Publications

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2017
McCormick, LR, Levin LA.  2017.  Physiological and ecological implications of ocean deoxygenation for vision in marine organisms. Philosophical Transactions of the Royal Society a-Mathematical Physical and Engineering Sciences. 375   10.1098/rsta.2016.0322   AbstractWebsite

Climate change has induced ocean deoxygenation and exacerbated eutrophication-driven hypoxia in recent decades, affecting the physiology, behaviour and ecology of marine organisms. The high oxygen demand of visual tissues and the known inhibitory effects of hypoxia on human vision raise the questions if and how ocean deoxygenation alters vision in marine organisms. This is particularly important given the rapid loss of oxygen and strong vertical gradients in oxygen concentration in many areas of the ocean. This review evaluates the potential effects of low oxygen (hypoxia) on visual function in marine animals and their implications for marine biota under current and future ocean deoxygenation based on evidence from terrestrial and a few marine organisms. Evolutionary history shows radiation of eye designs during a period of increasing ocean oxygenation. Physiological effects of hypoxia on photoreceptor function and light sensitivity, in combination with morphological changes that may occur throughout ontogeny, have the potential to alter visual behaviour and, subsequently, the ecology of marine organisms, particularly for fish, cephalopods and arthropods with `fast' vision. Visual responses to hypoxia, including greater light requirements, offer an alternative hypothesis for observed habitat compression and shoaling vertical distributions in visual marine species subject to ocean deoxygenation, which merits further investigation. This article is part of the themed issue 'Ocean ventilation and deoxygenation in a warming world'.

2014
Navarro, MO, Bockmon EE, Frieder CA, Gonzalez JP, Levin LA.  2014.  Environmental pH, O-2 and capsular effects on the geochemical composition of statoliths of embryonic squid Doryteuthis opalescens. Water. 6:2233-2254.   10.3390/w6082233   AbstractWebsite

Spawning market squid lay embryo capsules on the seafloor of the continental shelf of the California Current System (CCS), where ocean acidification, deoxygenation and intensified upwelling lower the pH and [O-2]. Squid statolith geochemistry has been shown to reflect the squid's environment (e. g., seawater temperature and elemental concentration). We used real-world environmental levels of pH and [O-2] observed on squid-embryo beds to test in the laboratory whether or not squid statolith geochemistry reflects environmental pH and [O-2]. We asked whether pH and [O-2] levels might affect the incorporation of element ratios (B:Ca, Mg:Ca, Sr:Ca, Ba:Ca, Pb:Ca, U:Ca) into squid embryonic statoliths as (1) individual elements and/or (2) multivariate elemental signatures, and consider future applications as proxies for pH and [O-2] exposure. Embryo exposure to high and low pH and [O-2] alone and together during development over four weeks only moderately affected elemental concentrations of the statoliths, and uranium was an important element driving these differences. Uranium: Ca was eight-times higher in statoliths exposed to low pHT (7.57-7.58) and low [O-2] (79-82 mu mol.kg(-1)) than those exposed to higher ambient pHT (7.92-7.94) and [O-2] (241-243 mu mol.kg(-1)). In a separate experiment, exposure to low pHT (7.55-7.56) or low [O-2] (83-86 mu mol.kg(-1)) yielded elevated U:Ca and Sr:Ca in the low [O-2] treatment only. We found capsular effects on multiple elements in statoliths of all treatments. The multivariate elemental signatures of embryonic statoliths were distinct among capsules, but did not reflect environmental factors (pH and/or [O-2]). We show that statoliths of squid embryos developing inside capsules have the potential to reflect environmental pH and [O-2], but that these "signals" are generated in concert with the physiological effects of the capsules and embryos themselves.

2010
Stramma, L, Schmidtko S, Levin LA, Johnson GC.  2010.  Ocean oxygen minima expansions and their biological impacts. Deep-Sea Research Part I-Oceanographic Research Papers. 57:587-595.   10.1016/j.dsr.2010.01.005   AbstractWebsite

Climate models with biogeochemical components predict declines in oceanic dissolved oxygen with global warming. In coastal regimes oxygen deficits represent acute ecosystem perturbations Here, we estimate dissolved oxygen differences across the global tropical and subtropical oceans within the oxygen minimum zone (200-700-dbar depth) between 1960-1974 (an early period with reliable data) and 1990-2008 (a recent period capturing ocean response to planetary warming) In most regions of the tropical Pacific. Atlantic, and Indian Oceans the oxygen content in the 200-700-dbar layer has declined. Furthermore, at 200 dbar, the area with O(2) < 70 mu mol kg(-1) where some large mobile macro-organisms are unable to abide, has increased by 4.5 million km(2) The tropical low oxygen zones have expanded horizontally and vertically Subsurface oxygen has decreased adjacent to most continental shelves However, oxygen has increased in sonic regions in the subtropical gyres at the depths analyzed According to literature discussed below, fishing pressure is strong in the open ocean, which may make it difficult to isolate the impact of declining oxygen on fisheries At shallower depths we predict habitat compression will occur for hypoxia-intolerant taxa, with eventual loss of biodiversity. Should past trends in observed oxygen differences continue into the future, shifts in animal distributions and changes in ecosystem structure could accelerate (C) 2010 Elsevier Ltd. All rights reserved