Invasive range expansion by the Humboldt squid, Dosidicus gigas , in the eastern North Pacific

Abstract

A unique 16-year time series of deep video surveys in Monterey Bay reveals that the Humboldt squid, Dosidicus gigas, has substantially expanded its perennial geographic range in the eastern North Pacific by invading the waters off central California. This sustained range expansion coincides with changes in climate-linked oceanographic conditions and a reduction in competing top predators. It is also coincident with a decline in the abundance of Pacific hake, the most important commercial groundfish species off western North America. Recognizing the interactive effects of multiple changes in the environment is an issue of growing concern in ocean conservation and sustainability research.invasive species ͉ top predators ͉ top-down forcing O ne of the greatest challenges in contemporary ocean science is that of predicting how oceanic communities will respond to impending changes, such as climatic warming and the removal of top predators (1). Interactive changes are of particular concern, but little information is available on the collateral effects of multiple factors. Rising temperatures have been implicated in shifting the geographical distribution patterns of fishes and plankton (2, 3) and in the disruption of plankton communities (4, 5). Removing top predators from an ecosystem can result in a cascade of effects that restructures the food web at lower trophic levels (6, 7) as well as at the top (8). Together, two or more such changes may act in ways that we cannot yet predict (9).Here we demonstrate that the Humboldt squid, Dosidicus gigas, has greatly extended its perennial range in the eastern North Pacific Ocean. This geographic expansion occurred during a period of ocean-scale warming, regional cooling, and the decline of tuna and billfish populations throughout the Pacific (10). In this case, environmental changes off California are concurrent with invasion by a species from an adjacent region. Examples of invasion by species at higher trophic levels are relatively rare. The subsequent ecological impact of the Humboldt squid invasion can be seen in possible top-down forcing on the local population of Pacific hake, but the ecological effects may not yet be fully expressed (11). The question of how an oceanic community will respond to climatic change must include the possibility of invading species (12), and the consequences of removing top predators may depend on whether there is an ecological understudy waiting in the wings. Dosidicus (Fig. 1) is a large, aggressive, abundant pelagic squid that reaches mantle lengths of 1.2 m, overall lengths Ͼ2 m, and weights up to 50 kg. Its geographical distribution is centered in the eastern equatorial Pacific. From these warm waters, its historical range extends along the subtropical coasts of both North and South America, with episodic but temporary range extensions to latitudes as high as 40°(13). Only a single species is known, although genetic evidence suggests that northern and southern populations are diverging (13,14). Dosidicus feeds opportunistically on a bro...

Genetic diversity and demographic history of Dosidicus gigas (Cephalopoda: Ommastrephidae) in the Humboldt Current System

“…ENSO) (Waluda et al 2006, Keyl et al 2008, Zúñiga et al 2008. Recently, after the 1997-98 ENSO event, D. gigas has experienced a range expansion in both hemispheres, linked to an increasing abundance and related to an expansion of the OMZ (Caddy & Rodhouse 1998, Zeidberg & Robison 2007, Bograd et al 2008, Keyl et al 2008. Moreover, the removal of top predators may have promoted the population increase of D. gigas by relaxing competition for their shared prey species, and by reducing mortality due to predation of juvenile squids (Zeidberg & Robison 2007).…”

Larval stage duration, age and growth of blue lanternfish Tarletonbeania crenularis (Jordan and Gilbert, 1880) derived from otolith microstructure

“…In turn, T. crenularis constitutes an important prey item for many predators in the North Pacific, including jumbo squid (Field et al 2007;Zeidberg and Robison 2007), salmon, Sockeye salmon, albacore, Pacific hake, and sablefish (Rogachev et al 2000;Hart 1973, Davies et al 1988Buckley et al 1999;Nomura and Davis 2005), and Dall's porpoises (Ohizumi et al 2003).…”

Range expansion of the Humboldt squid was not caused by tuna fishing

“…To the Editor: Zeidberg and Robison (1) infer that the range expansion of Dosidicus gigas resulted from a top-down cascade caused by fishing for tunas and billfishes in the eastern equatorial Pacific (EEP). We offer an alternative perspective supported on three grounds.…”