Naman Sean M, Greene Correigh M, Rice Casimir A, Chamberlin Joshua, Conway-Cranos Letitia, Cordell Jeffery R, Hall Jason E, Rhodes Linda D
Department of Zoology University of British Columbia Vancouver BC Canada.
NOAA Fisheries Northwest Fisheries Science Center Seattle WA USA.
Ecol Evol. 2016 Oct 18;6(22):8159-8173. doi: 10.1002/ece3.2450. eCollection 2016 Nov.
Identifying causes of structural ecosystem shifts often requires understanding trophic structure, an important determinant of energy flow in ecological communities. In coastal pelagic ecosystems worldwide, increasing jellyfish (Cnidaria and Ctenophora) at the expense of small fish has been linked to anthropogenic alteration of basal trophic pathways. However, this hypothesis remains untested in part because baseline description of fish-jellyfish trophic dynamics, and the environmental features that influence them are lacking. Using stable isotopes of carbon (δC) and nitrogen (δN), we examined spatiotemporal patterns of fish and jellyfish trophic structure in greater Puget Sound, an urbanizing fjord estuary in the NW United States. We quantified niche positions of constituent species, niche widths and trophic overlap between fish and jellyfish assemblages, and several community-level trophic diversity metrics (resource diversity, trophic length, and niche widths) of fish and jellyfish combined. We then related assemblage- and community-level measures to landscape gradients of terrestrial-marine connectivity and anthropogenic influence in adjacent catchments. Relative niche positions among species varied considerably and displayed no clear pattern except that fish generally had higher δN and lower δC relative to jellyfish, which resulted in low assemblage-level trophic overlap. Fish assemblages had larger niche widths than jellyfish in most cases and, along with whole community trophic diversity, exhibited contrasting seasonal patterns across oceanographic basins, which was positively correlated to landscape variation in terrestrial connectivity. In contrast, jellyfish niche widths were unrelated to terrestrial connectivity, but weakly negatively correlated to urban land use in adjacent catchments. Our results indicate that fish-jellyfish trophic structure is highly heterogeneous and that disparate processes may underlie the trophic ecology of these taxa; consequently, they may respond divergently to environmental change. In addition, spatiotemporal variation in ecosystem connectivity, in this case through freshwater influence, may influence trophic structure across heterogeneous landscapes.
确定生态系统结构变化的原因通常需要了解营养结构，这是生态群落中能量流动的一个重要决定因素。在全球沿海中上层生态系统中，水母（刺胞动物门和栉水母动物门）数量增加而小鱼数量减少，这与基础营养路径的人为改变有关。然而，这一假设仍未得到验证，部分原因是缺乏对鱼-水母营养动态的基线描述以及影响它们的环境特征。利用碳（δC）和氮（δN）的稳定同位素，我们研究了美国西北部一个正在城市化的峡湾河口——普吉特海湾地区鱼类和水母营养结构的时空模式。我们量化了组成物种的生态位位置、鱼类和水母组合之间的生态位宽度和营养重叠，以及鱼类和水母组合的几个群落水平的营养多样性指标（资源多样性、营养长度和生态位宽度）。然后，我们将组合水平和群落水平的测量结果与相邻流域陆地-海洋连通性和人为影响的景观梯度联系起来。物种之间的相对生态位位置差异很大，除了鱼类相对于水母通常具有更高的δN和更低的δC外，没有显示出明显的模式，这导致组合水平的营养重叠较低。在大多数情况下，鱼类组合的生态位宽度比水母大，并且与整个群落的营养多样性一起，在不同的海洋盆地呈现出相反的季节模式，这与陆地连通性的景观变化呈正相关。相比之下，水母的生态位宽度与陆地连通性无关，但与相邻流域的城市土地利用呈弱负相关。我们的结果表明，鱼-水母的营养结构高度异质，不同的过程可能是这些分类群营养生态学的基础；因此，它们可能对环境变化做出不同的反应。此外，在这种情况下，通过淡水影响的生态系统连通性的时空变化可能会影响异质景观中的营养结构。
