Search

Small variations in environmental parameters can substantially alter species composition, but the extent to which different species respond to these changes remains obscure. A synoptic survey of seagrass-associated faunal communities was performed across the Gulf of Mexico using otter trawls coupled with seagrass and water quality assessments. The abundance of eight central seagrass inhabitants, representing a range of functional groups, were quantified to identify factors that best predicted their prevalence across environmental gradients and the consistency of these ecological relationships. Seagrass density and drift algal biomass generally had the strongest influence on animal abundance (40–67%), although relationships with drift algae were species specific and seemingly related to faunal size and mobility. Abundances of free-swimming pinfish, pigfish, and silver perch were negatively related to drift algae biomass (0.7, 0.7, and 1.0% Δ per 1 g·m−2 drift algae, respectively), whereas the abundance of pipefish (Syngnathus spp.) and brown/pink shrimp (Penaeus spp.) tended to be positively related to algal biomass (0.8 and 1.6% Δ per 1 g·m−2 drift algae). Shrimp abundances increased by 3.6% per 1% increase in light attenuation while the abundance of a higher-order visual predator, silver perch, negatively responded to light attenuation (1.1% Δ per 1% Δ vertical light attenuation). Additionally, bivariate plots of organismal abundance and salinity or canopy height indicated a unimodal relationship with peaks in abundance associated with intermediate values for several species. This study explored the extent species and functional groups responded to variation in key elements of the abiotic and biotic environment, providing insight into community development and offering resource managers quantitative targets for aspects of habitat quality.

Halodule wrightii (shoal grass) is a dioecious seagrass with a widespread tropical and subtropical distribution. Like all seagrass species, H. wrightii has the ability to expand asexually through rhizome elongation and to reproduce sexually through seed. To better understand H. wrightii sexual recruitment dynamics in the northern Gulf of Mexico, we investigated seed bank densities at 815 sites from south Texas to the Florida Panhandle. H. wrightii seed reserves were spatially variable across the region, with seed densities ranging from 0 to 5290 seeds m−2. Spatial analysis revealed clusters of high seed densities (“hot spots”) in Upper Laguna Madre, TX, and Santa Rosa Sound, FL, and clusters of low seed densities (“cold spots”) in Lower Laguna Madre and Aransas Bay, TX. Hot spots were dominated by H. wrightii, whereas cold spots were dominated by Thalassia testudinum (turtle grass). We frequently found intact seed coat halves, suggesting germination; however, we also encountered broken seed coat pieces, characteristic of seed predation. Genotypic surveys within and adjacent to seed hot spots revealed genetically diverse adult populations 6 years post seed bank sampling. Our data show that H. wrightii seed reserves are heterogeneous across the northern Gulf of Mexico and that the factors driving variation in seed bank density, viability, and germination remain poorly understood. Information on the spatial heterogeneity of H. wrightii seed densities has relevance for seagrass management, including targeting meadows with high levels of reproductive effort for protection or designation as marine reserves.

Sexual reproduction remains an understudied aspect of seagrass ecology. We examined spatiotemporal variability in the percentage of short shoots with sexual reproductive structures and the proportion of sites that had flowered as an indicator of Thalassia testudinum sexual reproductive effort (RE) across Florida Bay, USA. Short shoots were collected annually during spring within 13 basins across the bay from 2006-2019. The sample period followed 2 very active hurricane seasons and included 2 subsequent major disturbance events, a large-scale die-off of seagrasses in 2015, and the passage of Hurricane Irma in 2017. On average, 4.7% of the collected short shoots had flowered between 2006 and 2019, ranging from 1.3-8.5% at the bay scale and 0-30% at the basin level. Regression analyses indicated that RE varied significantly among basins and years, with high multiyear variability in several basins. RE was negatively correlated with annual heat accumulation, and positively correlated with the number of days below 28°C. Annual heat accumulation rose steadily from 2006-2019; accordingly, bay-wide RE declined. RE was higher in western basins, which were the most affected by recent disturbance events, indicating a potentially important role for sexual reproduction in recovery from disturbance. However, significant reductions in RE following the 2015 die-off and Hurricane Irma show limits to the plasticity and resilience of T. testudinum, both in terms of reduced compensatory RE following successive disturbances and reductions in basal RE correlated with rising annual temperatures.

Hurricanes are some of the largest environmental drivers of change in coastal systems. We investigated the impacts of Hurricane Irma on benthic macrophyte communities in Florida Bay (FB) and the Florida Keys National Marine Sanctuary (FKNMS), USA. Spatiotemporal analyses were performed at multiple hierarchical levels (site, zone, region) to identify potential changes in the Braun-Blanquet (BB) densities of total seagrass (TSG) and total calcareous green macroalgae (TCAL) post-disturbance and to determine whether changes were attributable to hurricane impacts or normal seasonal and inter-annual variability. There were significant decreases in TSG in one of five zones in FKNMS and in one of six zones in FB, but no change in TCAL was recorded in either system. TSG in the Lower Keys Bayside declined from a mean BB score of 2.6 to 1.2, resulting from storm-induced erosion, whereas TSG in coastal FB declined from 1.05–2.4 to 0.36–2.0, likely due to prolonged hyposalinity and low dissolved oxygen following stormwater drainage. Overall, impacts to South Florida benthic macrophyte communities from Hurricane Irma were not catastrophic and were limited in spatial extent. Our results suggest that coastal areas hit by a storm with heavy winds are more likely to sustain direct physical impacts to the benthos, whereas estuarine areas with longer residence times are more at risk of the indirect effects of stormwater runoff and retention. Our analyses placed putative hurricane impacts within the context of recent variability and historical system baselines through the use of long-term monitoring data coordinated by multiple governmental and academic entities.

After several decades of research on edge effects in marine habitats, we still have little understanding of how organisms respond to marine ecotones, and methodological gaps appear to be limiting our progress. Using recent literature (2010–2018), we synthesized responses and processes of organisms across several marine habitats. Specifically, we examined the uniformity of studies across biogenic habitats, the scales selected for exploring edge effects, the experimental approaches used, and the confounding influences that muddle our interpretation of results. The majority of edge effect studies are still conducted in seagrass systems and focused on response patterns. We found that the majority of studies were equally likely to report an increase, decrease, neutral, or equivocal effect depending on the context of the organism or habitat. Additionally, only a single measure, or a few related responses, is assessed and causal mechanisms are rarely tested. We note that most studies quantitatively defined an edge habitat as a linear distance from a habitat boundary (e.g.

Both biotic and abiotic factors can affect whether seagrass meadows establish as large, continuous features or as a mosaic of smaller patches, and these processes act across multiple spatial scales. Of these processes, sexual recruitment is considered vital for the recovery and resilience of seagrass meadows. Because numerous estuarine fauna can impact sexual recruitment by consuming seeds, it is important to understand variation in seed consumption throughout the seascape. We sought to determine how cross‐scale processes affected seed consumption of Zostera marina, a widely distributed seagrass species. We deployed seed predation units (SPU) within patches ranging in size from 0.28 to 28.48 m², and on unvegetated, sandy bottom. Seed consumption was analysed across patch sizes, at patch centres and edges and within the context of total seagrass cover within buffer zones surrounding SPU locations. Using structural equation modelling, we found that measured seascape parameters explained 34% of the observed variation in seed consumption. Specifically, we found that seagrass presence had the strongest effect on seed predation followed by a negative effect of patch size on seed consumption. Although there was no direct effect of percent seagrass cover (within a 4‐m buffer of the SPU) on seed predation, percent seagrass cover had a negative indirect effect through its positive correlation with patch size. However, we found that once variation due to patch size and areal cover were accounted for, seeds placed at patch interiors actually experienced greater consumption rates. We did not find similar relationships with our potential seed consumers, although our snapshot sampling likely obscured transient effects. We argue that seagrass recruitment could be affected by seed predation, which is influenced by multiple processes, including predator dispersal, behaviour and aggregation. Since seed‐based restoration is becoming more common, and the role of sexual recruitment in meadow maintenance appears to be increasingly important for seagrass resilience, our results demonstrate that for current management strategies to be successful, there is a need to better understand seed predation in seagrass‐dominated seascapes. Synthesis. Factors that influence propagule supply and recruitment success of seagrass operate and interact across multiple spatial scales, which can have implications for management.

Seagrasses are threatened worldwide due to anthropogenic and natural disturbances disrupting the multiple feedbacks needed to maintain these ecosystems. If the disturbance is severe enough, seagrass systems may undergo a regime shift to a degraded system state that is resistant to recovery. In Florida Bay, Florida, United States, two recent, large-scale disturbances (a drought-induced seagrass die-off in 2015 and Hurricane Irma in 2017) have caused 8,777 ha of seagrass beds to degrade into a turbid, unvegetated state, causing a large sediment plume. Using satellite imagery digitization and long-term seagrass cover data, we investigate the expansion of this sediment plume between 2008 and 2020 and the potential interaction of this sediment plume with seagrass recovery in two focal basins in Florida Bay affected by the die-off, Johnson and Rankin. The average size of the sediment plume increased by 37% due to the die-off and Hurricane Irma, increasing from an average of 163.5 km2 before the disturbances to an average of 223.5 km2. The expansion of the plume was basin-specific, expanding into Johnson after the 2015 seagrass die-off with expansive and long-lasting effects, but only expanding into Rankin after Hurricane Irma with less severe and short-term effects. Furthermore, the sediment plume was negatively correlated with seagrass cover in Johnson, but held no relationship with seagrass cover in Rankin. Thus, different disturbances can act upon seagrass ecosystems at varying scales with varying consequences. This study illustrates the advantage of combining satellite imagery with field data to monitor disturbances as well as highlights the importance of investigating disturbances of seagrass ecosystems at various scales to comprehend seagrass resilience in the context of future extreme events.

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.

Seagrass wasting disease, caused by protists of the genus Labyrinthula, is an important stressor of the dominant macrophyte in Florida Bay (FB), United States, Thalassia testudinum. FB exhibits countervailing gradients in plant morphology and resource availability. A synoptic picture of the Thalassia-Labyrinthula relationship was obtained by assessing the activity of four immune biomarkers in conjunction with pathogen prevalence and load [via quantitative PCR (qPCR)] at 15 sites across FB. We found downregulated immune status paired with moderate pathogen load among larger-bodied host phenotypes in western FB and upregulated immunity for smaller-bodied phenotypes in eastern FB. Among the highest immune response sites, a distinct inshore-offshore loading pattern was observed, where coastal basins exposed to freshwater runoff and riverine inputs had the highest pathogen loads, while adjacent offshore locations had the lowest. To explain this, we propose a simple, conceptual model that defines a framework for testable hypotheses based on recent advances in resistance-tolerance theory. We suggest that resource availability has the potential to drive not only plant size, but also tolerance to pathogen load by reducing investment in immunity. Where resources are more scarce, plants may adopt a resistance strategy, upregulating immunity; however, when physiologically challenged, this strategy appears to fail, resulting in high pathogen load. While evidence remains correlative, we argue that hyposalinity stress, at one or more temporal scales, may represent one of many potential drivers of disease dynamics in FB. Together, these data highlight the complexity of the wasting disease pathosystem and raise questions about how climate change and ongoing Everglades restoration might impact this foundational seagrass species.

Seagrass meadows are important coastal ecosystems that are declining worldwide. Given the profound impact of the microbiome on plant health, exploration of the seagrass microbiome is critical for proper ecosystem management and conservation. Although prior studies have investigated seagrass‐associated bacteria, fungi, and protists, virtually nothing is known about viruses infecting these flowering marine plants. Here, we report genomic and microscopic evidence of a new positive‐sense, single‐stranded ribonucleic acid virus infecting apparently healthy Thalassia testudinum in Florida. The virus, named turtlegrass virus X (TVX), shares 66% genome‐wide pairwise identity with foxtail mosaic virus, a potexvirus that infects terrestrial grasses. Quantitative polymerase chain reaction revealed TVX presence in 10% to 80% of T. testudinum leaves from two Tampa Bay sampling locations in February and August 2017, with an average viral load of 4.65 × 108 copies per mg leaf tissue. The discovery of TVX advances seagrass microbiome research, prompting further studies to assess its ecological impact.

Seagrass meadows are important sites of nitrogen (N) transformations in estuaries, however, the role of N loading in driving relative rates of N fixation and denitrification in seagrass habitats is unclear. The current study quantified N fluxes in eelgrass meadows (Zostera marina (L.)) and nearby unvegetated sand in trials representing in situ and N enriched conditions. Net N2 fluxes were low or negative under in situ conditions in both eelgrass and sand. Under N enriched conditions, denitrification was higher than N-fixation, and denitrification in eelgrass was significantly higher than sand. Denitrification of water column NO3- was more significant than coupled nitrification-denitrification in the eelgrass. Denitrification was likely supported by greater organic carbon and N within the eelgrass sediment compared to sand. Eelgrass meadows in Shinnecock Bay may facilitate the ecosystem service of N removal and retention during short-term nutrient pulses that can originate from groundwater discharge and stormwater runoff.

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.

Clonal foraging in response to heterogeneously distributed water, light or mineral resources has been demonstrated for a number of terrestrial plant species. The existence of similar behavior in seagrasses and the cross-scale effects of clonal foraging on patch development, however, have not fully been explored. Our objective was to test whether spatial exploration by independent ramet clusters could generate emergent patch behavior consistent with clonal foraging theory. We also examined the effect of nutrient amendment on reproductive effort and seedling recruitment. Working in Shinnecock Bay, New York, USA, with the clonal marine angiosperm, Zostera marina, we attempted to stimulate directional growth along ten patch edges over a two-year period using subterranean fertilizer. Changes in ramet demography, patch expansion, seedling emergence and reproductive effort were quantified through repeated shoot censusing. We found that nutrient addition accelerated patch expansion. Enriched edges exhibited significantly higher shoot densities, indicating that a ramet proliferation, selective ramet placement or a combination of the two responses had occurred. The seasonality of this effect was different between treatments and consistent among years, representing a fundamental shift in the pattern and phenology of seagrass growth. Within patches, no detectable differences in per capita branching rates or reproductive effort were observed. This study provides the first evidence of foraging behavior by patches of Z. marina, and offers new insight into its seasonal growth patterns during the as yet poorly understood colonization period.

Zostera marina is a cosmopolitan, temperate seagrass species capable of both sexual and asexual (i.e., clonal) reproduction. Until recently, the importance of sexual reproduction has been largely dismissed, and clonal growth has dominated our understanding of space acquisition by Z. marina. This model of Z. marina growth was developed in locations where reproductive effort falls on the lower end of a wide range in sexual productivity. This study assessed Z. marina seed production as a function of patch size in a landscape where sexual reproduction has played a significant role in meadow expansion. Additionally, a landscape-scale analysis of seagrass proximity was performed to determine whether relationships between seed production and percent seagrass coverage exist. Reproductive shoots were collected from 58 seagrass patches of four different size classes: 2.5, 5, 10, and 20 m2 over a two-year period. Seeds were harvested, enumerated, and scored for viability. Viable seed density was significantly related to patch size, but no statistically significant difference was found for non-viable seed densities between patch sizes. Larger patches, with both an edge and center region, were evaluated by region; no difference was found between seed production at the edge vs. center for these size classes. Finally, seed densities were not positively correlated with the amount of proximate seagrass in the landscape. The results of this study suggest that more explicit regional studies of sexual reproduction dynamics must be undertaken to fully understand the complex reproductive ecology of this angiosperm.

Seagrasses are a diverse group of clonal marine macrophytes. Their disappearance in recent decades has been an alarming component of estuarine urbanization, effectively transitioning vast portions of global coverage to disturbed or recovering states. Understanding dispersal and recruitment patterns within and among extant populations is now vitally important to predicting both the form and pace of recovery. Working with a perennial ecotype of Zostera marina within a shallow lagoon in Long Island, New York, U.S.A., we combined high resolution, decade-long seagrass mapping with polymorphic microsatellite analysis to examine the interactive effects of pollination and seed dispersal distance on the dynamics of sexual recruitment across a range of spatial scales (centimeters to decameters). We found clone structure to be restricted to less than three meter across a 56,250-m2 study site. Pollination distances ranged from 0.57 m to 73.91 m, while seed dispersal varied systematically from 1.85 m to 5.31 m for naked seeds, and randomly throughout the study site (0.17 m to 34.54 m) for seeds deposited by floating reproductive shoots. Pedigree analyses corroborated these findings, with full sibling groups clustering neatly within larger half-sibling kinships at spatial scales of 2-6 m. We successfully demonstrate that over a four-year period sexual reproduction and seedling recruitment played appreciable roles in the colonizing process of Z. marina, configuring the landscape through the deposition of rafted seeds, and contributing to patch expansion via the limited dispersal of naked seeds.

Ecophysiological stress and physical disturbance are capable of structuring meadows through a combination of direct biomass removal and recruitment limitation; however, predicting these effects at landscape scales has rarely been successful. To model environmental influence on sexual recruitment in perennial Zostera marina, we selected a sub-tidal, light-replete study site with seasonal extremes in temperature and wave energy. During an 8-year observation period, areal coverage increased from 4.8 to 42.7%. Gains were stepwise in pattern, attributable to annual recruitment of patches followed by centrifugal growth and coalescence. Recruitment varied from 13 to 4,894 patches per year. Using a multiple linear regression approach, we examined the association between patch appearance and relative wave energy, atmospheric condition and water temperature. Two models were developed, one appropriate for the dispersal of naked seeds, and another for rafted flowers. Results indicated that both modes of sexual recruitment varied as functions of wind, temperature, rainfall and wave energy, with a regime shift in wind-wave energy corresponding to periods of rapid colonization within our site. Temporal correlations between sexual recruitment and time-lagged climatic summaries highlighted floral induction, seed bank and small patch development as periods of vulnerability. Given global losses in seagrass coverage, regions of recovery and re-colonization will become increasingly important. Lacking landscape-scale process models for seagrass recruitment, temporally explicit statistical approaches presented here could be used to forecast colonization trajectories and to provide managers with real-time estimates of future meadow performance; i.e., when to expect a good year in terms of seagrass expansion. To facilitate use as forecasting tools, we did not use statistical composites or normalized variables as our predictors. This study, therefore, represents a first step toward linking remotely acquired environmental data to sexual recruitment, an important measure of seagrass performance that translates directly into landscape-scale coverage change.

Edge effects are a dominant subject in landscape ecology literature, yet they are highly variable and poorly understood. Often, the literature suggests simple models for edge effects-positive (enhancement at the edge), negative (enhancement at the interior), or no effect (neutral)--on a variety of metrics, including abundance, diversity, and mortality. In the marine realm, much of this work has focused on fragmented seagrass habitats due to their importance for a variety of commercially important species. In this study, the settlement, recruitment, and survival of bay scallops was investigated across a variety of seagrass patch treatments. By simultaneously collecting settlers (those viable larvae available to settle and metamorphose) and recruits (those settlers that survive some period of time, in this case, 6 weeks) on the same collectors, we were able to demonstrate a "balance" between positive and negative edge effects, resulting in a net neutral effect. Scallop settlement was significantly enhanced along seagrass edges, regardless of patch type while survival was elevated within patch interiors. However, recruitment (the net result of settlement and post-settlement loss) did not vary significantly from edge to center, representing a neutral effect. Further, results suggest that post-settlement loss, most likely due to predation, appears to be the dominant mechanism structuring scallop abundance, not patterns in settlement. These data illustrate the complexity of edge effects, and suggest that the metric used to investigate the effect (be it abundance, survival, or other metrics) can often influence the magnitude and direction of the perceived effect. Traditionally, high predation along a habitat edge would have indicated an "ecological trap" for the species in question; however, this study demonstrates that, at the population level, an ecological trap may not exist.