Richness and distribution of sponge megabenthos in continental margin canyons off southeastern Australia

Abstract

Submarine canyons are spectacular topographical features that intersect the continental margins of the world's oceans. Canyons comprise unique habitats in terms of complexity, instability, material processing, and hydrodynamics, and they may support diverse assemblages of larger epibenthos. Yet, quantitative data on the biodiversity of the megabenthos in canyons are scant. Consequently, we quantified the diversity of sponges (a key and dominant group of the megabenthos) in 5 canyons located on the continental margin off southeastern Australia at depths from 114 to 612 m. The canyons harboured a rich sponge fauna, with a total of 165 species, belonging to 65 genera, 41 families, 10 orders, and 2 classes in 14 sled samples. Species richness declined with depth, but was positively linked to spatial heterogeneity of bottom types. Areas comprised of a broader range of bottom types (e.g. mixed rocky and sandy/muddy bottoms) contained more species than areas with more uniform substratum properties. Spatial patterns of the sponge assemblages were characterized by (1) high species turnover both between sites in individual canyons and between different canyons, and (2) low levels of site occupancy of the component species, with most species recorded from single canyons only. Variations in depth, substratum type and topographic relief resulted in heterogeneous environmental conditions of benthic habitats in canyons that corresponded to changes in the assemblage structure of sponges. A broad comparison with other abrupt topographical features in the bathyal zone of the region suggests that canyon assemblages may rival the diversity of sponges on seamounts. Site-to-site variation in diversity and species composition within individual canyons suggests that biological patterns may be finer-grained than the spatial scale of conventional geomorphological units. Consequently, from a perspective of conservation planning, a single or a few canyons are unlikely to accurately represent the regional faunal diversity, because of the strong biotic separation of communities between canyons and the limited distributional ranges of the component species.

Ecological Role of Submarine Canyons and Need for Canyon Conservation: A Review

“…In Halibut Channel, Haddock Channel, Desbarres Canyon, and The Gully (eastern Canada margin), observed species combinations were dependent on the dominant substrate type (Hargrave et al, 2004;Mortensen and Buhl-Mortensen, 2005;Baker et al, 2011). Sponge diversity was also positively correlated with substrate heterogeneity in five canyons off the southeastern Australian margin (Schlacher et al, 2007).…”

“…An increasing amount of data provides evidence of how canyons act benefiting and supporting fisheries (Yoklavich et al, 2000;Company et al, 2012), and enhance carbon sequestration and storage (Epping et al, 2002;Canals et al, 2006;Masson et al, 2010). Canyon habitats also provide nursery (Sardà and Cartes, 1994;Hoff, 2010;Fernandez-Arcaya et al, 2013) and refuge sites for other marine life (Tyler et al, 2009;De Leo et al, 2010;Vetter et al, 2010;Morris et al, 2013), including vulnerable marine ecosystems and essential fish-habitats such as cold-water corals and sponge fields (Schlacher et al, 2007;Huvenne et al, 2011;Davies et al, 2014). Canyons have also been shown to provide habitat for spawning females of pelagic and benthic species of commercial interest (Farrugio, 2012).…”

The Dangeard and Explorer canyons, South Western Approaches UK: Geology, sedimentology and newly discovered cold-water coral mini-mounds

“…Processes such as turbidity currents, the capture of along-shelf/-slope sediment, resuspension by internal tides and waves, and dense shelf water cascading result in either flushing of the canyon or the downslope deposition of sediments and organic matter , De Stigter et al, 2007, Hall et al, this issue, Huvenne et al, 2011, "Euroleón" Cruise Shipboard Party, 2011, Palanques et al, 2009and Ulses et al, 2008. The complex terrain and diverse range of sea-bed composition contribute to submarine canyons being described as areas of high habitat heterogeneity (Schlacher et al, 2007).…”

Habitat Differences in Deep-Sea Megafaunal Communities off New Zealand: Implications for Vulnerability to Anthropogenic Disturbance and Management

“…Sipuncula and M. musculus are both infaunal deposit feeders and their higher abundances in canyon habitats probably reflect the elevated levels of organic matter that can occur in canyons, and which have been observed previously to support high densities of these types of deposit-feeding organism in a New Zealand canyon . Differences in community structure between canyon habitats and other habitats in both regions could also be related to the higher topographic complexity of the seafloor at canyons (indicated by higher values of the SD of the slope, and rugosity), as suggested by Schlacher et al (2007) as a reason for the distinct nature of megafaunal communities in canyons.…”