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Interactions such as mutualism and facilitation are common in ecosystems established by foundation species; however, their outcomes vary and show conditionality. In a Mexican Caribbean Bay, a seagrass-coralline algae (rhodoliths) mutualism protects the seagrass Thalassia testudinum from green turtle overgrazing. We postulate that the state of the seagrass meadow in this bay depends on the strengths of the interactions among seagrasses, green turtles, and coralline algae. Spatio-temporal changes through satellite imagery showed rhodolith bed developed rapidly from 2009 (undetected) to 2016 (bed of 6934 m2). Typically, such rapid expansion of the rhodoliths does not occur in seagrass meadows. An in situ growth experiment of coralline algae showed that a combination of reduction in light and wave movement (usual in dense seagrass meadows) significantly reduced their growth rates. In the rhodolith beds, the growth rates of the coralline algae Neogoniolithon sp. and Amphiroa sp. were high at 9.5 mm and 15.5 mm per growth tip y−1, respectively. In a second experiment, we found lower mortality in coralline algae within a rhodolith bed compared to algae placed outside the bed, likely explained by the reduced resuspension that we found in a third experiment, and this positive feedback may explain the high population increase in the rhodoliths, once established when the turtles grazed down the seagrass canopy. Therefore, the grazing-protection mutualism between seagrasses and coralline algae is thus conditional and came into existence under a co-occurrence of intensive grazing pressure and rapid population growth of coralline algae facilitated by positive feedback from increased growth and reduced sediment resuspension by the dense rhodolith bed. [ABSTRACT FROM AUTHOR]

Thalassia testudinum has undergone die-offs in the past century due to seagrass wasting disease caused by Labyrinthula sp. Little is known about how seagrasses resist Labyrinthula infections, but metabolites that inhibit Labyrinthula were previously extracted from seagrass leaves. Furthermore, leaf fungal endophytes from seagrasses possess antipathogenic potential, but their activity against Labyrinthula is unknown. Here, we aimed to identify whether fungal endophytes of T. testudinum can aid in disease defense against Labyrinthula. Through Illumina amplicon sequencing of the leaves' mycobiome, we identified fungi that are known to produce antimicrobials. We also isolated and extracted organic compounds from endophytes to test their anti-Labyrinthula potential using disk diffusion assays. There were 22 isolates that inhibited Labyrinthula, from which two isolates, Trichoderma sp. P1a and Diaporthe sp. M14, displayed strong inhibition. LC-HRMS/MS analysis determined the likely bioactive compounds of Trichoderma as peptaibols and of Diaporthe as cytosporone B. Cytosporone B was confirmed bioactive against Labyrinthula via disk diffusion assays. While these organisms are low in abundance in the mycobiome, this study demonstrates that seagrass endophytes have the potential to play an important role in defense against Labyrinthula. [ABSTRACT FROM AUTHOR]

Plant microbiomes are known to serve several important functions for their host, and it is therefore important to understand their composition as well as the factors that may influence these microbial communities. The microbiome of Thalassia testudinum has only recently been explored, and studies to-date have primarily focused on characterizing the microbiome of plants in a single region. Here, we present the first characterization of the composition of the microbial communities of T. testudinum across a wide geographical range spanning three distinct regions with varying physicochemical conditions. We collected samples of leaves, roots, sediment, and water from six sites throughout the Atlantic Ocean, Caribbean Sea, and the Gulf of Mexico. We then analyzed these samples using 16S rRNA amplicon sequencing. We found that site and region can influence the microbial communities of T. testudinum, while maintaining a plant-associated core microbiome. A comprehensive comparison of available microbial community data from T. testudinum studies determined a core microbiome composed of 14 ASVs that consisted mostly of the family Rhodobacteraceae. The most abundant genera in the microbial communities included organisms with possible plant-beneficial functions, like plant-growth promoting taxa, disease suppressing taxa, and nitrogen fixers. [ABSTRACT FROM AUTHOR]

Thalassia testudinum has undergone die-offs in the past century due to seagrass wasting disease caused by Labyrinthula sp. Little is known about how seagrasses resist Labyrinthula infections, but metabolites that inhibit Labyrinthula were previously extracted from seagrass leaves. Furthermore, leaf fungal endophytes from seagrasses possess antipathogenic potential, but their activity against Labyrinthula is unknown. Here, we aimed to identify whether fungal endophytes of T. testudinum can aid in disease defense against Labyrinthula. Through Illumina amplicon sequencing of the leaves’ mycobiome, we identified fungi that are known to produce antimicrobials. We also isolated and extracted organic compounds from endophytes to test their anti-Labyrinthula potential using disk diffusion assays. There were 22 isolates that inhibited Labyrinthula, from which two isolates, Trichoderma sp. P1a and Diaporthe sp. M14, displayed strong inhibition. LC-HRMS/MS analysis determined the likely bioactive compounds of Trichoderma as peptaibols and of Diaporthe as cytosporone B. Cytosporone B was confirmed bioactive against Labyrinthula via disk diffusion assays. While these organisms are low in abundance in the mycobiome, this study demonstrates that seagrass endophytes have the potential to play an important role in defense against Labyrinthula.

Plant microbiomes are known to serve several important functions for their host, and it is therefore important to understand their composition as well as the factors that may influence these microbial communities. The microbiome of Thalassia testudinum has only recently been explored, and studies to-date have primarily focused on characterizing the microbiome of plants in a single region. Here, we present the first characterization of the composition of the microbial communities of T. testudinum across a wide geographical range spanning three distinct regions with varying physicochemical conditions. We collected samples of leaves, roots, sediment, and water from six sites throughout the Atlantic Ocean, Caribbean Sea, and the Gulf of Mexico. We then analyzed these samples using 16S rRNA amplicon sequencing. We found that site and region can influence the microbial communities of T. testudinum, while maintaining a plant-associated core microbiome. A comprehensive comparison of available microbial community data from T. testudinum studies determined a core microbiome composed of 14 ASVs that consisted mostly of the family Rhodobacteraceae. The most abundant genera in the microbial communities included organisms with possible plant-beneficial functions, like plant-growth promoting taxa, disease suppressing taxa, and nitrogen fixers.

Drift macroalgae, often found in clumps or mats adjacent to or within seagrass beds, can increase the value of seagrass beds as habitat for nekton via added food resources and structural complexity. But, as algal biomass increases, it can also decrease light availability, inhibit faunal movements, smother benthic communities, and contribute to hypoxia, all of which can reduce nekton abundance. We quantified the abundance and distribution of drift macroalgae within seagrass meadows dominated by turtle grass Thalassia testudinum across the northern Gulf of Mexico and compared seagrass characteristics to macroalgal biomass and distribution. Drift macroalgae were most abundant in areas with higher seagrass shoot densities and intermediate canopy heights. We did not find significant relationships between algal biomass and point measures of salinity, temperature, or depth. The macroalgal genera Laurencia and Gracilaria were present across the study region, Agardhiella and Digenia were collected in the western Gulf of Mexico, and Acanthophora was collected in the eastern Gulf of Mexico. Our survey revealed drift algae to be abundant and widespread throughout seagrass meadows in the northern Gulf of Mexico, which likely influences the habitat value of seagrass ecosystems. [ABSTRACT FROM AUTHOR]

Drift macroalgae, often found in clumps or mats adjacent to or within seagrass beds, can increase the value of seagrass beds as habitat for nekton via added food resources and structural complexity. But, as algal biomass increases, it can also decrease light availability, inhibit faunal movements, smother benthic communities, and contribute to hypoxia, all of which can reduce nekton abundance. We quantified the abundance and distribution of drift macroalgae within seagrass meadows dominated by turtle grass Thalassia testudinum across the northern Gulf of Mexico and compared seagrass characteristics to macroalgal biomass and distribution. Drift macroalgae were most abundant in areas with higher seagrass shoot densities and intermediate canopy heights. We did not find significant relationships between algal biomass and point measures of salinity, temperature, or depth. The macroalgal genera Laurencia and Gracilaria were present across the study region, Agardhiella and Digenia were collected in the western Gulf of Mexico, and Acanthophora was collected in the eastern Gulf of Mexico. Our survey revealed drift algae to be abundant and widespread throughout seagrass meadows in the northern Gulf of Mexico, which likely influences the habitat value of seagrass ecosystems.

Seagrass has important ecological functions, namely as a nursery-grown, spawning and protection areas for marine biota. In the world, there are 60 species of seagrasses, and in Indonesia, there are 14 species from 7 genera. The waters of North Sulawesi store a high potential of seagrass ecosystems. This study aimed to observe the distribution of seagrass from the Bahoi, Manembo-Nembo, and Tandurusa coast, North Sulawesi, Indonesia. Sampling carried out at the lowest ebb at the lunar or full moon phase. The method used for sampling is random, both for transect and squared lines. The results showed that from the Bahoi, Menembo-Nembo and Tandurusa coast, ten seagrass species from 7 genera and two families were found, namely Enhallus acoroides, Cymodocea rotundata, Cymodocea serrulata, Halodule uninervis, Halodule pinifolia, Halophila minor, Halophla ovalis, Syringodium isoetifolium, Thalassia hemprichii, dan Thalassodendron ciliatum. Information on seagrass distribution in an area can be taken into consideration for the government and related agencies in drafting a regulation in the management of seagrass ecosystem resources.

The intensity of major storm events generated within the Atlantic Basin is projected to rise with the warming of the oceans, which is likely to exacerbate coastal erosion. Nature-based flood defence has been proposed as a sustainable and effective solution to protect coastlines. However, the ability of natural ecosystems to withstand major storms like tropical hurricanes has yet to be thoroughly tested. Seagrass meadows both stabilise sediment and attenuate waves, providing effective coastal protection services for sandy beaches. To examine the tolerance of Caribbean seagrass meadows to extreme storm events, and to investigate the extent of protection they deliver to beaches, we employed a combination of field surveys, biomechanical measurements and wave modelling simulations. Field surveys of seagrass meadows before and after a direct hit by the category 5 Hurricane Irma documented that established seagrass meadows of Thalassia testudinum remained unaltered after the extreme storm event. The flexible leaves and thalli of seagrass and calcifying macroalgae inhabiting the meadows were shown to sustain the wave forces that they are likely to experience during hurricanes. In addition, the seagrass canopy and the complex biogeomorphic landscape built by the seagrass meadows combine to significantly dissipate extreme wave forces, ensuring that erosion is minimised within sandy beach foreshores. The persistence of the Caribbean seagrass meadows and their coastal protection services during extreme storm events ensures that a stable coastal ecosystem and beach foreshore is maintained in tropical regions. [ABSTRACT FROM AUTHOR]

Abstract Background Seagrasses are foundation species in estuarine and lagoon systems, providing a wide array of services for the ecosystem and the human population. Understanding the dynamics of their stands is essential in order to better assess natural and anthropogenic impacts. It is usually considered that healthy seagrasses aim to maximize their stand biomass (g DW m−2) which may be constrained by resource availability i.e., the local environment sets a carrying capacity. Recently, this paradigm has been tested and reassessed, and it is believed that seagrasses actually maximize their efficiency of space occupation—i.e., aim to reach an interspecific boundary line (IBL)—as quick as possible. This requires that they simultaneously grow in biomass and iterate new shoots to increase density. However, this strategy depresses their biomass potential. Results to comply with this new paradigm, we developed a seagrass growth model that updates the carrying capacities for biomass and shoot density from the seagrass IBL at each time step. The use of a joint biomass and density growth rates enabled parameter estimation with twice the sample sizes and made the model less sensitive to episodic error in either of the variables. The use of instantaneous growth rates enabled the model to be calibrated with data sampled at widely different time intervals. We used data from 24 studies of six seagrass species scattered worldwide. The forecasted allometric biomass–density growth trajectories fit these observations well. Maximum growth and decay rates were found consistently for each species. The growth rates varied seasonally, matching previous observations. Conclusions State-of-art models predicting both biomass and shoot density in seagrass have not previously incorporated our observation across many seagrass species that dynamics depend on current state relative to IBL. Our model better simulates the biomass–density dynamics of seagrass stands while shedding light on its intricacies. However, it is only valid for established patches where dynamics involve space-filling, not for colonization of new areas.

This study empirically examines predictions concerning boundary permeability as a function of patch contrast (i.e., the magnitude of difference in measures across patch interfaces), light level, and faunal mobility and density, as well as relative rates of emigration and immigration. I assessed permeability using invertebrate transfer in a macroalgal-seagrass-sand landscape, with particular emphasis on the caridean shrimp Thor floridanus. Proportional emigration was estimated by staining algal fauna in situ using neutral red (a live immersion stain) and then later collecting all animals in the algal clumps and in the surrounding sand or seagrass. Permeability was in part a function ofboundary contrast in this milieu; macroalgal patches were more of a closed system in sand than in seagrass. Contrary to predictions, proportional emigration across both the algal-seagrass and algal-sand boundaries was inversely related to faunal density. Another unexpected result was that the rate of change in emigration with increasing density was unaffected by differential contrast among habitat types. The observed enhanced permeability for more motile fauna was consistent with predictions. A related finding was thatpermeability was greater at night than during the day, probably as a function ofincreased nocturnal vagility of benthic fauna. Emigration was not in equilibriumwith immigration at the temporal scale of this study (hours) for the majority ofspecies tested. Emigration-immigration disequilibria should be most likely whenthe temporal scale is small, and in such cases caution should be exercised whenextrapolating from one transfer parameter to the other.

ABSTRACT Thalassia testudinum and Halodule wrigthii are the dominant seagrasses in the Caribbean, being common across shallow shorelines, either as monospecific or as intermixed meadows. Among the macrofauna associated with these beds, crustaceans are considered essential for the whole ecosystem functioning. However, knowledge about the associated community of decapod crustaceans in assemblages of T. testudinum and H. wrigthii is still scarce, particularly outside of protected areas. Here we report eight new decapod species for the Paraguaná Peninsula (Falcón State, Venezuela) in association with intermixed seagrass beds: Achelous tumidulus Stimpson, 1871, Alpheus aff. floridanus Kingsley, 1878, Chorinus heros (Herbst, 1790), Clibanarius antillensis (Stimpson, 1859), Clibanarius sclopetarius (Herbst, 1796), Latreutes parvulus (Stimpson, 1866), Panopeus occidentalis Saussure, 1857, and Processa fimbriata Manning & Chace, 1971. These records represent habitat extensions and fill gaps in the geographical distribution of the species along the northern coast of South America. Furthermore, we found that statistical differences in decapod species abundance and composition are likely to be caused by the joint action of coverage and heterogeneity of the beds. Our results indicate that typical Caribbean species were the most influential in the community; nevertheless, the abundance of juvenile Penaeus schmitti Burkenroad, 1936 was notable, since they have rarely been found in these habitats. This finding highlights the role of non-protected areas as nursery habitats for economically important species. Our results show that seagrass meadows in the Paraguaná Peninsula reflect overall good health when compared to other Caribbean zones, representing an important habitat for the maintenance of crustacean populations.

Background: Seagrasses are foundation species in estuarine and lagoon systems, providing a wide array of services for the ecosystem and the human population. Understanding the dynamics of their stands is essential in order to better assess natural and anthropogenic impacts. It is usually considered that healthy seagrasses aim to maximize their stand biomass (g DW m−2) which may be constrained by resource availability i.e., the local environment sets a carrying capacity. Recently, this paradigm has been tested and reassessed, and it is believed that seagrasses actually maximize their efficiency of space occupation—i.e., aim to reach an interspecific boundary line (IBL)—as quick as possible. This requires that they simultaneously grow in biomass and iterate new shoots to increase density. However, this strategy depresses their biomass potential. Results: to comply with this new paradigm, we developed a seagrass growth model that updates the carrying capacities for biomass and shoot density from the seagrass IBL at each time step. The use of a joint biomass and density growth rates enabled parameter estimation with twice the sample sizes and made the model less sensitive to episodic error in either of the variables. The use of instantaneous growth rates enabled the model to be calibrated with data sampled at widely different time intervals. We used data from 24 studies of six seagrass species scattered worldwide. The forecasted allometric biomass–density growth trajectories fit these observations well. Maximum growth and decay rates were found consistently for each species. The growth rates varied seasonally, matching previous observations. Conclusions: State-of-art models predicting both biomass and shoot density in seagrass have not previously incorporated our observation across many seagrass species that dynamics depend on current state relative to IBL. Our model better simulates the biomass–density dynamics of seagrass stands while shedding light on its intricacies. However, it is only valid for established patches where dynamics involve space-filling, not for colonization of new areas. [ABSTRACT FROM AUTHOR]

The abundance and distribution of Thalassia hemprichii (Ehrenb.) Aschers and Cymodocea rotundata Asch. & Schweinf. based on their different degrees of wave exposure and shore levels were investigated. T. hemprichii was the most dominant seagrass and occupied large areas from sheltered to exposed shores with the greatest percentage of cover (46±4.63%) whereas C. rotundata was restricted to the sheltered shore with a 12.22±4.95% cover. There were significant differences in abundance of these two species among the different degrees of wave action, shore sites, and month. Wave action might be the main influence on the percentage cover and distribution of these two seagrasses. In this study, the area covers of T. hemprichii and C. rotundata were around 0.104 km² and 0.096 km², respectively. [ABSTRACT FROM AUTHOR]

Introduction: Diabetes mellitus (DM) is an endocrine disorder characterized by high blood glucose levels. One of the approaches for treating DM is by regulating the postprandial blood glucose via inhibition of α-glucosidase enzymes. Seagrass is known as a plant containing bioactive compounds, especially for therapy antidiabetic. This research aims to evaluate the α-glucosidase inhibition activity of three species seagrasses (Enhalus acoroides, Thalassia hemprichii and Cymodocea rotundata) from the Banten Bay, Indonesia. Methods: The extracts of all parts (root, leaf, and stem) from three seagrasses were prepared with maceration method using 80% ethanol solvents. The α-glucosidase inhibitory activity was conducted by microplate reader at 400 nm using acarbose as a positive control. Furthermore, the kinetics of α-glucosidase inhibition, phytochemical screening, and total phenolics content were evaluated against extract which has the most potential α-glucosidase inhibition. Results: The result showed that the 80% ethanol extracts of Enhalus acoroides (IC50 values 168.15 ± 2.71 µg/mL) had the most potential α-glucosidase inhibitors activity compared with the positive control acarbose, Thalassia hemprichii and Cymodocea rotundata (IC50 values 197.27 ± 3.07 µg/mL, 425.86 ± 5.15 µg/mL and 429.28 ± 8.89 µg/mL). The kinetic type of inhibition against α-glucosidase was noncompetitive inhibition. The phytochemical compounds were phenols, flavonoid, terpenes, and tannin with the total phenolic content was 28.76 ± 2.46 mgGAE/g. Conclusion: Enhalus acoroides has the strongest inhibitor of α-glucosidase and can be further developed for DM therapy agents. [ABSTRACT FROM AUTHOR]

Copyright of Iheringia. Série Zoologia is the property of Fundacao Zoobotanica do Rio Grande do Sul and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Seagrass beds are the largest organism-built marine habitat in Dominica, yet have only been surveyed since 2007. Standardized examinations along a depth gradient between 0 and 24m, focusing on magnoliophyte species composition and benthic cover of shoots at 17 seagrass bed sites, were carried out between September 10 and December 7, 2008. The Cymodoceaceae Syringodium filiforme (Kuetzing 1860) and Halodule wrightii (Ascherson 1868), as well as the Hydrocharitaceae Halophila decipiens (Ostenfeld 1902), H. stipulacea (Fosskal & Ascherson 1867) and Thalassia testudinum (Banks ex König 1805) displayed distinct regional and horizontal distribution patterns. Syringodium filiforme is the island’s dominant seagrass along the western and northern coasts, occurring at depths between 2 and 18m and with a mean benthic cover ranging from 0.9-10% along the West coast. Along the North coast it grew between 0.2 and 1m depth with a mean maximum benthic cover of 48.9%. Halodule wrightii grew along the North and West coasts, in depths between 1 and 14m in areas of recent and chronic disturbances. Its delicate morphology and sparse benthic cover (Pastos marinos son los ambientes más grandes constituidos por organismos en Dominica. Sin embargo, sólo se han examinado desde 2007. Entre el 10 de septiembre y 9 de diciembre 2008, se examinaron la composicion de especies y la densidad de magnoliofitas en profundidades de 0 a 24m. Los Cymodoceaceae: Syringodium filiforme y Halodule wrightii, tal como los Hydrocharitaceae: Halophila decipiens, H. stipulacea y Thalassia testudinum, mostraron una distribución regional y horizontal muy distinta. Syringodium filiforme fue la especie dominante en las costas del oeste y del norte de la isla. Se encontró en profundidades de 2 a 18m y con un promedio de cobertura béntica de 0.9-10% en la costa del oeste. En las costas del norte creció entre 0.2 y 1m de profundidad con un pormedio de cobertura béntica de 48.9%. Halodule wrightii creció en las costad del norte y oeste, en profundidades de 1 a 14m en áreas de perturbaciones recientes o crónicas. Su morfología delicada y su baja cobertura béntica (

The wide distribution of many seagrasses may be attributable to exploitation of currents. However, many species have seeds heavier than seawater, limiting surface floating, and thus, deep water becomes a potential barrier between suitable habitats. In this investigation, we studied the dispersal potential of various life history stages of two species of seagrasses, Thalassia hemprichii and Halophila ovalis, at Dongsha Atoll and Penghu Islands in Taiwan Strait, west Pacific. The adult plants of both species, often dislodged naturally from substrate by waves, could float, but only that of T. hemprichii could float for months and still remain alive and potentially able to colonize new territories. The seedlings of T. hemprichii could also float for about a month once failing to anchor to substrate of coral sand, but that of H. ovalis could not. The fruits and seeds of T. hemprichii could both float, but for too short a duration to enable long distance travel; those seeds released from long floating fruits had low germination rates in our tests. Obviously, their seeds are not adaptive for long distance dispersal. Fruits and seeds of H. ovalis do not float. The potential of animals as vectors was tested by feeding fruits and seeds of both species to a goose, a duck, and two fish in the laboratory. The fruits and seeds of T. hemprichii were digested and could no longer germinate; those of H. ovalis could pass through the digestive tracts and have a much higher germination rates than uningested controls. Therefore, birds could be important vectors for long distance dispersal of H. ovalis. The two seagrasses adopted very different dispersal mechanisms for long distance travel, and both exploited traits originally adaptive for other purposes. [ABSTRACT FROM AUTHOR]

Se estudio la diversidad y abundancia de la comunidad béntica malacológica asociada a Thalassia testudinum en cuatro localidades de la Bahía de Mochima, Estado Sucre, Venezuela. Las muestras fueron recolectadas mensualmente en cada localidad sobre transeptos perpendiculares a diferentes profundidades (0-4m) desde enero 1991 hasta diciembre 1991, utilizando una cuadrata de 0.25 m² para recolectar los organismos con el sedimento. Un total de 2 988 organismos de la infauna y epifauna, pertenecientes a las clases Gastrópoda (40) y Bivalvia (41) fueron identificados. Las especies más abundantes y en consecuencia mejor adaptadas a los habitats suministrados por la T. testudinum en la Bahía de Mochima fueron Anadara notabilis, Codakia orbicularis, Cerithium litteratum, Cerithium eburneum, Batillaria minima, Modiolus squamosus, Modulus modulus, Chione cancellata, Turritella variegata, Arca zebra, y Laevicardium laevigatum. Se determinaron diferencias significativas en el número de organismos en relación a la profundidad y el tiempo en la localidad de la Gabarra, la cual presentó los valores mas altos de diversidad total (4.51 bits/ind) y mensual (2.75-3.90 bits/ind). La biomasa y la abundancia de moluscos fueron bajas y la estación mas interna (Varadero) presentó los valores mas elevados. El bivalvo A. notabilis y el gastropodo Modulus modulus fueron las especies constantes en las cuatro estaciones.The diversity and abundance of benthic malacological communities associated to Thalassia testudinum beds was studied at four localities of Mochima Bay, Sucre state, Venezuela. At each locality, samples were taken monthly on perpendicular transect at different depths (0-4 m), from January 1991 to December 1991, using a quadrate (0.25 m 2 ) for collecting mollusks and sediments. A total of 2 988 organisms of infauna and epifauna belonging to 81 species of the classes Gastropoda (41) and Bivalvia (40) were collected. More abundant species were Anadara notabilis, Codakia orbicularis, Cerithium litteratum, Cerithium eburneum, Batillaria minima, Modiolus squamosus, Modulus modulus, Chione cancellata, Turritella variegata, Arca zebra, y Laevicardium laevigatum. There were significant differences in number of organisms between depth and month at La Gabarra which presented the highest value of total (4.51 bits/ind) and monthly diversity (2.71-3.90 bits/ind). Biomass and abundance were low in the Mochima Bay while Varadero station presented the highest value. The bivalve A. notabilis and gastropod M. modulus were species common to the four stations.

The benthic community associated with the turtlegrass Thalassia testudinum beds was analized at three localities of Morrocoy National Park, Venezuela. The localities were selected according to their exposure to the open sea : A (protected), B (intermediate) and C (exposed). At each locality, a 20 x 20 m area was randomly chosen, delimited and divided into 400 1x1 m quadrats. Inside each, ten randomly selected quadrats/month were sampled during 13 consecutive months. At each site all macroinvertebrates and several physical variables were recorded, as well as leaf and rhizome biomass of T. testudinum. All parameters had a step- wise gradient from A through C: organic matter, carbon nitrogen, oxygen, salinity and temperature gradient was: ABC. Percentages of sand, silt and clay showed an inverse gradient; ASe analizó la comunidad bentónica asociada a Thalassia testudinum y su relación con algunos parámetros bióticos y abióticos, en tres localidades del Parque Nacional Morrocoy, Falcón-Venezuela; éstas fueron seleccionadas de acuerdo al grado de exposición al mar abierto: A(protegída), B (intermedia) y C (expuesta). En cada localidad se demarcó un área de 20 x 20m, se muestrearon aleatoriamente 10cuadrantes/mes, (130 cuadrantes/localidad). Se efectuaron registros de oxígeno disuelto, salinidad, temperatura, porcentajes de materia orgánica, carbono y nitrógeno, textura del sedimento, biomasa foliar y de rizoma de T. testudinum. Todos los parámetros analizados presentaron un gradiente escalonado. Materia Orgánica, Carbono y Nitrógeno, Oxígeno disuelto, Salinidad y Temperatura presentaron el gradiente: ABC. Los porcentages de Arena, Limo y Arcilla presentaron un gradiente inverso. El patrón en la Diversidad, Equidad y Dominancia fue: BCA. La fauna colectada estuvo compuesta por los grupos: Coelenterata (Anthozoa), Polichaeta, Sipuncula, Molusca, Crustacea y Echinodermata. Se identificaron 15 especies de moluscos (gastrópodos y bivalvos), (3 % de los invertebrados colectados). La abundancia relativa y dominancia de los moluscos se incrementó en aquellos sitios donde hay un aumento en la biomasa de rizoma de T. testudinum (porcentaje de dominancia A

The article discusses a study on differences in the community structures of meiofauna in seagrass beds and adjacent unvegetated sediments. Topics covered include meiofaunal taxa and nematode genera identified from a tropical seagrass bed of Thalassia hemprichii in Ludao, Taiwan, infaunas possessed by both habitats, and the need for seagrass conservation strategies to consider seagrass beds' peripheral bare area.

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Returning to the sea, just like invasion of land, has occurred in many groups of animals and plants. For flowering plants, traits adapted to the terrestrial environments have to change or adopt a new function to allow the plants to survive and prosper in the sea where water motion tends to rotate and move seeds. In this investigation, how seeds of the seagrass Thalassia hemprichii (Hydrocharitaceae), a common monocotyledon in the Indo-Pacific, adapt to the wavy environment was studied. Mature seeds were collected from Dongsha Atoll in South China Sea. The effects of light qualities on seed germination, the seed morphology, the unipolar distribution of starch granules in the endosperms and growth of root hair-like filamentous cells from basal surface of the seeds were all found to differ from those of terrestrial monocotyledons. Physiologically, germination of the seeds was stimulated by blue light rather than red light. Morphologically, the bell-shaped seeds coupled with the unipolar distribution of starch granules in the enlarged bases helped maintain their upright posture on the tidal seafloor. Growth of root hair-like filamentous cells from the basal surface of the seeds prior to primary root growth served to attach onto sediments, providing leverage and attachment required by the primary roots to insert into sediments. These filamentous cells grasped coral sand but not silicate sand, demonstrating a habitat preference of this species. [ABSTRACT FROM AUTHOR]

Grazing by small epifauna on live seagrass leaves was formerly viewed as unimportant in controlling plant biomass and growth, instead researchers focused on the indirect benefits of small invertebrates that crop algal competitors. Recent evidence shows that the emerald nerite Smaragdia viridis preferentially ingests seagrass leaf tissue. In contrast, the button snail Modulus modulus feeds on epiphytes and periphyton coating the leaves. We conducted laboratory microcosm and field experiments to investigate how the different feeding preferences of these seagrass-associated snails affect turtlegrass Thalassia testudinum primary production. Data revealed that after 24 h S. viridis reduced foliar biomass (25%) and chlorophyll (30%) and injured the equivalent of 50% of daily seagrass growth per shoot. Conversely, M. modulus did not affect these variables. Our results emphasize that in subtropical seagrass communities not all small epifauna browse off leaf surfaces and some can have important direct negative impacts on their seagrass host. [ABSTRACT FROM AUTHOR]

Two new species of the genus Rissoella Gray, 1847 are described from Venezuela, one from the National Park Morrocoy, Rissoella morrocoyensis sp. n. and the other from the Wildlife Refuge Isla de Aves, Rissoella venezolanicola sp. n. R. morrocoyensis sp. n. has a deep umbilicus (partly closed), preumbilical cord, black head, hypobranchial gland marked by a pale yellow boomerang-shaped ribbon and it lives on the leaves of the seagrass Thalassia testudinum Banks & König, 1805. R. venezolanicola sp. n. has an angled preumbilical cord which extends to the columella delimiting a trapezoid, a hypobranchial gland marked by a yellow quaver-shaped ribbon and protoconch with fuchsia highlights. It lives on the brown alga Dictyota spp. The records of Rissoella in the Caribbean are revised and illustrations, a comparative table and a key to the Caribbean species known for the genus are provided. [ABSTRACT FROM AUTHOR]

Generally, the foliar sheaths of seagrass contribute a large biomass to the dry weight of plants, and are found to be above-sediment biomass or, sometimes, below-sediment biomass. However, the role of foliar sheaths of seagrass in nutrient uptake has not yet been established. Thus, this study was performed to test whether the growth form of foliar sheaths affects the nutrient uptake properties of the seagrass. Two separate sets of morphotypes of the seagrass Thalassia hemprichii were collected from two different tropical meadows in coastal Hainan Island, China in the South China Sea. Ammonium (NH) and phosphate (P) uptake by solely blades and roots (experiment I), and above and below-sediment tissues (experiment II) of the two sets of specimens were examined in partitioned chambers using laboratory incubations. Curve profiles of the blade and root saturation uptake kinetics were shown to be similar for the two morphotypes of T. hemprichii. However, the above and below-sediment tissues uptake kinetics had different characteristics between the two morphotypes. For plants with above-sediment foliar sheaths, uptake by the above-sediment tissues contributed an important part of the whole plants' nutrient acquisition. In contrast, for plants with below-sediment foliar sheaths, the contribution of nutrient uptake by above-sediment foliar blade tissues seemed almost negligible. Therefore, the results demonstrated that foliar sheaths of the tropical seagrass T. hemprichii were able to absorb NH and P. Especially interesting is that the capacity for uptake by robust foliar sheaths growing beneath the sediment was remarkable (we termed this the Zhang-Huang-Thorhaug effect). The role of sheaths in nutrient acquisition found in this study is critical in elucidating seagrass nutrient uptake strategies. [ABSTRACT FROM AUTHOR]

The article presents a study on the impact of experimental pollen reduction or addition of pollen on the fruit and seed-set of Thalassia testudinum at Puerto Morelos reef lagoon in Mexico. For the study, researchers examined flowers and flower buds at pre-anthesis in April of 2008 and 2009. They analyzed pollen production and potential restriction of pollen availability in the seagrass. They observed a decline of fruit production from 83 to 60 percent following experimental removal of half of the male flowers in April 2008.

The effects of CO2 enrichment on various ecophysiological parameters of tropical seagrass Thalassia hemprichii (Ehrenb.) Aschers were tested. T. hemprichii, collected from a seagrass bed in Xincun Bay, Hainan island of Southern China, was cultured at 4 CO2(aq) concentrations in flow-through seawater aquaria bubbled with CO2. CO2 enrichment considerably enhanced the relative maximum electron transport rate (RETRmax) and minimum saturating irradiance (Ek) of T. hemprichii. Leaf growth rate of CO2-enriched plants was significantly higher than that in unenriched treatment. Nonstructural carbohydrates (NSC) of T. hemprichii, especially in belowground tissues, increased strongly with elevated CO2(aq), suggesting a translocation of photosynthate from aboveground to belowground tissues. Carbon content in belowground tissues showed a similar response with NSC, while in aboveground tissues, carbon content was not affected by CO2 treatments. In contrast, with increasing CO2(aq), nitrogen content in aboveground tissues markedly decreased, but nitrogen content in belowground was nearly constant. Carbon: nitrogen ratio in both tissues were obviously enhanced by increasing CO2(aq). Thus, these results indicate that T. hemprichii may respond positively to CO2-induced acidification of the coastal ocean. Moreover, the CO2-stimulated improvement of photosynthesis and NSC content may partially offset negative effects of severe environmental disturbance such as underwater light reduction. [ABSTRACT FROM AUTHOR]

The article presents the results of field experiments in subtropical turtlegrass Thalassia testudinum meadows to look at their nutrient enrichment, grazer identity and effects on epiphytic algal assemblages. The researchers have failed to detect any strong grazer effects and found very few significant nutrient-grazer interactions. They conducted the experiments in Florida Bay which is a shallow estuarine system dominated by Thalassia testudinum. A figure that shows the combined effects of nutrients and grazers on fall 2003 chlorophyll b concentration is presented. In order to estimate feeding rates of amphipods, they took the average of the feeding rates of Ampithoe longimana on various types of algae in no-choice feeding experiments.

The article examines the significance of seagrass as a nursery habitat for the Caribbean spiny lobster (Panulirus argus) in Florida. It notes on the experiment that analyzes the role of seagrass and hard-bottom habitats for the marine species recruitment in three ways. These include exploring for possible density-dependent regulation of early benthic juvenile lobster in seagrass and hard-bottom habitats, comparing its settlement and survival in both habitats, and assessing the relative abundance of juvenile lobsters in each habitat. However, macroalgae-dominated hard-bottom habitat appears to be the preferred and optimum nursery for Caribbean spiny lobster.

Passage of hurricane Wilma (October 2005, category 4, duration ∼ 60 h) over Puerto Morelos, Mexican Caribbean, allowed verification of a previous experiment simulating hurricane-like impacts on the seagrass beds in its back-reef lagoon. At two mid-lagoon stations, numbers of the seagrass Syringodium filiforme and macro-algae Udotea spp., Penicillus spp., and Rhipocephalus spp. were reduced significantly, whereas populations of the seagrass Thalassia testudinum and Halimeda spp. were unaffected. These impacts of the hurricane supported the results of the simulation experiment. Differential results were registered at one station for the spongy-like algae Anrainvillea spp. and Cladocephalus sp., which were not affected by the simulation treatments but were reduced in number by the hurricane. Thus, apart from known impacts such as complete or partial destruction of seagrass beds, hurricanes may also change the community structure of persistent beds through species-specific elimination. [ABSTRACT FROM AUTHOR]

• Here, the leaf photoacclimatory plasticity and efficiency of the tropical seagrass Thalassia testudinum were examined. • Mesocosms were used to compare the variability induced by three light conditions, two leaf sections and the variability observed at the collection site. • The study revealed an efficient photosynthetic light use at low irradiances, but limited photoacclimatory plasticity to increase maximum photosynthetic rates ( Pmax) and saturation ( Ek) and compensation ( Ec) irradiances under high light irradiance. A strong, positive and linear association between the percentage of daylight hours above saturation and the relative maximum photochemical efficiency ( FV/ FM) reduction observed between basal and apical leaf sections was also found. • The results indicate that T. testudinum leaves have a shade-adapted physiology. However, the large amount of heterotrophic biomass that this seagrass maintains may considerably increase plant respiratory demands and their minimum quantum requirements for growth (MQR). Although the MQR still needs to be quantified, it is hypothesized that the ecological success of this climax species in the oligotrophic and highly illuminated waters of the Caribbean may rely on the ability of the canopy to regulate the optimal leaf light environment and the morphological plasticity of the whole plant to enhance total leaf area and to reduce carbon respiratory losses. [ABSTRACT FROM AUTHOR]

Seagrasses provide a physical connection between the water column and sediments by transporting photosynthetic-and seawater-derived oxygen to their roots and rhizomes. In this paper, we present a single-shoot reaction-transport model that incorporates the biological, chemical and physical processes in the water column, seagrass plant, and sediments and that simulates oxygen and hydrogen sulfide dynamics in the system. The model reproduces oxygen and sulfide patterns observed in laboratory manipulations and field measurements of Thalassia testudinum and Zostera marina. Model results reinforce experimental conclusions that (1) meristem oxygen is tightly coupled to water column oxygen and diel patterns of sunlight, (2) sediment sulfide enters the plant when plant tissues are hypoxic, and (3) internal sulfide is rapidly depleted once oxic seawaters are re-established or with the onset of photosynthesis. Sensitivity analysis further emphasizes that water column oxygen concentration has a strong influence on the minimum oxygen concentration and maximum sulfide concentration in the meristem at night. The model indicates that diffusion is the dominant transport process in the lacunae, though advective mass flow can account for nearly a quarter of oxygen transport during periods of increasing sunlight. In the model, biological sulfide oxidation and plant dissolved organic carbon exudation both play significant roles in determining patterns of sediment oxygen consumption and sulfide intrusion into the plant. [Copyright &y& Elsevier]

Lucinid bivalves dominate the infauna of tropical seagrass sediments. While the effect of seagrass on lucinids has been studied, the reverse effect has largely been ignored. Lucinids can alter porewater chemistry (i.e., increase porewater nutrients by suspension feeding and decrease porewater sulfides by oxygen introduction and bacterial oxidation), which can potentially change seagrass productivity and growth morphology. To observe correlations between porewater chemistry and lucinid presence, a field survey and laboratory microcosm experiment were conducted. Survey sampling sites with lucinids had significantly lower sulfide and higher ammonium concentrations than sampling sites without lucinids. There was no difference in phosphate concentration among sampling sites. Both lucinid species used in the microcosm experiment (Ctena orbiculata and Lucinesca nassula) significantly lowered sulfide concentrations in the sediment porewater. Microcosm and field survey results were incorporated into a sulfide budget. In seagrass sediments, lucinids remove 2-16% of the total sulfide produced. Sulfide is a major stressor to both plants and animals in Florida Bay sediments; this removal may be important to maintaining seagrass productivity and health. Oxygen introduction into sediments by C. orbiculata was estimated in a dye experiment. C. orbiculata were added to small tubes containing sieved mud and incubated in a bath of seawater with a Rhodamine WT. Rhodamine WT accumulation in the sediment was measured. A first order estimate showed that oxygen introduction can account for less than 5% of C. orbiculata sulfide removal. [ABSTRACT FROM AUTHOR]

A technique for the rapid surveying of submersed aquatic vegetation by post-processing of data collected using a high frequency (420 kHz) digital echo sounder (BioSonics DT4000) has recently been developed and successfully tested in an estuarine environment by Sabol et al. [Sabol, B. M., R. E. Melton, R. Chamberlain, P. Doering & K. Haunert, 2002. Evaluation of a digital echo sounder system for detection of submersed aquatic vegetation. Estuaries 25: 133–141.], where it was used to map the cover and height of freshwater tape grass ( Vallisneria americana) and seagrasses ( Thalassia testudinum, Haladule wrightii and Syringodium filiforme). This technique, which is also spatially referenced by input from a global positioning system, has many potential applications in macrophyte studies in shallow lakes, although it has not yet been extensively tested in such habitats using systems of lower sound frequency. This paper reports such a test in two shallow (maximum depth c. 5.9 m) lakes of the Cotswold Water Park, U.K., using a 200 kHz digital echo sounder (BioSonics DT6000 and DT-X upgrade) and post-processing analysis using the now commercially available software EcoSAV, which incorporates the algorithms of Sabol et al. (). Hydroacoustic assessment of the coverage by macrophytes, mainly Nuttall’s pondweed ( Elodea nuttallii) and charophytes ( Chara spp.), showed high agreement with those recorded during a simultaneous visual survey by underwater video recording ( r 2 = 0.8478, n = 74, P < 0.001). Assessment of macrophyte height was also apparently consistent between the two systems, although the video system could not produce quantitative data and so statistical assessment of the agreement was not possible. Repeated hydroacoustic surveys over the course of the winter of 2003–2004 were conducted in one lake and illustrate the application of this new macrophyte survey technique. Such applications include the rapid measurement of mean Percentage Volume Inhabited (PVI), which fell from 12.15% (95% confidence limits, ±0.55%) to 7.10% (±0.40%) over the course of the winter. [ABSTRACT FROM AUTHOR]

The seagrass of Perezoso (Cahuita National Park, Caribbean coast of Costa Rica) was monitored using the CARICOMP protocol. Productivity (2.7±1.15 g/m²/d; n=74) was intermediate, compared to other Caribbean sites. Total biomass was intermediate to high (750-1500 g/m²) at most CARICOMP sites (Colombia, Cuba, Mexico, Puerto Rico and Venezuela) including Costa Rica (822.8±391.84 g/m²; n=32). Turnover rates were high (5.5±1.36 %; n=74) compared to what was found in March and August at other sites. Shoot densities average 725 shoots/m², in the Caribbean region, while in Costa Rica the value was higher (1184±335.5 shoots/m²). Average leaf length and width in the entire region were 14.4 cm and 10.6 mm, respectively, similar to what we found, but leaf area index average 3.4 m²m-2, higher than what was found in Costa Rica (0.92 m²m-2). At Cahuita, seagrass productivity was significantly lower in March 2005 compared with the previous six years, and biomass has decreased with time. Seagrass productivity and biomass are being affected by the maximum temperatures, which increased by almost 10 °C from 1999 to 2005, and show a high negative correlation. Turnover rate and temperature were not correlated. Recreational boating, swimming and nutrient loading from deforested lands in the coast, the upstream rivers and local pollution are potential sources of impact to the seagrass beds at Cahuita. [ABSTRACT FROM AUTHOR]

The effects of light reduction on community metabolism and sediment sulfate reduction rates (SRR) were assessed experimentally in a shallow (< 2.0 m) seagrass (Thalassia testudinum) meadow along Florida's north-central Gulf coast. Nine experimental plots (1.5 m x 1.5 m) were shaded differentially to achieve a 0-90% gradient in light reduction within the seagrass meadow. Gross primary production and net community production (NCP), estimated with in situ benthic chamber incubations, decreased with increasing light reduction. The compensation irradiance for community metabolism, i.e., the shading level at which NCP shifted from net autotrophic to net heterotrophic, was determined to be 52.5% of the incoming irradiance at canopy height in the seagrass bed (308.7 µE m-2 s-1 PAR at noon). Sediment SRR, determined with the use of a 35S-SO42- radiotracer technique, increased quickly (within 5 d) and markedly with increased shade, i.e., simulated light reduction. SRR increased 50-fold when shading exceeded the light compensation point for the seagrass community, rendering the community net heterotrophic. Five days after restoring ambient light conditions, SRR had decreased sharply for all shading treatments. The observed decrease in NCP, coincident with the increase in the SRR with light reduction, suggests that light reduction has an indirect influence on sediment SRR mediated through its effect on seagrass metabolism. [ABSTRACT FROM AUTHOR]

The spatial and temporal distributions of the epiphytic diatom flora on Thalassia testudinum was described within the Florida Bay estuary and at one Atlantic site east of the Florida Keys over a 1-year period. Species of the genus Mastogloia dominated the epiphytic diatom flora (82 out of 332 total species). Nonmetric Multidimensional Scaling (NMDS) and Analysis of Similarity (ANOSIM) revealed four distinct spatial assemblages and two temporal assemblages. Eastern and western Florida Bay assemblages were identified within the estuary. The eastern diatom assemblage was characterized by high relative abundances of Brachysira aponina and Nitzschia liebetruthii, while the western assemblage was characterized by the abundance of Reimerothrix floridensis, particularly during summer. Two diverse and distinct marine assemblages, one located in the Gulf of Mexico along the western edge of Florida Bay and the other behind the Florida reef tract in the Atlantic Ocean, were also identified. Analysis of the spatial distribution of diatoms and water quality characteristics within Florida Bay suggest that these assemblages may be structured by salinity and nutrient availability, particularly P. The Gulf of Mexico and the western Florida Bay assemblages were associated with higher water column salinities and TP concentrations and lower DIN concentrations and TN:TP ratios relative to the eastern Florida Bay assemblage. The temporal variation in diatom assemblages was associated with water temperature, though temporal indicator species were few relative to the number of spatial indicators. [ABSTRACT FROM AUTHOR]

The capacity of epifauna to control algal proliferation following nutrient input depends on responses of both grazers and upper trophic level consumers to enrichment. We examined the responses of Thalassia testudinum (turtle grass) epifaunal assemblages to nutrient enrichment at two sites in Florida Bay with varying levels of phosphorus limitation. We compared epifaunal density, biomass, and species diversity in 2 m2 plots that had either ambient nutrient concentrations or had been enriched with nitrogen and phosphorus for 6 months. At the severely P-limited site, total epifaunal density and biomass were two times higher in enriched than in unenriched plots. Caridean shrimp, grazing isopods, and gammarid amphipods accounted for much of the increase in density; brachyuran crabs, primary predatory fish, and detritivorous sea cucumbers accounted for most of the increase in biomass. At the less P-limited site, total epifaunal density and biomass were not affected by nutrient addition, although there were more caridean shrimp and higher brachyuran crab and pink shrimp biomass in enriched plots. At both sites, some variation in epifaunal density and biomass was explained by features of the macrophyte canopy, such as T. testudinum and Halodule wrightii percent cover, suggesting that enrichment may change the refuge value of the macrophyte canopy for epifauna. Additional variation in epifaunal density and biomass was explained by epiphyte pigment concentrations, suggesting that enrichment may change the microalgal food resources that support grazing epifauna. Increased epifaunal density in enriched plots suggests that grazers may be able to control epiphytic algal proliferation following moderate nutrient input to Florida Bay. [ABSTRACT FROM AUTHOR]

We present here a 4-year dataset (2001–2004) on the spatial and temporal patterns of aboveground net primary production (ANPP) by dominant primary producers (sawgrass, periphyton, mangroves, and seagrasses) along two transects in the oligotrophic Florida Everglades coastal landscape. The 17 sites of the Florida Coastal Everglades Long Term Ecological Research (FCE LTER) program are located along fresh-estuarine gradients in Shark River Slough (SRS) and Taylor River/C-111/Florida Bay (TS/Ph) basins that drain the western and southern Everglades, respectively. Within the SRS basin, sawgrass and periphyton ANPP did not differ significantly among sites but mangrove ANPP was highest at the site nearest the Gulf of Mexico. In the southern Everglades transect, there was a productivity peak in sawgrass and periphyton at the upper estuarine ecotone within Taylor River but no trends were observed in the C-111 Basin for either primary producer. Over the 4 years, average sawgrass ANPP in both basins ranged from 255 to 606 g m−2 year−1. Average periphyton productivity at SRS and TS/Ph was 17–68 g C m−2 year−1 and 342–10371 g C m−2 year−1, respectively. Mangrove productivity ranged from 340 g m−2 year−1 at Taylor River to 2208 g m−2 year−1 at the lower estuarine Shark River site. Average Thalassia testudinum productivity ranged from 91 to 396 g m−2 year−1 and was 4-fold greater at the site nearest the Gulf of Mexico than in eastern Florida Bay. There were no differences in periphyton productivity at Florida Bay. Interannual comparisons revealed no significant differences within each primary producer at either SRS or TS/Ph with the exception of sawgrass at SRS and the C−111 Basin. Future research will address difficulties in assessing and comparing ANPP of different primary producers along gradients as well as the significance of belowground production to the total productivity of this ecosystem. [ABSTRACT FROM AUTHOR]