Record and effects of fouling macrophytes on the mole crab Emerita analoga.

FAUSTO N. FIRSTATER; FERNANDO J. HIDALGO; BETINA J. LOMOVASKY; PATRICIA GAMERO; GIULIANA QUEZADA; PERCY GALLEGOS; OSCAR O. IRIBARNE

Concepción, Chile

Simposio; CENSOR Midterm Symposium; 2006

Universidad de Concepción, Chile

Epibiosis is one of the closest possible associations between different species. Through direct and indirect interactions, this association has major effects on the species involved and on community dynamics. In Ancón Bay (11°46’ S, 77°11’ W; central Peru), the mole crab Emerita analoga inhabits all sandy beaches, and we have found them commonly covered with epibionthic macrophyte. They play an important role in secondary production as prey for many crustaceans, fish, birds and even humans. Given that this pattern has never been reported, here we described the epibiosis, assessed its prevalence in the population and tested its effects in E. analoga burrowing abilities. Based on rostrum individual percent cover by algae (only site with epibiosis), a qualitative scale was designed: level 0 (no epibiontic algae observed), level 1 (algae covering 0 to 50% rostrum surface), and level 2 (algae covering 50 to 100% rostrum surface). To analyze E. analoga population characteristics and epibiosis occurrence, we performed, in February 2006, samplings in two beaches of Ancon Bay: San Francisco Grande (SFG) and Las Conchitas (LCB), and one south of the bay, in Huaquillo beach (HB). To assess effects of epibiosis, in March 2006 burrowing ability experiments were performed at HB, where burrowing time and depth were measured. The epibiontic algae found on E. analoga was identified as Enteromorpha spp., and was settled mainly on the rostrum, but was also found on primary and secondary antennae and maxillipeds. In some cases, Polisiphonia spp. has been also found under Enteromorpha canopy. Algae dry weight rage from 0.0004 to o.oo91 g for epibiosis 1 and from 0.0062 to 0.1899 g for epibiosis 2. These values corresponding to categories 1 and 2 of our visual-based scales were significantly different (t-test, p < 0.001). In SFG the density was 433 ind/m2, the sex ratio was 6.75:1, and 0.8% of individuals had epibiosis 1. In HB the density was 1091 ind/m2, the sex ratio was 4.36:1; 0.32% of individuals had epibiosis 1 and 1.76% had epibiosis 2. In LCB the density was 284 ind/m2, the sex ratio was 1.81:1 and there were not fouled individuals. Ovigerous females with epibiosis 2 spent more time in burrowing than ovigerous females with epibiosis 0 and 1 (ANCOVA, p < 0.001, Tukey post hoc, p < 0.001 for both comparisons). Burrowing speed was significantly lower for ovigerous females with epibiosis 2 than for ovigerous females with epibiosis 0 and 1 (ANCOVA, p < 0.001; Tukey post hoc, p < 0.05 for both comparisons). The degree of epibiosis had no effects on the maximum burrowing depth of ovigerous females (ANOVA, p > 0.05). The designed scale resulted to be effective in assessing the degree of fouling. Epibiosis prevalence was overall low and densities and sex ratios resulted consistent with other studies in the Peruvian coast. The effect of epibiosis on mole crab burrowing abilities may have profound influence on its population dynamic by modifying their availability to predators. Enteromorpha has been characterized as opportunistic algae, proliferating in eutrophicated shores and therefore we conclude that the interaction reported in this work should occur in other impacted areas of the large distribution of E. analoga. Nevertheless further studies are necessary in order to assess other direct effects of epibiosis on mole crab, such as effects on life history characteristics. In addition, as the epibiont is strongly influenced by seasons, prevalence and effects should be surveyed throughout the year