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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.

Anthropogenic disturbances such as oil spills can cause mortality in benthic infaunal communities, reducing diversity and abundance and impeding sediment ecosystem functions. Sublethal effects of oil exposure have received less attention, however. We conducted a mesocosm experiment exposing 2 infaunal taxa, the polychaete Owenia fusiformis and the brittle star Hemipholis elongata, to sublethal concentrations of the water-accommodated fraction (WAF) of oil. We evaluated the effects of WAF on animal behavior, bioturbation, and sediment oxygen demand (SOD) in infaunal assemblages of both mixed and single species. WAF exposure did not affect O. fusiformis feeding behavior, nor did it influence bioturbation. Compared to O. fusiformis, the brittle star H. elongata mixed more surface sediments to greater depths and to a greater extent horizontally. Bioturbation in mesocosms with both taxa was consistent with predictions from monocultures for substitutive densities, but lower than predicted for additive densities. This indicates that taxa interacted (negatively) only at higher densities. SOD was higher in oiled than unoiled treatments initially (at 1-3 d), but this difference disappeared after the first sampling, consistent with a decrease in total petroleum hydrocarbons in the WAF treatment over the same time period. Higher SOD in WAF-exposed faunal treatments than sediments with no fauna suggested that faunal activities may enhance microbial degradation of hydrocarbons. These findings suggest that exposure to WAF stimulated microbial metabolism in the first few days of the experiment, but did not affect macrofaunal behavior/function, nor have lasting effects on sediment ecosystem functions.

Funding: K.L.Y. was funded by a NERC Knowledge Exchange Fellowship NE/P00668X/1. Seascape ecology, the marine-centric counterpart to landscape ecology, is rapidly emerging as an interdisciplinary and spatially explicit ecological science with relevance to marine management, biodiversity conservation, and restoration. While important progress in this field has been made in the past decade, there has been no coherent prioritisation of key research questions to help set the future research agenda for seascape ecology. We used a 2-stage modified Delphi method to solicit applied research questions from academic experts in seascape ecology and then asked respondents to identify priority questions across 9 interrelated research themes using 2 rounds of selection. We also invited senior management/conservation practitioners to prioritise the same research questions. Analyses highlighted congruence and discrepancies in perceived priorities for applied research. Themes related to both ecological concepts and management practice, and those identified as priorities include seascape change, seascape connectivity, spatial and temporal scale, ecosystem-based management, and emerging technologies and metrics. Highest-priority questions (upper tercile) received 50% agreement between respondent groups, and lowest priorities (lower tercile) received 58% agreement. Across all 3 priority tiers, 36 of the 55 questions were within a ±10% band of agreement. We present the most important applied research questions as determined by the proportion of votes received. For each theme, we provide a synthesis of the research challenges and the potential role of seascape ecology. These priority questions and themes serve as a roadmap for advancing applied seascape ecology during, and beyond, the UN Decade of Ocean Science for Sustainable Development (2021-2030). Publisher PDF

Recently, Manderson (2016, Seascapes are not landscapes: an analysis performed using Bernhard Riemann's rules: ICES Journal of Marine Science, 73: 1831-1838) argued that landscape ecology approaches developed in terrestrial habitats have little practical application for the study of marine “seascapes”. Here, we offer a contrasting perspective to this over-generalization. We first focus on historical uses of the term “seascape” to delineate the wide range of habitats that have been designated as such. After providing a brief overview of the study of seascape ecology, we argue that concepts and methodology originating from terrestrial disciplines have, in fact, provided an important cornerstone for investigating the dynamics of nearshore marine ecosystems. We present examples of coastal seascape research that have successfully applied terrestrial landscape theory and revisit points raised by Manderson regarding the application of landscape approaches to the marine environment. Overall, we contend that Manderson’s thesis may apply to some, but not most, use of landscape constructs for investigating aquatic environments. Moreover, we suggest that the study of coastal landscapes will continue to yield valuable insight into the spatiotemporal workings of aquatic ecosystems, and that this particular avenue of ecological investigation will only increase in its relevance as human impacts intensify.

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.

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.

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 habitat quality for estuarine nekton, we characterized body condition and reproduction for common nekton from tidal tributaries classified as undeveloped, industrial, urban or man-made (i.e., mosquito-control ditches). We then evaluated these metrics of nekton performance, along with several abundance-based metrics and community structure from a companion paper (Krebs et al. 2013) to determine which metrics best reflected variation in land-use and in-stream habitat among tributaries. Body condition was not significantly different among undeveloped, industrial, and man-made tidal tributaries for six of nine taxa; however, three of those taxa were in significantly better condition in urban compared to undeveloped tributaries. Palaemonetes shrimp were the only taxon in significantly poorer condition in urban tributaries. For Poecilia latipinna, there was no difference in body condition (length–weight) between undeveloped and urban tributaries, but energetic condition was significantly better in urban tributaries. Reproductive output was reduced for both P. latipinna (i.e., fecundity) and grass shrimp (i.e., very low densities, few ovigerous females) in urban tributaries; however a tradeoff between fecundity and offspring size confounded meaningful interpretation of reproduction among land-use classes for P. latipinna. Reproductive allotment by P. latipinna did not differ significantly among land-use classes. Canonical correspondence analysis differentiated urban and non-urban tributaries based on greater impervious surface, less natural mangrove shoreline, higher frequency of hypoxia and lower, more variable salinities in urban tributaries. These characteristics explained 36 % of the variation in nekton performance, including high densities of poeciliid fishes, greater energetic condition of sailfin mollies, and low densities of several common nekton and economically important taxa from urban tributaries. While variation among tributaries in our study can be largely explained by impervious surface beyond the shorelines of the tributary, variation in nekton metrics among non-urban tributaries was better explained by habitat factors within the tributary and along the shorelines. Our results support the paradigm that urban development in coastal areas has the potential to alter habitat quality in small tidal tributaries as reflected by variation in nekton performance among tributaries from representative land-use classes.

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

Utilization of fish as indicators of environmental quality in estuarine systems has received much recent attention, although some results have raised questions about using these taxa for such a role. We attempted to identify a fish response to a horticultural practice which removes portions of mangrove forest canopy to create unobstructed vistas. Fish were sampled monthly from six pairs of sites within the mangrove-forested intertidal zone of Rookery Bay, FL over two years. Following a first year of baseline sampling, the mangroves in one site from each pair of sites were pruned in accordance to Florida State law (Mangrove Trimming and Preservation Act of 1996), resulting in a mean 46% and 50% reduction in canopy coverage and litter fall, respectively. However neither the abundance nor species composition of fish in trimmed versus control plots were significantly different (Two-Way Repeated Measures ANOVA's for paired plot differences in fish density and biomass; nonmetric multidimensional scaling, and ANOSIM) suggesting that fish did not respond to mangrove canopy damage. Our results show that due to rather high spatial and temporal variability in fish abundance, it would be difficult to detect any but extreme changes of these taxa in the mangrove intertidal zone, and this may be a common feature of the fish communities of mangrove intertidal zones and other coastal systems. We suggest that improved use of fish as indicators of intertidal habitat quality would benefit from improved information on environmental factors which determine fish distribution and abundance in these areas. Moreover, since a majority of the fish in the intertidal zone is habitat generalists, we propose that individual-level measures of fish response to habitat quality may be more effective than fish abundance.

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.

The vegetated intertidal zone has long been acknowledged as an important habitat for fish, but our understanding of the dynamics of intertidal migrations by these fish is limited. Using in situ video recordings, we examined fish movements into and out of the waterward margin of a fring- ing mangrove forest during spring tides at 27 haphazardly chosen sites throughout the Rookery Bay National Estuarine Research Reserve, Florida. Our results indicate that fish respond to tide stage in a species-specific manner. Based on the changes in relative abundance throughout the tide cycle, we identified 4 general intertidal migration patterns: (1) tide-level proportionate, with greatest abun- dance during high tide; (2) flood- and ebb-tide concentrated, with lowest abundance during high tide; (3) peak abundance at ebb and low tide; and (4) depth-limited but tidally independent. Given that the distribution of the fish within the intertidal zone was heterogeneous, we suggest that the placement of sampling gear within the intertidal zone and the timing of samples within the tide cycle can greatly influence the species composition of fish inventories.

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.

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.

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.

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.

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.

Landscape ecology focuses on questions typically addressed over broad spatial scales. A landscape approach embraces spatial heterogeneity, consisting of a number of ecosystems and/or landscape structures of different types, as a central theme. Such studies may aid restoration efforts in a variety of ways, including (1) provision of better guidance for selecting reference sites and establishing project goals and (2) suggestions for appropriate spatial configurations of restored elements to facilitate recruitment of flora/ fauna. Likewise, restoration efforts may assist landscape-level studies, given that restored habitats, possessing various patch arrangements or being established among landscapes of varying diversity and conditions of human alteration, can provide extraordinary opportunities for experimentation over a large spatial scale. Restoration studies can facilitate the rate of information gathering for expected changes in natural landscapes for which introduction of landscape elements may be relatively slow. Moreover, data collected from restoration studies can assist in validation of dynamic models of current interest in landscape ecology. We suggest that restoration and landscape ecology have an unexplored mutualistic relationship that could enhance research and application of both disciplines.

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.

We evaluate the use of the Bartholomew Sp/Pr index with reference to the collection of information to be used in index calculation and interpretation. Through exami- nation of hypothetical structural arrangements, we address issues related to determining the spacing between structures which are non-uniformly distributed. We also utilize field- collected data to examine how measures of inter-structural spacing may vary when (1) 2 different field methods are used and (2) measurements of the same structures are made over different spatial scales. Using a mangrove prop-root system, measures of inter-structural spacing within 2900 m 2 areas using a 100 point confined arc method were obtained, as were small quadrat samples conducted within the same sites using the confined arc and nearest neighbor method. In small quadrat sampling, mean between-root distances using the arc method were nearly 20% less than those obtained from the 900 m 2 plots. The greatest difference in spacing measure- ments, and accordingly Sp values, was recorded when the confined arc and nearest neighbor methods were applied to the same inter-structural spaces. Our combined results illustrate that quantification of spatial arrangement can vary with both method and scale of measurement and suggest that across-study comparisons using the index developed by Bartholomew et al. (2000, Mar Ecol Prog Ser 206:45-58) will be difficult to interpret unless the same method of structural complexity measurement is employed, and similar spatial arrangements are compared.

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.

The role of meiobenthic copepod emergence in linkages among benthic, pelagic, and phytal habitats was examined in a subtidal seagrass (Tl~alassia testudjnurn) bed at the mouth of Tampa Bay, Florida. USA. On 4 dates the ability of emerging copepods to affect the density and composition of benthic and phytal assemblages was tested during 2 h periods of minimum and maximum emergence. Copepod exchanges between benthic and phytal habitats and the duration of pelagic excursions also were examined throughout a night by measuring settlement into 2 types of sediment traps and onto natural and defaunated seagrass blades. The ability of emerging fauna to disperse through the water column was determined from horizontal collectors. Changes In copepod densities and composition during periods of active emergence did not indicate an unequivocal exchange between sediment and seagrass blade assemblages. Copepod resettlement onto the sediments was greater during periods of increased emergence and suggested that emerging copepods typically did not remain in the water column for a prolonged (> 2 h) time. The dispersal of copepods through the water column was haphazard and unaffected by prevailing currents. Species and habitat affiliation influenced both the dispersal and settlement behaviors of emerging copepods. Although appreciable numbers of sediment-associated copepods can enter and disperse through the water column, our results suggest that the effects of emergence on linkages between benthic, pelagic, and phytal habitats are minimal or limited in duration.

The composition and abundance of bladedwelling meiofauna was determined over a 15 mo period (1983–1984) from a Thalassia testudinum Banks ex Konig meadow near Egmont Key, Florida, USA. Harpacticoid copepods, copepod nauplii, and nematodes were the most abundant meiofaunal taxa on T. testudinum blades. Temporal patterns in species composition and population life-history stages were determined for harpacticoid copepods, the numerically predominant taxon. Sixteen species or species complexes of harpacticoid copepods were identified. Harpacticus sp., the most abundant harpacticoid, comprised 47.8% of the total copepods collected, and was present throughout the study. Copepodites dominated the population structures of the blade-dwelling harpacticoid species on most collection dates. Ovigerous females and/or copepodites were always present, indicating continuous reproductive activity. Results suggest that epiphytic algae influence meiofaunal abundance on seagrass blades, as densities of most meiofaunal taxa at Egmont Key were positively associated with percent cover of epiphytic algae throughout the study. The majority of significant correlations between meiofaunal density and cover of epiphytic algae involved filamentous algae, although encrusting algae dominated the epiphytic community. It appears that resources provided by epiphytic algae to seagrass meiofauna (additional food, habitat, and/or shelter from predation) may be associated with algal morphology.

The role of predators in shaping prey life histories is a central theme in the ecological literature. However, the association between degree of predation risk and prey reproductive strategies has not been clearly established. We examined reproduction in the sailfin molly (Poecilia latipinna) from small tidal tributaries in a subtropical estuary. Our results revealed a gradient along which females produced many, small offspring at one extreme (mean = 42 offspring, 17 mg each) and fewer, larger offspring at the other (24 offspring, 29 mg each). Reproductive allotment ranged from 14.9-21.5% of maternal biomass. Based on our observation of divergent reproductive strategies, we experimentally tested the null hypothesis of no difference in predation risk among tributaries using a novel quantitative approach to estimate predation. We predicted greater risk in tributaries where mollies produced many, small offspring. Tethering confirmed increasing risk from 16.2 ± 5.3% SE to 54.7 ± 3.6% fish lost h(-1) across sites in agreement with observed variation in reproduction. Predation was unexpectedly higher than predicted at one of the four sites suggesting that additional factors (e.g., food) had influenced reproduction there. Our results provide insight into the well-studied concept of predator-mediated variation in prey reproduction by quantitatively demonstrating differential risk for mollies exhibiting divergent reproductive strategies. While the observed range of variation in reproductive traits was consistent with previous studies reporting strong predator effects, higher than expected predation in one case may suggest that the prey response does not follow a continuous trajectory of incremental change with increasing predation risk, but may be better defined as a threshold beyond which a significant shift in reproductive strategy occurs.

The relationship between the emergence (= active upward swimming) of phytal-dwelling meiobenthic copepods from blades within subtropical seagrass beds and dispersal of copepods was examined. Samples of copepods emerging from blades were collected using emergence traps. The distances to which copepods dispersed were measured using horizontal traps positioned at 0, 5, 10, 15, and 20 m outside the source of colonists. On each of two dates, experimental (defaunated) blades were sampled from patches at various distances from the source bed to assess copepod colonization; additionally, patches were arranged to determine if they served as “trapping stones” to accelerate copepod invasion of nearby patches. Twelve species of copepods vertically migrated from seagrass blades; these same species moved horizontally through the water column at all distances tested (up to 20 m). Species richness, abundances of total adults and copepodites, and total nauplii, did not decrease as patch distance from the source bed increased. Diosaccid sp. A and Scottolana canadensis ([Wiley] Coull) were the only copepod species displaying differences in abundance with distance (patch location). Colonization was extremely rapid, with ambient densities being attained within 2 days. The frequency of adults and copepodites was dependent upon patch location for 9 and 12 species on sampling dates 2 and 4, respectively. On day 2 copepodites dominated patches for most species, while adults dominated on day 4, although no consistent trend in location of patch containing the highest frequencies of copepodites or adults was detected. The frequency of males and females was dependent upon patch location for only 1 species on each date, with numbers of females exceeding males. Although no “stepping stone” effect was detected, active emergence of phytal-dwelling meiobenthic copepods from blade surfaces contributed to their dispersal to newly created patches of vegetation.

The influence of plant landscapes on recruitment of meiofaunal copepods was investigated in a New Zealand seagrass bed. Artificial plant mimics were placed into sediments at levels equivalent to natural blade densities (100 units per 0.5 X 0.25 m plot) in a variety of experimental treatments and retrieved 3 or 5 d later. To assess the effect of plant arrangement on faunal recruitment, plots were established within a seagrass bed in areas clipped of vegetation with (1) natural vegetation immediately surrounding the experimental plot; (2) natural vegetation clipped up to 0.5 m from plot edges; and (3) vegetation clipped up to 1 m from plot edges. Outside the natural seagrass bed plots were established in unvegetated sediments 0.5 m from the edge of the bed. Additionally, mimics were placed into plots 0.5 m from the edge of the bed which had sediment surfaces covered by plastic sheeting to determine whether recruitment onto plant mimics was from underlying sediments or from outside plots. Density of total copepods was highest on plant mimics with vegetation immediately adjacent to clipped areas inside the natural seagrass bed after 5 d. Densities of total copepods on mimics placed outside the bed were 5 x higher than those inside the bed and the covering of sediment significantly reduced recruitment. The dominant copepod species, Bulbarnphiascus sp., recruited to mimics irrespective of sediment border and probably invaded mimics from underlying sediments, although this was not true for other common species. While plant arrangement may influence recruitment of some copepod species, altering access to a source pool had a much greater effect on copepod densities on plant mimics.

An experimental investigation of drift macroalgal accumulation in seagrass beds was conducted to determine if the relationship between passively dispersed plant structure and the spatial arrangement of rooted macrophytes differed when examined across two spatial scales. Experiments were performed from December 1992 to April 1993 at four different sites in Tampa Bay, Florida, utilizing artificial seagrass units (ASUs) of uniform shoot length and density but with different areal dimensions [1 m2 (S) versus 4 m2 (L)]. Drift macroalgae were also collected from 1 m×1 m plots of natural seagrass at each of the experimental sites from November 1990 to May 1992 to determine the relationship between macroalgal abundance and structural characteristics of natural seagrass. Disproportionately higher amounts of macroalgae were captured in L compared to S plots suggesting that macroalgal accumulation does not scale up directly with the areal dimensions of ASU patches. Higher amounts of algae recovered in L plots is in accordance with patterns expected if algae accumulate in zones of attenuated water flow. Neither seagrass shoot density nor blade length could adequately describe the patterns of algal accumulation. These combined results suggest that explanations for trapping/retention of passively dispersed particles should extend beyond traditional measures of vegetation complexity.

Presence of meiofauna in resuspended sediments was investigated in a tidal creek system employing a specially designed core sampler and quick freezing techniques. Forty core samples were taken during 4 successive ebb tides to determine the distribution of meiofauna in (a) overlying water; (b) resuspended sediment; and (c) undisturbed sediment fractions of each sample. Our experiments demonstrate that 1 3 4 4 % of the meiobenthic copepod subcommunity was present in overly~ng and resuspended sediment fractions, while only a small percentage of nematodes was found simultaneously in these layers. We suggest that selected rneiofauna may disperse through tidally coupled mechanisms and that such phenomena should be addressed in demographic and community studies.