Zeilinger, Torge (2004) Prädationsdruck auf die epibenthische Fauna eines eulitoralen Seegrashabitats im Wattenmeer. (Diploma thesis), Christian-Albrechts-Universität zu Kiel, Kiel, 70 pp.

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Abstract

Predation pressure was examined for the epibenthic fauna of a intertidal seagrass bed of the Sylt-Rømø bight. Starting from the question for the dominant epibenthic prey and the intensity of predation pressure in seagrass habitats, we investigated a seegrasbed in the Sylt- Rømø bight. in sommer 2003. A predator enclosure experiment has been carried out in artificial tide pools of similar size, and a bait experiment were carried out in the surrounding seagrass bed.
The most frequent epibenthic organisms within the intertidal seagrass beds consist of four dominant species: The brown shirmp (Crangon crangon, Linnaeus), the sand goby (Pomatoschitus microps, Krøyer), the isopode (Idotea balthica, Pallas) and the shore crab (Carcinus maenas, Linnaeus.). C. crangon showed an average annual abundance during high water of approximately 80 animals per m-2 (P.POL TE pers. Com.). Pomatoschistus microps and Carcinus maenas showed an average annual abundance of 7 animals m 2 and of 195 animals m-2. An abundance of 26 individuals m-2 was found for I. balthica (P.POLTE pers. Com.). As shown for the seagrass bed, C.crangon, P.microps and C.maenas were also the dominant forms in the tide pools. I. balthica could be found with 26 individuals m-2. The abundance of C. crangon were measured with an Annual average of 157 animals m-2 and therefore showed different results for the seagrassbeds. P. microps and C. maenas showed an average annual abundance of 15 animals m-2 and of 22 animals m-2 respectively. Mobile fauna migrates with the ebb tide into deeper waters (e.g. Pomatoschistus microps.) The substantially lower results of C. maenas within tide pools compared to adjacent seagrass beds can be partly explained by sampling time. In the seagrasbed sampling started earlier in the year (of May), and included the larval and juvenile stages of C. maenas. This led to a substantially higher abundance. Low abundance of I. balthica can be explained by its requirement for a structured habitat. I. balthica needs branched algal structures as a firm substrat. Such structures were hardly available in the tide pools...

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