1. A trade‐off was predicted between investment in defence and growth rate in the encrusting sponge Crambe crambe (Schmidt), while survival rates were expected to correlate positively with the production of defences. Previous studies have demonstrated that this sponge is better defended (chemically and physically) in shaded animal‐dominated habitats than in well‐illuminated habitats, dominated by algae. It was determined whether these habitat‐associated differences in investment correlate with differences in growth, regeneration and mortality rates of small specimens (initial average area less than 100 mm2) of this sponge. 2. In the 2 years of the study the sponge grew slowly (size increased 2·5 times on average), and showed high interindividual variation in growth rates. A seasonal pattern was evident, with marked size increases from May to October. Significantly higher growth rates (on a monthly basis) were found in the well‐illuminated habitat during the second year of study. There was also a negative relationship between monthly growth rate and toxicity (measured in previous studies). No differences were found in sponge regeneration rates between communities. 3. Mortality was significantly higher in individuals from the well‐illuminated habitat, and mainly affected the smallest sponges (< 150 mm2). 4. This sponge was significantly more abundant in the shaded habitat, but the mean size of the sponges was greater in the well‐illuminated habitat. The size distributions in the two communities were also significantly different. Sponges of the smallest size classes were more abundant in the shaded community. 5. It is concluded that sponges in the shaded habitat, in which investment in defence was greatest, featured higher survival but grew more slowly than those in the well‐illuminated habitat. Differential mortality and growth observed in the study were sufficient to explain the patterns of abundance and size distributions of the established sponge populations from these two habitats.

The temporal patterns of larval abundance, recruitment and early mortality in the sea urchin Paracentrotus lividus (Lamarck) in the northwestern Mediterranean were studied by combining planktonic and benthic surveys. The abundance of planktonic stages was monitored by weekly plankton hauls from 1992 to 1996. The presence of juveniles was studied by collecting epibenthic samples at monthly intervals from 1992 to 1995. The size distribution of the same population was studied in 1993. A main recruitment episode in late spring-summer occurred every year, although small recruitment events had been observed in autumn and winter. Interannual variability in larval abundance and recruitment was high, both being most intense in 1992, when up to 33.47 larvae m'3 were recorded in plankton samples, and up to 23000 recruits (sea urchins <2 mm) m-' were found in the benthic samples. We estimated that only about 12.7% of larvae (from the 8-armed stage onwards) survived the planktonic life, and that 0.5 to 0.7% of the settlers survived until they reached a diameter of 2 mm, while 0.040% of settlers survived the first year of benthic life and only 0.028% of settlers may attain reproductive size. The main bottlenecks in the dynamics of this species occurred, therefore, during the planktonic phase and the first year of benthic existence, particularly during the early post-settlement phase. The benthic samples provided a more robust depiction of events than planktonic data, which featured a higher variability. There was a significant relationship between the interannual variation in the late winter phytoplankton bloom and the spring peak of larvae of this species, indicating that changes in larval abundance are coherent with changes in planktonic primary production. There was also an exponential negative relationship between the abundance of larvae and abundance of recruits relative to larvae over the years studied, indicating density-dependent mortality rates in the planktonic and early benthic stages. Successful cohorts of this species can be traced to years with high larval abundance, which in turn are related to episodes of high planktonic primary production.

Variation in pigmentation is common in marine invertebrates, although few studies have shown the existence of genetic differentiation of chromatic forms in these organisms. We studied the genetic structure of a colonial ascidian with populations of different colour morphs in the northwestern Mediterranean. A fragment of the c oxidase subunit 1 (COI) mitochondrial gene was sequenced in seven populations of Pseudodistoma crucigaster belonging to three different colour morphs (orange, yellow and grey). Maximum likelihood analyses showed two well-supported clades separating the orange morph from the yellow-grey morphotypes. Genetic divergence between these clades was 2.12%, and gamma(ST) values between populations of the two clades were high (average 0.936), pointing to genetic isolation. Nested clade and coalescence analyses suggest that a past fragmentation event may explain the phylogeographical origin of these two clades. Non-neutral mtDNA evolution is observed in our data when comparing the two clades, showing a significant excess of nonsynonymous polymorphism within the yellow-grey morphotype using the McDonald-Kreitman test, which is interpreted as further support of reproductive isolation. We conclude that the two clades might represent separate species. We compare the population genetic differentiation found with that estimated for other colonial and solitary ascidian species, and relate it to larval dispersal capabilities and other life-history traits.

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Clavelina lepadiformis is a colonial ascidian found in harbour and rocky littoral habitats. The populations of these 2 habitat types in the Western Mediterranean showed marked genetic differences in mtDNA sequence data in previous works. However, no morphological differences between the forms inhabiting the 2 habitat types have been found. Here, we compared the biology and accumulation of heavy metals in populations of both habitats in NE of Spain. Abundance and seasonal cycles showed contrasting trends in the 2 habitat types: harbour populations reached densities of ca. 3900 zooids m -2 and active colonies were found all year round. Abundance in the rocky littoral environment was 1 order of magnitude lower and showed a clear seasonal pattern, with the disappearance of zooids during summer (aestivation). Reproductive cycles also differed, as larvae were present in the harbour population from November through June, with several sexual cycles during this period. In contrast, in the open littoral, larval occurrence was restricted to 2 to 3 mo during winterspring, with only 1 gonadal cycle yr -1. The zooids and larvae of the harbour were significantly larger. However, neither the total reproductive effort, tunic production (in weight ratios) nor fecundity significantly differed between these habitats. The harbour population accumulated significantly more Cu and Pb, and heavy metal concentrations showed a seasonal cycle with minima in summer. On the other hand, both populations accumulated a similar amount of V, a metal involved in ascidian metabolism. The production of secondary metabolites and the toxicity of polar extracts were higher in the open littoral form. These results, however, did not correlate with the outcome of palatability tests carried out with specialist and generalist predators, in which no preference was observed. Experimental juvenile transplantation between habitats showed that newly settled individuals from the rocky littoral habitat can survive in both environments (with survival rates of 30 to 50% during the first 4 wk), while those from harbours show low survivorship when moved out (ca. 5% survival after 4 wk). We conclude that there was a marked ecophenotypic variation between populations of both habitat types.