Shift in seagrass food web structure over decades is linked to overfishing
Shift in seagrass food web structure over decades is linked to overfishing
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DOI：
10.3354/meps09585
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发表时间：
2012-01-01
影响因子：
2.5
通讯作者：
Aberg, Per
中科院分区：
文献类型：
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作者：
Baden, Susanne;Emanuelsson, Andreas;Aberg, Per
对海草的经验实地研究表明，丝状藻类的过度生长减少了海草的生长，这可以用顶端捕食者减少引起的自上而下的级联效应来解释，这是由富营养化加强的。在瑞典西海岸，自20世纪80年代以来，60%的海草已经消失。我们假设，过度捕捞导致鳕鱼数量下降了90%，自20世纪30年代以来营养负荷增加了4到8倍，在最近几十年里改变了海草的结构和功能。我们利用20世纪80年代和2000年代的定量样本，分析了顶端捕食性鱼类、中级捕食性鱼类、甲壳类杂食性动物和中草性动物4个食性类群的丰度趋势。自20世纪80年代以来，瑞典西海岸商业捕获量减少了90%，我们在这里发现，以海草为食的顶级捕食者(牛形目和鲑鱼)的生物量减少了约80%。相比之下，中级捕食性鱼类(刺鱼和刺鱼)的生物量在夏季增加了8倍，在秋季增加了11倍，而中草性动物(软体动物和伽马鱼)或多或少从海草床上消失了。因此，我们发现了明确的证据，表明在过去的30年里，海草食物网络结构发生了变化。结合这些发现和我们最近在Skagerrak海草进行的野外网箱实验的经验结果，我们得出结论，缺乏食草动物和富营养化很可能是丝状藻类过度生长和瑞典西海岸海草消失的原因。
Empirical field studies in seagrass have revealed that overgrowth by filamentous algae which reduces seagrass growth can be explained by a top-down cascading effect caused by declines in top predators, which is enforced by eutrophication. On the Swedish west coast, 60% of the seagrass has disappeared since the 1980s. We hypothesised that overfishing, responsible for a >90% decline in the cod stock, and the 4 to 8 times increase in nutrient load since the 1930s have altered the seagrass structure and function during recent decades. We used quantitative samples from the 1980s and 2000s and analysed the trends in abundance of the 4 feeding guilds: top predatory fish, intermediate predatory fish, crustacean omnivores and mesoherbivores. Since the 1980s, the commercial catch of gadoids on the Swedish west coast has decreased by >90 %, and here we found that the biomass of top predators (gadoids and trout) that forage in seagrass has decreased by approximately 80%. In contrast, the biomass of intermediate predatory fish (gobids and sticklebacks) has increased 8 times during summer and 11 times during autumn, while mesoherbivores (idoteids and gammarids >7 mm) have more or less disappeared from the seagrass bed. We thus found clear evidence that a shift in seagrass food web structure has taken place over the last 3 decades. Combining these findings with our recent empirical results from field cage experiments in the Skagerrak seagrass, where we manipulate top-down and bottom-up regulation, we conclude that lack of grazers in concert with eutrophication most likely contributed to the overgrowth by filamentous algae and disappearance of the seagrass on the Swedish west coast.