Macroalgal fouling on the intertidal mole crab Emerita analoga facilitates bird predation

Abstract

In this work, we studied the effects of predation by birds on the intertidal mole crab Emerita analoga fouled by macroalgae in a sandy beach of central Peru (11°S). The epibiosis affected mostly the larger animals, especially adult females. Epibiosis prevalence for the entire intertidal population was relatively low (1-2%), however, within the size range affected by epibiosis in the intertidal zone (18-23 mm in carapace length), 20-38% of the animals were fouled. Focal observations of birds showed that fouled animals are preferred over those non-fouled of the same size class and hence the same sex, being consumed at a higher rate than their proportion in the intertidal (Chesson's alpha index of prey selection[0.96), and estimations of mortality rates indicated that more than 35% of the intertidal fouled animals are removed everyday by birds. The effect of epibiosis may be mainly attributed to a higher burrowing time or an increased visual attractive effect of the algae, which make fouled animals more conspicuous to predatory birds, or because of fouling enhances profitability of the animals.The results show that epibiosis has negative effects on E. analoga through increasing predation by birds, which in turn restricts the distribution and abundance of fouled E. analoga in the intertidal zone.

Parasite infection and sand coarseness increase sand crab (Emerita analoga) burrowing time

“…obs. ; also see Hidalgo et al, 2010;MacGinitie, 1938). Large females may be better equipped to burrow in coarse sand despite strong wave action than smaller crabs (including males).…”

“…If slower burrowing increases vulnerability to bird predators, then infected crabs may be more likely to be captured by these definitive hosts for the parasite Oliva et al, 2008). For example, female E. analoga infested with epibiotic algae have reduced burrowing speeds, and are more likely to be preyed upon by birds as a consequence (Firstater et al, 2009;Hidalgo et al, 2010). Although the negative effect of parasite infection on burrowing speed was not large, it may nonetheless cause meaningful differences in predation risk because the crabs burrow incredibly quickly (MacGinitie, 1938) and because predatory birds, including definitive hosts for P. altmani, sometimes visually locate crabs prior to attempting to capture them (Blokpoel et al, 1992), and are less successful at capturing buried crabs than crabs that are at or near the surface (Ryan et al, 1987).…”

Functional morphology, coaptation and palaeoecology of Hollardops (Trilobita, Acastidae), with descriptions of new species and two new genera from the Devonian of Morocco

“…Epizoic growth on contemporary crustaceans has been shown to decrease swimming or burrowing capabilities and can even lead to significantly increased casualties from predation (e.g. Bauer, 1981;Hidalgo et al, 2010). Grooming, i.e., preening and cleaning of various parts of the body involving secondary modification of locomotory or feeding appendages, is a frequent and important strategy adopted by a range of crustaceans (Bauer, 2013).…”

Limpets and Their Algal Epibionts: Costs and Benefits ofAcrosiphoniaspp andUlva lactucaGrowth

“…Another dynamic that is not explored here is the potential to increase or decrease predation. Past research on the crab Emerita analoga found that algal epibiont growth increased predation possibly due to negative effects on burrowing time and increased visualization by predators [22].…”