Resource-driven colonization by cod in a high Arctic food web

Climate change is commonly associated with many species redistributions and the influence of other factors may be marginalized, especially in the rapidly warming Arctic. The Barents Sea, a high latitude large marine ecosystem in the Northeast Atlantic has experienced above average temperatures since the mid 2000’s with divergent bottom temperature trends at sub-regional scales. Concurrently, the Barents Sea stock of Atlantic cod Gadus morhua, one of the most important commercial fish stocks in the world, increased following a large reduction in fishing pressure and expanded north of 80°N. We examined the influence of food availability and temperature on cod expansion using a comprehensive data set on cod stomach fullness stratified by sub-regions characterized by divergent temperature trends. We then tested whether food availability, as indexed by cod stomach fullness, played a role in cod expansion in sub-regions that were warming, cooling or showed no trend. The greatest increase in cod occupancy occurred in three northern sub-regions with contrasting temperature trends. Cod apparently benefited from initial high food availability in these regions that previously had few large-bodied fish predators. The stomach fullness in the northern sub-regions declined rapidly after a few years of high cod abundance, suggesting that the arrival of cod caused a top down effect on the prey base. Prolonged cod residency in the northern Barents Sea is, therefore, not a certainty.

气候变化通常与众多物种的分布范围转移密切相关，而其他影响因素往往被忽视，在快速变暖的北极地区这一现象尤为突出。作为东北大西洋的高纬度大型海洋生态系统，巴伦支海（Barents Sea）自2000年代中期以来，水温持续高于平均水平，且不同次级区域的底层水温变化趋势存在显著差异。与此同时，作为全球最重要的商业鱼类种群之一的大西洋鳕（Gadus morhua）巴伦支海种群，在捕捞压力大幅降低后种群数量得以恢复，并向北扩展至北纬80°以北海域。本研究基于按水温变化趋势不同的次级区域分层的鳕鱼胃饱满度综合数据集，探讨了食物可获得性与水温对鳕鱼北扩过程的影响。随后，我们分别检验了在升温、降温或水温无明显变化的次级区域中，以鳕鱼胃饱满度为指标的食物可获得性是否对鳕鱼的北扩起到了调控作用。鳕鱼占据率增幅最大的区域为3个水温变化趋势迥异的北部次级海域。此前这些区域大型鱼类捕食者稀少，鳕鱼最初凭借当地充足的食物可获得性获益良多。在鳕鱼种群数量达到高位后的数年内，北部次级海域的鳕鱼胃饱满度迅速下降，这表明鳕鱼的迁入对当地饵料基础产生了下行效应（top-down effect）。因此，鳕鱼能否长期定居于巴伦支海北部海域仍未可知。