Metabolic responses of the Nereid polychaete, Alitta succinea, to hypoxia at two different temperatures S. Kersey Sturdivant a,b, ⁎, Marieke Perchik c , Richard W. Brill d,e , Peter G. Bushnell f a Division of Marine Science and Conservation, Nicholas School of the Environment, Duke University, 135 Duke Marine Lab Rd., Beaufort NC 28516, USA b INSPIRE Environmental, 251 Eustis Ave., Newport RI 02840, USA c Department of Environmental Sciences, Allegheny College, 520 North Main St., Meadville, PA 16335, USA d Department of Fisheries Science, Virginia Institute of Marine Science, College of William & Mary, P.O. Box 1346, Gloucester Point, VA 23062, USA e National Marine Fisheries Service, Northeast Fisheries Science Center, James J. Howard Marine Sciences Laboratory, 74 Magruder Rd., Sandy Hook, Highlands, NJ 07732, USA f Department of Biological Sciences, Indiana University South Bend, P.O. Box 7111, South Bend, IN 46634, USA abstract article info Article history: Received 4 November 2014 Received in revised form 1 July 2015 Accepted 1 September 2015 Available online xxxx Keywords: Stopflow respirometry Oxyregulation Oxygen Critical saturation Benthic function Coastal hypoxia has detrimental effects to community ecology, degrading community structure and diminishing benthic function. Benthic function is largely driven by infauna bioturbation, which facilitates life-supporting processes by increasing the quality of marine sediments for nearly all biota. These infauna-mediated processes are diminished by coastal hypoxia. However, some infauna have been documented to exhibit metabolic plasticity to low oxygen allowing them to maintain some form of benthic function. Of particular interest to this study is the Nereid polychaete Alitta succinea. Stopflow respirometry was used to assess the hypoxic tolerance of A. succinea, by quantifying resting metabolic rate (V O 2 ), critical oxygen saturation (i.e. the oxygen level below which worms could not maintain aerobic metabolism), and the oxyregulation ability at an acclimation temperature (25 °C) and after an acute temperature increase (to 30 °C). The acute Q 10 during normoxia was 4.6, though this effect of temperature on V O 2 was completely muted during hypoxia with a Q 10 of 1. Compared among other polychaetes, A. succinea was the most efficient at oxyregulation, resulting in low critical oxygen saturation levels of 16% and 10% at 25 and 30 °C, respectively. Finally, there was a significant effect of hypoxia on the mass metabolism relationship of A. succinea. Oxygen consumption rates were significantly higher during hypoxia only for smaller A. succinea, suggesting a physiological size selection for hypoxia response. These findings demonstrate the significant effect of hypoxia on A. succinea metabolism, but also provide the metabolic justification for survival of this infaunal worm during severe hypoxia. © 2015 Elsevier B.V. All rights reserved. 1. Introduction High human densities in coastal areas have adverse effects for marine systems (Mee, 2012; Vitousek et al., 1997); urbanization and agricultural activity along coastal river drainages results in fertilization of the marine environment, causing eutrophication (Nixon, 1995). The visible response to eutrophication is a greening of the water, as phyto- plankton and aquatic vegetation directly respond to nutrient input (Rabalais, 2002); a more serious concern is the unseen decline in bottom-water dissolved oxygen (DO). Excess production from phyto- plankton settles to the bottom and is heterotrophically consumed, pri- marily by microbes, adding to DO consumption in bottom-waters (Rabalais et al., 2010; Turner et al., 2012). This depletion is exacerbated in stratified water bodies where surface DO does not reach the bottom and hypoxia can develop (Levin et al., 2009). Hypoxia affects marine systems globally (Diaz and Rosenberg, 2008), degrading benthic community structure and quality, and diminishing benthic function and services (Steckbauer et al., 2011). Coastal hypoxia, a shortage in DO concentrations, is diffi- cult to define, as different taxonomic groups, body sizes, and skel- etal types have varying oxygen tolerances and thresholds (Diaz and Rosenberg, 1995; Vaquer-Sunyer and Duarte, 2008). A meta-analysis found that sublethal effects were elicited in benthic invertebrates at a median DO concentration of 2.13 mg O 2 l -1 (Vaquer-Sunyer and Duarte, 2008). Coastal hypoxia is often defined as DO concentrations ≤ 2 mg O 2 l -1 or ~24% O 2 saturation at 25 °C (Diaz and Rosenberg, 2008; Murphy et al., 2011; Turner et al., 2012), and this is the classification used in this study. Benthic systems exhibit a predictable and graded series of responses to hypoxia (Rabalais et al., 2010). At the initial onset organisms increase respiration (Wannamaker and Rice, 2000), and mobile fauna migrates from the area (Ludsin et al., 2009; Seitz et al., 2009). As DO further declines, sessile fauna ceases feeding and decreases activities not related to respiration (Diaz and Rosenberg, 1995). Infauna migrate closer to the Journal of Experimental Marine Biology and Ecology 473 (2015) 161–168 ⁎ Corresponding author. E-mail address: kersey@inspireenvironmental.com (S. Kersey Sturdivant). http://dx.doi.org/10.1016/j.jembe.2015.09.001 0022-0981/© 2015 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Journal of Experimental Marine Biology and Ecology journal homepage: www.elsevier.com/locate/jembe