Sponges as “living hotels” in Mediterranean marine caves

Vasilis Gerovasileiou,Despoina Konstantinou,Chariton Charles Chintiroglou,Eleni Voultsiadou

doi:10.3989/scimar.04403.14b

Abstract

Although sponges constitute the dominant sessile organisms in marine caves, their functional role as ecosystem engineers has received little attention in this habitat type. In this study the associated macrofauna of the massive/tubular ecosystem-engineering sponges Agelas oroides and Aplysina aerophoba was studied across distinct ecological zones of two eastern Mediterranean caves. Our results revealed that the examined sponges supported a considerable associated macrofauna. A total of 86 associated taxa were found, including species reported for the first time as sponge symbionts and typical cave dwellers. Crustaceans predominated in terms of abundance but polychaetes showed the highest number of taxa. A clear differentiation was observed in the structure of the associated assemblage between the two sponges, attributed not only to the sponge species but also to differences in the surrounding environment. Density, diversity and the trophic structure of the sponge-associated macrofauna did not vary significantly along the horizontal axis of the surveyed caves. These findings suggest that sponges form a quite stable habitat, maintaining their functional role as ecosystem engineers across the studied marine caves and increasing habitat complexity in the impoverished inner dark cave sectors.

Highlights

One of the most important roles of sponges in the marine ecosystem is that they function as ecosystem engineers or “living hotels”, providing micro-habitat to diverse organisms (e.g. Koukouras et al 1985, Ribeiro et al 2003, Padua et al 2013)
Navarro-Barranco et al (2016) studied the crustaceans associated with invertebrate hosts, among which the sponge Ircinia variabilis, in a marine cave in the Alboran Sea and found that all the examined species were used as refuges by crustaceans
The motile invertebrate diversity of Mediterranean marine caves has received limited interest compared with the sessile biota; the few relevant studies have mainly taken place in the northwestern Mediterranean Sea (Ledoyer 1965, Navarro-Barranco et al 2014, 2016), while such data are lacking from the eastern basin

Summary

Introduction

One of the most important roles of sponges in the marine ecosystem is that they function as ecosystem engineers or “living hotels”, providing micro-habitat to diverse organisms (e.g. Koukouras et al 1985, Ribeiro et al 2003, Padua et al 2013). Sponges constitute the dominant sessile organisms in marine cave environments (Gerovasileiou and Voultsiadou 2012, 2016), their functional role as ecosystem engineers in this habitat type has received little attention. Sessile invertebrates have been shown to increase the structural complexity of hard substrates (Voultsiadou et al 2010, Navarro-Barranco et al 2014, 2016). This complexity in the space-limited oligotrophic environment of the dark caves could be significant for the motile cave dwellers. The motile invertebrate diversity of Mediterranean marine caves has received limited interest compared with the sessile biota; the few relevant studies have mainly taken place in the northwestern Mediterranean Sea (Ledoyer 1965, Navarro-Barranco et al 2014, 2016), while such data are lacking from the eastern basin (but see Gerovasileiou et al 2015b)

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Conclusion