Feeding ecology of the freshwater crab Trichodactylus borellianus (Decapoda: Trichodactylidae) in the floodplain of the Parana River, southern South America

Abstract

ABSTRACT. Freshwater crabs are not commonly considered to be an important group in trophic webs, and this might be due to a lack of knowledge about their trophic roles in aquatic ecosystems. Trichodactylus borellianus is one of the most common and widely distributed freshwater crabs in the floodplains of the southern South American rivers. The main objective of the present study was to examine the trophic role of T. borellianus, in the floodplain of the Paraná River, and its relationships with the freshwater littoral community. The trophic spectrum of this species was characterized for both sexes and individuals of different sizes (adults and juveniles), throughout daily and seasonal cycles. Samples were collected from the aquatic vegetation of three shallow lakes. The diet composition and the feeding activity of T. borellianus were evaluated through the examination of the stomach contents and their degree of emptiness. This crab species consumed several plant and animal items, including amoebas, rotifers, oligochaetes, copepods, cladocerans, and insect larvae. Moreover, this species consumes filamentous and unicellular algae, diatoms, fungi, and macrophytic remains. The predatory habits varied with the season and time of day, and variations in the feeding activity of the juveniles and adults were detected and documented. The diversity of food items eaten by this crab suggests that its trophic role in the community as an omnivore and opportunistic predator provides a connection among several trophic levels from both aquatic and terrestrial communities. Keywords: omnivore, trophic habits, stomach contents, detritus, macro-invertebrates. Ecología trófica del cangrejo dulceacuícola Trichodactylus borellianus (Decapoda:Trichodactylidae) en el valle de inundación del río Paraná, sur de Sudamérica RESUMEN. Los cangrejos de agua dulce no son comúnmente considerados como un grupo importante en las redes tróficas, y esto podría ser debido a falta de conocimiento acerca de sus funciones tróficas en los ecosistemas acuáticos. Trichodactylus borellianus es uno de los cangrejos de agua dulce más comunes y ampliamente distribuido en llanuras de inundación del los ríos del sur de Sudamérica. El objetivo principal del presente estudio fue examinar el rol trófico de T. borellianus en la llanura de inundación del río de Paraná, y sus relaciones con la comunidad litoral de agua dulce. El espectro trófico de esta especie se caracterizó en ambos sexos e individuos de diferentes tamaños (adultos y juveniles), a través de los ciclos diarios y estacionales. Se tomaron muestras en la vegetación acuática de tres lagunas diferentes. La composición de la dieta y la actividad de alimentación de T. borellianus fueron evaluados mediante la observación de contenidos estomacales y grado de repleción. Esta especie consume plantas y animales, incluyendo amebas, rotíferos, oligoquetos, copépodos, cladóceros y larvas de insectos. Además, consume algas filamentosas y unicelulares, diatomeas, hongos y restos de macrófitas. Los hábitos de consumo vari...

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).…”

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

“…The three prey types represent the range of bioforms (shape, mobility, and hardness) of the natural prey in the littoral, benthic, and plankton communities (Collins et al 2006;Williner and Collins forthcoming). Prey types supplied in the experiment were: (1) a prey type that was mobile and spherical (cladoceran: Daphnia magna); (2) a type that was slow moving and long (oligochaete: Limnodrilus udekemianus); and (3) a type that was hard and sessile (golden mussel: Limnoperna fortunei).…”

“…The distribution range of this species extends from the equator to 35 S, with the Paran a and Paraguay rivers being the major regions of occurrence (Melo 2003). This crab is considered omnivorous because of its wide, natural trophic spectrum composed of a variety of prey types that inhabit the littoral-benthic zone (Collins et al , 2006Williner and Collins forthcoming). Animal items include oligochaetes and insect larvae which are usually found in the digestive tract of these crabs along with macrophyte remains.…”

“…Microcrustaceans and rotifers have also been found in the stomach contents. Algae and other groups are consumed to a lesser extent or even sporadically (Collins et al 2007;Williner and Collins forthcoming). T. borellianus exhibits direct development meaning the hatched juvenile crabs have all of the characteristics of the adult (von Sternberg et al 1999).…”