Mass recruitment of Ophiothrix fragilis (Ophiuroidea) on sponges:settlement patterns and post-settlement dynamics

Abstract

The main recruitment of Ophiothrixfragilis occurs in the northwestern Mediterranean in late spring-early summer. Recruits are whitish and aggregate visibly on the surfaces of some sponge species, where they can reach densities above 50 ind. cm-2. In order to investigate this association, we monitored larval abundances in the plankton, and recruit distribution and dynamics on the benthos. Settlement took place in several batches, with peak abundance of recruits on sponges in June. The mean diameter of juveniles was 0.2 mm in June and grew to 0.4 mm in September. In July, after the settlement ceased, juveniles were more abundant on the surfaces of the sponges Crambe crambe, Scop a h a lophyropoda and Dysidea avara (14 to 20 ind. cm-2) than on the adjacent algal turf (4 ind. cm-2). No preference could be substantiated for 6 other encrusting sponge species. In contrast, juveniles were not significantly more abundant on these 3 sponges in June while settlement was under way. Recruitment on experimental sponges covered with plastic lids was reduced by two-thirds, indicating an initial colonization directly from the water column. However, clearing experiments demonstrated the ability of the young brittle stars to recolonise sponges, and brittle stars were more abundant at the periphery than at the centre of the sponges. These results indicate that brittle star recruits can select their substrata, possibly as a result of post-settlement lateral migration, resulting in an uneven distribution among sponge species. We set forth the hypothesis that this association between brittle stars and sponges is based on a trophic relationship, small brittle stars taking advantage of the inhalant currents of the sponge. In sponges with well-defined inhalant fields, almost all recruits concentrate on them, with arms flat against the sponge. When the brittle stars grow to a size above 1 mm (disk diameter) they abandon sponge surfaces and hide in small crevices between algae and invertebrates.

Juvenile-adult associations in sea urchins Strongylocentrotus franciscanus and S. droebachiensis: Is nutrition involved?

“…This appears to be the case for members of the genus Strongylocentrotus, where post-settlement mortality may be as high as 90% within the first year (Pearse & Hines 1987, Rowley 1990. Nutrition has been shown to affect post-settlement distribution in juvenile ophiuroids (<1 mm disk diameter, Turon et al 2000), but our data do not support a nutritional advantage for juvenile S. franciscanus and S. droebachiensis sheltering under adults (Tegner & Dayton 1977, RogersBennett et al 1995. Whereas post-settlement mortality has been argued to be more important than other processes (i.e.…”

Sponges as “living hotels” in Mediterranean marine caves

“…The high abundance of some of these species has been attributed either to parasitism (e.g. the amphipod L. spinicarpa according to Connes 1967) or to specific stages of their life cycle, such as recruitment (Turon et al 2000). Sponges have been reported to function as "reproduc- tive centres" or "resting places" for larvae and adults of several macrobenthic species (Klitgaard 1991, Turon et al 2000.…”

“…the amphipod L. spinicarpa according to Connes 1967) or to specific stages of their life cycle, such as recruitment (Turon et al 2000). Sponges have been reported to function as "reproduc- tive centres" or "resting places" for larvae and adults of several macrobenthic species (Klitgaard 1991, Turon et al 2000. This was also evidenced in our study but only for sponge specimens collected near the cave entrance; juveniles of the amphipod C. pusilla and eggcarrying individuals of the tanaid Paradoxapseudes intermedius were found in the cavities of A. oroides, while egg-carrying individuals of the decapods Athanas nitescens and Eualus occultus were found in the sponge A. aerophoba.…”

Checklist de Porifera do Estado de São Paulo, Brasil

“…Estas associações são extremamente variadas, e incluem crustáceos (Ribeiro et al 2003, Abdo 2007, poliquetos (Çinar et al 2002), equinodermos (Turon et al 2000, Henkel & Pawlik 2005 e peixes (Rocha et al 2000). Além dos componentes da macrofauna associada, há também uma microfauna abundante e bastante diversificada, que inclui bactérias, algas e fungos, em alguns casos representando mais de 60% da biomassa total (Wilkinson 1978, Bugni & Ireland 2004.…”