Environmental Conservation Department, University of Massachusetts Amherst, Amherst, Massachusetts, United States of America.
CAPES Foundation, Ministry of Education of Brazil, Brasília-DF, Brazil.
PLoS One. 2019 May 23;14(5):e0217008. doi: 10.1371/journal.pone.0217008. eCollection 2019.
Reduction of ecosystem connectivity has long-lasting impacts on food webs. Anadromous fish, which migrate from marine to freshwater ecosystems to complete reproduction, have seen their historically larger ecosystem role undercut by widespread riverine habitat fragmentation and other impacts mainly derived from anthropogenic sources. The result has been extensive extirpations and increased susceptibility to a suite of environmental factors that currently impede recovery. Under this present-day context of reduced productivity and connectivity, aggressive management actions and enforcement of catch limits including bycatch caps and complete moratoria on harvest have followed. What remains less understood are the implications of changes to food webs that co-occurred. What benefits restoration could provide in terms of ecosystem functioning in relation to economic costs associated with dam removal and remediation is unknown and can limit the scope and value of restoration activities. Here we employ, historical landscape-based biomass estimates of anadromous alosine for the first time in an ecosystem modeling of the Northeast US large marine ecosystem (LME), to evaluate the value of improving connectivity by measuring the increase in energy flow and population productivity. We compared a restored alosine model to a contemporary model, analyzing the impacts of the potential increase of connectivity between riverine and oceanic systems. There was the potential for a moderate biomass increase of piscivorous species with high economic value, including Atlantic cod, and for a major increase for species of conservation concern such as pelagic sharks, seabirds and marine mammals. Our study highlights the benefits of increased connectivity between freshwater and ocean ecosystems. We demonstrate the significant role anadromous forage fish could play in improving specific fisheries and overall ecosystem functioning, mainly through the diversification of species capable of transferring primary production to upper trophic levels, adding to benefits associated with their restoration.
生态系统连通性的降低会对食物网产生持久的影响。洄游鱼类从海洋洄游到淡水生态系统完成繁殖，它们在历史上更大的生态系统角色被广泛的河流栖息地破碎化和其他主要来自人为来源的影响所削弱。其结果是大量物种灭绝，并且更容易受到一系列环境因素的影响，这些因素目前阻碍了它们的恢复。在这种生产力和连通性降低的当下背景下，采取了积极的管理行动，并执行了捕捞限额，包括副渔获物上限和完全禁止捕捞。然而，对于共同发生的食物网变化的影响，人们的理解还不够充分。与大坝拆除和修复相关的经济成本相比，恢复可能会在生态系统功能方面提供哪些益处尚不清楚，这可能会限制恢复活动的范围和价值。在这里，我们首次在新英格兰大海洋生态系统（LME）的生态系统模型中，利用历史上基于景观的洄游褐大麻哈鱼的生物量估计，来评估通过测量能量流动和种群生产力的增加来改善连通性的价值。我们将恢复的褐大麻哈鱼模型与当代模型进行了比较，分析了增加河海系统之间连通性的潜在影响。具有高经济价值的肉食性物种，包括大西洋鳕鱼，以及包括远洋鲨鱼、海鸟和海洋哺乳动物在内的受保护物种，其生物量可能会适度增加。我们的研究强调了淡水和海洋生态系统之间增加连通性的好处。我们表明，洄游性饲料鱼类在改善特定渔业和整体生态系统功能方面可以发挥重要作用，主要是通过增加能够将初级生产转移到上层营养级的物种的多样性，从而增加与它们的恢复相关的益处。
