Predation ability of freshwater crabs: age and prey-specific differences inTrichodactylus borellianus(Brachyura: Trichodactylidae)

Abstract

Freshwater crabs are rarely represented in food webs and their role in these ecosystems has been largely ignored. Trichodactylus borellianus is an omnivorous crab species that has a diverse natural trophic spectrum. This paper evaluates, in a laboratory assay, the ability of three ages of this crab to prey on three different organisms. The prey selectivity and relative importance of each prey item was also analyzed. Prey items (cladocerans, oligochaetes, and golden mussels) consisted of organisms of different shapes and mobility, representing the natural diet of this crab. Crabs were sorted according to size (juvenile, sub-adult, and adult) and increasing amounts of one prey was offered to each crab after 24 hrs of starvation. In the selectivity trial, all prey types were offered in a fixed set. Crabs in all three age categories were able to prey on all organisms. Cladocerans and oligochaetes were consumed in greater quantities compared to golden mussels when offered separately. However, only the consumption of oligochaetes exhibited a positive correlation with the crabs' size. When cladocerans and oligochaetes were offered together, more oligochaetes were consumed, both as percentage of volume and occurrence. Age-specific changes in consumption could be related to differences in the stomach capacity of the crab, the digestion time of each prey, and the predator-prey encounter probability. The selection of the most elongated prey with the lowest mobility indicated that the balance of the gain and loss of energy made it an advantageous species to prey on, as it was susceptible to predation. Additionally, the mussel, which is an invasive species, although not positively selected by T. borellianus in the present study, represented a new trophic resource for this crab.

Ecosystem impacts of the invasive bivalve Limnoperna fortunei (golden mussel) in South America

“…In addition to fishes, two crab species (Zilchiopsis collastinensis and Trichodactylus borellianus) and one turtle have been observed to feed on L. fortunei (Bujes et al, 2007;Torres et al, 2012;Carvalho et al, 2013), but data on the importance of this item in their diet are still scarce.…”

Feeding spectra and activity of the freshwater crab Trichodactylus kensleyi (Decapoda: Brachyura: Trichodactylidae) at La Plata basin

“…However, among freshwater crabs, the research effort in this area is more recent with little emphasis in trichodactylid crabs (Collins et al 2007;Carvalho et al 2013a;Williner and Collins 2013;Pirela and Rincón 2013). Knowledge about trophic ecology aspects of any species is essential to understand the nutritional requirements and how species interact with the environment and with other organisms.…”

“…Trophic ecology studies (e.g., behavior, feeding habits) on trichodactylid crabs in Argentina have reported a variety of aquatic environments (e.g., in subtropical savannah and alluvial valley of template rivers) and feeding habits (Williner and Collins 2002;Collins et al 2006;Collins et al 2007;Williner and Collins 2013;Carvalho et al 2013aCarvalho et al , 2013b. In general, these crustaceans are omnivorous with a wide trophic spectrum that ranges from algae and plant remains to insect larvae and even vertebrates (Collins et al 2006).…”

Ecosystem services provided by the exotic bivalves Dreissena polymorpha, D. rostriformis bugensis, and Limnoperna fortunei

“…Comparisons of L. fortunei densities on unprotected artificial substrates with those on substrates protected with 5–40 mm meshes indicate that up to over 90% of their yearly production is lost to predators, presumably fishes and invertebrates (Sylvester et al, 2007a ; Nakano et al, 2010 ; Duchini et al, 2018 ). In South America, two crab species and one turtle have been observed to feed on L. fortunei (Bujes et al, 2007 ; Torres et al, 2012 ; Carvalho et al, 2013 ), but the importance of this item in their diets is unknown.…”