Harding Joel M S, Segal Michelle R, Reynolds John D
Earth to Ocean Research Group, Department of Biological Sciences, Simon Fraser University, Burnaby, BC, Canada; The Hakai Institute, Heriot Bay, BC, Canada.
Earth to Ocean Research Group, Department of Biological Sciences, Simon Fraser University, Burnaby, BC, Canada.
PLoS One. 2015 May 18;10(5):e0125167. doi: 10.1371/journal.pone.0125167. eCollection 2015.
Estuaries are amongst the world's most productive ecosystems, lying at the intersection between terrestrial and marine environments. They receive substantial inputs from adjacent landscapes but the importance of resource subsidies is not well understood. Here, we test hypotheses for the effects of both terrestrial- and salmon-derived resource subsidies on the diet (inferred from stable isotopes of muscle tissue), size and percent nitrogen of the soft-shell clam (Mya arenaria), a sedentary estuarine consumer. We examine how these relationships shift across natural gradients among 14 estuaries that vary in upstream watershed size and salmon density on the central coast of British Columbia, Canada. We also test how assimilation and response to subsidies vary at smaller spatial scales within estuaries. The depletion and enrichment of stable isotope ratios in soft-shell clam muscle tissue correlated with increasing upstream watershed size and salmon density, respectively. The effects of terrestrial- and salmon-derived subsidies were also strongest at locations near stream outlets. When we controlled for age of individual clams, there were larger individuals with higher percent nitrogen content in estuaries below larger watersheds, though this effect was limited to the depositional zones below river mouths. Pink salmon exhibited a stronger effect on isotope ratios of clams than chum salmon, which could reflect increased habitat overlap as spawning pink salmon concentrate in lower stream reaches, closer to intertidal clam beds. However, there were smaller clams in estuaries that had higher upstream pink salmon densities, possibly due to differences in habitat requirements. Our study highlights the importance of upstream resource subsidies to this bivalve species, but that individual responses to subsidies can vary at smaller scales within estuaries.
河口是世界上生产力最高的生态系统之一，位于陆地和海洋环境的交汇处。它们从相邻的景观中获得大量资源输入，但资源补贴的重要性尚未得到充分理解。在这里，我们测试了陆地和鲑鱼来源的资源补贴对软壳蛤（Mya arenaria）的饮食（从肌肉组织的稳定同位素推断）、大小和氮含量百分比的影响，软壳蛤是一种定居的河口消费者。我们研究了这些关系如何在加拿大不列颠哥伦比亚省中部海岸的14个河口的自然梯度上发生变化，这些河口在上游流域大小和鲑鱼密度方面各不相同。我们还测试了河口内较小空间尺度上同化和对补贴的反应如何变化。软壳蛤肌肉组织中稳定同位素比率的消耗和富集分别与上游流域大小和鲑鱼密度的增加相关。陆地和鲑鱼来源的补贴的影响在靠近溪流出口的位置也最为强烈。当我们控制个体蛤的年龄时，在较大流域下方的河口有更大的个体，其氮含量百分比更高，尽管这种影响仅限于河口下方的沉积区。粉鲑对蛤的同位素比率的影响比狗鲑更强，这可能反映了产卵的粉鲑集中在下游较浅区域，更靠近潮间带蛤床，从而增加了栖息地重叠。然而，在上游粉鲑密度较高的河口，蛤的个体较小，这可能是由于栖息地需求的差异。我们的研究强调了上游资源补贴对这种双壳类物种的重要性，但个体对补贴的反应在河口内较小尺度上可能会有所不同。
