Syringodium Filiforme Research Articles

Characterization of the Sargassum buxifolium, Syringodium filiforme, and Thalassia testudinum biomass for the removal of Pb(II) in aqueous solution

Characterization of the Sargassum buxifolium, Syringodium filiforme, and Thalassia testudinum biomass for the removal of Pb(II) in aqueous solution

Movements, foraging and habitat selection of southern stingrays (Hypanus americanus) in a tropical ecosystem altered by an invasive seagrass

This study provides some of the first evidence of how a common Caribbean fish species that relies on seagrass and sand habitats interacts with an invasive seagrass. The invasive seagrass Halophila stipulacea, first documented in the Caribbean in 2002, has rapidly expanded its range, displacing native seagrasses, and overgrowing bare sand. The southern stingray (Hypanus americanus) uses shallow seagrass and sand habitats for foraging. This paper examined the impacts of the invasive seagrass, H. stipulacea, on southern stingray behavior, foraging and movement patterns using acoustic telemetry and visual observations. From 2015 to 2018, 15 southern stingrays (14 juveniles of unknown sex and 1 female) were tagged with acoustic transmitters and passively monitored within an acoustic array in Brewers and Perseverance Bays, St. Thomas, United States Virgin Islands. The residence time, rates of movement and activity spaces for 50% and 95% utilization distributions (UD) were calculated for day and night periods. Tagged southern stingrays were detected within the array on average for 260 d (range 11–801 d) and residency for all individuals averaged 53% over the monitoring period (1079 d). Mean rates of movement per individual ranged from 40 to 150 m h−1, was lowest during the nighttime and were significantly higher during crepuscular periods. Activity spaces during day and night periods were nearly identical and averaged 0.05 km2 and 0.25 km2 for 50% and 95% UD, respectively. Distances between day and night 50% UD activity spaces was 148 m (range 8–409 m) and mean percent overlap was 38%. In addition to acoustic monitoring, benthic cover of available habitats and visual surveys of stingray behavior and habitat preferences were conducted along fixed transects. Monotypic stands of the invasive H. stipulacea seagrass represented 42% of benthic cover, followed by bare sand (27%), mixed patches of native and invasive seagrasses (23%) and the native Syringodium filiforme (7%). A habitat selection index (HSI) comparing the percent cover of available habitats and habitats occupied by stingrays found a strong preference for the native seagrass S. filiforme (HSI = 2.30) and bare sand (HSI = 1.79) compared to H. stipulacea (HSI = 0.70). Visual surveys also revealed that 50% of foraging stingrays were in S. filiforme, while 28% and 17% were foraging in H. stipulacea and bare sand, respectively. Our results are an important baseline for examining how further expansion of H. stipulacea may affect southern stingray movement patterns and foraging preferences.

First record of the seagrass Halophila stipulacea (Forsskal) Ascherson in the waters of the continental United States (Key Biscayne, Florida)

The first record of Halophila stipulacea is reported for the continental waters of the United States. In August 2024, a small meadow was identified inside Crandon Marina on Key Biscayne, Florida, USA. Following surveys have revealed that H. stipulacea has spread to adjacent areas immediately outside of the marina, often growing either in close proximity to, or interspersed with, the native seagrasses Thalassia testudinum, Syringodium filiforme, and Halodule wrightii. This serves as an initial report and extends the geographic scope of this introduced species in the Western Atlantic basin.

Limited potexvirus diversity in eastern Gulf of Mexico seagrass meadows.

Turtlegrass virus X, which infects the seagrass Thalassia testudinum, is the only potexvirus known to infect marine flowering plants. We investigated potexvirus distribution in seagrasses using a degenerate reverse transcription polymerase chain reaction (RT-PCR) assay originally designed to capture potexvirus diversity in terrestrial plants. The assay, which implements Potex-5 and Potex-2RC primers, successfully amplified a 584 nt RNA-dependent RNA polymerase (RdRp) fragment from TVX-infected seagrasses. Following validation, we screened 74 opportunistically collected, apparently healthy seagrass samples for potexviruses using this RT-PCR assay. The survey examined the host species T. testudinum, Halodule wrightii, Halophila stipulacea, Syringodium filiforme, Ruppia maritima, and Zostera marina. Potexvirus PCR products were successfully generated only from T. testudinum samples and phylogenetic analysis of sequenced PCR products revealed five distinct TVX sequence variants. Although the RT-PCR assay revealed limited potexvirus diversity in seagrasses, the expanded geographic distribution of TVX shown here emphasizes the importance of future studies to investigate T. testudinum populations across its native range and understand how the observed fine-scale genetic diversity affects host-virus interactions.

Sediment carbon storage in subtidal beds of the invasive seagrass Halophila stipulacea along an extreme water depth gradient, St. Thomas, U.S. Virgin Islands

Blue carbon ecosystems such as mangroves, salt marshes, and seagrass beds are found globally and are fundamental to fisheries production, storm surge protection, and carbon sequestration. The contribution of seagrass ecosystems to global carbon stocks is still not well understood, including in the United States Virgin Islands (USVI). No study has been published to-date assessing the sediment carbon density (SCD) in seagrass beds in the USVI. This study focused on the carbon storage ability of the invasive species, Halophila stipulacea, which is compact in size compared to common native seagrasses and has spread rapidly to become a dominant seagrass in the USVI. This species forms dense mats across a wide depth range (<1 m to 50 m) typically uninhabitable to its native counterparts (Syringodium filiforme and Thalassia testudinum). Several biotic and abiotic factors influence the carbon storage ability of seagrass, yet little is known about carbon storage sequestration along a depth gradient for H. stipulacea. This study provides the first assessment of the biological characteristics (shoot density, leaf area, leaf height, and percent cover) and carbon storage ability of H. stipulacea across a depth gradient (shallow: 5–10 m; medium: 15–20 m; deep: 25–30 m) at two sites in St. Thomas, USVI. Mean sediment carbon density (SCD) values per core reported for H. stipulacea in this study ranged from 3.88 to 15.67mgC/cm3; these were comparable to regional and global seagrass studies. Biological characteristics were not an accurate predictor of SCD. A significant interaction between water depth and site was found to affect mean SCD of H. stipulacea beds. It is likely that site-specific factors most likely account for variations seen within the data. Although carbon values in this study compared to values reported in the literature, other factors such as land use, proximity to carbon sources, sediment microbial community, and water current patterns may be driving SCD values. These findings highlight the need for site and species-specific carbon storage assessments on local to regional scales to accurately estimate current and forecasted blue carbon stocks.

Rapid sea level rise causes loss of seagrass meadows

As global declines in seagrass populations continue to cause great concern, long-term assessment of seagrass meadows show promise in furnishing valuable clues into fundamental causes of seagrass loss and drivers of environmental change. Here we report two long-term records of seagrass presence in western Gulf of Mexico coastal waters (Laguna Madre) that provided insight into their rapid decline in a relatively pristine ecosystem. Coincident with unprecedented increases in water depth starting in 2014 (14–25 mm y−1), monthly measurements at a deep edge fixed station revealed that two ubiquitous seagrass species (Halodule wrightii and Syringodium filiforme) vanished altogether in just five years; a subsequent basin-wide assessment revealed that seagrasses disappeared at 23% of 144 sentinel stations. Models that incorporate differing sea level rise scenarios and water depth thresholds reveal potential global losses of seagrass habitat (14,000 km2), with expansion into newly created shallow habitats constrained by altered natural shorelines.

A successful method to restore seagrass habitats in coastal areas affected by consecutive natural events.

Seagrass meadows, known for providing essential ecosystem services like supporting fishing, coastline protection from erosion, and acting as carbon sinks to mitigate climate change effects, are facing severe degradation. The current deteriorating state can be attributed to the combination of anthropogenic activities, biological factors (i.e., invasive species), and natural forces (i.e., hurricanes). Indeed, the global seagrass cover is diminishing at an alarming mean rate of 7% annually, jeopardizing the health of these vital ecosystems. However, in the Island Municipality of Culebra, Puerto Rico, losses are occurring at a faster pace. For instance, hurricanes have caused over 10% of cover seagrass losses, and the natural recovery of seagrasses across Culebra's coast has been slow due to the low growth rates of native seagrasses (Thalassia testudinum and Syringodium filiforme) and the invasion of the invasive species Halophila stipulacea. Restoration programs are, thus, necessary to revitalize the native seagrass communities and associated fauna while limiting the spread of the invasive species. Here, we present the results of a seagrass meadow restoration project carried out in Punta Melones (PTM), Culebra, Puerto Rico, in response to the impact of Hurricanes Irma and María during 2017. The restoration technique used was planting propagation units (PUs), each with an area of 900 cm2 of native seagrasses Thalassia testudinum and Syringodium filiforme, planted at a depth between 3.5 and 4.5 m. A total of 688 PUs were planted between August 2021 and August 2023, and a sub-sample of 88 PUs was monitored between August 2021 and April 2023. PUs showed over 95% of the seagrass survived, with Hurricane Fiona causing most of the mortalities potentially due to PUs burial by sediment movement and uplifting by wave energy. The surface area of the planting units increased by approximately 200% (i.e., 2,459 cm2), while seagrass shoot density increased by 168% (i.e., 126 shoots by PU). Additionally, flowering and fruiting were observed in multiple planting units, indicating 1) that the action taken did not adversely affect the PUs units and 2) that the project was successful in revitalizing seagrass populations. The seagrass restoration project achieved remarkable success, primarily attributed to the substantial volume of each PUs. Likely this high volume played a crucial role in facilitating the connection among roots, shoots, and microfauna while providing a higher number of undamaged and active rhizome meristems and short shoots. These factors collectively contributed to the enhanced growth and survivorship of the PUs, ultimately leading to the favorable outcome observed in the seagrass restoration project.

Shifts in biodiversity and physical structure of seagrass beds across 5 decades at Carriacou, Grenadines.

Caribbean seagrass beds are facing increasing anthropogenic stress, yet comprehensive ground-level monitoring programs that capture the structure of seagrass communities before the 1980s are rare. We measured the distribution of seagrass beds and species composition and abundance of seagrass and associated macroalgae and macroinvertebrates in 3 years over a 47-year period (1969, 1994, 2016) at Carriacou, Granada, an area not heavily impacted by local human activity. Seagrass cover and physical parameters of fringing beds were measured in transects at high (HWE) and low wave energy (LWE) sites; frequency of occurrence of all species, and biomass and morphology of seagrasses, were measured at 100 m2 stations around the island. Losses in nearshore seagrass cover occurred at HWE but not LWE sites between 1969 and 2016 and were associated with increases in the seagrass-free inshore zone (SFI) and erosional scarps within beds. Total biomass did not vary across years although there were progressive changes in seagrass composition: a decline in the dominant Thalassia testudinum and concomitant increase in Syringodium filiforme, and establishment of invasive Halophila stipulacea in 2016 at LWE sites. Species richness and diversity of the seagrass community were highest in 1994, when 94% of macroalgae (excluding Caulerpa) were most abundant, and sea urchins were least abundant, compared to 1969 and 2016. Multivariate statistical analyses showed differences in community composition across the 3 years that were consistent with trends in urchin abundance. Increases in SFI and scarp number in seagrass beds at HWE sites occurred mainly after 1994 and likely were related to increased wave forcing following degradation of offshore coral reefs between 1994 and 2016. Our observations suggest that landward migration of seagrass beds with rapidly rising sea level in future will not be realized in reef-protected seagrass beds at Carriacou barring reversal in the processes that have caused reef flattening.

Impact of invasive seagrass Halophila stipulacea on life history characteristics of juvenile yellowtail snapper (Ocyurus chrysurus)

Seagrass ecosystems provide essential nursery habitat to numerous coral reef fishes. Native Caribbean seagrasses Syringodium filiforme and Thalassia testudinum provide several juvenile fish species with foraging habitat and protection during this vulnerable stage of life. In 2002, an invasive seagrass Halophila stipulacea was discovered off the coast of Grenada and has since rapidly spread throughout the Caribbean. Halophila stipulacea has been shown to displace native seagrass species and may pose additional threats to juvenile reef fish populations that depend on native seagrass habitats as nurseries. The purpose of this study was to determine the effects of H. stipulacea on the early life history of yellowtail snapper (Ocyurus chrysurus). Settlement, mortality, and condition of juvenile yellowtail snapper were compared among native and invasive seagrass habitats around southern St. Thomas, United States Virgin Islands. From May 2020 to June 2021, monthly surveys within fixed plots during new moon periods provided information on settlement rates and survivorship among seagrass types. Length and weight of 260 juvenile yellowtail snapper were measured to derive condition factor among seagrass species. Significantly higher settlement and similar trends in mortality were seen in H. stipulacea when compared to native seagrasses. No significant difference was observed in condition factor of juvenile yellowtail snapper among seagrass species, although trends demonstrated a higher condition in individuals from native seagrass species. This study is the first of its kind to identify the direct effects of H. stipulacea during the early life history stages of a commercially important fish species in the Caribbean.

Sediment carbon storage differs in native and non-native Caribbean seagrass beds

Non-native species are expanding globally and can alter ecosystem functions, including food web dynamics, community structure and carbon storage. Seagrass are foundation species that contribute a variety of ecosystem services in near-shore coastal ecosystems, including a significant sink of carbon. In the Caribbean, the rapidly expanding non-native Halophila stipulacea has unknown impacts on carbon storage. To investigate the impacts on carbon storage, we quantified organic carbon (Corg) content in sediment and seagrass tissues from monotypic H. stipulacea beds, mixed native seagrass beds dominated by Thalassia testudinum and Syringodium filiforme, and unvegetated substrate in St. John, USVI. We found native seagrass-vegetated sediment contained 1.3 times more Corg than sediment covered by H. stipulacea, and 1.6 times more Corg than unvegetated areas on average. Whereas, H. stipulacea-dominated substrate stored 1.2 times more Corg than unvegetated substrate. Likewise, native species contained 2.2 times more aboveground biomass and 6.0 times more belowground biomass than H. stipulacea. Since seagrasses are critical sources of carbon sequestration, our results suggest that invading H. stipulacea is associated with lower carbon stocks which has potential implications for conservation activities and climate change mitigation.

Common ecological indicators identify changes in seagrass condition following disturbances in the Gulf of Mexico

Seagrasses are long-lived, clonal plants that can integrate fluctuations in environmental conditions over a range of temporal scales, from days to years, and can act as barometers of coastal change. There are many estimated seagrass traits and ecosystem parameters that have the potential to reflect ecosystem status, linking seagrass condition to natural and anthropogenic drivers of change. We identified five seagrass indicators and seven metrics that are suitable, affordable and frequently measured by 38 monitoring programs across the Gulf of Mexico (GoM). A specific set of ratings and assessment points were formulated for each measurable metric. We determined metric ratings (Acceptable, Concerning, Alarming) and validated assessment points using long-term monitoring data from Texas and Florida, coupled with existing literature and input from a panel of seagrass biologists. We reported scores using a blue-gray-orange (Acceptable-Concerning-Alarming) scale to summarize information in a format accessible to the public, resource managers, stakeholders, and policymakers. Seagrass percent cover, shoot allometry and species composition were sensitive indicators of large-scale climatic disturbances (droughts, hurricanes). Severe drought led to reductions in total seagrass cover and leaf length in Upper Laguna Madre, Texas, and Florida Bay; however, Syringodium filiforme was disproportionally affected in Texas while Thalassia testudinum beds responded strongly to drought impacts in Florida. Hurricanes Harvey (TX) and Irma (FL) also resulted in loss of seagrass cover and diminished leaf length in the Texas Coastal Bend and Florida Keys; both storms largely impacted T. testudinum and to a lesser extent, S. filiforme. Many of the metrics within these affected bays and basins received either a “Concerning” or “Alarming” rating, driven by the impacts of these disturbances. Our proposed indicators serve as a tool to evaluate seagrass condition at the bay or basin scale. Moreover, the indicators, metrics, and assessment points are amenable to large-scale evaluations of ecosystem condition because they are economically feasible. This framework may provide the foundation for a comprehensive assessment of seagrass status and trends across the entire GoM.

Variation in nutritional quality of an invasive seagrass does not explain its low palatability to two key herbivores in a Caribbean Bay

The seagrass Halophila stipulacea continues to spread rapidly through the Caribbean. Documenting native herbivore use of this invasive plant is important for understanding its impacts on marine communities and the mechanisms favoring its expansion. This study used observational and experimental data to determine if juvenile green turtles (Chelonia mydas) and long-spine urchins (Diadema antillarum) from the US Virgin Islands consumed H. stipulacea in the presence of native seagrass. Juvenile turtles associated significantly more with beds of native seagrass than mixed (native and invasive), and monospecific H. stipulacea, beds or sand bottoms. When individuals were followed, turtles foraged significantly more within mixed beds, but selectively fed on native species within them and were never observed feeding on monospecific H. stipulacea stands. When offered the native Thalassia testudinum and Syringodium filiforme, along with H. stipulacea, sea urchins significantly preferred S. filiforme over the other two choices. Measurements of fourteen nutritional and chemical parameters in these three seagrasses showed strong interspecific differences, with fewer and less predictable seasonal variations. Expressing these nutritional data by wet mass, rather than dry mass, also decreased the number of significant seasonal contrasts. Despite these differences, no parameters explained low herbivore preference for the invasive seagrass satisfactorily because nutrient values of H. stipulacea were often similar to those of the preferred natives. Our results conflict with recent studies pointing at low nutritional quality aiding against herbivory and suggest other mechanisms, such as herbivore learning and recognition of a novel resource, could be more important than currently appreciated.

Detecting Trends in Abundance and Distribution of Seagrasses in Lake Worth Lagoon, Palm Beach County, Florida

Over the past 15 years, seagrass community stability has varied in estuaries throughout Florida. This study sought to model potential patterns of physiochemical parameters and community composition that may correlate with the fluctuation of seagrass populations in Lake Worth Lagoon (LWL), Palm Beach County, FL over time (2007–2019). Seven transects and 4 polygon areas throughout the LWL were established and stratified along a north—south gradient. Sites were sampled annually (May–August) for water quality, seagrass and macroalgal abundance, and community composition. Models developed to explain macrophyte abundance and composition were assessed using Akaike Information Criterion. Interaction between year and site best explained seagrass abundance and community composition in transect and polygon sites. Transect data revealed that seagrass and macroalgae declined after 2012 and continued until barely detected after 2016. This die off was not consistent for all transects and there was site variability in annual dissolved oxygen, nitrate, phosphate, and salinity levels. Polygon sites exhibited a shift in community composition after 2013, initially dominated by seagrass species Syringodium filiforme and Halodule wrightii before transitioning in 2012–2013 to Halophila decipiens and Caulerpa spp. Central lagoon sites transitioned to communities devoid of nearly all vegetative species. The loss of seagrass and the change in community composition could be explained by a transient dry period in 2012 and a subsequent inflow of freshwater. These events (sudden drought followed by an increase in freshwater) likely compounded the stress on the system between 2011–2014, leading to a drastic change in seagrass community.

Interspecies differences in food sources for the tropical callichirid shrimp Neocallichirus spp. on San Salvador Island, Bahamas

At least 4 species of callichirid shrimp coexist in the shallow marine settings of San Salvador Island, an isolated, small platform of the all-carbonates Bahama Archipelago, implying that interspecific competition or trophic niche segregation occurs between these shrimp species. Carbon and nitrogen stable isotope analyses were conducted on soft tissues of 3 callichirid species, Neocallichirus cacahuate, N. grandimana, and N. maryae, to determine the food sources for each species. These analyses revealed that the isotopic trophic niches for these 3 species do not overlap. The most important food source for all 3 species was manatee grass Syringodium filiforme. The second most important food source for N. cacahuate and N. grandimana was drifting seaweed Sargassum sp., whereas that for N. maryae was turtle grass Thalassia testudium. These food-source adaptations likely contribute to the high species diversity of callichirid shrimp in tropical settings such as those found on San Salvador Island.

The Association of Bay Scallops (Argopecten irradians concentricus) with Seagrass and Macroalgae along the Florida Gulf Coast

Bay scallops (Argopecten irradians concentricus Say, 1822) exhibit a strong association with seagrass habitat from the time of larval settlement, but alternative habitats, such as macroalgae species, may also serve as important habitats for this species. The association of Florida bay scallops with the percent cover of observed seagrass, macroalgal species, and several substrate types (e.g., mud, shell, and rocks) was examined to determine whether a variety of seagrass and macroalgal species significantly influences the abundance of bay scallops in Florida. Sampling occurred at eight study sites along the Gulf coast of Florida, from Tampa Bay in the south to St. Andrew Bay in the north. SCUBA divers used a point-intercept approach along a transect to assess habitat type and percent cover, in addition to recording bay scallop abundance. Generalized additive models for location, scale, and shape were used to model bay scallop abundance as a function of habitat type. Across all sites, bay scallop abundance was positively correlated with percent cover of seagrass and negatively correlated with bare substrate, such as mud and sand. Five out of the 13 habitat types observed in association with bay scallops in this study were significant factors in models of bay scallop abundance including Acetabularia spp. (J.V. Lamouroux, 1812), Caulerpa spp. (J.V. Lamouroux, 1809), Gracilaria spp. (Greville, 1830), Syringodium filiforme (Kütz, 1860), and Thalassia testudinum (Koenig, 1805). The two most important habitat variables were T. testudinum and Gracilaria spp., and there was an observed threshold response of bay scallop abundance to these habitat variables at low to medium percent cover. This is the first study to identify the importance of both seagrass and several macroalgal species for Florida bay scallops and suggests that bay scallop restoration efforts may benefit from restoring seagrass and macroalgae.

Mapping the structure of mixed seagrass meadows in the Mexican Caribbean

The physical and ecological importance of seagrass meadows in coastal processes is widely recognized, and the development of tools facilitating characterization of their structure and distribution is important for improving our understanding of these processes. Mixed (multi-specific) meadows in a Mexican Caribbean reef lagoon were mapped employing a multiparameter approach, using PlanetScope remote sensing images, and supervised classification based on parameters related to the structure of the seagrasses meadows, including the cover percentages of seagrass/algae/sediment, algae thalli and seagrass shoot densities, canopy heights and estimated leaf area index (LAI). The cover, seagrass and algae densities, and seagrass canopy heights were obtained using ground truth sampling, while the LAI was estimated using data obtained from long-term monitoring programs. The maps do not show the differentiation of seagrass species, but ground truthing contemplated characterization of the density of Thalassia testudinum, Syringodium filiforme and Halodule wrightii and their respective LAIs. S. filiforme was the dominant species in terms of shoot density, and T. testudinum was dominant in terms of LAI. In the multiparameter-based map four classes were defined, based on the cover and structural characteristics, and its overall accuracy was very high (~90%). Maps based on sediment cover and LAI alone also had 4 classes, but they were less accurate than the multiparameter-based map (~70% and ~80%, respectively). The multiparameter-based seagrass map provided spatially-explicit data on the abundance and structure of seagrasses, useful for future monitoring of the changes in the meadows, and also for studies of that require data of large-scale meadow structure, such as inventories of associated biota, blue carbon storage, or modelling of the local hydrodynamics.

An invasive seagrass drives its own success in two invaded seas by both negatively affecting native seagrasses and benefiting from those costs

The nature and strength of interactions between native and invasive species can determine invasion success. Species interactions can drive, prevent or facilitate invasion, making understanding the nature and outcome of these interactions critical. We conducted mesocosm experiments to test the outcome of interactions between Halophila stipulacea, a seagrass that invaded the Mediterranean and Caribbean Seas, and native seagrasses (Cymodocea nodosa and Syringodium filiforme, respectively) to elucidate mechanisms explaining the successful invasions. Mesocosms contained intact cores with species grown either mixed or alone. Overall, in both locations, there was a pattern of the invasive growing faster with the native than when alone, while also negatively affecting the native, with similar patterns for shoot density, aboveground and belowground biomass. In the Caribbean, H. stipulacea increased by 5.6 ± 1.0 SE shoots in 6 weeks when grown with the native while, when alone, there was a net loss of −0.8 ± 1.6 SE shoots. The opposite pattern occurred for S. filiforme, although these differences were not significant. While the pattern in the Mediterranean was the same as the Caribbean, with the invasive grown with the native increasing shoots more than when it grew alone, these differences for shoots were not significant. However, when measured as aboveground biomass, H. stipulacea had negative effects on the native C. nodosa. Our results suggest that a seagrass that invaded two seas may drive its own success by both negatively affecting native seagrasses and benefiting from that negative interaction. This is a novel example of a native seagrass species facilitating the success of an invasive at its own cost, providing one possible mechanism for the widespread success of this invasive species.

Sponges facilitate primary producers in a Bahamas seagrass system

Seagrass beds are important coastal ecosystems worldwide that are shaped by facilitative interactions. Consequently, it is important to identify which taxa facilitate seagrasses. In other ecosystems, sponges contribute to the maintenance of diverse and productive systems through their facilitation of foundation species (e.g., mangroves) and the retention and recycling of energy and nutrients. Sponges are common in tropical and subtropical seagrass beds, yet we know little about how their presence impacts these communities. Here, we examine the impact of the sponge Ircinia felix on primary producers in a Thalassia testudinum dominated seagrass bed using a long-term field experiment in The Bahamas. We transplanted live sponges into the center of 5 × 5 m plots and monitored the response of seagrasses and macroalgae. Sponge presence increased seagrass nutrient content and growth, as well as the abundance of macroalgae and non-dominant seagrass species (Syringodium filiforme and Halodule wrightii). These changes were not seen in the control (unmanipulated) or structure (where we placed a polypropylene sponge replica) plots. We conclude that I. felix facilitates seagrass bed primary producers in oligotrophic systems, likely due to nutrients supplied by the sponge. Our study shows that sponges can have a positive influence on seagrass bed foundation species. Since recent theoretical work emphasizes the potential for facilitative interactions involving foundation species to be destabilized in the face of anthropogenic change, further work, is needed to understand how this facilitation impacts the stability of seagrass beds in areas where human activities have increased ambient nutrient levels.

Spatial configuration of seagrass community attributes in a stressed coastal lagoon, southeastern Gulf of Mexico

Terminos Lagoon is the largest coastal lagoon in the southern Gulf of Mexico and is a highly biodiverse and productive system that supports important seagrasses. These key habitats are under significant stress due to anthropic activities around and inside the lagoon. Considering the lack of updated information about their distribution, cover, and ecological condition, the objectives of this study were to assess the current morphological and seascape conditions of seagrass meadows in Terminos Lagoon and to evaluate their morphological changes in almost one decade (2010–2018). We combined remote sensing and fieldwork to assess environmental parameters (sea surface temperature and a light attenuation index), quantify seascape metrics, evaluate morphometric variables of seagrasses, and quantify organic carbon budgets. Three species of seagrasses (Thalassia testudinum, Syringodium filiforme and Halodule wrightii) were distributed in the lagoon and showed the highest densities and cover in sheltered zones, where shallow and more transparent water conditions occurred. In general, the seascape-cover diversity was regularly distributed in the study area, with the highest meadow connectivity mainly along the inner littoral region of the island. While the values we recorded for T. testudinum leaf length (X̄ = 18.6 cm), shoot densities (X̄ = 249.5 m−2) and total biomass (X̄ = 195.2 g DW m−2) were consistent with other recent studies, they were lower compared with other coastal systems in southeastern Gulf of Mexico and different between 2010 and 2018 in the lagoon, presumably associated with strong anthropic influences in the region. Finally, we provide a spatially explicit baseline information on morphology, seascape configuration and the first sensitivity map for one of the most important coastal lagoons in Mexico.

Influence of several stressful factors on the condition of seagrasses at Sabana–Camagüey​ Archipelago, Cuba

The influence of three potential anthropogenic stressful factors (coastal pollution from the mainland, the causeway Caibarién–Santa María and fishing with bottom-trawling nets) on the condition of seagrasses was assessed at 12 sites in two bays of Sabana–Camagüey​ archipelago, between 2010 and 2013. As for indicators of the condition of the seagrass ecosystem, the structure of the macrophyte community, marine angiosperm’s shoot density, and shoot length of marine angiosperms were analyzed. Abiotic variables as depth, turbidity, temperature, pH, dissolved oxygen, oxygen saturation, and chemical oxygen demand of seawater, were evaluated. The relationships of the three potential anthropogenic stressful factors and the abiotic factors (predictor variables) with the biological response variables were analyzed. Seagrass meadows in better condition, with higher values of cover and density of Thalassia testudinum, and lower values of depth, turbidity, salinity, chemical oxygen demand, were found at sites out of the bays and furthermost from the causeway and mainland. Areas without vegetation or with lower values of cover and density of T. testudinum, and higher cover of macroalgae and pioneer species of marine angiosperms as Syringodium filiforme and Halodule wrightii, were found in both bays. Turbidity and depth were the abiotic factors with the stronger negative influence on the structure of the seagrass community. Chemical oxygen demand and salinity also showed negative influences. Coastal pollution seems to be the anthropogenic factor that most influences the condition of seagrasses. No recovery of seagrasses was observed in areas where bottom-trawling fisheries had ceased. Distance to the causeway was not correlated with the condition of seagrass, but the potential for a negative influence on circulation persists. Seagrasses in the studied bays remain affected by the above-mentioned predictor abiotic factors, whose effects may be reinforced by the three anthropogenic stressful factors, acting synergistically with the bays’ oceanographic characteristics.