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、保护海岸带的人工防护结构（artificial defence structures）重要性将愈发凸显。然而，此类结构对周边自然环境的生态效应仍未明晰。本研究于北海南部的一处硬质底质生境中开展实验，探究了人工投放的四脚消波块阵列（tetrapod fields）对底栖鱼类群落（demersal fish community）的影响。研究结果显示，受鱼类向人工防护结构迁移行为的影响，周边海域的鱼类丰度出现显著下降；四脚消波块投放后，鱼类多样性（HB）与均匀度（E）的数值波动幅度显著增大。此外，在投放后的第二年，结构附近海域的当年幼鱼（young-of-the-year, YOY）丰度出现明显提升。我们推测，人工防护结构所提供的充足庇护场所与额外食物资源，对鱼类产生了极强的物种特异性吸引效应。但本研究结果同时表明，当前学界对于人工防护结构对温带鱼类群落的影响认知仍较为有限，尚无法完全阐明人工结构投放所引发的各类生态过程。若要全面理解海岸防护结构与近岸环境的相互作用机制，在全球范围内开展长期调查与更多原位实验研究将是不可或缺的。