Record and effects of fouling macrophytes on the Mole crab Emerita analoga

FIRSTATER F. N.; HIDALGO F. J.; LOMOVASKY B. J.; GAMERO P.; QUEZADA G.; GALLEGO P.; IRIBARNE O. O.

Concepción

Simposio; Censor Midterm Symposium; 2006

COPAS; Alfred Wegener Institute for Polar and Marine Research; National Oceanography Centre

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