Pattern of spatial distribution of a brood-protecting schizasterid echinoid, Abatus cordatus, endemic to the Kerguelen Islands

Abstract

ABSTRACT. This study examined the spatial distribution at different geographic scales of the echinoid Abatus cordatus which is endemic to the Kerguelen Islands. Special attention was paid to the nondispersal strategy of the specles. It lives burrowed in the sediment and females brood t h e~r young in dorsal pouches. The dispersal of this species is therefore characterised by a limited mobility among adults and the lack of a free-swimming larval phase. Using SCUBA and dredging, A . cordatus was sampled all around Kerguelen. The spatial distribution from the island scale to the bay scale shows discontinuities at 2 levels: (1) at the island level favourable sectors (princ~pally characterised by jagged coastline with numerous sheltered bays) are separated by linear coastline or swell exposed sectors; (2) at the bay scale A. cordatus lives in high density, isolated demes in shallow water of sheltered bays. A . cordatus was most numerous in sediments that ranged from medium to fine sand. The granulometry of the sed~ment and the lack of predation determine this aggregated spatial distrlbution pattern. Considering that the scale of larval dispersal is the consequence of spatial and temporal habitat structure, the non-dispersal strategy of A. cordatus is associated with a spatially varying but temporally constant habitat as predicted by theoretical models.

Why Are There So Many Species of Brooding Antarctic Echinoids?

“…The nondispersal strategy is favored only if the habitat is heterogeneous (in terms of low and high density sites) and if habitat is stable in time (in the sense of persistence). The temporal and spatial habitat structure of the brood-protecting echinoid Abatus cordatus, endemic of the subantarctic Kerguelen Islands, fits the prediction of the models (Poulin and Feral 1995). A similar habitat structure was found for the tropical brood protecting Cassidulus caribaearum (Gladfelter 1978), although indications of high mortality suggest instability of this habitat over time.…”

“…Marine benthic invertebrates are generally either sessile or slow moving as adults, and pelagic larvae are considered as the dispersal stage in the life cycle of the species. Plankto- Poulin and Feral 1994 cies lacking a larval stage are differentiated over a scale of kilometers (Kwast et al 1990;Poulin and Feral 1994). However, the hypothesis that potential for larval dispersal equates with high rates of gene flow is not the rule and the role of pelagic larvae in population genetics has been overestimated (Hedgecock 1986).…”

Is the Species Flock Concept Operational? The Antarctic Shelf Case

“…All species of the monophyletic brooding group are Subantarctic or Antarctic. Some species can locally dominate the echinoid fauna in term of abundance [70], but they display a limited ecological diversity (all are infaunal or partly infaunal deposit feeders) and consequently are not considered as a true flock. A recent population genetic study [71] confirms that the brooding schizasterids display highly reduced dispersal rates, a feature which may favour high speciation rates [72], independently of any key innovation.…”

Benthic species of the Kerguelen Plateau show contrasting distribution shifts in response to environmental changes

“…The four selected species are known by a sufficient number of presence records to perform robust species distribution models. These four species are common on the Kerguelen Plateau and constitute substantial representatives of Antarctic benthic ecosystems (De Ridder, David, & Larrain, 1992;Díaz, Féral, David, Saucède, & Poulin, 2011;Hardy et al, 2011;Linse et al, 2008;Moya, Saucède, & Manjón-Cabeza, 2012;Poulin & Féral, 1995). Namely, we selected Abatus cordatus and Brisaster antarcticus, two species endemic to sub-Antarctic regions, and Ctenocidaris nutrix and Sterechinus diadema that present broader distribution ranges in the Southern Ocean ( Figure 1).…”