Thalassia Testudinum Research Articles

An acoustic investigation of seagrass photosynthesis

The use of high-frequency acoustics has recently emerged as a viable method for mapping the areal coverage of seagrasses. Since the bubbles produced by seagrass plants are partly responsible for the observed acoustic signature, it is likely that sound transmission throughout a seagrass canopy varies on circadian cycles coinciding with photosynthetic bubble production. This study examined the propagation of high-frequency (100 kHz) sound energy through the seagrass canopies of Syringodium filiforme, Halodule wrightii and Thalassia testudinum in a shallow outdoor mesocosm. Relative changes in the received acoustic energy were recorded every hour during a 24-h period and compared to independently measured rates of oxygen production. The mean acoustic intensity of energy transmitted throughout the seagrass canopy varied by 3.5 dB for S. filiforme, 4.4 dB for T. testudinum and 4.7 dB for H. wrightii over a 24-h period. These transmission characteristics are encouraging for the future development of in situ acoustic assessments of seagrass photosynthesis.

Using habitat suitability models to predict changes in seagrass distribution caused by water management practices1This article is derived from a special session entitled “A New Hydrology: Inflow Effects on Ecosystem Form and Functioning” that took place at the February 2011 ASLO Aquatic Sciences conference in San Juan, Puerto Rico.

Habitat suitability (HS) models can help elucidate the relationship between organisms and their environment and simulate the potential impacts of human activities on species distributions. Here, we developed HS models for Thalassia testudinum and Halodule wrightii , two seagrasses found in Biscayne Bay (Florida, USA). These species are mostly found in nearshore habitats of the bay that are highly susceptible to changes in water quality because of their proximity to the city of Miami and activities and projects associated with the restoration of the Florida Everglades . The HS models parameterized with data collected at >900 sites highlighted salinity as a key factor determining habitat suitability for these seagrass species. Thalassia ’s suitable habitat was associated with higher, more stable salinity compared with that of Halodule , which was associated with lower salinity and shallower depths. Both species benefited under a simulated scenario of increased freshwater flow, but Halodule’s suitable habitat increased by 71% compared with that of Thalassia’s, which exhibited only an 18% increase. HS models such as those described here provide spatial modeling tools that can contribute science-based input into the management of coastal resources within an adaptive management framework.

Bacterial diversity of siliciclastic sediments in a Thalassia testudinum meadow and the implications for Lucinisca nassula chemosymbiosis

Despite the ecological and economic importance of Thalassia testudinum (turtle grass) meadows along the Caribbean and Gulf of Mexico coasts, and recognition that microbial activities are critical to plant growth and health, the bacterial diversity of these habitats has been poorly studied. Based on comparative analyses of 16S rRNA gene sequences from sediments in a T. testudinum meadow, 25 major taxonomic groups (excluding candidate divisions) were retrieved, including Alpha- Delta-, and Gamma-proteobacteria, Chloroflexi, Bacteroidetes, Acidobacteria, Spirochaetes, and Firmicutes. The distribution of bacterial groups was linked to a strongly hypoxic and sulfidic redox gradient. The diversity is potentially novel because phylogenetic affinities of sediment sequences compared to contextually annotated environmental clones from different habitats or to cultured representatives indicated approximately 41% were more closely related to each other than to sequences retrieved from these other habitats. Of all the relationships, very few (2.4%) were to cultured organisms, but 27% were to environmental clones retrieved from shallow marine shelf and coastal sediments or from mangroves, estuarine, or wetland sediments. Rare sequences were closely related to endosymbiont groups of Lucinisca nassula (Lucinidea: Bivalvia) hosts collected from the same meadow, which may indicate that the sediment is a potential reservoir for free-living symbionts. This study provides insight into the ecological and evolutionary relationships of the Thalassia–lucinid–bacteria system in tropical to sub-tropical regions.

Epiphytes mediate the trophic role of sea urchins in Thalassia testudinum seagrass beds

The trophic role of the sea urchin Lytechinus variegatus (Lamarck) and the impor- tance of epiphytes as mediators of trophic interactions were evaluated in a Thalassia testudinum meadow, St. Joseph Bay, Florida, in fall 2010. Tethering experiments were deployed within the meadow to assess consumption rates, and food choice experiments, with combinations of different types of T. testudinum leaves, green leaves and detached (decayed) leaves, both with and without epiphytes, were carried out with individual urchins in 4 different 24 h feeding trials. Lytechinus variegatus had higher consumption rates on decayed (12.15 ± 1.3 mg DW shoot �1 d �1 ; mean ± SE) compared to an undetectable consumption of green seagrass leaves, and consistently chose epi- phytized leaves of both type. Therefore, consumption rates were highest for decayed leaves with epiphytes. This choice may be related to the significantly higher epiphytic biomass on decayed (3.64 ± 0.28 mg DW cm �2 ) than on green leaves (2.11 ± 0.25 mg DW cm �2 ). Stable isotope analyses pointed to epiphytes and green leaves as the main sources of nitrogen and carbon in L. variegatus diet. These results suggest that epiphytes mediate trophic interactions between sea urchins and turtlegrass. Therefore, changes in epiphytes and decayed leaf biomass can regulate sea urchin foraging and its impact on the trophic dynamics of the meadows.

Population dynamics and reproductive aspects of the decorator crab Microphrys bicornutus (Crustacea: Brachyura: Majidae) in an extreme shallow Thalassia complex

The decorator crab, Microphrys bicornutus, is a common inhabitant of the turtle grass Thalassia testudinum. In order to establish the behaviour of a population of this species in an extreme shallow Thalassia complex (maximum depth less than 50 cm, and often exposed to the air), size distribution, population dynamics, reproductive effort and egg size were studied in Buchuaco—Venezuela. Monthly sampling was undertaken between June 1988 and December 1990. A total of 1403 specimens of M. bicornutus were captured. In each of the sampled years, size distribution was strongly skewed to the predominance of small size crabs. Females were significantly larger than males in all the three years. Small size and large size crabs showed periodic annual fluctuations in abundance, with peaks during the last months of the year for the first, and peaks between April and June for the latter. Medium size crabs showed no periodicity at all. Number of eggs per female ranged between 40 and 4305 (mean = 1067.4), and was positively correlated with female body size. Eggs increased their size gradually during their development, and differences in egg size between development stages were significant. The biological parameters found in this study are compared with other populations of this crab, found in Venezuela and Brazil, in different ecosystems. Results acquired in this work add new insights to the behaviour of this decorator crab, specifically on density variation and egg size (among others), living in an environment that is constantly exposed to air and to other physicochemical variations.

Permanent and transient leaf reddening in the seagrass Thalassia testudinum

Seagrasses with red leaves have been observed growing in areas with high light intensities at numerous locations around the world. To test whether variations in light conditions affect anthocyanin accumulation and red coloration in leaves, we performed reciprocal transplants of green- and red-leafed Thalassia testudinum banks & sol. ex K.D. Koenig shoots among patches with high and low self-shading (determined from canopy height and leaf area index measurements) located along a depth related gradient of light availability in the lower florida Keys, USA, and monitored them for 3 yrs. All red-leafed shoots continuously produced red leaves with high concentrations of anthocyanins regardless of self-shading or depth. Transplanted green-leafed shoots transiently turned red during periods of high solar UV and visible light intensity, with the reddening process influenced by self-shading and depth. Green-leafed shoots also increased UV absorbing compounds, but increases were not related to anthocyanin content or reddening. There was a significant relationship between UV-B absorbing compounds and anthocyanin content in red-leafed shoots. We conclude that anthocyanin accumulation and the expression of red coloration can be permanent or temporarily photo-induced in T. testudinum leaves. We also suggest that this species produces a genetic variant with permanently red leaves in the lower florida Keys.

Negative relationships between the nutrient and carbohydrate content of the seagrass Thalassia testudinum

This study documents relationships between plant nutrient content and rhizome carbohydrate content of a widely distributed seagrass species, Thalassia testudinum, in Florida. Five distinct seagrass beds were sampled for leaf nitrogen, leaf phosphorus, and rhizome carbohydrate content from 1997 to 1999. All variables displayed marked intra- and inter- regional variation. Elemental ratios (meanN:P±S.E.) were lowest for Charlotte Harbor (9.9±0.2) and highest for Florida Bay (53.5±0.9), indicating regional shifts in the nutrient content of plant material. Rhizome carbohydrate content (mean±S.E.) was lowest for Anclote Keys (21.8±1.6mgg−1 FM), and highest for Homosassa Bay (40.7±1.7mgg−1 FM). Within each region, significant negative correlations between plant nutrient and rhizome carbohydrate content were detected; thus, nutrient-replete plants displayed low carbohydrate content, while nutrient-deplete plants displayed high carbohydrate content. Spearman's rank correlations between nutrient and carbohydrate content varied from a minimum in Tampa Bay (ρ=−0.2) to a maximum in Charlotte Harbor (ρ=−0.73). Linear regressions on log-transformed data revealed similar trends. This consistent trend across five distinct regions suggests that nutrient supply may play an important role in the regulation of carbon storage within seagrasses. Here we present a new hypothesis for studies which aim to explain the carbohydrate dynamics of benthic plants.

Phytochemical Analysis and Antioxidant Capacity of BM-21, a Bioactive Extract Rich in Polyphenolic Metabolites from the Sea Grass Thalassia testudinum

The aqueous ethanol extract of Thalassia testudinum leaves (BM-21) is now being developed in Cuba as an herbal medicine due to its promising pharmacological properties. Although some interesting biological activities of BM-21 have already been reported, its chemical composition remains mostly unknown. Thus, we now describe the qualitative and quantitative analyzes of BM-21 using standard phytochemical screening techniques, including colorimetric quantification, TLC and HPLC analyses. Phytochemical investigation of BM-21 resulted in the isolation and identification of a new phenolic sulfate ester (1), along with ten previously described phenolic derivatives (2-11), seven of which have never been previously reported from the genus Thalassia. The structures of these compounds were established by analysis of their spectroscopic (1D and 2D NMR) and spectrometric (HRMS) data, as well as by comparison of these with those reported in the literature. Furthermore, BM-21 was found to exhibit strong antioxidant activity in four different free radical scavenging assays (HO*, RO2*, O2-* and DPPH*). Consequently, this is the first study which highlights the phytochemical composition of BM-21 and demonstrates that this product is a rich source of natural antioxidants with potential applications in pharmaceutical, cosmetic and food industries.

Using PAM fluorometry for landscape-level assessment of Thalassia testudinum: Can diurnal variation in photochemical efficiency be used as an ecoindicator of seagrass health?

Landscape-scale measurements of PSII photochemical efficiency (ΔF/Fm′) by pulse-amplitude modulated (PAM) fluorometry were evaluated from 2006 to 2009 as a non-invasive method for monitoring the physiological condition of the seagrass, Thalassia testudinum Banks ex König, in Florida Bay, USA. Previous landscape-scale studies have shown that PAM-derived measurements of effective (ΔF/Fm′) and maximum (Fv/Fm) photochemical efficiencies, as well as rapid light curves (RLC), exhibit significant diurnal variation. In this study, a regression approach was used to assess the magnitude of diurnal variation of ΔF/Fm′ versus irradiance at the bay scale and among 12 sample basins. Variation in ΔF/Fm′ versus irradiance reflects changes in the efficiency of dissipation of excess energy (photoprotection) and PSII inactivation (photodamage), which would be expected to vary with changes in physiological condition or photoacclimation state. ΔF/Fm′ significantly decreased with increasing irradiance at both the bay and basin scales. Regression slopes of ΔF/Fm′ versus irradiance were highly variable among years in 8 of the 12 sampled basins, ranging 5.6-fold from lowest to highest slopes. In contrast, regression derived y-intercepts varied only 1.7-fold over the 4-year period, but intercepts were significantly correlated with response slopes. Analyses of covariance indicated that diurnal response slopes significantly decreased from 2006 to 2009 at the bay scale, which corresponded to increasing water clarity and increased ambient irradiance at the leaf canopy as widespread phytoplankton blooms, which had initiated in the fall of 2005, dissipated. The results indicated a shift in the photo-acclimation state of T. testudinum with the cessation of phytoplankton blooms. They also suggest that regressions of ΔF/Fm′ versus irradiance, rather than absolute ΔF/Fm′ values, better reflect seagrass physiological condition when PAM-fluorescence measurements are obtained at landscape scales over diurnal periods.

Notes on marine algae in the International Biosphere Reserve Seaflower, Caribbean Colombian I: new records of macroalgal epiphytes on the seagrass Thalassia testudinum

Abstract Six species of macroalgae are newly reported for the Caribbean International Biosphere Reserve Seaflower. All the algae were found growing epiphytically on Thalassia testudinum in shallow (<1 m) meadows around San Andrés Island. Two of these species, Stylonema alsidii and Colaconema hypneae, have been previously reported from Colombian waters, whereas Chroodactylon ornatum, Colaconema dasyae, Colaconema hallandicum and Herposiphonia parca are new records for Colombia.

Modulation of biotransformation and elimination systems by BM-21, an aqueous ethanolic extract from Thalassia testudinum, and thalassiolin B on human hepatocytes

BM-21 is an extract obtained from Thalassia testudinum marine plant with pharmacological properties. The effects of BM-21 and thalassiolin B (TB), its main component, on enzyme and transport proteins involved in drug metabolism and excretion in human cultured hepatocytes were evaluated. Cells were exposed for 48h to sub-cytotoxic concentrations of BM-21 or TB. Effects on P450 isoforms revealed significant reductions of CYP1A2, 3A4 and 2D6 activities (up to 56%, 66% and 44% inhibition, respectively) after exposition to BM-21, no changes on CYP2A6 and 2C9 activities. TB produced a concentration-dependent reduction of all P450 activities. In addition, a decrease in total UGT and UGT2B7 activities was found at 250μg/mL BM-21, while UGT1A1 and 1A9 were significantly reduced (50μg/mL). TB only inhibited significantly UGT1A9 activity. Both products were able to reduce P-gp activity in treated hepatocytes. Quantification of specific mRNAs revealed a reduction in CYP3A4 and 3A5 mRNAs content and an increase in CYP1A1 and 1A2 mRNAs. No appreciable effects in the levels of CYP2A6, 2B6, 2C9, 2C19, 2D6, 2E1, UGT1A1, UGT1A9 and ABCB1 (P-gp) were found. BM-21 inhibited P450, UGTs and P-gp activities in human hepatocytes; therefore, it should be examined for potential pharmacokinetic drug interactions in vivo.

Changes in trace metals in Thalassia testudinum after hurricane impacts

Major hurricanes Emily and Wilma hit the Mexican Caribbean in 2005. Changes in trace metals in the seagrass Thalassiatestudinum prior to (May 2004, 2005) and following passage of these hurricanes (May, June 2006) were determined at four locations along a ∼130km long stretch of coast. Before the hurricanes, essential metals were likely limiting and concentrations of potentially toxic Pb were high in a contaminated lagoon (27.5μgg−1) and near submarine springs (6.10μgg−1); the likely sources were inland sewage disposal or excessive boat traffic. After the hurricanes, Pb decreased to 2.0μgg−1 in the contaminated lagoon probably through flushing. At the northern sites, essential Fe increased >2-fold (from 26.8 to 68.3μgg−1 on average), possibly from remobilization of anoxic sediments or upwelling of deep seawater during Wilma. Thus, hurricanes can be beneficial to seagrass beds in flushing toxic metals and replenishing essential elements.

Starch grain morphology of the seagrasses Halodule wrightii, Ruppia maritima, Syringodium filiforme, and Thalassia testudinum

Starch grains are a ubiquitous component of plants that have been used in tandem with phytoliths, pollen, and macrofossils to reconstruct past floral diversity. This tool has yet to be fully explored for aquatic plants, specifically seagrasses, which lack phytoliths and are rarely preserved as macrofossils or pollen. If starch grains in seagrasses are morphologically distinct, this method has the potential to improve seagrass identification in the fossil record in such cases where its starch is preserved (e.g. scratches and occlusal surfaces of tooth enamel from seagrass consumers). The goals of this study were twofold: (1) to determine if starch is present in seagrass material and (2) to assess how starch grain morphology differs between different seagrasses. This study focused on four abundant and ecologically distinct seagrasses from the Caribbean: Halodule wrightii, Ruppia maritima, Syringodium filiforme, and Thalassia testudinum. Starch grains were observed in all species except S. filiforme. Grains from H. wrightii are typically observed in side-on orientation, are sub-round to angular, and are fairly small (3-19 μm, end-on). Grains of R. maritima are small spherical grains (4–8 μm) that have a centric hilum and a straight extinction cross with a median angle between the arms of 90°. Grains from T. testudinum are large (9–31 μm, end-on), conical in side-on and round/sub-round in end-on orientation, have a slightly eccentric hilum with an obvious particle, and prominent lamellae. Visual assessment and comparative statistics demonstrate that the morphology of starch grains from T. testudinum, R. maritima, and H. wrightii are significantly different. With more extensive research, there is potential for the positive identification of starch grains from an unknown seagrass. The ability to identify seagrass from starch grains could facilitate the identification of seagrasses in the fossil record and supply information on seagrass evolution and distribution, climate effects on seagrass distribution, and the diets of seagrass consumers.

UV-B induces leaf reddening and supports photosynthesis in the seagrass Thalassia testudinum

Numerous seagrass species growing in intertidal and shallow subtidal areas around the world produce red leaves, but the factors responsible for the induction of leaf reddening in seagrasses are poorly understood. We investigated the responses of transplanted green-leafed and in situ red-leafed Thalassia testudinum shoots growing in high light areas in the lower Florida Keys, USA, to four light treatments: 1) full solar radiation with UV excluded (PAR); 2) full solar radiation with UV–B excluded (PAR + UV–A); 3) full solar radiation reduced by 50% (50% Ambient); and 4) full solar radiation (Ambient). In our first experiment, green-leafed shoots were transplanted from a 1 m depth (MLW) to the four light treatments in 0.2 m depth (MLW). In our second experiment, in situ red-leafed shoots growing at depths between 0.2 m and 0.5 m were exposed to the four light treatments. Within one week, new leaf tissue from green-leafed shoots transplanted into shallow water accumulated anthocyanins and began to turn red in treatments receiving full spectrum solar radiation (Ambient; 50% Ambient) while transplanted green-leafed shoots in the two treatments that excluded UV–B (PAR and PAR + UV–A) had low anthocyanin content and remained green. Although we quickly induced red coloration in leaves of green-leafed shoots, reducing light levels (including UV–B) for seven weeks did not cause leaves of in situ red leafed shoots to decrease anthocyanin content or turn green. Instead, red leaves increased photosynthetic pigments in all treatments except Ambient. In addition, the PAR+UV -A treatment had lower effective quantum yields at midday compared to the PAR, 50% Ambient, and Ambient treatments, as well as lower relative electron transport rates compared to the PAR and Ambient treatments. We conclude that exposure to UV–B induces anthocyanin accumulation and red coloration in green-leafed shoots and contributes to the maintenance of high levels of photosynthesis in red-leafed shoots of T. testudinum. We also propose that T. testudinum in the clear, shallow waters of the lower Florida Keys produces a red-leafed variant, a genetically differentiated form of this species, with permanently red leaves since anthocyanin accumulation and red coloration in leaves of red-leafed shoots was not reversible in this and a longer-term study.

Atmospheric Deposition of Nitrogen to a Caribbean Coastal Zone (Cayo Coco, Cuba): Temporal Trends and Relative Importance as a Nitrogen Source

Nitrogen (N) deposition to the ocean is thought to be increasing worldwide, but the amount of coastal and open ocean measurements is very limited. In this paper, we assess N deposition in the coastal zone of Cayo Coco, in central Cuba, during a multi-annual period (2005–2007). Wet and dry N depositions were estimated based on the NH 4 + and NO x – concentrations in the rain. Cold fronts and troughs, coming from the west, contributed most to rain (41%) and to N deposition, followed by tropical waves and storms coming from the east, which caused 31% of the rain. Average concentrations of NH 4 + and NO x – in the rain were 8.8 and 8.3 μM. NO x – presented a clearly decreasing trend (0.26 μM per month), decreasing by half during 2005–2007. Total N deposition averaged 3.23 kg N ha−1 year−1, similar to that found in Virgin Islands and Puerto Rico, but lower than previously measured in Cuba and in nearby areas of the USA and than model predictions for the oceanic region around Cuba. These low values and the decreasing trend found are attributed to drastic reduction of fossil fuel and fertilizer use in Cuba since 1990. Because land input has decreased even more drastically, deposition seems to be nowadays the most important N source to the coastal zone of Cayo Coco. The δ15N range of seagrass (Thalassia testudinum) and macroalgae (Penicillus dumetosus) in the area (−1.83‰ to 3.02‰ and +1.02‰ to +4.17‰, respectively) sustain that atmospheric sources (deposition and N2 fixation) comprise 70–90% of the N budget.

Revision of the taxonomic status of Lysidice (Polychaeta, Eunicidae) in the Western Caribbean Sea with observation on species reproductive features and habitat preference

Although most of the Eunicidae (Polychaeta) of the Western Caribbean Sea appear to be well studied, the taxonomic status of Lysidice has yet to be evaluated. A first attempt to revise the taxonomy of this genus is here presented, based on material collected at Carrie Bow Cay (CBC, Belize), as well as at other sites along the Yucatan Peninsula, representing a variety of habitat types (coralline rock–coral rubbles, sponges, coralline sands, Thalassia testudinum meadows) and depths (0.5–20 m). The collected new taxa found were described and compared with literature description of other known species, as well as with museum specimens of the type-species of the genus, Lysidice ninetta Audouin & Milne Edwards, which has been confused with and synonymized with many Caribbean morphotypes of Lysidice. The analysis reveals the presence of five previously undescribed species of Lysidice: L. caribensis n. sp. and L. adrianae n. sp., preferentially associated with coralline rock; L. thalassicola n. sp. associated with Thalassia testudinum meadows, as a borer in the seagrass sheaths, and representing the only polychaete species strictly associated with Thalassia; lastly, L. carriebowensis n. sp. and L. phyllisae n. sp. are less common and collected only at CBC in association with coralline rock (coral rubble). Several specimens of the three more common new species, L. caribensis, L. thalassicola and L. adrianae were found mature, both males and females, with an epitokous transformation in which nearly two-thirds of the body is swollen and full of gametes, and with eyes extraordinarily enlarged. The ultrastrucure analysis of mature spermatozoa of L. caribensis and L. adrianae shows a typical ect-aquasperm structure. These show that Lysidice is a highly diversified genus in the Western Caribbean, with the different species showing clear habitat and geographic separation.

Photoprotecting Action and Phytochemical Analysis of a Multiple Radical Scavenger Lipophilic Fraction Obtained from the Leaf of the SeagrassThalassia testudinum

The apolar fraction F1 of Thalassia testudinum was chemically characterized by gas chromatography-mass spectrometry, which led to the identification of 43 metabolites, all of them reported for the first time in the genus Thalassia. More than 80% of the F1 composition was constituted by aromatic metabolites including the major components 1,1-bis(p-tolyl)ethane (6.0%), 4,4'-diisopropylbiphenyl (4.8%) and a 1,1-bis(p-tolyl)ethane isomer (4.7%). This lipophilic fraction was assayed for its antioxidant effects and skin protective action. In vitro assays showed that F1 strongly scavenged DPPH* (IC(50) 312.0 ± 8.0 μg mL(-1)), hydroxyl (IC(50) 23.8 ± 0.5 μg mL(-1)) and peroxyl radical (IC(50) 6.6 ± 0.3 μg mL(-1) ), as well as superoxide anion (IC(50) 50.0 ± 0.7 μg mL(-1)). Also, F1 markedly inhibited the spontaneous lipid peroxidation (LPO) in brain homogenates (IC(50) 93.0 ± 6.0 μg mL(-1)) and the LPS-stimulated nitrite generation on RAW624.7 macrophages (58.6 ± 3.2%, 400 μg mL(-1)). In agreement with these findings, its topical application at 250 and 500 μg cm(-2) strikingly reduced skin damage on mice exposed to acute UVB radiation by 45% and 70%, respectively and significantly attenuated the LPO developed following the first 48 h after acute exposure to UVB irradiation, as manifested by the decreased malondialdehide level and by the increased of reduced gluthatione content. Our results suggest that F1 may contribute to skin repair by attenuating oxidative stress due to its antioxidant activity.

Description of two new species of Rissoella Gray, 1847 (Mollusca, Gastropoda, Heterobranchia) from Venezuela, with a key to the Caribbean species known for the genus

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. Rissoella 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. Rissoella 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.

The Relationship Between Imposex and Tributyltin (TBT) Concentration in Strombus Gigas from the British Virgin Islands

The queen conch, Strombus gigas (Linnaeus, 1758), was collected from sites with substantial boating activity and adjacent reference sites from the British Virgin islands in 2008-2009 to determine the incidence and severity of imposex. Comparisons were made to a previous study by phillip (2000) in the same area to determine if there were any changes in imposex over the last decade. imposex was present in S. gigas at all sites with boating activity, but not found in individuals collected at reference sites. Tributyltin (TBT) and its degradative product, dibutyltin (DBT), were found in S. gigas, turtle grass, Thalassia testidium (Banks ex Konig), and marine algae from sites with known point sources of TBT. we established a relationship between the highest incidence and severity of imposex and TBT concentrations in the tissues of S. gigas from sites with elevated boating activity (Road Harbour > Nanny Cay > Trellis Bay), suggesting that TBT, a known inducer of imposex in female prosobranch gastropods, is the causative agent. Strombus gigas is the second most important commercial fishery species in the Caribbean and any factors that could affect reproduction and population ecology are important in maintaining a viable population and managing a sustainable fishery. we suggest using S. gigas as a sentinel of TBT pollution despite not meeting all of the recommended criterion, such as lack of non-dispersive larvae.

Effects of short-term hypersalinity exposure on the susceptibility to wasting disease in the subtropical seagrass Thalassia testudinum

Seagrass meadows are a vital component of coastal ecosystems and have experienced declines in abundance due to a series of environmental stressors including elevated salinity and incidence of disease. This study evaluated the impacts of short-term hypersalinity stress on the early stages of infection in Thalassia testudinum Banks ex König by assessing changes in cellular physiology and metabolism. Seagrass short shoots were exposed to ambient (30 psu) and elevated (45 psu) salinities for 7 days and subsequently infected for one week by the causative pathogen of wasting disease, Labyrinthula sp. The occurrence of wasting disease was significantly lower in the hypersalinity treatments. Additionally, while exposure to elevated salinity caused a reduction in chlorophyll a and b content, T. testudinum's health, in terms of photochemical efficiency, was not significantly compromised by hypersalinity or infection. In contrast, plant respiratory demand was significantly enhanced as a function of infection. Elevated salinity caused T. testudinum to significantly increase its in vivo H(2)O(2) concentrations to levels that exceeded those which inhibited Labyrinthula growth in a liquid in vitro assay. The results suggest that while short-term exposure to hypersalinity alters selected cellular processes this does not necessarily lead to an immediate increase in wasting disease susceptibility.