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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.

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.

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.

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 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 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.

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.

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 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.

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.

Dynamics of the aboveground and belowground structure of the seagrass Halodule wrighti~ (Asherson) Asherson was studied from April 1984 to March 1985. Seasonality of plant structure was evident, with the highest abundance of short shoots and belowground structures occuning in June. An Inverse relationship between root and rhizome biomass was observed with the former reachng a n~aximum in February and March, while the latter attained highest values in July and August. The number of short shoots produced per branch varied over the year, ranging from a low of 0.4 to a high of 1.5. The ratio number of branches/rhzome length was relatively constant over the study period with a slight decrease in summer. Examination of underground architecture revealed that, in contrast to plants that have highly branched underground structure, high belowground complexity of H. wrightfi is achleved by a dense intermingling of many plants with unidirectional rhizomes.

Examination of harpacticoid copepod morphology was conducted to determine whether morphological resemblance provides a reasonable index of habltat utilization and movement. Discriminant analysis was used to explore the relationship between body form and habitat utilization for copepod species collected from 3 subhabitats within seagrass beds in Tarnpa Bay, Florida. To examine the accuracy of our procedure the discriminant function derived for Tarnpa Bay copepods was apphed to copepods collected in worldwide studies. Three morphological characteristics ratlo of the length of Pereopod 1 first endopod segment to the remaining endopod segments, area of the cephalosome, and length of the first antennule significantly contributed to vanation in habitat util~zation by identifiable groups. Habitat utilization suggested from the literature corresponded well to that predicted by the dlscnrninant function derived for Tarnpa Bay harpacticoids. Our findings will be useful to suggest which copepods should (1) be associated with vegetation (2) display active migration and (3) be linked to sediment processes.

Patterns of acbve vertical migration exhibited by sediment-associated meiofauna were examlned in a subtropical seagrass meadow. Total numbers, species composition and percentage of sediment meiofauna found to migrate were examined during two 24 h s tudes . Large numbers (>20 000h-' m-2) of harpacticoid copepods representing a substantial proporbon (>50 "10) of the total benthic harpacticoid community migrated from the sediment into the water column. Nineteen of 36 harpacticoid species identified migrated actively. Migration was greatest during nighttime. Results indicate the importance of vertical migration to benthic-pelagic interactions in shallow seagrass environments.

The diets of juvenile (