Trophic interactions under stress: hypoxia enhances foraging in an estuarine food web

Abstract

Ecosystem-level effects of stressors are critical to understanding community regulation, and environmental stress models are useful in describing such effects. Hypoxia is an important stressor in aquatic ecosystems that usually decreases abundance and biomass of benthic fauna. In field surveys, predator abundance is low in hypoxic areas, and in lab experiments, predators reduce their feeding rates under hypoxic conditions, leading to the hypothesis that consumer stress models (CSMs), rather than prey stress models (PSMs), apply to the systems. We tested predictions from these models with manipulative field experiments wherein we varied predator access to marked Macoma balthica clams at deep and shallow sites in the York River, Chesapeake Bay, before (June) and during (August) hypoxic episodes. In June, dissolved oxygen in deep and shallow sites was normoxic (> 2 mg l -1 ) for most of the experiment. In August, the shallow zone remained normoxic, while the deep zone experienced several hypoxic episodes. During hypoxia, predation rates in hypoxic sites were more than twice those in normoxic sites, whereas mortality due to physical stress did not differ between time periods or depths. Ambient clam densities were lower at the deep sites than at the shallow sites, and in August than in June. We conclude that hypoxia increased the susceptibility of benthic prey to predation, enhancing infaunal secondary production available to predators, but concurrently reducing the resilience of the benthic community. These findings are inconsistent with the predictions of CSMs, indicating that PSMs better describe this system. KEY WORDS: Environmental stress models · Food web · Hypoxia · Predation · Predator-prey · Macoma balthica Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 362: [59][60][61][62][63][64][65][66][67][68] 2008 long-lived species to small, opportunistic species. The magnitude of these effects generally increases with the severity of hypoxic stress.Hypoxia has a multitude of non-lethal effects. Metabolism, and thus oxygen demand, decreases (Wu 2002), reducing growth and reproductive output (e.g. Grove & Breitburg 2005, Long 2007. Infaunal organisms migrate vertically in the sediment, stretching their siphons or palps above the benthic boundary layer into higher DO concentrations, and they may expose themselves on the surface or float in the water column (Brafield 1963, Rosenberg et al. 1991, Taylor & Eggleston 2000, Seitz et al. 2003. Almost all species decrease oxygen demand by decreasing activity and feeding rates (Sagasti et al. 2001).These effects, especially the behavioral responses, potentially increase the availability of benthic fauna to their predators. The closer proximity of infaunal prey to the sediment surface and extension of siphons and palps decrease predator searching time. However, the responses of predators to hypoxia may jeopardize their ability to take advantage of stressed prey. Many predators in these systems are highly mobile, and ...

Aggregation on the edge: effects of hypoxia avoidance on the spatial distribution of brown shrimp and demersal fishes in the Northern Gulf of Mexico

“…Such behavior probably induces a tradeoff between foraging and physiological stress that may lead to enhanced prey consumption in the short term. However, hypoxiainduced increases in short-term foraging may also lead to negative effects in the long term such as prey depletion, a less resilient prey community, and cumu lative effects of physiological stress (Wu 2002, Costantini et al 2008, Long & Seitz 2008. The higher avoidance thresholds under more severe hypoxia documented here suggest that hypoxia avoidance is context-dependent, as has been shown in other systems (Bell & Eggleston 2005, Pierson et al 2009).…”

“…Supporting this possibility, sediment cores taken in 2003 indicated that infaunal prey were moderately abundant at hypoxic sites, with the highest prey densities within the upper 1 to 2 cm layer of the sediment ). Numerous studies have demonstrated that mobile organisms will tolerate shortterm exposure to low DO in order to access hypoxic habitats that harbor food resources (Rahel & Nutzman 1994, Nestlerode & Diaz 1998, Taylor et al 2007, Long & Seitz 2008, Craig et al 2010. Such behavior probably induces a tradeoff between foraging and physiological stress that may lead to enhanced prey consumption in the short term.…”

Modeling the Population Effects of Hypoxia on Atlantic Croaker (Micropogonias undulatus) in the Northwestern Gulf of Mexico: Part 2—Realistic Hypoxia and Eutrophication

“…Croaker appears to remain benthic feeders under hypoxia rather than switching to a more pelagic diet (Mohan and Walther 2016). However, there is some evidence that, at least under episodic hypoxia, croaker can even, at least temporarily, increase their predation rates by taking advantage of more vulnerable prey (Long and Seitz 2008). There are other pathways by which hypoxia could affect croaker population dynamics that were not included in our model simulations.…”

Effect of hypoxia and anoxia on invertebrate behaviour: ecological perspectives from species to community level

“…Change in one behaviour may influence the outcome of others, for example altered locomotion can affect reproduction and/or food finding behaviour (Boyd et al, 2002). Interspecifically, shifts in locomotion -migration to a new region, shallower burial depths or exposure atop elevated substrates -may change predator-prey relationships (Pihl et al, 1992;Riedel et al, 2008a;Long and Seitz, 2008). Behavioural parameters thus integrate direct and indirect responses across several levels of biological organisation, from individual fitness to community composition, reflecting cascading changes in biodiversity, biogeochemical processes and ecosystem function (e.g.…”