Intertidal mudflats in Suriname are formed from fine sediments that travel northward on the Guiana current from the Amazon River and are part of the longest muddy coastline in the world. Crustaceans living in these mudflats serve as key prey items for millions of migratory shorebirds that breed in the Canadian Arctic and travel to Suriname to overwinter, which has led to the designation of mudflats in Suriname as Western Hemispheric Shorebird Reserves. We studied the abundance, size distributions, and reproductive biology of two species of tanaid crustaceans, Halmyrapseudes spaansi and Discapseudes surinamensis, living within three intertidal mudflats in Suriname. Tanaids were collected by removing 13-15 cores of mud from across each site (cores were 86.5 cm-2 in diameter and taken to a depth of 10 cm). Cores were sieved in seawater (500-µm wire mesh) and the size, sex, and reproductive status (presence of secondary sexual characteristics; number and developmental stages of embryos) of each tanaid were assessed.
Results/Conclusions
Tanaids of Halmyrapseudes spaansi were very abundant at all sites (often >10,000 individuals m-2 of mud), which was unexpected given that prior studies reported this species as uncommon or absent from mudflats in Suriname. Tanaids of a larger species, Discapseudes surinamensis, were found in samples from all sites, but densities were typically more than 90% lower (<1000 m-2) than those reported from collections made 30–40 years earlier. Although prior studies likely underestimated densities of tanaids, differences in species compositions and densities could not be explained by differences in sampling techniques among studies. Sex ratios of both species were female-biased (approximately two females per male) and larger females were more likely to carry broods as well as larger broods. Females of both species were less likely to be observed carrying broods than in previous studies, although brood sizes of females that carried embryos were larger. Female reproduction was relatively synchronous in that females at each site tended to carry broods in similar stages of development. Changes in the abundance and species composition of tanaid prey might negatively impact shorebirds that rely on these animals to fuel their migration from overwintering grounds in Suriname to breeding sites in North America.
