Variability in Fish Tissue Proximate Composition is Consistent with Indirect Effects of Hypoxia in Chesapeake Bay Tributaries

Troy D Tuckey,Mary C Fabrizio

doi:10.1080/19425120.2015.1103824

Abstract

AbstractThe spatial and temporal extent of summer hypoxia (dissolved oxygen [DO] concentration ≤ 2 mg/L) in Chesapeake Bay and its tributaries has been increasing for decades, consequently affecting fish distribution and abundance by shifting biomass to non‐hypoxic habitats. Hypoxia in coastal waters impacts food web dynamics, thereby limiting ecosystem productivity and affecting regional fisheries. Additionally, laboratory studies of Atlantic Croakers Micropogonias undulatus have shown that hypoxia serves as an endocrine disruptor, reducing the production of the yolk precursor vitellogenin as well as affecting other biochemical pathways. Reproductive potential is therefore lower in hypoxia‐exposed Atlantic Croakers than in fish that are taken from normoxic conditions. We examined field‐caught Atlantic Croakers from three Chesapeake Bay tributaries with different DO levels to evaluate patterns in the lipid content of somatic and gonadal tissues. We found that somatic lipid content was not affected by the presence of hypoxia, whereas ovarian lipid content was significantly affected by the severity of hypoxia. Furthermore, Atlantic Croakers that were exposed indirectly to mild hypoxia (lasting hours to days) exhibited greater ovarian lipid content than fish that were captured from normoxic sites. As expected, severe hypoxia reduced the ability of Atlantic Croakers to accumulate lipids in their ovaries, likely affecting reproductive output. Stock assessment models that ignore the effects of hypoxia may yield overly optimistic production estimates for hypoxia‐exposed populations, particularly if environmentally invariant fecundity and growth are assumed.Received December 16, 2014; accepted September 24, 2015

Highlights

S (Diaz and Rosenberg 2008; Seitz et al 2009)
The proportion of routine trawl stations exhibiting hypoxia during May–August 2011 was greatest in the Rappahannock River followed by the York River (9% of trawl stations); no stations in the James River were hypoxic (Figure 2)
We observed that lipid allocation to ovaries in adult female Atlantic Croakers was consistent with predictions resulting from laboratory-based studies of the sublethal and indirect effects of hypoxia

Summary

Introduction

S (Diaz and Rosenberg 2008; Seitz et al 2009). For example, severe seasonal hypoxia in coastal systems can redirect energy from higher trophic levels (e.g., fish) to microbes, resulting in a loss of fish production and a subsequent decrease in ecosystem services (Baird et al 2004; Diaz and Rosenberg 2008). Mild periodic hypoxia (lasting hours to days) may increase food availability as the fish feed opportunistically on stressed benthos (Pihl et al 1992; Long and Seitz 2008) In between these extremes, seasonal hypoxia may lead. With the increasing occurrence and extent of summer hypoxia, critical habitat needs of Atlantic Croakers may coincide with hypoxic episodes, thereby affecting population productivity from an energetic standpoint by reducing prey availability or forcing a shift in fish spatial distribution to less-favorable habitats (e.g., suboptimal salinity or temperature ranges) that limit growth and reproduction. Energy that is needed for growth or reproduction may be allocated to maintenance metabolism if hypoxia-displaced fish are unable to forage in favorable environments This reallocation of energy resources to fish maintenance metabolism may affect population-level responses by reducing growth and reproductive potential (i.e., indirect effects). Stock assessment models that ignore the effects of hypoxia may yield overly optimistic production estimates for hypoxia-exposed populations, if environmentally invariant fecundity and growth are assumed

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Results

Conclusion