Record and Effects of Fouling Macrophytes on the Mole Crab Emerita analoga

FIRSTATER, F.; HIDALGO, F.; BETINA JUDITH LOMOVASKY; GAMERO, P.; QUEZADA, G.; PERCY, G.; OSCAR IRIBARNE,

Concepción, Chile

Congreso; CENSOR Midterm Symposium; 2006

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 (Wahl & Mark, 1999). In Ancón Bay (11º46’ S, 77º11’ W; Central Peru), the mole crab Emerita analoga inhabits all sandy beaches, and we have found them commonly covered with epibiontic macrophyte. The mole crab is one of the most abundant decapod of the Peruvian sandy beach communities. They play an important role in secondary production as prey for many crustaceans, fishes, birds, and even humans (Alvitres et al. 1998). 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 Ancón Bay: San Francisco Grande (SFG) and Las Conchitas (LCB), and one south of the bay, in Huaquillo beach (HB). To assess direct 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 ranged from 0.0004 to 0.0091g for epibiosis 1 and from 0.0062 to 0.1899 g for epibiosis 2. These values of algae dry weight corresponding to categories 1 and 2 of our visual-based scale were significantly different (t-test, P<0.001). In SFG the density was 433 ind/m2, the male:female ratio was 6.75:1, and 0.8% of individuals had epibiosis 1. In HB the density was 1091 ind/m2, the male:female ratio was 4.63:1; 0.32% of individuals had epibiosis 1 and 1.76% epibiosis 2. In LCB the density was 284 ind/m2, the male:female 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 test, 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 test, P<0.05 for both comparisons). The degree of epibiosis had no effect 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 rates 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 opportunist algae, proliferating in eutrophicated shores, 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.