Interference competition as a key determinant for spatial distribution of mangrove crabs

Abstract

BackgroundThe spatial distribution of mangrove crabs has been commonly associated with tree zonation and abiotic factors such as ground temperature and soil granulometry. Conversely, no studies were designed to investigate the role of competition for resources and predation in shaping crab distribution in mangroves, despite these biotic factors are recognised as key determinants for spatial patterns observed in the communities colonising rocky and sandy intertidal habitats.We studied floral and faunal assemblages in two zones of a Sri Lankan mangrove, a man-made upper intertidal level and a natural eulittoral, mid-shore one. Leaf choice experiments were designed to study both feeding rate and intra and inter-specific interactions for food of sesarmid crabs in the two habitats in order to better understand crab spatial distribution.ResultsThe two intertidal belts differed in terms of floral composition and crab species abundance. The eulittoral zone was strongly dominated by Neosarmatium smithi, while within the elevated littoral fringe four sesarmids (N. smithi, N. asiaticum, N. malabaricum and Muradium tetragonum) were more evenly distributed. At both levels, all sesarmids showed to collect significantly more Bruguiera spp. and Rhizophora apiculata leaves than Excoecaria agallocha ones. There was no temporal segregation in feeding activity among the four species, resulting in a high interference competition for leaves. Regardless of the habitat, N. smithi was always successful in winning inter-specific fights.ConclusionsOur results showed that the elevated littoral fringe was more crowded with crabs, but was less favourable in terms of food availability and environmental conditions. The dominance of N. smithi in gathering mangrove leaves suggests that this species may segregate the other sesarmids into less favourable habitats. The present data strongly suggest for the first time that interference competition for food can contribute to shape mangrove crab spatial distribution.

Assessing the relationship between macro-faunal burrowing activity and mudflat geomorphology from UAV-based Structure-from-Motion photogrammetry

“…Such spatial heterogeneity occurs naturally in ecosystems and is maintained by spatio-temporal variations in a range of physical conditions in areas subjected to the impacts of benthic activity. Crab communities and their bioturbation intensity, for instance, vary as a function of tidal range, vegetation structure, microhabitat, and seasonality (Aschenbroich et al, 2016;Cannicci et al, 2018;Escapa et al, 2007;Li et al, 2018). The spatial scales of patchiness in the variables being measured are often not known before sampling.…”

Crab‐driven processing does not explain leaf litter‐deposition in mangrove crab burrows

“…In fact, Steinke et al (1993) observed that, if two crabs grab the same leaf when it falls, a fight will usually ensue with the stronger individual eventually pulling the leaf out of the other's grasp and retreating to its burrow. More recently, Cannicci et al (2018) proposed that interference competition for food may be a major force shaping the spatial distribution of sesarmids in the mangroves of Sri Lanka. Thus far, however, rigorous testing of hypothesis (i) or (ii) has not been undertaken.…”

Interrelationships among ecological factors of brachyuran crabs, trees and soil in mangrove community assemblage in Northeast Brazil

“…Goniopsis is a dominant species in Neotropical mangroves, and other crabs use burrows to protect themselves from their predatory habits (McNaughton and Wolf 1970, Ferreira et al 2013, Cannicci et al 2018). This crab is observed gnawing on the cortexes of red mangrove roots, which induces their sprouting (Calderon and Echeverri 1997).…”