Abstract
The feeding guild composition of a macrobenthic community from southern Portugal was studied along a depth gradient (1.3 to 32 m). This gradient comprised shallow areas with severe physical stress and deeper areas with no significant hydrodynamic impact at the seafloor. The main goal was to determine the influence of the spatial and temporal differences of the hydrodynamic impact at the seafloor on the feeding guild composition of the macrobenthic community. The feeding guild composition changed gradually with depth, which reflects the differences in the hydrodynamics impact at the seafloor. Herbivores and sand-lickers dominated at the shallowest depths with fine sands, which correlated with higher levels of primary production. Scavengers were also distributed in the shallow areas, which was associated with the lower predation impact. Suspension feeders, in accordance with their physiological requirements, were distributed in coarser sands subjected to a physical impact. Carnivores, surface deposit feeders and sub-surface deposit feeders were distributed mainly below 8 m depth, where there was no significant impact from the wave climate. Carnivores were associated with coarser sands and were mainly small polychaetes and nemerteans. Sub-surface and surface deposit feeders were more abundant in the deepest areas of the depth gradient with fine sands and mud deposits with higher organic content. However, surface deposit feeders also occurred at shallower depths. Some seasonal differences related to disturbance impacts were found in the numerical dominance of the feeding guilds.
Highlights
In marine soft sediments, the hydrodynamics can be considered as a source of natural disturbance that structures species’ distributions (Rosenberg, 1995; Levin and DiBacco, 1995; Roth and Wilson, 1998; Hewitt et al, 2003)
A previous study on the macrobenthic community was performed in southern Portugal (Dolbeth et al, 2007), along a depth continuum (1.3 m to 32 m depth), which comprised areas subjected to a hydrodynamic impact on the seafloor and areas below the depth of closure, i.e. with limited sediment transport due to wave action (Nicholls et al, 1998)
The present study showed spatial differences in the feeding guild composition of the macrobenthic community along the depth gradient, but no clear spatial groups of feeding guilds were formed as observed with the species composition
Summary
The hydrodynamics can be considered as a source of natural disturbance that structures species’ distributions (Rosenberg, 1995; Levin and DiBacco, 1995; Roth and Wilson, 1998; Hewitt et al, 2003). To a large extent, the direct result of near-bed flow conditions, which influence grain size, sedimentary organic matter content, pore-water chemistry, microbial content, larval supply (Snelgrove and Butman, 1994) and food availability (Morin et al, 1985; Incera et al, 2003) These variables can directly or indirectly influence the benthic community’s distribution (Snelgrove and Butman, 1994) and functioning. A previous study on the macrobenthic community was performed in southern Portugal (Dolbeth et al, 2007), along a depth continuum (1.3 m to 32 m depth), which comprised areas subjected to a hydrodynamic impact on the seafloor and areas below the depth of closure, i.e. with limited sediment transport due to wave action (Nicholls et al, 1998) Both physical and biological environments were studied spatially and over time. General considerations on the structure of the macrobenthic community are presented
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