The dynamics of biogeographic ranges in the deep sea

Abstract

Anthropogenic disturbances such as fishing, mining, oil drilling, bioprospecting, warming, and acidification in the deep sea are increasing, yet generalities about deep-sea biogeography remain elusive. Owing to the lack of perceived environmental variability and geographical barriers, ranges of deep-sea species were traditionally assumed to be exceedingly large. In contrast, seamount and chemosynthetic habitats with reported high endemicity challenge the broad applicability of a single biogeographic paradigm for the deep sea. New research benefiting from higher resolution sampling, molecular methods and public databases can now more rigorously examine dispersal distances and species ranges on the vast ocean floor. Here, we explore the major outstanding questions in deep-sea biogeography. Based on current evidence, many taxa appear broadly distributed across the deep sea, a pattern replicated in both the abyssal plains and specialized environments such as hydrothermal vents. Cold waters may slow larval metabolism and development augmenting the great intrinsic ability for dispersal among many deep-sea species. Currents, environmental shifts, and topography can prove to be dispersal barriers but are often semipermeable. Evidence of historical events such as points of faunal origin and climatic fluctuations are also evident in contemporary biogeographic ranges. Continued synthetic analysis, database construction, theoretical advancement and field sampling will be required to further refine hypotheses regarding deep-sea biogeography.

Figure 1.

Profile of typical continental margin and deep-sea system. Major regions are labelled. Adapted from Gage & Tyler (Gage & Tyler 1991).

Figure 2.

The geological, biological, chemical and physical history of the deep sea. Figure shows from left to right sea-level change in metres (light blue line); deep-sea bottom temperate in degrees celsius (orange line); major anoxic events (dark red blocks, width denotes regional vs. global); major extinction events (grey arrows within timescale), major migrations of fauna into the deep (text); circulation mode (dark blue line) and proposed origins of deep-sea fauna (light red blocks). Data for figure come from (Menzies & Imbrie 1958; Clarke 1962; Bensen 1975; Allen 1978; Lipps & Hickman 1982; Jeppsson 1990; Jacobs & Lindberg 1998; Horne 1999; Wilson 1999; Rogers 2000; Waelbroeck et al. 2001; Little & Vrijenhoek 2003; Smith & Stockley 2005; Kiel & Goedert 2006; Linder et al. 2008; Strugnell et al. 2008).

Figure 3.

Potential larval dispersal distance of deep-sea fauna based on current speed, and published estimates of planktonic larval duration (Young & George 2000; Marsh et al. 2001; Watanabe et al. 2004; Havenhand et al. 2005; Buhl-Mortensen & Hoeg 2006; Miyake et al. 2006; Mercier & Hamel 2008; Arellano & Young 2009; Rouse et al. 2009). The two trajectories assume constant and unidirectional currents, and represent published estimates for lowest and highest velocity currents associated with surface waters or benthic storms (Havenhand et al. 2005). Note that currents demonstrating periodic changes in direction would greatly limit dispersal (Marsh et al. 2001).