Marine litter is a notable challenge to crabs in highly impacted mangrove areas: a case study in Guanabara Bay, SE Brazil

Abstract

Mangroves represent a particularly vulnerable coastal ecosystem to the problem of marine litter. However, research addressing the impact of macroscopic litter on mangrove crabs remains limited. The aim of this study was to characterize diversity, abundance, and size of the semi-terrestrial crabs in a mangrove swamp heavily affected by macroscopic marine litter, in Southeastern Brazil. It was also aimed at verifying any potential correlations between crab parameters and the percentage of substrate covered by marine litter. Quadrats of 3.0 m × 3.0 m were used in three subzones of the intertidal zone (lower, middle, and transition—between upper intertidal and supralittoral). The litter was characterized after collection, and marine litter coverage was assessed using 1.0 m × 1.0 m photographs, which were analyzed using CPCe software. The fiddler crabs were analyzed by catch and release and the crab Ucides cordatus by examination and counting of burrows. The abundance of marine litter ranged from 69.6 to 120.3 items.m −2 , and the marine litter coverage varied between 26.0 and 100.0%. The diversity and abundance of crab species was found to be low (0.32 to 1.46 bits; 0.1 to 2.0 ind.m −2 ). The marine litter coverage had a significant negative effect on crab abundance ( R = −0.63; p = 0.03). In addition, a strong and significant influence of marine litter coverage on the size of both U. cordatus (Pearson, R = 0.83; p = 0.02) and Minuca spp. (only females; Pearson, R = 0.80; p < 0.001) was observed.

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