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Large grazers (megaherbivores) have a profound impact on ecosystem functioning. However, how ecosystem multifunctionality is affected by changes in megaherbivore populations remains poorly understood. Understanding the total impact on ecosystem multifunctionality requires an integrative ecosystem approach, which is especially challenging to obtain in marine systems. We assessed the effects of experimentally simulated grazing intensity scenarios on ecosystem functions and multifunctionality in a tropical Caribbean seagrass ecosystem. As a model, we selected a key marine megaherbivore, the green turtle, whose ecological role is rapidly unfolding in numerous foraging areas where populations are recovering through conservation after centuries of decline, with an increase in recorded overgrazing episodes. To quantify the effects, we employed a novel integrated index of seagrass ecosystem multifunctionality based upon multiple, well-recognized measures of seagrass ecosystem functions that reflect ecosystem services. Experiments revealed that intermediate turtle grazing resulted in the highest rates of nutrient cycling and carbon storage, while sediment stabilization, decomposition rates, epifauna richness, and fish biomass are highest in the absence of turtle grazing. In contrast, intense grazing resulted in disproportionally large effects on ecosystem functions and a collapse of multifunctionality. These results imply that (i) the return of a megaherbivore can exert strong effects on coastal ecosystem functions and multifunctionality, (ii) conservation efforts that are skewed toward megaherbivores, but ignore their key drivers like predators or habitat, will likely result in overgrazing-induced loss of multifunctionality, and (iii) the multifunctionality index shows great potential as a quantitative tool to assess ecosystem performance. Considerable and rapid alterations in megaherbivore abundance (both through extinction and conservation) cause an imbalance in ecosystem functioning and substantially alter or even compromise ecosystem services that help to negate global change effects. An integrative ecosystem approach in environmental management is urgently required to protect and enhance ecosystem multifunctionality.

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.

Thalassia propinqua Hutton, 1882 Pl. 4, fig. C Hutton, 1882. New Zealand Journal of Science, 1: 281. Type material. Lectotype (designated here), CMNZ M168.4, and paralectotypes, CMNZ M168.1–3 (3) and CMNZ M12772 [ex M168] (1) (dry shells). The molluscan collection at CMNZ has a radula and jaw mounted on a glass slide with the label details ‘ Thalassia propinqua, Weka Pass, XVI p. 169’, in Hutton’s handwriting (i.e., CMNZ 2017.17.83), which is probably primary type material (see description of radula by Hutton 1883d: 137). Label details. M168—‘65. Thalassia propinqua Hutton, Weka Pass, Canterbury’, pillbox label in Hutton’s handwriting. Type locality. ‘Weka Pass (C. Chilton)’ (Hutton 1882p: 281, 1883d: 137). Previous illustrations of type material. Pilsbry (1892 [in 1892–1893]: 72, 304, pl. 22, figs. 55–57—‘drawn from the type, ‘H. Suter, del.’), Suter (1915: pl. 9, figs. 1, a—same shell as illustrated by Pilsbry). Remarks. Hutton submitted a description of Thalassia (?) propinqua to the Transactions and Proceedings of the New Zealand Institute issue for 1882, but publication was delayed until May 1883 (Hutton 1883d: 137), and was pre-empted by a brief description in an account of a meeting of the Philosophical Institute of Canterbury (Hutton 1882p: 281). A description by Hutton (1884b: 169, pl. 10, fig. G, pl. 11, fig. V) of a jaw and radula purported to be from propinqua was based on a specimen from Southland collected by G. M. Thomson (i.e., CMNZ 2017.17.82) that is not type material of, or conspecific with, Thalassia propinqua Hutton, 1882. From Pilsbry (1892 [in 1892– 1893]: 72) onwards propinqua has generally been assigned to Thalassohelix Pilsbry, 1892 at subgenus or genus level, and it has been interpreted as having a wide distribution in New Zealand, between Auckland in the North Island, and the southern South Island (e.g., Hutton 1884c: 203, Hedley & Suter 1893: 636, Suter 1913: 631, Powell 1979: 318). However, preliminary results of a phylogenetic study indicate that propinqua belongs in genus Therasia Hutton, 1883; the genetic data and examination of museum collections indicate that it has a distribution spanning the south-eastern North Island and north-eastern South Island, only (M. Kennedy unpub. data). Taxonomy. Here treated as Therasia propinqua (Hutton, 1882) n. comb. Distribution. New Zealand; south-eastern North Island from East Cape to Cape Palliser; Marlborough and Canterbury in the South Island (AIM and NMNZ collection records)., Published as part of Brook, Fred J., Kennedy, Martyn, King, Tania M., Ridden, Johnathon, Shaw, Matthew D. & Spencer, Hamish G., 2020, Catalogue of New Zealand land, freshwater and estuarine molluscan taxa named by Frederick Wollaston Hutton between 1879 and 1904, pp. 1-73 in Zootaxa 4865 (1) on page 34, DOI: 10.11646/zootaxa.4865.1.1, http://zenodo.org/record/4428428, {"references":["Hutton, F. W. (1883 d) Descriptions of new land shells. Transactions and Proceedings of the New Zealand Institute, 15, 134 - 141. [May]","Hutton, F. W. (1882 p) Meetings of Societies, Philosophical Institute of Canterbury. Christchurch, 7 th September, 1882. Descriptions of new land shells. The New Zealand Journal of Science, 1 (6), 281 - 282. [November]","Suter, H. (1915) Manual of the New Zealand Mollusca, Atlas of Plates. MacKay, Government Printer, Wellington, 72 pls.","Hutton, F. W. (1884 b) Notes on New Zealand land shells. Transactions and Proceedings of the New Zealand Institute, 16, 161 - 186. [May]","Hutton, F. W. (1884 c) Revision of the land Mollusca of New Zealand. Transactions and Proceedings of the New Zealand Institute, 16, 186 - 212. [May]","Hedley, C. & Suter, H. (1893) Reference list of the land and freshwater Mollusca of New Zealand. Proceedings of the Linnean Society of New South Wales, Series 2, 7, 613 - 665. [May]","Suter, H. (1913) Manual of the New Zealand Mollusca. MacKay, Government Printer, Wellington, 1120 pp.","Powell, A. W. B. (1979) New Zealand Mollusca: Marine, Land and Freshwater Shells. Collins, Auckland, xiv + 500 pp."]}

1. Seagrasses provide an important ecosystem service by creating a stable erosion-resistant seabed that contributes to effective coastal protection. Variable morphologies and life history strategies, however, are likely to impact the sediment stabilisation capacity of different seagrass species. We question how opportunistic invasive species and increasing grazing by megaherbivores may alter sediment stabilisation services provided by established seagrass meadows, using the Caribbean as a case study. 2. Utilising two portable field-flumes that simulate unidirectional and oscillatory flow regimes, we compared the sediment stabilisation capacity of natural seagrass meadows in situ under current- and wave-dominated regimes. Monospecific patches of a native (Thalassia testudinum) and an invasive (Halophila stipulacea) seagrass species were compared, along with the effect of three levels of megaherbivore grazing on T. testudinum: ungrazed, lightly-grazed and intensively-grazed. 3. For both hydrodynamic regimes, the long-leaved, dense meadows of the climax species, T. testudinum, provided the highest stabilisation. However, the loss of above-ground biomass by intensive grazing reduced the capacity of the native seagrass to stabilise the surface sediment. Caribbean seagrass meadows are presently threatened by the rapid spread of the invasive opportunistic seagrass, H. stipulacea. The dense meadows of H. stipulacea were found to accumulate fine sediment, and thereby, appear to be effective in reducing bottom shear stress during calm periods. This fine sediment within the invasive meadows, however, is easily resuspended by hydrodynamic forces, and the low below-ground biomass of H. stipulacea make it susceptible to uprooting during storm events, potentially leaving large regions vulnerable to erosion. Overall, this present study highlights that intensive megaherbivore grazing and opportunistic invasive species threaten the coastal protection services provided by mildly grazed native species. 4. Synthesis: Seagrass meadows of dense, long-leaved species stabilise the sediment surface and maintain the seabed integrity, thereby contributing to coastal protection. These services are threatened by intensive megaherbivore grazing, which reduces the stability of the surface sediment, and opportunistic invasive species, which are susceptible to uprooting in storms and thereby can leave the seabed vulnerable to erosion.

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. Electronic supplementary material The online version of this article (10.1186/s12898-019-0221-4) contains supplementary material, which is available to authorized users.

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. RESUMEN Thalassia testudinum y Halodule wrigthii son las hierbas marinas dominantes en el Caribe, siendo comunes en costas someras, tanto en monocultivos como en cultivos mixtos. Entre la macrofauna asociada a estas comunidades, los crustáceos son considerados esenciales para el funcionamiento del ecosistema. Sin embargo, el conocimiento sobre la comunidad de crustáceos decápodos asociada a praderas mixtas de T. testudinum y H. wrigthii es escaso, en particular fuera de zonas protegidas. En este trabajo presentamos ocho nuevas especies de decápodos para la Península de Paraguaná (estado Falcón, Venezuela) asociados a praderas mixtas de hierbas marinas: Achelous tumidulus Stimpson, 1871, Alpheus floridanus Kingsley, 1878, Chorinus heros (Herbst, 1790), Clibanarius antillensis (Stimpson, 1859), Clibanarius sclopetarius (Herbst, 1796), Latreutes parvulus (Stimpson, 1866), Panopeus occidentalis Saussure, 1857, y Processa fimbriata Manning & Chace, 1971. Estos registros representan extensiones de hábitat y completan brechas en la distribución geográfica de las especies a lo largo de la costa septentrional de Sudamérica. Diferencias estadísticas en la abundancia y composición de las especies de decápodos fueron posiblemente causadas por la acción conjunta de cobertura y heterogeneidad de las praderas. Las especies más influyentes en la comunidad son típicas para el Caribe; no obstante, la abundancia de Penaeus schmitti Burkenroad, 1936 juveniles fue notable, puesto que raramente han sido encontrados en estos hábitats. Este hallazgo resalta el rol de áreas no protegidas como hábitats de cría para especies de importancia comercial. Nuestros resultados muestran que las praderas de hierbas marinas en la Península de Paraguaná reflejan un buen estado en comparación con otras zonas del Caribe, y representan un hábitat importante para el mantenimiento de las poblaciones de crustáceos.

Songklanakarin Journal of Science and Technology, 40, 6, 1446-1450

There exists increasing evidence that top-down ecological processes, such as herbivory are key in controlling marine ecosystems and their community structure. Herbivory has the potential to be altered by numerous environmental and ecological factors that operate at a variety of temporal and spatial scales, one such spatial factor is the influence of the marine landscape. We know little about how ecological processes, such as herbivory change throughout the marine landscape and how the effects of these processes cascade. This is because most landscape scale studies observe species richness and abundance patterns. In terrestrial systems the landscape is well documented to influence ecological processes, but empirical evidence of this is limited in marine systems. In tropical seagrass meadows direct herbivory by parrotfish can be readily observed due to the clear hemispherical bite marks they leave on the seagrass. As with herbivory in other systems, this leaf consumption is thought to assist with leaf turnover, positively influencing leaf growth. Changes in its rate and extent are therefore likely to influence the characteristics of the plant. The faunal communities of seagrass meadows alter with respect to changes in the landscape, particularly with respect to connectivity to adjacent habitats. It might therefore be expected that a key ecological process, such as herbivory will change with respect to habitat configuration and have cascading impacts upon the status of the seagrass. In the present study we examined indirect evidence of parrotfish grazing throughout the marine landscape and assessed this relative to plant condition. Seagrasses in locations of close proximity to mangroves were found to have double the amount of parrotfish grazing than sites away from mangroves. Evidence of herbivory was also found to be strongly and significantly negatively correlated to the abundance of plant attached epicover. The decreased epicover in the presence of elevated herbivory suggests increased leaf turnover. These results indicate that seagrass may have higher levels of ecosystem resilience in the presence of mangroves. Our research highlights how ecological processes can change throughout the marine landscape with cascade impacts on the resilience of the system.

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.

ResumenSe cita por primera vez para Venezuela el dótido Doto chica Ev. Marcus y Er. Marcus, 1960 encontrado sobre hojas de Thalassia testudinum. Ha sido citado para Florida, Curasao, Puerto Rico, Cuba, México y Costa Rica.AbstractThe presence of Doto chica Ev. Marcus and Er. Marcus, 1960 is recorded for the first time in Venezuela, found on Thalassia testudinum leaves. It has been recorded in Florida, Curasao Puerto Rico, Cuba, Mexico and Costa Rica.

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 (

39-53 semestral Referencia analítica

68-76 semestral Referencia analítica

Mediante análisis comparativo de mapas, fotografías aéreas e imágenes de satélite, complementados con observaciones de campo, se reconstruyó la distribución de las praderas de pastos marinos en la bahía de Cartagena y áreas aledañas en cinco periodos que abarcan las últimas seis décadas. De algo más de 1,000 hectáreas calculadas de praderas existentes en 1935-45, en el año 2001 quedaban un remanente de apenas 76, lo que equivale a menos del 8%. La tasa de pérdida del área de praderas en el interior de la bahía reveló una tendencia exponencial inversa, en tanto que en las zonas externas a ésta la tendencia fue lineal. La casi erradicación de esta importante comunidad biótica fue desencadenada probablemente por la reapertura del canal del Dique en la década de 1930, introduciendo cantidades importantes de aguas dulces, turbias y de sedimentos a la bahía, y subsecuentemente acelerada por el desarrollo de la zona industrial, el vertimiento de aguas servidas industriales y domésticas, dragados y obras de infraestructura en el litoral. La reducción de la extensión de las praderas parece haber sido acompañada de cambios en la estructura de la comunidad faunística asociada, que se manifiestan en la aparente desaparición de algunos invertebrados filtradores que eran dominantes hasta hace al menos tres décadas. La pérdida de las áreas de pastos marinos en la bahía en el transcurso del siglo XX parece ser parte del prolongado proceso de transformación antrópica de este ecosistema iniciado tres siglos antes. The spatial distribution of seagrass beds within the Cartagena Bay and neighboring areas was reconstructed through comparative analyses of maps, aerial photographs and satellite imagery, as well as observations in the field for five time periods within the last six decades. From slightly more than 1,000 hectares of seagrass beds existing in 1935-45, only 76 remained in 2001, which is less than 8%. The loss rate of seagrass within the bay showed an inverse exponential pattern, whereas outside of the bay the tendency was linear. The almost disappearance of this community was probably raged by the reopening of the Canal del Dique early in the thirties, causing the introduction of important amounts of turbid freshwater and sediments into the bay, and subsequently accelerated by the rapid development of the industrial zone, spilling of polluted industrial and domestic waters, dredging and coastal development. The reduction of seagrass areas has been seemingly accompanied by changes in the structure of the animal community, becomig apparent through the evident disappearance of suspension feeding invertebrates which were so far dominant elements three decades earlier. The loss of seagrass beds in the bay during the 20th century seems likely to be part of the long lasting human transformation process of this ecosystem, which started three centuries before.

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

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.

The basic ecology of seagrass beds was investigated by comparing biomass, productivity and density of Thalassia testudinum (turtle grass) at three sites: Puerto Vargas, Punta Cahuita and Río Perezoso, in Cahuita National Park, Limón, Costa Rica, over a two month period (March-April 1999). Above ground biomass, density, and productivity were highest in the Puerto Vargas site while Punta Cahuita had the least non-green above ground biomass was significantly lower in total biomass than Puerto Vargas. Punta Cahuita was distinguished by the largest grain size, a very hard substrate, and shallower water. Río Perezoso, on the other hand, had extremely fine sediment and lower salinity, while Puerto Vargas was intermediate both in sediment size and environmental conditions. It appears, therefore, that higher biomass and productivity result from a combination of moderate environmental characteristics and an intermediate sediment size. Se investigó la ecología básica del pasto marino Thalassia testudinum (pasto de tortuga), comparando biomasa, productividad y densidad, en tres sitios en el Parque Nacional Cahuita, Costa Rica: Puerto Vargas, Punta Cahuita y Río Perezoso. Se tomaron muestras de biomasa, sedimentos, crecimiento y densidad durante dos meses (marzo y abril, 1999), además se midió la temperatura del aire y agua, la visibilidad, la profundidad, y la salinidad. La biomasa de hojas, densidad y productividad fueron más altas en Puerto Vargas. Punta Cahuita tuvo la menor biomasa de hojas que no eran verdes y fue menor que Puerto Vargas en biomasa total. Punta Cahuita se caracterizó por tener sedimentos gruesos, el substrato duro y la profundidad baja, mientras que Río Perezoso tenía sedimentos muy finos y la salinidad más baja. Puerto Vargas era intermedio en ambos: tamaño de sedimentos y condiciones ambientales. Parece que la biomasa y la productividad alta resultan de la combinación de características ambientales moderadas y el tamaño de sedimentos intermedios.