Ecology and conservation status of endemic freshwater crabs in Lake Tanganyika, Africa

Abstract

Sedimentation resulting from riparian deforestation has a wide range of detrimental eVects on aquatic biodiversity, but predicting the full consequences of such disturbances requires an understanding of the ecosystem's key functional components. We investigated the ecology and response to sedimentation of the diverse, endemic freshwater crabs of Lake Tanganyika, which may occupy important positions in littoral foodwebs. Our surveys revealed crab distribution patterns to be patchy, and that crabs can be locally abundant (0-28 individuals m ¡2 ). Crab densities decreased with depth and the dry mass of crab assemblages ranged from 0.0 to 117.7 g m ¡2 . Comparisons among sites revealed signiWcant eVects of sedimentation on crab assemblage evenness, but provided no evidence that sedimentation has altered densities, incidence or species richness. The resilience of crabs to sedimentation might be related to their intraspeciWc dietary breadth. Stable isotope data ( 13 C and 15 N) from crabs and their potential food resources indicated diVerences in trophic roles among endemic crab species. Overall, crabs occupy higher trophic positions than most other invertebrates, and they draw upon both benthic and planktonic energy pathways. The high biomass and top-predator status of some crab species suggests the potential for cascading eVects on organisms lower in the food web.

Winning the biodiversity arms race among freshwater gastropods: competition and coexistence through shell variability and predator avoidance

“…For example, as discussed below, the endemic thiarid gastropods in Lake Tanganyika are an exceptional radiation of species that could likely have resulted from interactions with evolving cichlid and crab predators and with changes in water levels. Several studies document changes in gastropod assemblages that provide insights to how water-level changes likely alter predator-prey interactions and gastropod distributions (Michel, 2000;West & Michel, 2000;Van Damme & Pickford, 2003;Marijnissen et al, 2009).…”

“…Freshwater crabs, crayfish, prawns, and fishes are effective snail predators in many types of freshwater habitats and can exert top-down control on highly diverse gastropod assemblages (e.g., West & Cohen, 1994von Rintelen et al, 2004;Schubart & Ng, 2008;Marijnissen et al, 2009). Freshwater decapod crustaceans in particular consume a wide range of foods (Hanson et al, 1990;Nyström et al, 1996;Parkyn et al, 2001;Zimmerman & Covich, 2003) but many species are especially well adapted to chip and crush gastropod shells (Gherardi et al, 1989;Alexander & Covich, 1991a;Snyder & Evans, 2006;Brown & Lydeard, 2010;Covich et al, 2010;Hobbs & Lodge, 2010).…”

“…These endemic gecarcinucid crabs influenced the diversity of endemic hydrobioid gastropods (Haase & Bouchet, 2006) and pachychilid gastropods (von Rintelen et al, 2004;Glaubrecht & von Rintelen, 2008) in these lakes and adjoining rivers. Another well-studied example is the evolution of 10 species of crabs such as Platythelphusa armata in the Potamonautidae (West & Cohen, 1994;Van Damme & Pickford, 2003;Marijnissen et al, 2009) in Lake Tanganyika is well documented. This assemblage illustrates how species of crabs have evolved in lakes and rivers where[90 species of gastropods have also undergone extensive evolution.…”

Predation on a Cave Fish by the Freshwater Crab Avotrichodactylus Bidens (Bott, 1969) (Brachyura, Trichodactylidae) in a Mexican Sulfur Cave

“…Their biomass in tropical streams can make up 58-94% of the total benthic macroinvertebrate biomass (Abdallah et al, 2004;Dobson et al, 2007). Freshwater crabs take a central position in tropical aquatic food webs: they act as prey for vertebrates, as primary and secondary consumers, and as detritivores (Williams, 1961;Gherardi et al, 1987;Dobson et al, 2002;Marijnissen et al, 2009). Furthermore, many species of freshwater crabs have an amphibious mode of life, thus linking terrestrial and aquatic energy flows (Gherardi et al, 1989).…”

A freshwater biodiversity hotspot under pressure – assessing threats and identifying conservation needs for ancient Lake Ohrid

“…As a consequence, benthic communities are altered and eventually food webs become interrupted (Marijnissen et al, 2009). Highly adapted and specialized species often cannot cope with these sometimes rapid environmental changes (Noges et al, 2008).…”