A temperate gorgonian coral garden in the shallow sublittoral off Buenos Aires, Argentina

Abstract

This study explores the previously unknown Banco Patria, a rocky reef located near Mar del Plata, Argentina. The reef stands out for its unique composition – coquina, a sedimentary rock formed from shells and sand – in contrast to the neighboring quartzite outcrops. SCUBA dives (26–32 m depth) were conducted to characterize the reef's topography, geology, and biological community. This reef is dominated by the unbranched, azooxanthellate soft coral Tripalea clavaria, reaching up to 240 colonies per square meter. This represents the first record of a coral garden in shallow waters of the Argentinean Continental Shelf (Buenos Aires). Tripalea clavaria densities are considerably lower in shallower areas and on quartzite outcrops. The Banco Patria reef community is characterized by a high abundance of filter feeders, including gorgonian, hydroids, bryozoans, and sponges. They play a crucial role in nutrient cycling and provide food for other members of the community. Notably, blue mussels, ubiquitous in neighboring reefs, are entirely absent at this reef. The complex topography of Banco Patria provides a haven for a diverse assemblage of fish species, which utilize the reef's intricate structure for feeding, refuge, and reproduction, including typical reef fish such as the Brazilian sandperch, the Patagonian grouper, and the cocherito and big transient school of silver and red porgy. The reef's unique composition, substrate characteristics, and distinctive community highlight its ecological significance. Monitoring programs, educational initiatives, and government action are crucial to safeguarding this unique and potentially vulnerable reef ecosystem.