Species richness of marine Bryozoa in the continental shelf and slope off Argentina (south‐west Atlantic)

Abstract

A total of 246 marine bryozoan species was recorded within an area of the southwest Atlantic between 35° and 56°S, and between the coast of Argentina and 50°W. The distribution pattern of benthic stations surveyed during the most important cruises in the area shows that the sampling effort has been biased towards southern shelf areas off Santa Cruz and Tierra del Fuego, as well as around the Malvinas (Falkland) islands. The littoral zone, Patagonian gulfs and the continental shelf off Chubut, Río Negro and Buenos Aires state received less attention, and should be surveyed more intensively in the future. Only 2% of the species can be regarded as non-indigenous, all of them inhabiting biofouling communities in harbour environments. With the exception of some thoroughly surveyed localities, the number of species recorded for different areas of the coast, shelf and slope is estimated to be just a small fraction of the actual number of species present. A distinct diversity gradient was found, with species-rich stations located only in the southern shelf. Highest diversity occurred in shelf areas dominated by coarse sediments, and along a high-productivity shelf-break front. A remarkable decrease in species richness was found in inner and middle shelf areas off Chubut, Río Negro and Buenos Aires state. This pattern may be related to the Pacific origin of the Magellanic fauna, since the diversity of bryozoans is higher in the Pacific than in the Atlantic Ocean. The trend of species richness is, however, overemphasized by the fact that the least diverse faunistic assemblage occurs in areas where surveys have been relatively less frequent. An up-todate checklist of species recorded for the study area is included.

Macrofaunal assemblages associated with coralline turf: species turnover and changes in structure at different spatial scales

“…Factors operating at the biogeographic scale, such as a smaller species pool at lower than at higher latitudes off Argentina may be responsible for this pattern. Biogeographic analyses of several macrobenthic groups in the southwestern Atlantic have shown that species richness is higher in the cold-temperate Magellan region than in warm-temperate waters at lower latitudes (Bastida et al 1992, López Gappa 2000, López Gappa et al 2006. Similarly, a review of Chilean benthic nearshore ecosystems suggested that there is a biodiversity hotspot south of 42°S in the southeastern Pacific (Fernández et al 2000, Valdovinos et al 2003.…”

Species richness and distribution patterns of echinoderms in the southwestern Atlantic Ocean (34-56°S)

“…The squares were numbered from west to east and from north to south, following a procedure applied for the study of other groups of benthic invertebrates (see López Gappa 2000, López Gappa and Landoni 2005, Montiel et al 2005, López Gappa et al 2006and Genzano et al 2009). …”

Bryozoan-dominated benthos of Otago shelf, New Zealand: its associated fauna, environmental setting and anthropogenic threats

“…The heterogeneous, poorly sorted facies of the midand outer-shelf were noted by Probert & Wilson (1984) as a possible explanation for the species-rich infaunal assemblages of Otago shelf, given that poorly sorted sediments tend to support richer faunal assemblages (Gray 1974). The richness of ostracod assemblages on Otago shelf was also positively correlated with sediment coarseness and heterogeneity (Swanson 1979), while for the New Zealand region, Rowden et al (2004) found a correlation between heterogeneous bryozoan/molluscan-derived sediments and the diversity of all bryozoans (see also Gappa 2000).…”