title: The impact of coastal defence structures (tetrapods) on decapod crustaceans in the southern North Sea.
abstract: Although the use of coastal defence structures is expected to increase, little is known about the ecological impact of such structures on the natural environment. In particular, the temporal and spatial patterns of communities in association with artificial substrate are still poorly understood. This study examined possible effects of experimental tetrapod fields on the decapod crustacean community in a subtidal hard-bottom area in the southern North Sea. We performed in situ studies in the fields and along transects oriented away from the tetrapod fields. Species composition and abundances were assessed before and after the introduction of the artificial material. The study revealed a significant decrease of smaller, less vagile species (Pisidia longicornis, Pilumnus hirtellus, Galathea squamifera) over the entire study area in the years following the tetrapod introduction. For 2 species, Hyas araneus and Homarus gammarus, the tetrapods appeared to be highly attractive as habitat and shelter because their abundance increased over time. No distinct spatial or temporal effects were observed for mobile predatory crabs, such as Cancer pagurus and Liocarcinus spp. The results of the study demonstrate that possible effects of artificial structures on macro-invertebrates in temperate hard-bottom areas are highly species-specific and depend on the size, lifestyle and ecological requirements of the species. This work highlights the importance of long-term studies. Our findings clearly indicate that more time is needed to distinguish between natural and anthropogenic influences on species distributions.
authors.affiliation: Biologische Anstalt Helgoland, Center for Scientific Diving, Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung, Kurpromenade 207, D 27498 Helgoland, Germany. Electronic address: stephanie.wehkamp@hotmail.de.
authors.forename: Stephanie
authors.initials: S
authors.lastname: Wehkamp
authors.forename: Philipp
authors.initials: P
authors.lastname: Fischer
mesh_terms: D000818:Animals; D003386:Brachyura; D033364:Decapoda / Q000502:physiology*; D017753:Ecosystem; D009659:North Sea; D013696:Temperature
keywords: Artificial habitats; Coastal habitats; Coastal structures; Crabs; Decapods; North Sea; SCUBA; Sublittoral; Temperate waters