How do reproductive output, larval behaviour, and recruitment contribute to adult spatial patterns in Mediterranean encrusting sponges?

Abstract

We studied the abundance and spatial pattern of 2 Mediterranean enci-ust~ng sponges, Crambe crambe (highly toxic) and Scopalina lophyropoda (non-toxic), at 4 spatial scales (0.5, 1, 2 and 4 m2). We also examined the reproductive output, larval behaviour and recruitment in these species, and assessed the relative importance of these parameters in explaining the abundance and spatial patterns of adults. We also determined, in field experiments, whether the presence of adults induces or inhibits recruitmenl in these 2 species. We found that C. crambe was much more abundant than S. lophyropoda at the site stu.died in both number of individuals per m? (67 * 2.7 vs 10.2 + 2.1, mean i SE) and coverage (47 + 1 9 vs l l . l * 1.4 Y o ) At the smallest scale sampled (0.5 m'), both species showed an aggregated pattern Aggregation \vas also detected for S. lophyropoda, but not for C crambe, at the scales of 1 and 2 m2 The number of embryos incubated per cm2 by C. crambe and S. lophyropoda was 76.2 + 12.5 and 1 4 * 1.7 (mean i SE), respectively. We estimated that the potential number of larvae of C. crambe released into the water column was about 20 times higher than that of S. lophyropoda. Larva! beha\.',ol?r was meni!ored in the !aSeratory and in !he fie!-'. La:...ae of S. !ophyropoda did not swim away from the release point. They maintained a vertical posture that minimised horizontal dispersal, and soon began crawling. In contrast, the larvae of C. crambe swam actively and had a comparatively delayed crawling phase. Recmitment of the 2 speries in scraped quadrats surrounded by individuals of C, cran~be and S lophyropoda, and in controls (rocky areas with no sponges), was monitored weekly for a month. Recruitment of both specles was higher in scraped quadrats surrounded by conspecifics. This effect was notably more marked for S. lophyropoda than for C. crambe recruits. The toxicity of C. crambe did not inhibit settlement of S. lophyropoda with respect to controls. The mean number of recruits per unit surface area after 1 mo (all substrates pooled) was ca 3.5 times higher for C. crambe than for S. lophyropoda. This difference was smaller than expected given that larval production of C. crambe was ca 20 times higher. This indicates that a significant proportion of C. crambe's offspring did not contribute to the maintenance of the local population. The aggregated pattern of S. lophyropoda at scales ranging from 0.5 to 2 m' and its discontinuous geographic distribution may be partially explained by strong phylopatry of its larvae due to their poor swimming ability and limited dispersal. The dominance of C crambe in littoral assemblages, its random distribution at scales larger than 0.5 m', and its ublquity along the littoral are traits that are consistent with high reproductive output, the swimming behaviour of larvae which facilitates wide dispersal, and patterns of recruitment found in this study. Therefore. S. lophyropoda populations appear to be maintained by offspring supplied by autochthonous individuals while...

Biogeography and phylogeny of Chondrilla species (Demospongiae) in Australia

“…However, caution is necessary when making assumptions on the dispersal ability of larvae based on knowledge from other sponge species with an apparently similar mode of reproduction. For example, Uriz et al (1998) found that the behaviour of the larvae of 2 species of viviparous sponges, Scopalina lophyropoda and Crambe crambe, greatly affected their dispersal ability. Ayre (1990) stated that severely restricted larval dispersal is common for marine invertebrates which have extensive geographic ranges and cautioned that there are difficulties with using observational data of larvae to infer dispersal distances.…”

Small-scale spatial genetic structure in Scopalina lophyropoda, an encrusting sponge with philopatric larval dispersal and frequent fission and fusion events

“…Uriz et al 1998, Mariani et al 2006) but the extent of sponge sperm dispersal is unknown. Graft acceptance and rejection experiments indicate that clonality may be important in shaping the genetic structure of a sponge population (see Boury-Esnault & Solé-Cava 2003 for review).…”

“…Vacelet 1979), and have life-history traits that might lead to a high level of spatial genetic structure (e.g. Uriz et al 1998), only 1 study to date addresses sponge genetic structure at small spatial scales (Calderon et al 2007).…”

Methodological bias in the estimations of important meroplanktonic components from near-shore bottoms

“…In contrast, despite the many direct observations on larval release from sponges and bryozoans in the literature (e.g. Ryland 1976, Amano 1988, Keough 1989, Hurlbut 1991, Linquist et al 1997, Uriz et al 1998, and with the exception of the anecdotal collection of sponge larvae made by Rützler et al (1980), and the report of Trégouboff (1939) for the non-swimming, long-distance dispersing hoplitomella larva of Alectona, no plankton studies have ever mentioned the presence of sponge and coronate bryozoan larvae within the samples. The incongruity between direct observations of larval release and the results of plankton samplings conducted near habitats colonised by sponges and bryozoans deserves further investigation.…”