Opening the tap: Increased riverine connectivity strengthens marine food web pathways

• Published in: PloS one 2019-05, Vol.14 (5), p.e0217008
• Main Authors: Dias, Beatriz S, Frisk, Michael G, Jordaan, Adrian
• Format: Article
• Language: English
• Subjects: Anadromous fishes; Anadromous species; Animals; Anthropogenic factors; Aquatic birds; Aquatic ecosystems; Atlantic Ocean; Biology and Life Sciences; Biomass; Bycatch; Cod; Commercial fishing; Conservation; Conservation of Natural Resources; Dam effects; Dam removal; Dams; Distribution; Earth Sciences; Ecological function; Ecology and Environmental Sciences; Economic conditions; Economic impact; Economics; Ecosystem models; Ecosystems; Energy flow; Energy measurement; Environment models; Environmental aspects; Environmental changes; Environmental factors; Environmental restoration; Fish; Fish conservation; Fish migration; Fish reproduction; Fisheries; Fishes; Fishing; Food Chain; Food chains; Food webs; Foraging habitats; Freshwater ecosystems; Freshwater fish; Habitat fragmentation; Habitats; Historical account; Human influences; Landscape; Management; Marine ecosystems; Marine mammals; Migration; New England; Primary production; Production management; Restoration; Retirement benefits; River ecology; Rivers; Schools; Seabirds; Sharks; Trophic levels; Watersheds; Wildlife conservation
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0217008

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.