Crustaceans and fish abundances and species at and around artificially introduced tetrapod fields in the southern North Sea, 2010-2011

In the coming decades, artificial defence structures will increase in importance worldwide for the protection of coasts against the impacts of global warming. However, the ecological effects of such structures on the natural surroundings remain unclear. We investigated the impact of experimentally introduced tetrapod fields on the demersal fish community in a hard-bottom area in the southern North Sea. The results indicated a significant decrease in fish abundance in the surrounding area caused by migration effects towards the artificial structures. Diversity (HB) and evenness (E) values exhibited greater variation after the introduction of the tetrapods. Additionally, a distinct increase in young-of-the-year (YOY) fish was observed near the structures within the second year after introduction. We suggest that the availability of adequate refuges in combination with additional food resources provided by the artificial structures has a highly species-specific attraction effect. However, these findings also demonstrate that our knowledge regarding the impact of artificial structures on temperate fish communities is still too limited to truly understand the ecological processes that are initiated by the introduction of artificial structures. Long-term investigations and additional experimental in situ work worldwide will be indispensable for a full understanding of the mechanisms by which coastal defence structures interact with the coastal environment.未来数十年间，全球范围内用于抵御全球变暖影响、保护海岸的人工海岸防护结构的重要性将日益凸显。然而，此类结构对周边自然环境的生态效应仍有待厘清。本研究以北海南部一处硬底质海域为研究区域，探究了实验性投放的四脚护块场（tetrapod fields）对底栖鱼类（demersal fish）群落的影响。结果表明，受鱼类向人工结构迁移的效应影响，周边海域的鱼类丰度出现显著下降；四脚护块投放后，多样性指数（HB）与均匀度（E）的波动幅度显著增大。此外，在投放后的第二年，结构附近的当年幼鱼（YOY）数量出现明显提升。我们认为，人工结构所提供的充足庇护场所与额外食物资源，对不同鱼类物种产生了具有物种特异性的吸引效应。但本研究结果同时显示，当前学界对人工结构对温带鱼类群落的影响认知仍较为有限，尚无法充分理解人工结构引入所触发的生态过程。若要全面阐明人工海岸防护结构与近岸海洋环境的相互作用机制，在全球范围内开展长期调查与原位实验研究将不可或缺。