Biodiversity of Spongosorites coralliophaga (Stephens, 1915) on coral rubble at two contrasting cold-water coral reef settings

Georgios Kazanidis,Ursula F M Witte,Lea-Anne Henry,J Murray Roberts

doi:10.1007/s00338-015-1355-2

Abstract

Cold-water coral reefs (CWRs) in the northeast Atlantic harbor diverse sponge communities. Knowledge of deep-sea sponge ecology is limited and this leaves us with a fragmented understanding of the ecological roles that sponges play in CWR ecosystems. We present the first study of faunal biodiversity associated with the massive demosponge Spongosorites coralliophaga (Stephens, 1915) that typically colonizes coral debris fields of CWRs. Our study focused on the sessile fauna inhabiting sponges mixed with coral rubble at two contrasting settings in the northeast Atlantic: the shallow inshore (120–190 m water depth) Mingulay Reef Complex (MRC) and the deep offshore (500–1200 m) Logachev Mound (LM) coral province. MRC is dominated by the scleractinian Lophelia pertusa, while LM is dominated by L. pertusa and Madrepora oculata. Nine sponge–coral rubble associations were collected from MRC and four from LM. Measurements of abundance, species richness, diversity, evenness, dry biomass, and composition of sessile fauna on sponge and coral rubble microhabitats were undertaken. Differences in community composition between the two regions were mainly a response to changes in fauna with depth. Fauna composition was also different between sponge and coral rubble within each region. Infauna constituted a minor component of the sponge-associated fauna in MRC but had a higher contribution in LM. Sponge and coral rubble sessile fauna in both regions was mainly composed of cnidarians and molluscs, similarly to some previous studies. Sponges’ outer surfaces at MRC were colonized by a species-rich community with high abundance and biomass suggesting that S. coralliophaga at MRC acts as a settlement surface for various organisms but such a role is not the case at LM. This difference in the role of S. coralliophaga as a biological structure is probably related to differences in fauna composition with depth, bottom current speed, and the quantity/quality of food supplied to the benthos.

Highlights

Sponges (Phylum Porifera) constitute a highly diverse faunal group that create ecologically significant biological structures (Buhl-Mortensen et al 2010; Hogg et al 2010) as they supply substrate for attachment, food particles, and shelter from predation to various epifaunal organisms (Bell 2008 and references therein; Wulff 2012 and references therein)
Our study focused on the sessile fauna inhabiting sponges mixed with coral rubble at two contrasting settings in the northeast Atlantic: the shallow inshore (120–190 m water depth) Mingulay Reef Complex (MRC) and the deep offshore (500–1200 m) Logachev Mound (LM) coral province
MRC is dominated by the scleractinian Lophelia pertusa, while LM is dominated by L. pertusa and Madrepora oculata

Summary

Introduction

Sponges (Phylum Porifera) constitute a highly diverse faunal group that create ecologically significant biological structures (Buhl-Mortensen et al 2010; Hogg et al 2010) as they supply substrate for attachment, food particles, and shelter from predation to various epifaunal organisms (Bell 2008 and references therein; Wulff 2012 and references therein). In comparison with shallow-water ecosystems, knowledge of the physiology and ecology of deep-sea sponges is still very limited (Witte and Graf 1996; Witte et al 1997; Pile and Young 2006; Yahel et al 2007), as is knowledge of their role as biological structures (Klitgaard 1995; Beaulieu 2001; Buhl-Mortensen et al 2010). This hampers our understanding of the deep-sea ecosystem functions provided by sponge habitats. CWRs are themselves ecosystems with high ecological and economic values, and they are very sensitive to anthropogenic disturbance (Roberts et al 2009; Henry et al 2013b); knowledge of their structure and function is a prerequisite for the implementation of efficient management strategies (Henry et al 2013a)

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Results

Conclusion