Data from: The density and spatial arrangement of the invasive oyster Crassostrea gigas determines its impact on settlement of native oyster larvae

Understanding how the density and spatial arrangement of invaders is critical to developing management strategies of pest species. The Pacific oyster, Crassostrea gigas, has been translocated around the world for aquaculture and in many instances has established wild populations. Relative to other species of bivalve, it displays rapid suspension feeding, which may cause mortality of pelagic invertebrate larvae. We compared the effect on settlement of Sydney rock oyster, Saccostrea glomerata, larvae of manipulating the spatial arrangement and density of native S. glomerata, and non-native C. gigas. We hypothesized that while manipulations of dead oysters would reveal the same positive relationship between attachment surface area and S. glomerata settlement between the two species, manipulations of live oysters would reveal differing density-dependent effects between the native and non-native oyster. In the field, whether oysters were live or dead, more larvae settled on C. gigas than S. glomerata when substrate was arranged in monospecific clumps. When, however, the two species were interspersed, there were no differences in larval settlement between them. By contrast, in aquaria simulating a higher effective oyster density, more larvae settled on live S. glomerata than C. gigas. When C. gigas was prevented from suspension feeding, settlement of larvae on C. gigas was enhanced. By contrast, settlement was similar between the two species when dead. While the presently low densities of the invasive oyster C. gigas may enhance S. glomerata larval settlement in east Australian estuaries, future increases in densities could produce negative impacts on native oyster settlement. Synthesis and applications: Our study has shown that both the spatial arrangement and density of invaders can influence their impact. Hence, management strategies aimed at preventing invasive populations reaching damaging sizes should not only consider the threshold density at which impacts exceed some acceptable limit, but also how patch formation modifies this.明晰入侵物种的种群密度与空间分布格局，是制定有害生物防治策略的核心前提。太平洋牡蛎（*Crassostrea gigas*）因水产养殖需求被全球引种，且在诸多区域成功建立野生种群。相较于其他双壳类物种，该物种具备高效的悬浮摄食能力，可能导致浮游无脊椎动物幼虫死亡。本研究通过调控本土悉尼岩牡蛎（*Saccostrea glomerata*）与外来太平洋牡蛎的空间分布格局与种群密度，对比了二者对悉尼岩牡蛎幼虫附着过程的影响。本研究提出如下假说：以死亡牡蛎作为底物时，两种牡蛎的附着表面积与悉尼岩牡蛎幼虫附着率均呈正相关关系，且二者规律一致；而以活体牡蛎作为底物时，本土与外来牡蛎的密度依赖效应会存在显著差异。野外实验结果表明：当底物以单物种集群形式布置时，无论牡蛎存活与否，太平洋牡蛎表面附着的幼虫数量均高于悉尼岩牡蛎。但当两种牡蛎混合布置时，二者表面的幼虫附着率无显著差异。与之相对，在模拟更高有效牡蛎密度的实验水族箱中，活体悉尼岩牡蛎表面附着的幼虫数量高于太平洋牡蛎。当阻断太平洋牡蛎的悬浮摄食功能后，其表面的幼虫附着率显著提升。与之相反，以死亡牡蛎作为底物时，二者表面的幼虫附着率无显著差异。当前入侵物种太平洋牡蛎在澳大利亚东部河口的种群密度较低，或可提升悉尼岩牡蛎的幼虫附着率；但未来种群密度上升后，可能会对本土牡蛎的幼虫附着过程产生负面影响。研究总结与应用启示：本研究证实，入侵物种的空间分布格局与种群密度均可影响其生态影响强度。因此，旨在防止入侵种群达到有害种群规模的防治策略，不仅需要考量影响超出可接受阈值的临界密度，还应关注斑块形成对该临界密度的调控作用。