Hard substrate structures, biologically formed, have an important impact on species diversity both regionally and in the immediate area (Buhl-Mortensen et al., 2009). These structures allow attachment for various organisms and can furthermore be a source of food. Finally, they can act as a safe haven in which organisms can rest and take shelter (Wulff, 2006).
Deep-sea sponges aggregations form such a biological structure. The high diversity and biomass of these aggregations allow sponges to play a fundamental ecological role. Large numbers of species from a variety of taxa take advantage of this oasis of hard substrate in an otherwise open sediment situation (Bett and Rice, 1992; Beaulieu, 2001a). Sponges provide refuge from predators and boost the food supply of the area (Wulff, 2006). They act as a source of food for numerous predators. Those that feed on sponges range in size from microscopic endofauna to sea turtles. However, it should be noted that most predators, apart from those most adapted, avoid feeding on sponges due to the toxic nature of the secondary metabolites produced by many sponge species (Rutzler, 2004).
An individual sponge can play host for many species of invertebrate (Figure 4). These organisms live within the sponge’s canals, feeding on any plankton not utilised by the host and sometimes consuming the host itself (IIan et al., 1994; Wulff, 2006). The simple structure of canal-riddled sponges is thought to drive these close relationships. It has been observed that as the canal volume of a sponge increases, it’s associations with endofauna is more pronounced (Rutzler, 1976).
Sponge associates get numerous benefits from the interaction. By enveloping their host, sponges protect them from boring organisms such as bivalves and scleractinian corals. Endosymbionts (organisms that live within other organisms) such as the juvenile spiny lobster and other small crustaceans, use sponges as protection from predators. Ophuroids, zoanthids and scyphozoans are likewise known to utilise sponges this way. Organisms that feed within sponges include polychaetes, copepods, amphipods, isopods and snapping shrimps (Wulff, 2006) (Figure 5). Sponge associates show greater diversity in tropical waters than deep (Buhl-Mortensen et al., 2009).
Deep-sea sponge aggregations have been described as “porous hard-substrate microhabitat islands” by IIan et al., 1994. In this paper, three species of deep-sea sponge, found at >830m depth, were studied. Various species were noted to encrust on the sponges and live within them. The sponges contained snapping shrimps (Synalpheus gambarelloides) and polycheates (e.g. Harmothoe spinifera), while serpulid tubeworms encrusted on to the sponge surfaces. These species were found far beyond their known depth range, which really demonstrates the amazing influence of a deep-sea sponge aggregation.
To reinforce the role of sponges, read “Case Study“. To read about glass sponges in particular and how they survive at these depths to provide this ecosystem role in the first place, read “Glass Sponges” plus the associated “Case Studies“. Finally for a summary of all topics covered in this blog, head to the “Conclusions” page.