Marine photosynthetic picoeukaryotes: community structure at different spatial scales

Programa de doctorado en Oceanografía. En portada: Institut de Ciènces del Mar. Instituto Español de Oceanografía. La fecha de publicación es la fecha de lectura

Is there a link between the type of habitat and the patterns of abundance of holothurians in shallow rocky reefs?

[EN] The presence of a mosaic of habitats, largely determined by sea urchin grazing, across shallow rocky reefs may potentially influence in differences in the distribution patterns of invertebrates. The aim of this paper was to assess, using a correlative approach, whether the type of habitat influences the abundance patterns of holothurians in the eastern Atlantic. We hypothesized that abundances of large (> 10 cm) holothurians varied among four types of habitat (3 vegetated habitats with low abundances of the sea urchin D. antillarum versus ?barrens? with hyperabundances of sea urchins), and that these differences were consistent at a hierarchy of spatial scales, including two islands and several replicated sites within each type of habitat and island. Three species of large holothurians were found, accounting for a total of 300 specimens. We found remarkable differences in abundances of holothurians between the ?barrens? and the three vegetated habitats. This pattern was strongest for the numerically dominant species, Holothuria sanctorii. Total abundances of holothurians were between 5 ? 46 times more abundant in ?barrens? compared with the vegetated habitats. Inter-habitat differences were species-specific with some inconsistent patterns from one island to the other. The total abundances of holothurians tended to increase with the abundance of sea urchins within ?barrens?. Our study suggests that there may be a link, at least for the dominant species Holothuria sanctorii, between the distribution and abundances of large holothurians and the habitat across shallow-waters of the eastern Atlantic.

Understanding the zooplankton ammonium excretion : from biogeochemical implications to intracellular regulatory mechanisms

[EN]Zooplankton play a key role in marine ecosystems and their biogeochemical cycles. They exert control over the primary productivity through the consumption of organic matter and, at the same time, the release of nutrients that sustains the phytoplankton growth. This thesis focuses on the NH+ 4 excretion processes related to these heterotrophic organisms that support, at a global scale, about the 80% of the phytoplankton requirements. However, thereisno clear constant pattern in the zooplankton contribution to theNH+ 4 regeneration throughout thedifferent pelagic ecosystems, so continuousmonitoring of thismetabolic processisessential at widetemporal and spatial scales...