Seasonal changes in the subtidal benthic macrofauna of a mangrove coast in northern Brazil

Abstract

Melo, K.R., Tagliaro, C.H. and, Beasley, C.R., 2013.Seasonal changes in the subtidal benthic macrofauna of a mangrove coastMangrove coasts in northern Brazil are subject to seasonal discharges of freshwater input from rivers and terrestrial runoff. However, little is known about the effects of freshwater discharge on the subtidal benthos in the region. Thus, three sites, each representing a different level of seasonal discharge, Canela island (low), Ajuruteua beach (medium), and the Caeté Bay (high) were sampled in the dry (October) and wet (April/May) seasons of 2007 and 2008, respectively. Sampling was carried out using a Petersen grab and a bottom dredge (total n=74). Additional replicas (n=12) were obtained by grab for sediment analyses. Salinity and turbidity of the bottom waters, and percentage of silt/clay in the sediment were also measured. Benthic macrofauna and environmental data were analyzed using uni- and multivariate techniques. A total of 661 individuals were distributed among 47 taxa of which polychaetes and crustaceans dominated at all three sites. No significant differences in macrofaunal abundance were found among sites and dates. At all sites, in the wet season, the number of taxa was low and dominance was high, especially in the Caeté Bay. The polychaete Nephtys fluviatilis only occurred in the Caeté Bay in the wet season, and yet was the dominant taxon (22.7% of total abundance). The Ajuruteua beach and Canela island samples were composed of typically marine taxa. The polychaete Armandia sp., the gastropod Olivella minuta, mysiid and phoxocephalid crustaceans and the echinoderm family Mellitidae were most abundant in the dry season at Canela island. Salinity was the most important environmental factor associated with high numbers of taxa in the dry season. Silt and turbidity were associated with low numbers of taxa in the wet season. In conclusion, the subtidal benthic macrofauna at Canela island, Ajuruteua beach and the Caeté Bay is mainly composed of polychaetes and crustaceans. The higher freshwater discharge in the wet season, resulting in lower salinity, higher percentage silt and greater turbidity, is associated with lower abundance, fewer taxa and a different faunal composition at Canela and Ajuruteua, and strong dominance of an oligohaline polychaete in the Caeté Bay