Predictable Habitat Associations of Four Crab Species Across the Low Intertidal Landscape of a Tropical Estuary over Time

Abstract

To address the increasing threats from urbanization and climate change, an improved understanding of ecosystem processes at large, estuary-wide scales is required. Intertidal crabs contribute to estuarine functioning via trophic interactions and ecosystem engineering. Previous studies on crab spatial distribution patterns have focused on site- or transect-specific scales and consequently do not address spatial distribution patterns relative to the full environmental landscape within estuaries. In the present study, predictive habitat modeling using data collected with high replication photographic sampling revealed distinct habitat associations for four crab species across the low intertidal landscape (between mean low tide at spring and the edge of the mangrove forest) of Stuart Creek, northeast Australia (19° 17′ S, 146° 50′ E). Seasonal sampling was conducted on 10 dates from April 2009 to July 2011. Uca coarctata occurred nearly everywhere but achieved highest abundance on intertidal banks with pneumatophores and at least some canopy overhang. Uca seismella occurred in habitats with low intertidal vegetation and almost no structural complexity. By contrast, Metopograpsus frontalis was associated with habitats with at least 4 % of the substratum containing structure, and Metopograpsus latifrons with habitats with at least 22 % of the substratum containing structure. While overlap occurred between species, a taxon-specific separation of Metopograpsus spp.-dominated habitats and Uca spp.-dominated habitats was related to the availability of structural complexity, suggesting that it is a niche-defining factor. Sensitivity tests indicated high predictability of habitat associations among pre-dry, dry, pre-wet, and wet seasons from April 2009 to July 2011, suggesting high stability in spatial distribution patterns of intertidal crabs. Results provide a scientific basis for increased understanding of the spatial distribution patterns of intertidal crabs at landscape scales.