Explore the vast range of titles available.

A partir del erizo de mar Mellita quinquiesperforata (Leske), recolectado en el Caribe colombiano fueron obtenidos sus extractos acuoso, metanólico y de diclorometano, a los cuales se les determinó el contenido de fenoles totales encontrando valores de 10,97, 9,47 y 9,22 mg EAG/g, respectivamente. Moderada actividad antioxidante fue encontrada frente al radical catiónico (ABTS) con valores IC50 = 85,60, 76,75 y 98,19 μg/ml para los mismos extractos, mientras que frente al radical DPPH, se encontró baja actividad con valores de IC50 superiores a 200 μg/ml, en todos los casos evaluados. En la determinación del potencial de reducción férrica, se encontraron valores moderados de reducción, los cuales fueron de 3,24, 3,37 y 3,42 mg EAA/g para los extractos metanólico, diclorometano y acuoso, respectivamente. De otra parte, del extracto de diclorometano se obtuvo la fracción lipídica, de la cual fueron identificados 38 compuestos orgánicos, 30 ácidos grasos y 8 esteroles, con variaciones estructurales. Los resultados obtenidos muestran que M. quinquiesperforata es capaz de producir compuestos que logran inhibir el radical ABTS, así como de reducir el Fe+3, pero no son eficientes para inhibir el radical DPPH.

Removal of important predators by fishing can result in trophic cascades and indirect effects on marine benthic communities. Indirect effects are especially evident when prey populations released from predation by fishing have the ability to modify entire benthic communities, as do sea urchins. Sea urchins have been shown to dramatically alter the underwater landscape by grazing, by converting stands of large erect algae into coralline barrens. In the western Mediterranean, a recent extension of coralline barrens into areas formerly dominated by erect algal assemblages has been attributed to release of predation on sea urchins by overfishing. Most suggestions concerning the transition from erect algal assemblages to coralline barrens, however, have been speculative, and little descriptive and experimental work has been carried out to verify the hypothesis that fish predation on sea urchins (and its subsequent release by overfishing) drives this transition. Here we critically review the literature concerning the effect of fishing on sea urchin populations and its subsequent maintenance of different algal assemblages in the Mediterranean. The extant data cannot refute the \"fishes as important predators\" model, but we argue that other processes (recruitment, pollution, disease, large-scale oceanographic events, sea urchin harvesting, food subsidies, and availability of shelters) may also be important in regulating the structure of Mediterranean algal assemblages.

Recovery criteria for depleted species or populations normally are based on demographic measures, the goal being to maintain enough individuals over a sufficiently large area to assure a socially tolerable risk of future extinction. Such demographically based recovery criteria may be insufficient to restore the functional roles of strongly interacting species. We explored the idea of developing a recovery criterion for sea otters ( Enhydra lutris) in the Aleutian archipelago on the basis of their keystone role in kelp forest ecosystems. We surveyed sea otters and rocky reef habitats at 34 island-time combinations. The system nearly always existed in either a kelp-dominated or deforested phase state, which was predictable from sea otter density. We used a resampling analysis of these data to show that the phase state at any particular island can be determined at 95% probability of correct classification with information from as few as six sites. When sea otter population status (and thus the phase state of the kelp forest) was allowed to vary randomly among islands, just 15 islands had to be sampled to estimate the true proportion that were kelp dominated (within 10%) with 90% confidence. We conclude that kelp forest phase state is a more appropriate, sensitive, and cost-effective measure of sea otter recovery than the more traditional demographically based metrics, and we suggest that similar approaches have broad potential utility in establishing recovery criteria for depleted populations of other functionally important species.

Within-plant variation in the concentration of secondary metabolites, nutritive value, toughness, and susceptibility to herbivory was assessed for the brown alga Dictyota ciliolata. When young apices and older tissue from the same plant were offered in equal abundance to the herbivorous amphipod Ampithoe longimana and the sea urchin Arbacia punctulata, young apices were consumed about 2 times more than older tissue. Compared to young apices, the less preferred older tissue had a less palatable lipophilic extract, significantly higher concentrations of two secondary metabolites (another secondary metabolite did not differ significantly), 33% more soluble protein, and was 233% tougher. Higher levels of chemical defenses in older tissues, and not tissue toughness or nutritive value, appear to be responsible for the preference of Ampithoe longimana for young apices. The pattern of lower levels of chemical defenses in young than older tissues of D. ciliolata is the opposite of the pattern observed in coenocytic seaweeds and most vascular terrestrial and marine plants, all of which have translocation systems for moving materials among plant portions. Unlike these other plants, which preferentially allocate chemical defenses to young tissues, D. ciliolata cannot readily translocate secondary metabolites. The growth-differentiation balance hypothesis suggests that actively dividing and expanding cells are less able to produce secondary metabolites. This hypothesis may help explain why older tissues are better defended than young, rapidly growing apices.

Algal-herbivore (fish and sea urchin) interactions in shallow (<10 m) and deeper (>15 m) coral forereef communities off Discovery Bay, Jamaica, were investigated and compared. Algal functional form groups exhibited different bathymetric distribution patterns. Crustose corallines, the most abundant group in shallow water, decreased in abundance with increasing depth, whereas erect macroalgae increased in abundance with depth, predominating in deeper water. This distribution pattern was correlated with a decline in herbivory over depth. The hypothesis that herbivory affects algal abundance and distribution was tested using grazer exclusions and algal transplants. Five 1-m^2 exclusion fences, which excluded the sea urchin Diadema antillarum but not fish, were erected in both shallow (7-8 m) and deeper (17-18 m) water. Removal of Diadema resulted in a pronounced change in the shallow algal community; erect and filamentous algae rapidly overgrew crustose corallines in 2 mo. In contrast, Diadema exclusion had little effect on the deeper algal community. In another experiment, which prevented both fish and urchin grazing, unaltered natural substrates with attached algae were suspended on racks in the water column 30-40 m from the reef at depths corresponding to the fences. Abundances of erect and filamentous algae increased on both shallow and deeper racks. The erect species that increased in abundance in the fences were resistant to fish, whereas only fish-susceptible species increased on the racks. Transplanting the most abundant erect species from the reef crest (Laurencia obtusa, Caulerpa racemosa) and deeper forereef (Lobophora variegata, Dictyota divaricata, Halimeda goreauii) to the shallow forereef revealed that all, except L. obtusa, were readily consumed by Diadema, but all exhibited low susceptibility to fishes. The reef crest and deeper reef are spatial refuges from urchin predation for erect macrophytes. In summer 1983, the Diadema population experienced >95% mortality. On the shallow reef, erect and filamentous algae and fish grazing intensity increased substantially following urchin death, while crustose corallines declined. Conversely, Diadema mortality had little effect on the deeper reef. Algal responses were similar to those observed in the urchin exclusion experiments. The erect species that increased most after mortality are resistant to fishes via chemical defenses. These findings demonstrate that herbivory is largely responsible for the algal distribution pattern on the reef. The results suggest that Diadema plays a major role in structuring the shallow community, but only a minor role relative to fishes in structuring the deeper community. They also indicate that different herbivores can have a differential effect on erect macroalgal composition.

The echinoid Diadema antillarum Philippi was an important herbivore in many areas of the Caribbean prior to the mass mortality that eliminated 95-99% of the individuals throughout the Caribbean in 1983-84. Five days after the mass mortality in St. Croix, U.S. Virgin Islands, algal biomass increased by 20% and algal community primary productivity dropped on both a per unit area basis (37% decrease) and per unit algal biomass basis (61% decrease). This accompanied a 50% decrease in the amount of algal biomass removed by herbivores. Concurrent with the changes in the algal community were increases in the rates of grazing by herbivorous fishes, suggesting that exploitative competition for food was occurring between D. antillarum and some herbivorous fish species. These results suggest that D. antillarum has an important role in structuring both the producer and consumer components of Caribbean coral reef ecosystems.

Patterns of survival of juvenile giant kelp (Macrocystis pyrifera) were examined in relation to grazing by sea urchins, shading by adult kelp, density of recruits, densities of other algal species, and substrate distribution. Survival was poorer in areas where white sea urchins (Lytechinus anamesus) were abundant or where there was an overlying canopy of adults. At other sites, the density of recruits explained the greatest proportion of variability in survival, and the proportion of juveniles that survived was negatively correlated with the number of recruits. Potential algal competitors (Pterygophora californica and Cystoseira osmundacea), red sea urchins (Strongylocentrotus franciscanus), and substrate distributions had no significant effect on survival. The mechanisms of density-dependent survival were similar to @'dominance and suppression@' models that explain self-thinning in many terrestrial plant populations. In stands where densities of recruits were high, skewed size distributions developed, probably as the result of competition for light. High-density stands had proportionally more small plants than low-density stands, and, during subsequent storms, only the larger plants survived. This led to a more equitable distribution of survivors than would be expected based on the number of recruits. Intraspecific interactions, both between adults and juveniles and among juveniles of the same cohort, appear to be important structuring forces in most giant kelp populations. The parallels in many terrestrial populations. However, in other algal populations, there is little evidence for density-dependent mortality or for the dominance-suppression hypothesis. These differences may relate to competition for light, which is intense in Macrocystis forests and many terrestrial populations, but less so in assemblages of other benthic algae.

The study ascertained whether zygote exposure to pure oestrogen 17beta-oestradiol would result in developmental anomalies similar to those reported for methoxychlor (MXC), a widely-used pesticide with known adverse effects on reproduction and development. Chronic exposure of embryos to 0.5 ppm 17beta-estradiol reduced the percentage of embryos completing normal first cleavage from 90 to 80. Second cleavage was reduced from 88 to 68 per cent. More than 99 per cent of control gastrulae had normal developing guts but among 17beta-estradiol exposed gastrulae, 9 per cent were normal, 37 per cent showed no gut development and 54 per cent had evaginated guts (exogastrulae). At the pluteus stage, exposed embryos exogastrulated with tripartite exoguts. Exposure to 17beta-estradiol resulted in exogastrulation but did not inhibit further differentation of the exogut. The effect of MXC was different: induced stunted guts and abnormal spicules but not exogastrulae. The effects of MXC could not be ascribed to its oestrogenic metabolites because of different development effects.

Sea urchin (Strongylocentrotus purpuratus) sperm exposed to 3 ppm methoxychlor (MXC) for 10 minutes had approximately 30 per cent reduction in fertilization. Exposure to MXC for 30 minutes was spermiotoxic giving virtually no fertilization. However, eggs exposed to 3 ppm MXC for 30 minutes before insemination had a mean fertilization rate of 95 per cent, similar to controls. When gametes were exposed to MXC for 10 minutes (sperm) or 30 minutes (eggs) before fertilization and the resulting embryos allowed to develop, approximately 3.5 and 5.5 per cent of these embryos, respectively, displayed an abnormal stunted gut, or had only a thickened vegetal plate epithelium with disorganized clusters of mesenchymal cells. These abnormalities persisted to the pluteus stage (72 h). MXC-exposed embryos were spherical rather than the usual tetrahedral shape.

Las huevas frescas del erizo de mar Echinometra lucunter lucunter presentan un alto valor alimenticio, lo cual potencia su pesquería y maricultura; no obstante, su composición bioquímica y desarrollo están influenciadas por las condiciones ambientales. Para evaluar el contenido de proteínas, carbohidratos y lípidos, y poder establecer cómo varía el almacenamiento en las gonadas durante las temporadas de surgencia (alta productividad primaria/22-24°C) y estratificación (baja productividad pr¡maria/28-30°C), erizos de mar adultos (> 30 mm) fueron recolectados mensualmente en el Islote Lobos (Venezuela). La salinidad, temperatura, oxígeno disuelto, transparencia, seston total y clorofila a en aguas superficiales fueron estimadas. A cada individuo se le determinó su biometría, sexo, estadio reproductivo, índice gonadosomático (IGS) y contenido de biomoléculas en las gonadas. El desarrollo gonadal de E. lucunter lucunter se inicia durante la transición de surgencia a estratificación, coincidiendo con los aumentos en la temperatura del agua. Las biomoléculas mostraron variaciones temporales asociadas con la producción de gonadas; existiendo una relación negativa entre la preferencia de uso de carbohidratos y lípidos. La maduración gonadal máxima y acumulación de carbohidratos y proteínas fueron alcanzadas durante la estratificación; sin embargo, durante la surgencia se observaron desoves sincronizados, así como un descenso en los lípidos y carbohidratos. Las condiciones ambientales durante la estratificación estimulan el desarrollo gonadal de E. lucunter lucunter, en contraste, la surgencia costera actúa como detonante de los desoves de manera sincronizada para ambos sexos. El almacenamiento de biomoléculas energéticas ocurre principalmente durante la estratificación, usando preferiblemente los carbohidratos para suplir la demanda metabolica.