Changes of Benthic Macrofaunal Composition on a Tidal Flat of Río Gallegos Estuary, Argentina

Abstract

This work analyzed the variation in composition and abundance of benthic assemblages in an intertidal environment of the Rio Gallegos estuary, Argentina (51°35′ S - 69° 01′ W). The macrofauna was sampled in a tidal flat adjacent to the city in late summer of 2006 and 2013 (March). In total 27 macrofauna taxa were identified; the most abundant species were Darina solenoides (44%) in 2006 and Fabricinuda sp. (89%) in 2013. Biogenic structures composed of aggregates of polychaete (Fabricinuda sp.) tubes and sediment were observed for the first time in December 2006; they are spherical or of irregular shape, 1 to 3 m2 in area, and up to 50 cm in height. In 2013 benthic composition was compared between biogenic aggregates (“patch”) and the area outside them (“non-patch”). Species richness and total abundance of individuals were higher in the patch. The associated benthos was different; Fabricinuda sp. was dominant in the patch (107,780.7 indiv.m-2, SD = 44,772.6), and Kinbergonuphis dorsalis (2139 indiv.m-2, SD = 840) and Notocirrus lorum (1830 indiv.m-2, SD = 516.4) in the non-patch. In 2013, four taxa that were not found in 2006 were recorded only in the patch samples, two bivalves (Sphenia hatcheri and Malletia cumingii) and two polychaetes (Fabricinuda sp. and Ophioglycera eximia). Polychaete aggregations have produced changes in number and abundance of benthic species at the lowest level of the tidal flat.