Feeding and decoration preferences of the epialtidae crab Acanthonyx scutiforms

Abstract

A B S T R A C TStudies on the feeding preferences of marine herbivores are very important for our better understanding of the biology and the ecological role of these organisms. Members of the family Epialtidae are usually herbivores that mask themselves with pieces of seaweed and other materials to avoid predation. In order to better understand the mechanisms of food and decorating choices of the decorator crab Acanthonyx scutiformis, two multiple-choice feeding assays were performed using fresh seaweeds and artificial food containing crude extracts of the four seaweeds Osmundaria obtusiloba, Plocamium brasiliense, Sargassum sp., and Dictyota menstrualis, offered simultaneously to this crab species. In both assays the seaweed most consumed was O. obtusiloba, followed by P. brasiliense and Sargassum sp., while D. menstrualis was the least consumed. It is suggested that A. scutiformis is a generalist feeder, but with some preference for the perennial red seaweed O. obtusiloba and the chemically-defended seaweed P. brasiliense. Decorating behavior observations revealed the preferences of A. scutiformis by P. brasiliense. This decorating behavior can be interpreted as a mechanism to avoid generalist predators, since feeding and decorating preference were not associated and the crab used only small pieces of chemically defended algae. R E S U M OEstudos sobre preferência alimentar de herbívoros marinhos são muito importantes para o melhor entendimento da importância biológica e ecológica destes organismos. Caranguejos majídeos são usualmente herbívoros que se camuflam com pedaços de macroalgas e outros materiais para evitar a predação. Para entender melhor os mecanismos de escolha de alimento e decoração do caranguejo decorador Acanthonyx scutiformis, foram realizados dois ensaios de múltipla escolha usando macroalgas frescas e alimentos artificiais contendo extratos brutos das macroalgas Osmundaria obtusiloba, Plocamium brasiliense, Sargassum sp. e Dictyota menstrualis, oferecidas simultaneamente a esta espécie de caranguejo. Em ambos ensaios, a macroalga mais consumida foi O. obtusiloba, seguida por P. brasiliense e Sargassum sp., enquanto D. menstrualis foi menos consumida. É sugerido que A. scutiformis é um consumidor generalista, mas com alguma preferência pela macroalga vermelha perenial O. obtusiloba e a macroalga quimicamente defendida P. brasiliense. Observações sobre o comportamento decorador revelaram a preferência de A. scutiformis por P. brasiliense. Este comportamento decorador pode ser interpretado como um mecanismo para evitar predadores generalistas, uma vez que as preferências por consumo e decoração não foram relacionadas e o caranguejo usou somente pequenos pedaços de algas quimicamente defendidas.

Food and habitat choice in the spider crab <em>Leucippa pentagona</em> (Majoidea: Epialtidae) in Bahía Bustamante, Patagonia, Argentina

“…Several marine invertebrates prefer algae with low seasonal variation (Paine and Vadas 1969). This fact was particularly observed in the spider crab Mycrophyris bicornutus (Kilar and Lou 1984) and has been suggested to account for the algal preferences of Notomithrax ursus (Woods and McLay 1994) and Acanthonyx scutiformis (Vasconcelos et al 2009). Martin et al (2013) reported a low seasonal variation of Sphacelariales biomass in Bahía Bustamante.…”

“…However, small gastropods, polychaetes, isopods and amphipods are also found in some Epialtidae species studied (Woods and McLay 1994, Stachowicz and Hay 1999, Paiva Barros et al 2008, Vasconcelos et al 2009). By contrast, L. pentagona in Bahía Bustamante shows a specialized diet.…”

Chemical defense in the red seaweed Plocamium brasiliense: spatial variability and differential action on herbivores

“…In contrast to the patterns verified for L. variegatus, crude extracts from specimens of P. brasiliense from Enseada do Forno and Praia Rasa had no significant effect on feeding by the crab A. scutiformis (Figure 3). In fact, this crab is a generalist feeder, but it exhibits some preference by the chemically-defended P. brasiliense and also uses this macroalga as decoration and probably protection against predation (Vasconcelos et al, 2009). In fact, this is a typical mechanism exhibited by small and more specialised marine organisms that live associated to and consume the chemically defended host to minimise predation (Hay, 1992).…”

An experimental evaluation of macroalgal consumption and selectivity by nominally herbivorous fishes on subtropical rocky reefs

“…A number of Codium species, including C. intertextum are known to possess dimethylsulfoniopropionate (DMSP), a substance that can decrease the activity of generalist feeders over their thalli (Van Alstyne and Puglisi, 2007). Similarly, P. brasiliense possesses halogenated monoterpenes (Vasconcelos et al, 2010) and Laurencia species produces elatol (Pereira et al, 2003), both of which prevent herbivore action towards these algae (Pereira et al, 2003;Vasconcelos et al, 2009).…”