T.N. Bezerra

Benthic-pelagic coupling: effects on nematode communities along southern European continental margins.

Along a west-to-east axis spanning the Galicia Bank region (Iberian margin) and the Mediterranean basin, a reduction in surface primary productivity and in seafloor flux of particulate organic carbon was mirrored in the in situ organic matter quantity and quality within the underlying deep-sea sediments at different water depths (1200, 1900 and 3000 m). Nematode standing stock (abundance and biomass) and genus and trophic composition were investigated to evaluate downward benthic-pelagic coupling. The longitudinal decline in seafloor particulate organic carbon flux was reflected by a reduction in benthic phytopigment concentrations and nematode standing stock. An exception was the station sampled at the Galicia Bank seamount, where despite the maximal particulate organic carbon flux estimate, we observed reduced pigment levels and nematode standing stock. The strong hydrodynamic forcing at this station was believed to be the main cause of the local decoupling between pelagic and benthic processes. Besides a longitudinal cline in nematode standing stock, we noticed a west-to-east gradient in nematode genus and feeding type composition (owing to an increasing importance of predatory/scavenging nematodes with longitude) governed by potential proxies for food availability (percentage of nitrogen, organic carbon, and total organic matter). Within-station variability in generic composition was elevated in sediments with lower phytopigment concentrations. Standing stock appeared to be regulated by sedimentation rates and benthic environmental variables, whereas genus composition covaried only with benthic environmental variables. The coupling between deep-sea nematode assemblages and surface water processes evidenced in the present study suggests that it is likely that climate change will affect the composition and function of deep-sea nematodes.

Two new species of Rhynchonema Cobb, 1920 from a Brazilian sandy beach

Rhynchonema Cobb, 1920 is a genus with worldwide distribution. It is found in diverse coastal environments ranging from brackish water to exposed beaches in intertidal and low subtidal zones, from clay to coarse sand and in sediments under seagrass beds. In this study we describe two new tropical species from Northeast South America: Rhynchonema cemae sp.n. and R. veronicae sp. n. from Olinda’s Isthmus, Pernambuco, Brazil. These two species are mainly characterized by the shapes of the spicules and gubernaculum, which are described here for the first time. The two species can be differentiated primarily on the basis of the spicules, which in R. cemae are symmetrical, fine and long, while in R. veronicae they are asymmetrical, more robust and shorter. We describe for the first time the presence of Rhynchonema species on the east side of South America and provide a review of the genus and a polytomous identification key. Our review of the literature and construction of a polytomous key demonstrated that most of the species descriptions are incomplete.