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.

未来数十年内，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）的重要性将日益提升。然而，此类结构对自然周边环境的生态效应仍有待厘清。本研究以北海南部某硬底质海域（hard-bottom area）为研究区域，探究了实验性投放的四面体消波块群（tetrapod fields）对底栖鱼类群落（demersal fish community）的影响。研究结果显示，受鱼类向人工结构迁移聚集的影响，周边海域的鱼类丰度出现显著下降。投放消波块后，群落多样性（HB）与均匀度（E）的数值波动幅度显著增大。此外，在投放后的第二年内，结构附近的当年幼鱼（young-of-the-year, YOY）数量出现显著增长。我们推测，人工结构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极强物种特异性的聚集吸引效应。但上述研究结果同时表明，当前我们对人工结构影响温带鱼类群落的认知仍较为匮乏，尚无法全面理解人工结构引入所引发的各类生态过程。若要全面厘清海岸防护结构与近岸环境的互作机制，在全球范围内开展长期监测与更多原位实验研究将是必不可少的。