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Infaunal responses to seagrass habitat structure: A study of life-history traits and population dynamics of Corophium volutator (Pallas)

Abstract Using a subtidal seagrass mosaic on the Åland Islands, northern Baltic Sea, as a model system, and the amphipod Corophium volutator as the main study organism, we investigated organism-, species- and community-level responses of macrofauna over two seasons in three habitats; the interior and the unvegetated edge of a seagrass (Zostera marina–Potamogeton pectinatus) meadow, and isolated seagrass patches (Ruppia spp.–Zannichellia spp.). Corophium volutator was the most abundant organism in the edge and patch habitats and the second most abundant in the interior habitat. Female biomass, reproduction and offspring fitness components of C. volutator did not seem constrained by habitat structure, and were synchronized across habitats. However, juvenile body length was significantly greater in the patches than in both meadow habitats. All habitats exhibited female-biased sex ratios, and the population was male dominated only on a single sampling occasion. The edge habitat did not support fewer macrofaunal individuals and species than the interior parts of the meadow. The patches supported the lowest animal densities, but were as equally diverse as the interior and edge habitats. When significant edge effects in terms of elevated faunal densities were found, they were usually species specific and consistent over time, e.g. the polychaete Nereis diversicolor showed consistently higher densities along the meadow edge. It is concluded that although devoid of above-ground structure, seagrass meadow edges are a critical part of the seagrass habitat, and thus of potential importance for higher trophic levels and energy transfer from the seagrass habitat.