Macrofauna and surface sediments in Sylt-Rømø Bight in the Northern Wadden Sea (North Sea)@en

Species with wide dispersal are expected to have little empty habitat. This was tested by analysing habitat use in the Wadden Sea near the island of Sylt (North Sea). Sampling covered 222 intertidal sites spread across the Königshafen tidal flats (4.5 km², mapping approach conducted once) and 270 subtidal sites along 12 km of a tidal channel system (stratified random sampling in spring and autumn). For any single species, 'suitable habitat' was extrapolated from the ranges of water depth and sediment composition present at the ten sites with the highest frequency or abundance of the species. On average, macrobenthic species actually used less than half of the suitable sites within the scale of local populations; this was far less than expected from a lognormal distribution. In the subtidal, abundance of most species changed between the two sampling seasons. A 50% increase in overall abundance was accompanied by a decrease in empty habitat of only about 25%. Thus, a doubling of abundances would not fill the empty space but just of half of it. The polychaete Scoloplos armiger was an exception in occupying almost all of its suitable habitat in the intertidal and subtidal sediments. A distinct patch of high species richness occurred where flood waters persistently form a large gyre which may enhance larval settlement. We suggest that limitations to larval settlement and/or juvenile survival primarily cause the extent of the observed habitat emptiness.具有广泛扩散能力的物种，其空余生境占比通常较低。本研究以北海（North Sea）叙尔特岛（Sylt）附近的瓦登海（Wadden Sea）为研究区域，通过分析物种的生境利用模式对该推论进行了验证。本次采样共涵盖两类样区：其一为科尼斯哈芬潮滩（Königshafen tidal flats，面积4.5 km²，采用一次性制图法完成样点布设）内的222个潮间带（intertidal）样点；其二为沿12 km潮汐水道系统（tidal channel system）分布的270个潮下带（subtidal）样点，该区域分别于春季与秋季开展了分层随机抽样（stratified random sampling）。针对单物种而言，其"适宜生境"的范围通过该物种出现频率或丰度最高的10个样点的水深区间与沉积物组成外推得到。平均而言，在局域种群尺度下，大型底栖生物（macrobenthic species）实际利用的适宜生境样点不足总适宜样点的一半，这一结果远低于对数正态分布（lognormal distribution）的理论预期值。在潮下带生境中，多数物种的丰度在两个采样季间存在显著差异。当总丰度提升50%时，空余生境仅减少约25%。由此可见，丰度翻倍并不会完全填补空余生境，仅能覆盖其中约一半的区域。多毛类（polychaete）物种Scoloplos armiger为特例，其几乎占据了潮间带与潮下带沉积物中全部适宜生境。在涨潮流持续形成大型环流的区域，出现了一处物种丰富度显著偏高的生境斑块，该环流或可促进幼虫沉降（larval settlement）。本研究认为，幼虫沉降限制以及/或幼体存活率不足，是导致观测到的生境空余现象的主要成因。