping to document the spatial heterogeneity within seagrass habitats previously mapped at a broad scale (0.202 ha resolution). Thirty randomly selected estuarine habitats in Tampa Bay, Florida, were manually interpreted and digitized using 0.3 m resolution imagery from 2004, 2006, and 2008. Seagrass patches and patterns of seagrass change were quantified at multiple levels of spatial organization and multiple temporal scales. Habitats classified as patchy seagrass were found to contain, on average, 52.7% less seagrass when mapped using the patch-based, fine-scale approach compared to broad-scale map data. In higher-resolution mapping, seagrass was increasingly differentiated from bare sediment and the amount of seagrass quantified within the study’s extent was reduced compared to broad-scale mapping, which included some bare area in estimates of seagrass cover. Additionally, fine-scale mapping detected the presence of seagrass on tidal flat habitat that was previously considered “unvegetated” in broad-scale mapping. These findings can be used to improve the definitions of broad-scale mapping classes and suggest the selection of smaller ratio digitizing scales when mapping complex or sparsely covered seagrass habitats. Overall, fine-scale mapping at a large spatial extent provided insights into the patterning and rate of seagrass gap formation and fragmentation, appears to be a reasonable method for local studies or resource disturbance assessments, and has potential applications as a training tool for further advancement of semi-automated classification techniques.

Kleptoplastic, sacoglossan sea slugs are some of the best known examples of specialist marine herbivores. However, while their chloroplast symbiosis (kleptoplasty) has been studied in many species, little is known about sacoglossan life histories or their seasonal and temporal variation in natural populations. Most sacoglossan species are associated with one or a few closely related algal species that provide the chloroplast source for the kleptoplastic association. Elysia papillosa, a small sacoglossan with a distribution ranging throughout the Caribbean to Florida, primarily feeds on the alga, Penicillus capitatus, although it has also been found on several additional species of algae. A yearlong field survey of E. papillosa in a rhizophytic algal bed in Tarpon Springs, FL, USA revealed a low density of slugs throughout the year except during April, when mean density sharply peaked to 7.0 ± 5.9 slugs (0.25 m2)−1 . Slugs were not found on any algae other than P. capitatus, except occasionally on P. lamourouxii, suggesting that the latter alga serves as a secondary chloroplast source for E. papillosa. The presence of slugs throughout the year implies a broad tolerance of both salinity and temperature although the peak numbers in April may indicate a physiological preference for warming spring temperatures and, perhaps, day length.

Globally, the conditions and time scales underlying coastal ecosystem recovery following disturbance remain poorly understood, and post-disturbance examples of resilience based on long-term studies are particularly rare. Here, we documented the recovery of a marine foundation species (turtlegrass) following a hypersalinity-associated die-off in Florida Bay, USA, one of the most spatially extensive mortality events for seagrass ecosystems on record. Based upon annual sampling over two decades, foundation species recovery across the landscape was demonstrated by two ecosystem responses: the range of turtlegrass biomass met or exceeded levels present prior to the die-off, and turtlegrass regained dominance of seagrass community structure. Unlike reports for most marine taxa, recovery followed without human intervention or reduction to anthropogenic impacts. Our long-term study revealed previously uncharted resilience in subtropical seagrass landscapes but warns that future persistence of the foundation species in this iconic ecosystem will depend upon the frequency and severity of drought-associated perturbation.

Identifying and quantifying the relevant properties of habitat structure that mediate predator-prey interactions remains a persistent challenge. Most previous studies investigate effects of structural density on trophic interactions and typically quantify refuge quality using one or two-dimensional metrics. Few consider spatial arrangement of components (i.e., orientation and shape) and often neglect to measure the total three-dimensional (3D) space available as refuge. This study tests whether the three-dimensionality of interstitial space, an attribute produced by the spatial arrangement of oyster (Crassostrea virginica) shells, impacts the foraging success of nektonic predators (primary blue crab, Callinectes sapidus) on mud crab prey (Eurypanopeus depressus) in field and mesocosm experiments. Interstices of 3D-printed shell mimics were manipulated by changing either their orientation (angle) or internal shape (crevice or channel). In both field and mesocosm experiments, under conditions of constant structural density, predator foraging success was influenced by 3D aspects of interstitial space. Proportional survivorship of tethered mud crabs differed significantly as 3D interstitial space varied by orientation, displaying decreasing prey survivorship as angle of orientation increased (0° = 0.76, 22.5° = 0.13, 45° = 0.0). Tethered prey survivorship was high when 3D interstitial space of mimics was modified by internal shape (crevice = 0.89, channel = 0.96) and these values did not differ significantly. In mesocosms, foraging success of blue crabs varied with 3D interstitial space as mean proportional survivorship (± SE) of mud crabs was significantly lower in 45° (0.27 ± 0.06) versus 0° (0.86 ± 0.04) orientations and for crevice (0.52 ± 0.11) versus channel shapes (0.95 ± 0.01). These results suggest that 3D aspects of interstitial space, which have direct relevance to refuge quality, can strongly influence foraging success in our oyster reef habitat. Our findings highlight the importance of spatial arrangement in mediating consumptive pathways in hard-structured habitats and demonstrate how quantifying the three-dimensionality of living space captures aspects of habitat structure that have been missing from previous empirical studies of trophic interactions and structural complexity. This article is protected by copyright. All rights reserved.

Seagrass restoration is a common tool for ecosystem service enhancement and compensatory mitigation for habitat loss. However, little is known about the long-term performance of these projects. We identified seagrass restoration projects by reviewing historic permitting documents, monitoring reports, and studies conducted in Florida, USA, most of which have not been cited previously in peer-reviewed literature. We then revisited 33 seagrass restorations ranging in age from 3 to 32 years to compare seagrass percent cover, species diversity, and community structure in restored and contemporary reference seagrass beds. We found that 88% of restoration projects continued to support seagrass and, overall, restored percent cover values were 37% lower than references. Community composition and seagrass percent cover differed from references in projects categorized as sediment modification and transplant restorations, whereas all vessel damage repair projects achieved reference condition. Seagrass diversity was similar between restored and reference beds, except for sediment modification projects, for which diversity was significantly lower than in reference beds. Results indicate that restored seagrass beds in Florida, once established, often exhibit long-term persistence. Our study highlights the benefit of identifying and surveying historic restorations to address knowledge gaps related to the performance and long-term fate of restored seagrass beds.

In Florida, resource use patterns by Armases cinereum (Armases), a highly abundant crab in coastal habitats, may serve as important indicators of habitat condition. Here we investigated feeding patterns of Armases in coastal palm scrub forest to intertidal mangrove forest transition zones (transitions) as well as the relationship between habitat disturbance and Armases' trophic position across three pairs of geographically separated populations in Tampa FL, USA. Each pair of sites represented an unmodified "natural" location as well as a "disturbed" location lacking upland terrestrial palm scrub forested habitat. Laboratory experiments established a baseline understanding of feeding preference of Armases offered strictly mangrove material as well as sources abundant at the transition. In-situ feeding behavior was examined using MixSIAR mixing models with δ13C and δ15N stable isotope tracers. Armases showed a strong preference for consuming partially-decomposed mangrove material from Avicennia germinans and an equally strong preference for Iva frutescens. Armases also displayed predatory behavior under laboratory conditions, confirming omnivory in the presence of mangrove material. Stable isotopes revealed a pattern of elevated trophic position of Armases in disturbed habitats over paired natural locations. Diet reconstruction provided coarse resolution of in-situ feeding and results show high spatial variation: in natural habitats, Armases appears to rely heavily upon upland plant material compared to disturbed habitats where it may consume more animal prey. Combined, these findings support that Armases trophic position and diet may indicate habitat quality in mangrove transitions in the southeastern United States.

We present evidence that the most recent redescription of Elysia patina Marcus, 1980, by Ortea et al. (2005) is incorrect. Instead, the redescribed characters used to classify E. patina exactly match those of Elysia papillosa Verrill, 1901. Therefore, Ortea et al.'s (2005) redescriptions of E. patina and E. papillosa should not be used.

Pu, R.; Bell, S., and English, D., 2015. Developing hyperspectral vegetation indices for identifying seagrass species and cover classes. Seagrass habitats are characteristic features of shallow waters worldwide and provide a variety of ecosystem functions. To date, few studies have evaluated the efficiency of spectral vegetation indices (VIs) for characterizing aquatic plants. Here we evaluate the use of in situ hyperspectral data and hyperspectral VIs for distinguishing among seagrass species and levels of percentage submerged aquatic vegetation (%SAV) cover in a subtropical shallow water setting. Analysis procedures include (1) retrieving bottom reflectance, (2) calculating correlation matrices of VIs with %SAV cover and F value matrices from analysis of variance among species, (3) testing the difference of VIs between levels of %SAV cover and between species, and (4) discriminating levels of %SAV cover and species by using linear discriminant analysis (LDA) and classification and regression tr...

Some seagrass meadows in coastal shallow waters have displayed large scale changes in seagrass spatial extent and hurricanes and/or tropical storms have been suggested as factors responsible for reduction in coverage. Taking advantage of the incidence of three tropical storms passing near a study site along the central west Florida coast within a two-month period in 2004, we evaluated whether satellite remote sensing techniques (Landsat 5 Thematic Mapper (TM) imagery) are useful for assessing dynamics of seagrass (=submerged aquatic vegetation: SAV) cover/abundance in response to these multiple disturbances. We also examined whether an image preprocessing procedure, which included water column correction, applied to the Landsat TM images could further improve the classification and mapping of detailed SAV coverage. We compared a historical set of Landsat TM images, acquired in Fall 2003 and Fall and late Summer 2005, which were processed to classify %SAV cover into five classes using a maximum likelihood classifier. Importantly, our experimental results demonstrated that the application of the image preprocessing procedures led to an overall accuracy 2–14% improvement in SAV classification due to water column correction compared to that currently reported in the literature when similar Landsat TM data are utilized. Based upon the classification results mapped from the TM images and as well as a similar classification of SAV interpreted from aerial photographs collected before and after the passage of these same storms, SAV coverage over the study areas was found to increase about 6% (integrating SAV losses and gains) by 2005/2006 in comparison to cover levels present prior to the repeated storm activity. We conclude that heavy rains during 2004 along with physical disturbance from gale force winds from the tropical storms/hurricanes did not produce any SAV bed loss at the study site that was sustained for more than one year after multiple storm passage.

The identity of food sources and feeding preferences of specialist herbivores have been commonly inferred from spatial associations between consumer and food items. However, such basic information for well-known marine herbivores, sacoglossans (sea slugs), and their algal diets remains disappointingly lacking, especially from field studies. The sacoglossan, Elysia clarki (Pierce et al. in Molluscan Res 26:23–38, 2006), is kleptoplastic and sequesters chloroplasts from algal food to photosynthesize, so DNA identification of sequestered chloroplasts was employed to verify the algal species fed upon by the slug across its geographic range. The molecular information on the algae consumed by E. clarki was combined with field surveys of slugs and algae in slug habitats in the Florida Keys in July and August of 2008 in order to evaluate whether the diet of this herbivore could be predicted based on its spatial association with algae in the field. A considerable mismatch between food availability and kleptoplast identity was recorded. E. clarki commonly occupied areas devoid of potential food and often contained symbiotic plastids from algal species different from those most frequently found in the surveyed habitats. In three of the four study sites, algal species present were poor predictors of slug diet. These findings suggest that the photosynthetic capability of E. clarki may release the slug from the constraint of requiring proximity to its food sources and may allow for the potential lack of spatial coupling between this herbivore and its algal food. This combination of field surveys and DNA barcoding provided critical and previously unavailable information on herbivore feeding in this marine system.

The importance of judging success of restoration studies over extended time periods has been repeatedly voiced but convincing information to justify increased monitoring is generally unavailable. Building on Bell et al. (2008), we investigated the development of areal coverage of the seagrass, Halodule wrightii, as a metric for assessing the outcome of a restoration effort conducted near Tampa Bay, Florida, U.S.A., over 7 years, thereby expanding the timescale over which a subtropical seagrass restoration project was evaluated for success. In each of 12 plots, 500 planting units of H. wrightii were introduced in 2002, and the seagrass cover level documented annually through 2009. Although only low-moderate levels of H. wrightii cover were recorded after 3 years, a rapid increase to high coverage levels was evident in many plots after 2006 and sustained through 2009. Plots that supported only low levels of seagrass cover initially remained poor performers, 4–7 years post-planting. By 2008, substantial seagrass spillover, contiguous with over 75% of plots, was recorded. When both within-plot coverage and spillover were considered, seagrass restoration success was attained 6 years after initiation. Our findings provide an example of comparatively longer-term monitoring of a restoration effort leading to reversal of an earlier evaluation of project success. Moreover, unique information on H. wrightii temporal dynamics emerged from the 7 year study, further illustrating the value of long-term assessment of restoration. Extending the duration of post-planting surveys of seagrass coverage may address multiple needs as it advances the field of seagrass restoration.

To assess the potential influence of coastal development on estuarine-habitat quality, we characterized land use and the intensity of land development surrounding small tidal tributaries in Tampa Bay. Based on this characterization, we classified tributaries as undeveloped, industrial, urban, or man-made (i.e., mosquito-control ditches). Over one third (37 %) of the tributaries have been heavily developed based on landscape development intensity (LDI) index values >5.0, while fewer than one third (28 %) remain relatively undeveloped (LDI

Seagrass habitats are characteristic features of shallow waters worldwide and provide a variety of ecosystem functions. Remote sensing techniques can help collect spatial and temporal information about seagrass resources. In this study, we evaluate a protocol that utilizes image optimization algorithms followed by atmospheric and sunglint corrections to the three satellite sensors [Landsat 5 Thematic Mapper (TM), Earth Observing-1 (EO-1) Advanced Land Imager (ALI) and Hyperion (HYP)] and a fuzzy synthetic evaluation technique to map and assess seagrass abundance in Pinellas County, FL, USA. After image preprocessed with image optimization algorithms and atmospheric and sunglint correction approaches, the three sensors’ data were used to classify the submerged aquatic vegetation cover (%SAV cover) into 5 classes with a maximum likelihood classifier. Based on three biological metrics [%SAV, leaf area index (LAI), and Biomass] measured from the field, nine multiple regression models were developed for estimating the three biometrics with spectral variables derived from the three sensors’ data. Then, five membership maps were created with the three biometrics along with two environmental factors (water depth and distance-to-shoreline). Finally, seagrass abundance maps were produced by using a fuzzy synthetic evaluation technique and five membership maps. The experimental results indicate that the HYP sensor produced the best results of the 5-class classification of %SAV cover (overall accuracy = 87% and Kappa = 0.83 vs. 82% and 0.77 by ALI and 79% and 0.73 by TM) and better multiple regression models for estimating the three biometrics ( R 2 = 0.66, 0.62 and 0.61 for %SAV, LAI and Biomass vs. 0.62, 0.61 and 0.55 by ALI and 0.58, 0.56 and 0.52 by TM) for creating seagrass abundance maps along with two environmental factors. Combined our results demonstrate that the image optimization algorithms and the fuzzy synthetic evaluation technique were effective in mapping detailed seagrass habitats and assessing seagrass abundance with the 30-m resolution data collected by the three sensors.

Rhizophytic green algae (e.g., Caulerpa, Halimeda, Penicillus, Rhipocephalus, and Udotea) are abundant macrophytes throughout tropical and subtropical regions that anchor with a net of rhizoids that binds sediments to form holdfasts in unconsolidated sediments. We examined both the above- and belowground components of these understudied algal communities with transect sampling at three tropical sites with carbonate sediments in the Lower Florida Keys and one subtropical site (Sunset Beach) with quartz sediments on the central west coast of Florida, an area previously unstudied. Species composition differed among sites, with Caulerpa spp. comprising >50% of organic biomass at Sunset Beach, and a greater diversity of calcified species present in the Keys. The mean density (365 vs 68-143 thalli m-2) and mean volume of holdfasts (1034 vs 504-199 ml m-2) of rhizophytic algae were greater at Sunset Beach than at Keys sites. For species found at both regions, analyses of morphometric measurements revealed taller thalli at Sunset Beach, larger holdfast volumes at sites with larger sediment grain size, a positive correlation between the wet weight of the aboveground portion of the thallus and the volume of the holdfast, and an anchorage depth generally shallower than the rooting depth of co-occurring seagrasses. Differences among species in contributions to above- and belowground components, even within a genus, indicate that species identity is important for predicting a rhizophytic alga's role in ecosystem function. These data are some of the first on both the above- and belowground components of natural mixed rhizophytic algal communities.

Seagrass habitats in subtidal coastal waters provide a variety of ecosystem functions and services and there is an increasing need to acquire information on spatial and temporal dynamics of this resource. Here, we explored the capability of IKONOS (IKO) data of high resolution (4 m) for mapping seagrass cover [submerged aquatic vegetation (%SAV) cover] along the mid-western coast of Florida, USA. We also compared seagrass maps produced with IKO data with that obtained using the Landsat TM sensor with lower resolution (30 m). Both IKO and TM data, collected in October 2009, were preprocessed to calculate water depth invariant bands to normalize the effect of varying depth on bottom spectra recorded by the two satellite sensors and further the textural information was extracted from IKO data. Our results demonstrate that the high resolution IKO sensor produced a higher accuracy than the TM sensor in a three-class % SAV cover classification. Of note is that the OA of %SAV cover mapping at our study area created with IKO data was 5–20% higher than that from other studies published. We also examined the spatial distribution of seagrass over a spatial range of 4–240 m using the Ripley’s K function [L(d)] and IKO data that represented four different grain sizes [4 m (one IKO pixel), 8 m (2 × 2 IKO pixels), 12 m (3 × 3 IKO pixels), and 16 m (4 × 4 IKO pixels)] from moderate-dense seagrass cover along a set of six transects. The Ripley’s K metric repeatedly indicated that seagrass cover representing 4 m × 4 m pixels displayed a dispersed (or slightly dispersed) pattern over distances of

Seagrass habitats provide a variety of ecosystem functions thus monitoring of seagrass habitat is a priority of coastal management. Remote sensing techniques can provide spatial and temporal information about seagrass habitats. Given the availability and accessibility of Landsat-5 Thematic Mapper (TM) and the advanced nature of Earth Observing-1 Advanced Land Imager (ALI) and Hyperion (HYP), we compared the capability of the three 30 m resolution satellite sensors and tested regression models based on two seagrass metrics [percent cover of submerged aquatic vegetation (%SAV) and leaf area index (LAI)] for mapping and assessing seagrass habitats within a shallow coastal area along the central western coast of FL, USA. We also evaluated a water depth correction approach to create water depth-invariant bands calculated from the three sensors' data. Then a maximum likelihood classifier was used to classify the %SAV cover into two classification schemes (3-class and 5-class). Based upon the two seagrass metrics measured in the field, six multiple regression models were developed and %SAV and LAI were estimated with spectral variables derived from the three sensors to assess the seagrass habitats in mapped units. Our results indicate that the HYP sensor produced the best seagrass cover maps in the two classification schemes: 3-class [overall accuracy (OA) = 95.9%] and 5-class (OA = 78.4%) and the best %SAV and LAI estimation models [R2 = 0.78 and 0.59, and cross-validation (CV) = 18.1% and 1.40 for %SAV and LAI, respectively] for assessing seagrass habitats. These results are likely due to the many narrow bands in the visible spectral range and rich subtle spectral information available in the HYP hyperspectral data. ALI outperformed TM (OA = 94.6% vs. 92.5% for the 3-class scheme, and OA = 77.8% vs. 66.0% for the 5-class scheme) for mapping %SAV likely due to its higher radiometric resolution. Our findings also demonstrate that the water depth correction approach was effective in mapping the detailed seagrass habitats with the data from the three sensors. The protocol developed and utilized here represents a new contribution to the existing set of tools used by researchers for documenting the amount of seagrass and which can guide future studies.

Pu, R.; Bell, S.; Baggett, L.; Meyer, C., and Zhao, Y., 2012. Discrimination of seagrass species and cover classes with in situ hyperspectral data. Seagrass habitats support a variety of ecosystem functions and an increasing interest has emerged for utilizing remote sensing to acquire information on the spatial extent and abundance of seagrass vegetation. Here we report on hyperspectral data collected from a combined laboratory and field-based study to examine the spectral qualities of seagrass species and evaluate whether seagrass species and levels of seagrass cover could be distinguished using true in situ hyperspectral data collected by a spectrometer overlying sea-grass-dominated vegetation in a shallow water setting in the central west coast of Florida. We also analyzed hyperspectral data measured in the lab to compare with those from in situ collections. Using a set of 97 field measurements we compared spectra qualities for different seagrass species, levels of seagrass cover, water depths...

Several species of kleptoplastic, sacoglossan sea slug photosynthesize using chloroplasts sequestered inside their digestive cells from algal food sources. However, sequestered chloroplasts alone are not sufficient for months-long, continuous photosynthesis and maintenance of the chloroplasts in absence of the algal nucleus. Some type of plastid maintenance mechanism must be present to help sustain photosynthetic activity in the long term kleptoplastic species, such as Elysia clarki. We demonstrate that E. clarki starved for 2 weeks are able to synthesize chlorophylls, but that slugs starved for 14 weeks no longer synthesize chlorophyll. The subsidence of chlorophyll synthesis is coincident with the cessation of photosynthesis by the starved slugs, but it is not yet known if the cessation of pigment synthesis is the cause or some other aspect of plastid degradation produces a loss of synthetic ability.

While associational defenses have been well documented in many plant and algal ecosystems, this study is the first to document associational resistance in mangroves. Mangrove tree crab ( Aratus pisonii ) density and herbivory on three life-stages of the red mangrove ( Rhizophora mangle ) were documented in pure red versus mixed-species and predominantly non-red mangrove stands containing black ( Avicennia germinans ) and white ( Laguncularia racemosa ) mangroves in 1999–2000 in Tampa Bay, Florida. This study first established that R. mangle is the focal species in the context of associational resistance because it is damaged more than either of the other mangrove species. Next, it was hypothesized that crab density and leaf damage on R. mangle would be lower when in mixed-species and predominantly non-red versus red mangrove stands. A non-significant trend suggested that crab density varies among stands, and crab damage on R. mangle leaves was significantly lower in mixed-species and non-red stands. Mechanisms to explain associational resistance were examined. Positive Pearson correlations between the percent of adult R. mangle in a stand and both crab density and R. mangle leaf damage provided support for the resource concentration hypothesis. Limited support was found for the attractant-decoy hypothesis because the total amount of damaged leaves of all mangrove species combined typically differed among stands, suggesting that crabs were not shifting to alternative mangrove species to offset reduced availability of R. mangle leaves. Finally, while R. mangle seedlings were shorter in non-red stands compared to others, intra-specific differences in R. mangle leaf chemistry and sclerophylly among stands failed to explain associational patterns. These combined results argue for the need for additional experiments to elucidate mechanisms responsible for defensive plant associations in mangrove ecosystems and to determine whether such associations could be of use in mangrove restoration.

Global climate change and invasive species represent two of the biggest threats to the environment. Biological communities are responding to global climate change through poleward shifts in distribution, and changes in abundance and phenology of both native and non-native species. An increase in the frequency and magnitude of extreme weather events is predicted with global climate change. Much is known about mortality events of marine organisms in relation to warm thermal stress with relatively little known about cold thermal stress, particularly in the tropics. Intertidal species are particularly susceptible to fluctuations in aerial conditions and many are considered indicators of climate change. Perna viridis is a recent invader to the United States where it fouls hard substrates and soft sediment habitats. During winter 2007/08, a mortality event was observed for P. viridis across Tampa Bay, Florida. This mortality event coincided with extreme weather conditions when air temperatures dropped below 2 °C for a period of 6 h during low water. The minimum air temperature recorded was 0.53 °C. During this period water temperature remained relatively constant (~ 20 °C). We provide strong evidence supporting the hypothesis that thermal stress relating to exposure to cold air temperatures during emersion was the primary factor underpinning the mortality event. Similar mortality events occurred in 2009 and 2010, also coinciding with prolonged exposure to low air temperatures. In the short term, weather may be responsible for the temporary trimming back of populations at the edge of their geographic range but in the longer-term, it is expected that climate warming will trigger the poleward movement of both native and non-native species potentially facilitating biotic homogenisation of marine communities. The challenge now is to devise adaptive management strategies in order to mitigate any potential negative impacts to native biodiversity.

article i nfo Field surveys indicated that individuals of Halimeda incrassata (Ellis) Lamouroux, a rhizophytic alga, were significantly more mineralized when collected from phosphate-limited carbonate sediments of the Florida Keys than those collected from siliciclastic sediments at Tarpon Springs on the west coast of Florida. Results from field experiments in Tarpon Springs, which compared growth of H. incrassata in enriched conditions to unmanipulated controls, indicated that biomineralization of new growth was significantly lower when phosphate was added to plots. After 18 days in a tank culture experiment, newly produced segments of H. incrassata grown in 20 µM phosphate showed a significant decrease in mineralization compared to the new growth in control tanks. Phosphate enrichment also led to a non-significant increase in segment mortality and a significant decrease in amountof newgrowth. Results fromthe surveyand experimental studies suggest that biomineralization of H. incrassata is negatively impacted by elevated phosphate levels.

Restoration has become an integral part of coastal management as a result of seagrass habitat loss. We studied restoration of the seagrass (Halodule wrightii) near Tampa Bay, Florida. Experimental plots were established in June 2002 using four planting methods: three manually planted and one mechanically transplanted by boat. Seagrass cover was recorded at high resolution (meter scale) annually through July 2005. Natural seagrass beds were concurrently examined as reference sites. We also evaluated the suitability of a commonly used protocol (Braun-Blanquet scores, BB) for comparing the development of seagrass cover using the planting methods and quantifying spatial patterns of cover over time. Results show that BB scores mirrored conventional measures of seagrass characteristics (i.e., shoot counts and above- and belowground biomass) well when BB scores were either low or very high. However, more caution may be required at intermediate cover scores as judged by comparison of BB scores with direct measurement of seagrass abundance. Significant differences in seagrass cover were detected among planting methods and over time (2002–2005), with manual planting of rubber band units resulting in the highest cover. In contrast, the peat pot and mechanical planting methods developed very low cover. Recovery rates calculated from development of seagrass spatial cover were less than those reported for natural expansion. Importantly, time to baseline recovery may be substantially greater than 3 years and beyond standard monitoring timelines. Prolonged recovery suggests that the rate of service returns, critical for estimating compensatory restoration goals under habitat equivalency analysis, may be severely underestimated.

The scale of landscape pattern formation of an ecological community may provide clues as to the processes influencing its spatial and temporal dynamics. We conducted an examination of the spatial organization of an annual seagrass ( Halophila decipiens ) in an open ocean setting at two spatial scales and growing seasons to identify the relative influence of external (hurricanes) versus internal (clonal growth) factors. Visual surveys of seagrass cover were conducted over 2 years within three replicate 1 km 2 study areas each separated by ∼25 km in an inshore–offshore transect along the southwest coast of Florida at depths between ∼10 and 30 m. A towed video sled allowed observations of seagrass cover of 1 m 2 areas approximately every 6 m over thousands of meters of evenly spaced transects within the study areas (coarse scale). The towed video revealed that 17.5% of the seafloor was disturbed irrespective of location or sample time. Randomly selected 10 × 10 m quadrats within the larger, 1 km 2 study areas were completely surveyed for seagrass cover by divers at 0.625 m 2 resolution (fine scale). The coarse-scale observations were tested using both conventional geostatistics and an application of a time-series technique (Runs test) for scale of seagrass cover contiguity. Fine-scale observations were examined using conventional geostatistics and a least squares approach (cumulative logistic). The coarse-scale observations revealed little scale dependency and indicated that the structure was organized at spatial extents finer than our sample spacing; the cumulative logistic technique revealed potential fine-scale patterns not otherwise discerned. In contrast, surveys of the 10 × 10 m quadrats detected strong scale dependency with multiple small gaps, indicating scale-dependent patterns arising from processes operating at extents generally Halophila decipiens that likely arose from transported seeds. Spatial analysis revealed that the storm led to a shift to greater frequency of H. decipien s, but lower density coverage. Seagrass density remained substantially depressed in all areas a full year following the storm. The short life history of H. decipiens and the apparent existence of a moveable seed bank means that spatial organization of this community is dictated first by large-scale dispersal of plant propagules (hundreds of meters) and then within a growing season, by clonal organization of the seagrass operating over very small distances (m). The two techniques (semivariance and Runs test) led to similar conclusions regarding the organizational scales of seagrass landscape pattern. As with terrestrial examples, this study demonstrates the importance of selecting the appropriate scale for detection of landscape pattern and processes influencing population ecology of a seagrass ecosystem.

Resorption, the remobilization and subsequent transport of leaf constituents (e.g. N, C, and P) into the perennial structures of the plant prior to leaf abscission, may be interrupted or prevented by stressors that interfere with the normal course of leaf senescence. Mangroves that lie along the latitudinal extremes of their distribution are susceptible to freeze damage that may periodically disrupt the normal resorptive process. On January 24, 2003, the white mangroves (Laguncularia racemosa) in a northern portion of Tampa Bay, Florida were exposed to freezing temperatures for 8 h. The leaves of these trees were noticeably withered by this freeze event. Over a four-month period following the freeze, we compared the subsequent rate of leaf litter production at this site to that of two, apparently undamaged, fringing mangrove forests in Tampa Bay. We also examined the carbon and nitrogen concentrations of the leaf litter from the litter traps at these three sites and compared it to that of green, yellow (nearly senescent), and freeze-damaged leaves hand-picked from the mangroves. A pronounced pulse of leaf litter fall (maximum: 7 g dw m−2 d−1) was found at the putatively freeze-damaged site but not at the two comparison sites. In addition, the leaf litter at the freeze-damaged site was richer in nitrogen and carbon, and had a lower C:N than litter collected at the comparison sites. Comparison of the elemental composition of this leaf litter with leaves hand-picked from the mangroves suggests that the freeze event killed the leaves of L. racemosa, interrupting the process of resorption. This perturbation to nutrient flow may have implications for mangrove forest structure and the entry of mangrove material into food webs.

An experimental study was conducted in Tampa Bay, FL to examine the response to disturbance of two co-occurring subtidal plants: the alga Caulerpa prolifera and the seagrass Halodule wrightii (Ascherson). Some recent studies have called into question the assumption that fast-growing rhizoidal Caulerpa species have the potential to outcompete and rapidly replace local seagrasses. In the Fall of 2002 an abrupt appearance of Caulerpa prolifera was noted in a shallow embayment in Tampa Bay previously dominated by seagrasses. Natural disturbance events were simulated by excavating 0.5 × 0.5 m plots in an area with monospecific C. prolifera and mixed C. prolifera and H. wrightii. Above and below-ground biomass were removed, and recovery of above-ground cover into the newly created gaps was monitored over 15 months. In addition to measuring the recovery of both species, the spatial pattern of Caulerpa recovery from the simulated disturbances was also analyzed. Simulated gaps were rapidly (5–8 months, depending on sampling resolution) and exclusively reoccupied by C. prolifera, with the recovery occurring predominantly via lateral expansion from gap edges rather than colonization by fragments. Therefore, while rhizoidal algae may or may not be able to supplant existing seagrasses by overgrowth or other forms of direct competition, disturbance events that remove seagrass and create bare areas may allow C. prolifera to replace seagrasses over time via preemption of space should an algal bloom such as this be persistent.

A descriptive study of the architecture of the red mangrove, Rhizophora mangle L., habitat of Tampa Bay, FL, was conducted to assess if plant architecture could be used to discriminate overwash from fringing forest type. Seven above-water (e.g., tree height, diameter at breast height, and leaf area) and 10 below-water (e.g., root density, root complexity, and maximum root order) architectural features were measured in eight mangrove stands. A multivariate technique (discriminant analysis) was used to test the ability of different models comprising above-water, below-water, or whole tree architecture to classify forest type. Root architectural features appear to be better than classical forestry measurements at discriminating between fringing and overwash forests but, regardless of the features loaded into the model, misclassification rates were high as forest type was only correctly classified in 66% of the cases. Based upon habitat architecture, the results of this study do not support a sharp distinction between overwash and fringing red mangrove forests in Tampa Bay but rather indicate that the two are architecturally undistinguishable. Therefore, within this northern portion of the geographic range of red mangroves, a more appropriate classification system based upon architecture may be one in which overwash and fringing forest types are combined into a single, “tide dominated” category.

Mangroves in Florida (USA) are subject to horticultural pruning that may increase the size of canopy gaps and alter rates of litter production and accumulation. Mangrove canopy gap formation is a common phenomenon, known to alter abiotic conditions near the forest floor. Using a series of field experiments in Rookery Bay, Florida, the effects of mangrove trimming on canopy density, mangrove litter production, standing litter stocks, and the decomposition rate of Rhizophora mangle leaves on the forest floor were assessed. Litter trap collections over the year following mangrove trimming indicated that pruned mangrove stands (canopy coverage: 42.8±0.9%; mean±S.E.) produced approximately one-half of the litter of mangrove stands with relatively complete canopies (canopy coverage: 72.1±0.5%). However, there was no significant difference between the mass of standing litter on the forest floor beneath reduced canopy and intact canopy mangroves. Also, R. mangle leaves held on the forest floor in fiberglass litter bags at both reduced canopy and control sites did not decompose at different rates over 28 days. These results indicate that while system-wide mangrove litter production should be reduced by the formation of these gaps in mangrove forests, postproduction influences may obscure any site-specific declines in standing litter stocks.

We examined feeding by the mangrove tree crab Aratus pisonii in Tampa Bay, Florida, in relation to the percent dry weight of carbohydrate, protein, phenolics, condensed tannins, ash, carbon, nitrogen, carbon:nitrogen ratio, water content, and sclerophylly for leaves of the red mangrove Rhizophora mangle. Comparisons of leaf chemistry were made among leaves that experienced variable levels of crab damage. Because R. mangle is the crab's preferred food source based on damage patterns in the field, comparisons of R. mangle leaf chemistry were made in relation to that of the black mangrove Avicennia germinans and the white mangrove Laguncularia racemosa. We observed a negative relationship between level of leaf damage and percent dry weight of nitrogen, carbohydrates, condensed tannins, and sclerophylly. In contrast, a positive relationship was found between leaf damage and the carbon:nitrogen ratio. The chemical constituents that provided the best explanation for differences in damage among the thre...

Abundance patterns of the hermit crab Pagurus maclaughlinae and its gastropod shell resources were compared to one another across the shallow subtidal landscape within Tampa Bay, Florida at a landscape (4.88 ha) and a sub-landscape (1 m 2 ) scale. Specifically, we investigated whether the spatial abundance patterns of P. maclaughlinae over time could be explained by the abundance patterns of either future resources (i.e. live gastropods) or present resources (i.e. empty gastropod shells). The seagrass landscape was sampled for seagrass, hermit crabs, live gastropods and empty gastropod shells during the spring and fall of 1994 and 1995. The distribution of P. mac- laughlinae could be explained by the distribution of its gastropod shell resources when the spatial organization of both P. maclaughlinae and these resources were compared across the landscape. Physical measures of the dominant seagrass Halodule wrightii (i.e. canopy height and shoot density) appeared to be unrelated to the distribution of P. maclaughlinae and either of its shell resources (pre- sent or future) across the landscape. These results suggest that hermit crabs track their 'limited' resources (i.e. gastropod shells) when viewed over the spatial scales examined here. Furthermore, our results suggest that the spatial distribution of future, as well as present resources, adds insight into patterns of hermit crab abundance.

An experiment was conducted in a Thalassia testudinum bed in SW Florida to examine the effect of simulated green turtle Chelonia mydas L. herbivory on the intensity of infection by Labyrinthula, which causes wasting disease in seagrass. Four pairs of 4.0 m 2 plots were established at the site, with each pair containing one plot subjected to simulated herbivory and the other serving as an unmanipulated control. Labyrinthula infection appeared abruptly during April, reached maxi- mum levels in May, and decreased to zero by September 2002. In plots subjected to simulated her- bivory, clipped seagrass blades were more likely to be infected than new blades emerging from clipped short shoots. Three months after clipping, disease levels in the new blades were not sig- nificantly different between simulated herbivory and control plots. These results suggest sea turtle herbivory is not likely to reduce disease levels in T. testudinum.

The diet of the mangrove crab, Aratus pisonii, was assessed by determining the percent of damaged leaves at selected mangrove communities and by examining herbivore gut contents. This study compared the utility of both methods and tested if comparable levels of damage and dietary preference occurred using the methods. Percent of damaged leaves was determined for the three species of mangroves within Tampa Bay, FL, USA, including: the red, black, and white mangroves (Rhizophora mangle, Avicennia germinans, and Laguncularia racemosa, respectively) in four 5×10-m quadrats during summer 2001. For each species, in each of the quadrats, 200 leaves per tree were assessed for the presence or absence of crab damage. A. pisonii were sampled from the same quadrats from which leaf damage data were collected. Stomach contents were dissected and food items were classified into a number of categories. Species damaged and preferred were determined by comparing relative numbers of mangrove leaf stomata from the three mangrove species in gut contents. Results suggested that both methods provide similar estimates of preference. R. mangle leaves were preferred over those of A. germinans and L. racemosa. The percent of R. mangle leaves with damage was about 20–30 times greater than the other species, and R. mangle leaf stomata were 3 to 20 times more abundant in crab guts compared to leaf stomata of the other species. Gut contents indicated that A. pisonii is omnivorous, that average-sized adult crabs (1.4–1.7-cm width) prefer R. mangle, and that the diet of males is more varied than of females. While use of both percent leaf damage and crab gut contents reliably indicates preference, gut contents may describe better the actual diet and elucidate trends for different size or sex classes within a population.

A predictive model for seagrass bed coverage (presence/absence at 1-m res- olution) and ecological attributes of the bed, such as biomass and shoot density, would be a valuable management tool. But forming such a predictive model is complicated by a number of factors that strongly influence seagrass bed structure and our interpretation of its ecological function. The factors include the effects of waves and water depth (hydro- dynamic setting) and the spatial and temporal scales of the sampling technique itself. In this study, we examined the coherence of predictions of seagrass cover and ecological attributes of temperate, mixed-species seagrass derived from two common sampling tech- niques, (video) line transect (commonly used by biologists) and grid-sampled surveys (often used in remote sensing). Mapping resolution was held constant at 1 m, and the two tech- niques applied across seagrass beds of varying coverage that reflected the effect of a hydrodynamic gradient ranging from patchy, high-energy beds to continuous cover, low- energy beds. We found that the prediction of seagrass coverage as a function of hydro- dynamic setting can be improved not only by increasing the spatial extent of sampling at a fixed resolution (1 m), but also by ensuring that data for both dependent (e.g., percent cover) and independent (e.g., wave exposure) variables are averaged over similar scales (spatial extent and resolution). Large-scale features of the landscape, such as patches several meters in width, appeared to be best quantified by sampling over a large spatial extent, as with the video transects. Therefore, contiguous sampling over a broad spatial extent, as opposed to our numerous, somewhat smaller sampling (grid-sampled, 50 3 50 m areas) is the more appropriate strategy for predicting the probability of seagrass bed cover. Con- versely, we found that ecological attributes of the seagrass bed (biomass, shoot density, and sediment composition) were best characterized by sampling over a shorter spatial extent (i.e., ,50 m), indicating that very localized conditions may have influenced patterns of seagrass community attributes. Generalizing information about seagrass bed ecological attributes obtained from high-resolution samples (fine scale) taken over a broad spatial extent (coarse or landscape scale), as may occur with resource surveys and impact assess- ments, has the potential to be highly misleading, especially in patchy environments. The influence of sampling scale and survey method on the prediction of coverage and ecological attributes of seagrass beds reveals the need to carefully choose sampling designs to evaluate seagrass distribution and their associated ecological characteristics in the Beaufort, North Carolina (USA) area, and perhaps in other like habitats.

We investigated the relationship between damage from boat propeller scarring in seagrass (Thalassia testudinum) beds and the abundance of three faunal taxa commonly associated with seagrass vegetation in Charlotte Harbor and Tampa Bay, Florida. We chose sites with no damage (reference sites) to compare to those with propeller scarring within each of the two geographic locations. Thirty 141-m2 sites in both Charlotte Harbor and Tampa Bay, representing a gradient of scarring from 6% to 31% of the total area, were sampled in spring and winter 1996 along with reference sites to evaluate effects of propeller damage on abundance of the pinfish, Lagodon rhomboides, and the pipefish, Syngnathus scovelli. Additionally, 60 sites in both Charlotte Harbor and Tampa Bay representing areas with up to 50% scarring and comparison reference sites were sampled in spring 1997 to investigate whether propeller scar damage impacted epibenthic shrimp abundance and community structure in seagrass. Our results indicated no signif...

The nature of the plant-animal interaction between wood-boring isopods and the red mangrove Rhizophora mangle L. has been controversial, with discussion ranging from the damage caused by the isopod being detrimental to beneficial for the mangroves they attack. Initiation of lateral roots by the mangrove in response to isopod burrowing has been one of the most commonly cited examples as support for the concept of beneficial herbivory. In this study, the possibility of root repair as a response of Rhizophora to burrowing by Sphaeroma terebrans Bate was evaluated. Previously burrowed prop roots were tagged in the field and the fate of all burrows followed over 14 wk at a site in Upper Tampa Bay, Florida. Results demonstrated that the most common response of the mangrove was to repair abandoned isopod burrows, with 99 % of all tagged roots and 66 % of all monitored burrows showing signs of repair. Lateral root production occurred at a lower frequency (32 % of roots). Similarly, transect surveys performed in Upper Tampa Bay and 2 additional locations (Anna Maria Island and Weedon Island) indicated a high incidence (57 to 82 %) of attacked aerial roots showing signs of burrow repair. Again, lateral root production was less commonly noted on transects (13 to 25 % of the roots surveyed). Initiation of lateral roots and burrow repair were not mutually exclusive responses and all instances of lateral root production were in conjunction with repair. Our results demonstrate that the most common response to damage is the replacement of root tissue rather than the stimulation of new tissue production.

Field experiments utilizing peak nighttime activity levels of amphipods were performed to determine if the spatial location of drift macroalgae in seagrass landscapes affected amphipod abundance on drift macroalgae. The study was conducted in Tampa Bay, FL over two nights in August 1995, within a Halodule wrightii Ascherson Phillips seagrass bed. Amphipod utilization of drift algae was assessed by defaunating the drift alga, Hypnea cervicornis J. Agardh, and recording net faunal movement onto algal clumps which were (1) stationary in bare sediment for 120 min; (2) stationary in H. wrightii for 120 min; (3) moved through H. wrightii for 90 min; and (4) moved through H. wrightii for 90 min and then across the seagrass sand ecotone and into bare sediment for 30 min. Amphipods, almost exclusively epiphytic taxa, were recovered from all experimental algal clumps placed both in seagrass and sand areas. Fourteen amphipod species were recovered with Ampithoe longimana and Cymadusa compta making up 77% of the total abundance. Greater abundances (but not diversity) of epifaunal amphipods were found on algae when they were located within a seagrass bed compared to bare sediment. Drift algal clumps that passed through the seagrass/sand ecotone had significantly higher amphipod abundance than (1) clumps that did not move through seagrass and were stationary in bare sediment and (2) clumps which moved through, but not out of, a seagrass bed. Demographic and ontogenetic differences were also detected among drift algal treatments. Gravid females were less abundant on algae that did not remain within or was not inside of the seagrass bed and proportionately more males and juveniles were found on algal clumps anchored away from seagrass vegetation. These findings demonstrate that drift algae acting as a mobile corridor provide epiphytal amphipods with a mechanism for dispersal within a seagrass landscape. Moreover, the drift algae that serve as a mobile corridor also act as a mechanism whereby the exchange of fauna is enhanced as drift algae move across the seagrass/sand ecotone. Thus, factors controlling drift algae movement, such as regional meteorological conditions, should have implications for interpatch dynamics of amphipods within a seagrass landscape.

Fragmentation in seagrass systems results in changes to landscape features that may have implications for fauna. We examine published studies to identify whether faunal abundance shows any relationship with patch size of seagrass beds, suggesting preferential use of the edge or interior by seagrass associated taxa. In a series of studies in Tampa Bay, FL, we also examined: (1) the relationship between abundance of both fish and amphipod fauna and seagrass patch size in 24 seagrass (Halodule wrightii) beds (5–93 m2) in 1994 and 1995; (2) whether abundance of the infaunal polychaete, Kinbergonuphis simoni, was significantly different within the 1 m edge versus interior of two seagrass (Halodule wrightii ) beds of similar size and age; and (3) compared the spatial distribution of the tube-building polychaete, Spirorbis spirillum, in Thalassia testudinum seagrass beds in two sites in Tampa Bay. Neither review of the published literature on fauna and seagrass patch size nor the data presented from our Tampa Bay studies suggest that habitat fragmentation has any consistent impact on fauna over the spatial scales that have been investigated. Likewise, little evidence exists that identifies any taxonomic group to be fragmentation sensitive in that they differentially utilized edge or core areas of seagrass patches. While we did detect a reduction of both infaunal and epibenthic polychaetes at the 1 m edges of seagrass beds relative to interior areas, the reduction was not similar along all edges. Events such as seagrass die off or a high incidence of boat propeller-damage over an extensive area may be required to detect effects of habitat fragmentation on fauna. Given that patch size alone does not appear to adequately account for variation in faunal abundance, we suggest that restoration efforts might best focus upon locating areas with similarity of landscape context or patch characteristics other than patch size.

The isopod Sphaeroma terebrans, which bores into the prop roots of the red mangrove, Rhizophora mangle, can cause death and subsequent breakage of the inhabited root and, debatably, may reduce the support system of the tree. We examined whether different characteristics of a root or its physical setting, both of which may relate to habitat quality, influence the colonization of S. terebrans. A series of in situ experimental manipulations were conducted over 2 years. The first experimental protocol examined colonization of intact root substratum. Free-hanging aerial prop roots which were previously unsubmerged were bent down and anchored underwater at high tide after which the colonization of S. terebrans was monitored. A second manipulation was performed to evaluate the relative roles of submergence depth and plant anatomy in isopod colonization preference. Detached aerial prop roots were oriented either with the root tip directed downward, or upside down with the root tip directed upward but at a constant water depth. Additionally, detached aerial prop roots were oriented so that their tips were in contact with the sediment surface in order to investigate whether colonization on grounded roots was prevented by benthic predators. For all experiments, colonization began within 24 h; juveniles were the predominant colonizers. The submergence depth of a prop root, a characteristic of a root's physical setting, was consistently the strongest component correlated with the abundance of colonizing S. terebrans. The root-quality feature of root diameter was also found to play a significant role in colonization. Biotic influences, such as predation, however, did not influence recruitment of the isopod onto a root. Additionally, the absence of burrowing on grounded roots appeared to be related to intrinsic plant features. Along a root there was a strong preference by S. terebrans to colonize the root tip region (i.e., youngest part of the root) especially when these roots were also the deepest. The results of our experimental manipulation using natural root substratum are the first to identify physical setting as an important feature of habitat suitability for S. terebrans.

By examining the spatial distribution of rhizome morphological characteristics of the seagrass Halodule wrightii, in relation to a seasonal pattern of seagrass patch dynamics, we attempted to derive a mechanistic explanation for the variety of changes exhibited by seagrass patch shapes. Rhizome morphological characteristics (mean internodal distance, branching frequency and biomass) were measured at three spatially-recognized regions (Flood edge, Center, Ebb edge) of 5 seagrass patches, reflecting position relative to hydrodynamic flow. In addition, maps (1 resolution) of the seagrass patches were used to quantify changes in seagrass patch margins across the growing season. Rhizome morphological characteristics varied with spatial position: longer internodal distances were recorded on both edges of the patch relative to patch center, and rhizomes from Flood edges exhibited longer internodes than plants on the Ebb edge of patches. Branching frequency showed no spatially-explicit distribution across the seagrass patches. Patch change analysis indicated a pattern of increase in patch area on the Flood edges of seagrass patches and recession (or no change) on the Ebb edges. Patch margin change was significantly correlated with internodal distances: the more positive the increase in patch seagrass coverage on an edge, the greater the internodal distances.

The spatial heterogeneity of a subtidal marine landscape and the areal extent of both monospecific and mixed patches of seagrass species were studied in Tampa Bay, Florida, USA. Specifically, we examined the temporal dynamics of seagrass distribution and its relationship to water depth and the serial replacement of one species by another. The ∼5-ha landscape was mapped at 1-m intervals in the spring and fall of 1994 and 1995. The landscape consisted of monospecific and mixed patches of seagrass (47%) and bare sediment (53%). Halodule wrightii was the most abundant seagrass (∼74%), while Thalassia testudinum was second most common (20%), and mixed patches of H. wrightii and T. testudinum composed the remaining 6%. There was an overall increase in seagrass of 14% from spring 1994 to fall 1995. The majority of change occurred along the margins of existing seagrass patches (i.e., H. wrightii invading bare sediment). Typically, “new” patches were the result of the transition of one seagrass species to another ...

We investigated gap dynamics within a shallow subtidal landscape characterized by seagrass vegetation and examined the relationship between gap formation and selected physical factors. The study was conducted over 2 y by using a biannual mapping of seagrass and water depth across an 48,800-m2 area in Tampa Bay, Florida. In addition, monthly sediment deposition or erosion was recorded at 96 locations within the landscape. Gaps represented from 2.4% to 5.7% of the seagrass landscape, and all were within monospecific stands of Halodule wrightii. Gaps ranged in size from 10 to 305 m2 and most frequently decreased in size over time. Most gaps were small and short lived (less than 6-mo duration), but the second age group most frequently recorded was at least 1.5 y old. No new species of seagrass invaded the gaps with Halodule replacing itself 100% of the time. Gaps were recorded over the entire range of water depths within the landscape. Neither gap area nor persistence of gaps was related to water depth. However gap area was associated positively with the number of extreme sedimentation events. Gaps originated not only from removal of interior vegetation (similar to classic gaps) but also from differential growth of the seagrass margin (similar to edaphic gaps). Distinct seasonal components to the mode of formation were detected with interior-produced gaps originating primarily in the winter and margin gaps most commonly during summer. These results combine to illustrate the importance of large-scale studies with fine-scale resolution for deciphering unique features of seagrass landscape dynamics. Our historical information suggests that a static enumeration of gaps may not provide an accurate assessment of disturbance intensity in this system, and the seagrass mosaic probably is explained best by a combination of disturbance regimes and edaphic factors, such as sediment stability. Moreover, we suggest that even in areas characterized by monospecific stands of vegetation and over short or moderate time periods, gaps indirectly may influence community structure and ecosystem function via modification of habitat arrangement.

Field surveys were conducted in Core and Back Sounds, North Carolina. USA, to relate the physical setting of seagrass beds, as measured by a wave exposure index (REI), tidal current speed and water depth, to various measures of the sedimentary environment, spatial heterogeneity of seagrass distribution and measures of seagrass abundance. Seagrass beds in this area form patterns ranging from continuous to semi-continuous to widely dispersed, discrete patches across a gradient of increasing hydrodynamic activity. Tidal current speeds, exposure to waves and relative water depths revealed strong correlative evidence that physical processes influenced landscape-scale (50 X 50 m range with 1 m resolution) features of seagrass beds. Some habitat attributes, such as percent cover of seagrasses, seagrass bed perimeter to area ratio, sediment organic content and percent silt-cldy, declined with increasing REJ and current speed. Increased aggregation of these data was observed above and below the 50% seagrass cover value, and, supported by principle components analysis, signaled an abrupt transition of environmental setting correlated with this coverage level. The 50% cover value also occurred at current speeds of -25 cm S-', which should be near the initiation of motion current speed for local sand sediments, and an RE1 of -3 X 10h This coverage is also near to the 59.28% coverage value, previously determined to be where landscape elements join and below which they tend to exist as discrete patches. We hypothesize that a rapid loss of seagrass habitat structural integrity may occur as the habitat fragments, and seagrass landscape elements become isolated, contributing to the observed transition and accompanying data aggregation above and below the -50% coverage level. We discuss the interaction of physical setting, disturbance, landscape contiguity and growth response by these modular plants in the production of the observed landscape patterns across these hydrodynamic gradients.

An investigation of the effects of mucous tubes produced by amphipods, polychaetes and harpacticoid copepods was conducted on meiofaunal organisms inhabiting Thalassia testudinum Banks ex Konig blades in Tampa Bay, Florida. Samples of seagrass blades were collected from the field in October 1991 and the numbers of meiofauna, percent cover of mucous tubes and distance from the base of the seagrass blade were determined. Results indicated that meiofauna densities were greater on blade areas with greater percent cover of mucous tubes and that meiofauna distribution was independent of physical position (height) on the blade. Second, observations of behavior of blade-dwelling meiofauna were conducted simultaneously in areas with and without mucous tubes. Total meiofauna, harpacticoids and turbellarians occurred in significantly greater abundances in mucous tube areas and along with ostracods spent significantly more time in mucous tube areas than in non-tube areas. In a field experiment using conditioned glass substrata significantly greater numbers of meiofauna immigrated onto substrata with mucous tubes, constructed by the harpacticoid, Dactylopodia tisboides (Claus), than substrata without tubes. Evidence supports the conclusion that relatively imperceptible, ephemeral structures such as mucous tubes can affect the distribution and behavior of epibenthic meiofauna on seagrass blades.

Seagrasses constitute an important component in the nearshore coastal ecosystem, and the declining seagrass habitat is well documented in some areas. A reconstructive technique developed to discern seagrass population demographics with a single sampling event previously predicted the decline of Thalassia testudinurn populations in Florida Bay. Florida, USA. The results of that model were tested by comparing predicted and actual populations in 1994. A predicted shoot density decline of 49% was not recorded in field populations; instead the population had increased by 51%. We explored 2 potential reasons for the inaccuracy: sampling design, to account for spatial and temporal variability; and data collection procedures that create a demographic bias in the model input. We found that both factors alter the demographic statistics, which modify the model's outcome. Limitations of the model are discussed with respect to its assumptions and interpretation of results.

Empirical patterns that emerge from an examination of food webs over gradients of environmental variation can help to predict the implications of anthropogenic disturbance on ecosystems. This "dynamic food web approach" is rarely applied at the coastal margin where aquatic and terrestrial systems are coupled and human development activities are often concentrated. We propose a simple model of ghost crab (Ocypode quadrata) feeding that predicts changing dominant prey (Emerita talpoida, Talorchestia sp., Donax variablis) along a gradient of beach morphology and test this model using a suite of 16 beaches along the Florida, USA coast. Assessment of beaches included quantification of morphological features (width, sediments, slope), macrophyte wrack, macro-invertebrate prey and active ghost crab burrows. Stable isotope analysis of carbon ((13)C/(12)C) and nitrogen ((15)N/(14)N) and the SIAR mixing model were used to determine dietary composition of ghost crabs at each beach. The variation in habitat conditions displayed with increasing beach width was accompanied by quantifiable shifts in ghost crab diet and trophic position. Patterns of ghost crab diet were consistent with differences recorded across the beach width gradient with respect to the availability of preferred micro-habitats of principal macro-invertebrate prey. Values obtained for trophic position also suggests that the generalist ghost crab assembles and augments its diet in fundamentally different ways as habitat morphology varies across a highly dynamic ecosystem. Our results offer support for a functional response in the trophic architecture of a common food web compartment (ghost crabs, macro-invertebrate prey) across well-known beach morphologies. More importantly, our "dynamic food web approach" serves as a basis for evaluating how globally wide-spread sandy beach ecosystems should respond to a variety of anthropogenic impacts including beach grooming, beach re-nourishment, introduction of non-native or feral predators and human traffic on beaches.

Field experiments were conducted at a black mangrove-salt-marsh ecotone in southwest Florida (U.S.A.) to investigate retention of propagules of the black mangrove, Avicennia germinans, by salt-marsh plants as a mechanism of facilitation operating on recruitment success at landward boundaries. Buoyant A. germinans propagules are dispersed by tides, and stranding is required for establishment; therefore, processes that enable stranding should facilitate mangrove recruitment. We expected the physical structure of salt-marsh vegetation to define propagule retention capacity, and we predicted that salt-marsh plants with distinct growth forms would differentially retain propagules. Experimental monoculture plots (1 m2) of salt-marsh plants with different growth forms (Sporobolus virginicus [grass], Sesuvium portulacastrum [succulent forb], and Batis maritima [succulent scrub]) were created, and A. germinans propagules were emplaced into these plots and monitored over time. For comparison, propagules were also placed into natural polyculture plots (1 m2). Polyculture plots contained at least two of the salt-marsh plant taxa selected for monoculture treatments, and S. virginicus was always present within these polyculture plots. Natural polyculture plots retained 59.3% +/- 11.0% (mean +/- SE) of emplaced propagules. Monocultures varied in their propagule retention capacities with plots of S. virginicus retaining on average 65.7% +/- 11.5% of transplanted propagules compared to 7.2% +/- 1.8% by B. maritima and 5.0% +/- 1.9% by S. portulacastrum. Plots containing S. virginicus retained a significantly greater percentage of emplaced propagules relative to the two succulent salt-marsh taxa. Furthermore, propagule entrapment, across all treatments, was strongly correlated with salt-marsh structure (r2 = 0.6253, P = 0.00001), which was estimated using an indirect quantitative metric (lateral obstruction) calculated from digital images of plots. Overall, our findings imply that entrapment of propagules by salt-marsh plants may be facilitative if propagules are dispersed beyond the established tree line by spring or storm tides, and that facilitation may be sustained over time. We conclude that salt-marsh ecotone permeability may modulate landward encroachment by A. germinans, and that interactions among the early life history stages of black mangroves and neighboring plants may direct community responses to climate change.

The regeneration rate of arms of the infaunal brittlestar Ophiophragmus filograneus was determined in natural and planted beds of the seagrass (Halodule wrighttii) in Tampa Bay, Florida, USA in 1990. Annually, brittlestar densities did not differ on average between the two beds, but they did show marked differences on individual dates. Rates of arm loss could not be determined for the two sites separately, but were estimated for the entire area. Between 52 and 94% of the brittlestars collected showed evidence of arm regeneration. Approximately one-third of those collected were regenerating one arm, with smaller proportions regenerating two or more arms. Regeneration rate was greater overall for individuals that had lost more tissue; however, the rate of soft-tissue regeneration per arm regenerated was significantly greater for those that had lost one arm compared to those that had lost three arms. The rate of soft-tissue regeneration did not differe between individuals from the two seagrass beds, and regeneration rate was lower than reported for other infaunal brittlestars. Skeletal regeneration per arm was similar in both arm-removal treatments. This result supports the hypothesis that echinoderm skeleton is energetically inexpensive and may help to lengthen arms during early regeneration. The rate of skeletal production was three-fold greater in individuals from the planted seagrass than in those from the natural. bed. As increased skeletal regeneration requires some additional energy, this indicates a greater energy expenditure and differential allocation by brittlestars regenerating in the planted seagrass areas.

Subtidal seagrass habitats are prime candidates for the application of principles derived from landscape ecology. Although seagrass systems are relatively simple compared to their terrestrial counterparts in terms of species diversity and structural complexity, seagrasses do display variation in spatial patterns over a variety of scales. The presence of a moving water layer and its influence on faunal dispersal may be a distinguishing feature impacting ecological processes in the subtidal zone. Studying seagrass-dominated landscapes may provide a novel approach to investigating questions regarding self-similarity of spatial patterns, and offers a new perspective for analysing habitat change in a variety of marine environments.