Facilitation of non-indigenous ascidian by marine eco-engineering interventions at an urban site

Marine artificial structures often support lower native species diversity and more non-indigenous species (NIS), but adding complex habitat and using bioreceptive materials have the potential to mitigate these impacts. Here, the interacting effects of structural complexity (flat, complex with pits) and concrete mixture (standard, or with oyster shell or vermiculite aggregate) on recruitment were assessed at two intertidal levels at an urban site. Complex tiles had less green algal cover, oyster shell mixtures had less brown (<i>Ralfsia</i> sp.<i>)</i> algal cover. At a low tidal elevation, the non-indigenous ascidian <i>Styela plicata</i> dominated complex tiles. Additionally, mixtures with oyster shell supported higher total cover of sessile species, and a higher cover of <i>S. plicata.</i> There were no effects of complexity or mixture on biofilm communities and native and NIS richness. Overall, these results suggest that habitat complexity and some bioreceptive materials may facilitate colonisation by a dominant invertebrate invader on artificial structures.

海洋人工构筑物通常伴随较低的本地物种多样性，且更易伴生更多外来物种（non-indigenous species, NIS）；而增设复杂生境、采用生物亲和性材料（bioreceptive materials）则有望缓解此类负面影响。本研究于城市沿岸的两处潮间带高程点位，评估了结构复杂度（平整型、带凹坑的复杂型）与混凝土混合料（标准型、添加牡蛎壳或蛭石骨料型）对生物招募（recruitment）的交互影响。试验结果显示，复杂型基板的绿藻盖度更低，添加牡蛎壳的混合料组的褐藻（<i>Ralfsia</i> sp.）盖度亦更低。在低潮高程处，外来被囊动物<i>Styela plicata</i>在复杂型基板上占据优势；此外，添加牡蛎壳的混合料组的固着生物（sessile species）总盖度及<i>S. plicata</i>的盖度均更高。结构复杂度与混凝土混合料类型对生物膜群落、本地物种及NIS的物种丰富度均无显著影响。综上，本研究结果表明，生境复杂度与部分生物亲和性材料或可促进优势无脊椎动物入侵者在人工构筑物上定殖。