Cold, Warm, Temperate and Brackish: Bivalve Biodiversity in a Complex Oceanographic Scenario (Uruguay, Southwestern Atlantic)*

Abstract

The temperate zone of the southwestern Atlantic Ocean (23-42°S), which includes the Patagonian Shelf Large Marine Ecosystem and the Subtropical Convergence Zone, is one of the most productive areas of the Southern Hemisphere. Key features of this region are a wide continental shelf, the convergence of cold and warm currents, and continental freshwater input of the La Plata River. The Uruguayan marine and estuarine waters are at the core of this zone. The marine and estuarine bivalve fauna of Uruguay has received good attention since the publication of the Voyage of Alcide d'Orbigny (1834)(1835)(1836)(1837)(1838)(1839)(1840)(1841)(1842)(1843)(1844)(1845)(1846). Here we provide an overview of taxonomic, faunistic and b iogeographic issues, identifying knowledge gaps and highlighting priorities for future research. The main threats for that fauna are discussed, with emphasis on species of current or potential socioeconomic interest. Of the 231 species reported from the area, only four species are strictly estuarine: Erodona mactroides Bosc, 1801, Tagelus plebeius (Lightfoot, 1786), Brachidontes darwinianus (d'Orbigny, 1842) and Mytella charruana (d'Orbigny, 1842). All of these have large biomasses, as is also the case for the marine eurihaline Mactra isabelleana d'Orbigny, 1846. A total of 112 deep-sea species (i.e., living deeper than 200 m) are recorded for the region, including almost every known group occurring elsewhere in deep-sea basins, with the exception of sunken wood associated species. Of these, 38 have been recorded only from the Argentine Basin. Some new records are preliminarily reported and discussed, including

Ascidiacea (Chordata, Tunicata) from Uruguay (SW Atlantic): checklist and zoogeographic considerations

“…This group consists of 11 species (Table 1), some of them occurring deeper than their Sub-Antarctic areas (e.g. Kott 1969;Monniot C. & Monniot F. 1983;Carranza et al 2007;2008;Scarabino et al 2016). Monniot C. & Monniot F. (1978) and Monniot F. (1979) had already noted the affinity of the Argentine Basin deep-sea ascidian fauna (mostly based on the records here listed) with the Southern Ocean.…”

“…At least one species may be synonymous with an Antarctic one (Styela flava) and several others described by Herdman are actually poorly described. Similarly, a high percentage of endemic deep-sea protobranch bivalves have already been reported from off Río de La Plata by Allen & Sanders (1997), although this has to be additionally assessed (Scarabino et al 2016). Deep-sea species having wide distributions.…”

“…A complex oceanographic system develops in the area, involving the confluence of warm and cold marine currents and the freshwater input of La Plata River. A general oceanographic, geomorphological and sedimentological outline of the zone can be found in Scarabino et al (2016) and Hanebuth et al (2018).…”

Vacant Bivalve Boreholes Increase Invertebrate Species Richness in a Physically Harsh, Low Intertidal Platform

“…The most prevalent species in the unengineered habitat were the mussel Brachidontes rodriguezii, the barnacle Balanus glandula, and the chiton Plaxiphora aurata (15,9, and 5% of samples, respectively; Figure 3). B. rodriguezii was also the most prevalent species in Petricola-engineered patches (78% of samples), followed by the polychaetes Lumbrineris sp., Syllis gracilis, and S. prolixa (26,23, and 14% of samples, respectively; Figure 3). Nine of the species sampled in Petricola-engineered patches were found only one time (in just one quadrat) during the sampled period.…”

“…Here we evaluate if the microhabitats created by a physical ecosystem engineer-the rock-boring bivalve, Petricola dactylus-positively contribute to species richness in the physically harsh, low intertidal zone of a southwestern Atlantic rocky shore. Petricola dactylus is a mechanical borer that inhabits soft rock in low intertidal and subtidal habitats of the southwestern Atlantic and southeastern Pacific, from Uruguay to Southern Chile [21][22][23]. The boreholes left vacant by dead P. dactylus reach high densities at our study site (often more than 600 boreholes m −2 ) and are prominent…”