An oceanographic, meteorological, and biological ‘perfect storm’ yields a massive fish kill

Abstract

Mass mortality events are ephemeral phenomena in marine ecosystems resulting from anthropogenically enhanced and natural processes. A fish kill in King Harbor, Redondo Beach, California, USA, in March 2011 killed ~1.54 × 10 5 kg of fish and garnered international attention as a marine system out of balance. Here, we present data collected prior to, during, and following the event that describe the oceanographic conditions preceding the event, spatial extent of hypoxia (dissolved oxygen < 1.4 ml l −1 ), and subsequent recovery of the harbor. In situ sensors within the harbor revealed rapid decreases in dissolved oxygen in surface waters from 7 to 9 March 2011, coincident with the mortality event on 8 March. Continuous observations provided evidence that respiration of a large population of fish within the harbor, potentially exacerbated by an incursion of upwelled low-oxygen water, resulted in significant oxygen reduction in the harbor and ultimately caused mortality of the fish population. The hydrodynamically constrained northern basin transitioned to nearly anoxic conditions, while spatially variable hypoxia was observed throughout the harbor and adjacent bay for >10 d following the event. Initial recovery of dissolved oxygen in the harbor was facilitated by storm-mediated mixing. No connection was apparent between increased algal biomass or phycotoxins within the harbor and the mortality event, although the fish showed evidence of prior exposure to the algal neurotoxin domoic acid. Our findings underscore the essential role of ocean observing and rapid response in the study of these events and the role that oceanographic processes play in hypoxia-driven fish mortalities. Alterations in upwelling regimes as a consequence of climate change are likely to further increase the frequency and magnitude of upwelling-driven hypoxia and mortality events. KEY WORDS: Fish kill · Hypoxia · Nearshore embayment · Upwelling · Mixing Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 468: [231][232][233][234][235][236][237][238][239][240][241][242][243] 2012 may also represent a severe depletion of local fish populations, and Lowe et al. (1991) documented 86 individual mortality events in which >1 million fish were killed from 1980 to 1989 nationwide in the USA.It is often difficult to directly attribute causation to mortality events due to their patchiness in time and space and potential forcing by multiple underlying processes; indeed, the complexity of such events can lead to great debate about the mechanisms underlying mass mortality events (e.g. Paerl et al. 1998, Burkholder et al. 1999. Surpassing the temperature limits of aquatic species has been implicated in some seasonally localized mortalities (Bohnsack 1983, Hoyer et al. 2009, Balayla et al. 2010. Phytoplankton biomass can also be a causative factor behind many mass mortality events, either through biomass accumulation and consequent oxygen de pletion during the night or termination of a bloom (Paerl et a...

Climate change and dead zones

“…Large-scale climate dynamics influence oceanic current patterns, which in turn affect coastal dead zones in two ways. First, hypoxic waters from deep water oxygen minimum zones (OMZs) can be shoaled onto the shelf (Grantham et al, 2004) and into bays (Stauffer et al, 2012) creating novel hypoxic conditions in coastal areas, a phenomenon now recognized to occur in all major OMZs (Gilly et al, 2013). Second, climate-related changes in oceanic current patterns can exacerbate preexisting dead zones by introducing additional hypoxic water, as in the St. Lawrence Estuary (Gilbert et al, 2005), and/or by precluding oxygen replenishment from oxygenated oceanic waters as seen in the Saanich Inlet (Matabos et al, 2012).…”

Dissolved oxygen as a constraint on daytime deep scattering layer depth in the southern California current ecosystem

“…Such expansions have already been observed in tropical and subtropical regions (Stramma et al , 2010, across the northern North Pacific (Watanabe et al 2003, Whitney et al 2007, Crawford & Peña 2013, and in the southern California Current Ecosytem (CCE) (Bograd et al 2008, McClatchie et al 2010) where deoxygenation has been linked to intensification of the California Undercurrent . Deleterious effects of ocean deoxygenation have been observed for shallow-dwelling and coastal organisms exposed to extreme hypoxic events such as the summertime "dead zone" appearance in the Gulf of Mexico (Rabalais et al 2002), entrapment of epipelagic fishes in California harbors (Stauffer et al 2012), and strong upwelling events along the Oregon coast (Grantham et al 2004, Chan et al 2008.…”

Global gene expression profile during low temperature in the brain of grass carp (Ctenopharyngodon idellus)

“…While the effect of high-temperature on fish has been concerned and studied extensively due to the acceleration of global warming [4], low temperature caused much more fish death and brought acute economic losses to aquaculture industry [5]. Compared with studies on mammals and birds, the research on cold adaptation of fish is relatively limited and the underlying mechanisms remains obscure.…”