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

Abstract

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.

Research Progress on Habitat Connectivity in Temperate Waters

“…Because of its high spatial heterogeneity and dynamic characteristics, the offshore ocean is often selected as a key research area. Compared with terrestrial ecological connectivity, research on offshore ecological connectivity started late in the mid-1990s, and habitat connectivity has been a popular research topic in recent years [6,25]. In this paper, the Web of Science database was used to input the keyword marine habitat connectivity, and the search results produced 3095 articles, of which nearly 1500 articles were published in the past five years (Figure 1).…”

“…Subsequently, various types of substrates from concrete structures to logs and abandoned cars were used as artificial habitats [20][21]. Since the 1960s, several studies abroad have focused on the relationship between ecological connectivity transformation by the construction of artificial habitats and the complexity, stability and diversity of marine ecosystems [22][23][24][25], and these studies have laid a solid foundation for further research on promoting the spatial integrity of marine ecosystems and protecting habitat fragmentation. In recent years, domestic researchers have gradually investigated and studied marine ecological connectivity [26][27][28][29].…”

Surgical Implantation of Acoustic Tags in American Shad to Resolve Riverine and Marine Restoration Challenges

“…; Dias et al. ). Riverine spawning migrations of American Shad are relatively well characterized; fish passage preferences and information from directed fisheries and historical landings have also been examined (Moser et al.…”

“…Since the late 1800s, a suite of factors, including habitat loss, pollution, and overfishing, has caused a decline in stocks of American Shad along the East Coast (Dadswell and Rulifson 1994;Limburg and Waldman 2009), with the loss of as much as 50% of historic populations (Limburg et al 2003). Reductions in American Shad and other alosine species have likely exerted negative effects on freshwater and marine food webs (Ames 2004;Mattocks et al 2017;Dias et al 2019). Riverine spawning migrations of American Shad are relatively well characterized; fish passage preferences and information from directed fisheries and historical landings have also been examined (Moser et al 2000;Limburg et al 2003;Bailey et al 2004;Haro and Castro-Santos 2012;Grote et al 2014;Raabe and Hightower 2014;Waldman et al 2014).…”

Contrasting fishing effort reduction and habitat connectivity as management strategies to promote alewife (Alosa pseudoharengus) recovery using an ecosystem model

“…Life history characteristics of forage fishes are related to variable population sizes over time, with relatively frequent sharp collapses and fast recoveries (Lindegren et al 2013). Fluctuations in the abundance of forage fish have been directly related to marine ecosystem regime shifts (Auber et al 2015), and resilience (Dias et al 2019). Given the importance of forage fish to marine ecosystem functioning, fisheries exploitation, and ecosystem-based management approaches (Francis et al 2007), linking their population dynamics through time to the broader ecosystem is essential for understanding consequences of management decisions.…”