Distribution, abundance and ecological requirements of the benthic phase of Munida gregaria (Anomura; Munididae) in the Puyuhuapi Fjord (Chilean Patagonia)

The squat lobster Munida gregaria is considered a key species within food webs of sub-Antarctic ecosystems of South America, and represents a fundamental link between detritus and higher-level predators. Although ecological aspects of its lengthy pelagic phase have been well described, those of the benthic stage remain poorly understood, particularly in Chilean Patagonia where information on the presence of benthic phases of M. gregaria has been scarce. The present paper aims to improve our knowledge of this important species, analysing benthic distribution, abundance and ecological requirements of the benthic phase of M. gregaria in the Puyuhuapi and Jacaf fjords in the Aysen Region of Chilean Patagonia. An extensive SCUBA diving survey, carried out between 2014 and 2019, allowed us to explore and document the soft seafloors inside these fjords. These benthic surveys conducted photographic transects between depths of 5 and 20 m to enumerate populations of M. gregaria and to measure sizes of individuals. The study revealed the presence of large aggregations of M. gregaria, with densities up to 4 times higher than previously reported maxima for South America. Munida gregaria appeared to be unable to live at the shallow depths of the brackish surface layer typical of fjords, though paradoxically, its presence on the seabed was linked to river outflow, and probably related to supply of organic matter. Chilean fjords are currently facing a number of challenges, particularly from climate change and other more direct anthropogenic impacts, and the key role of M. gregaria in these fjords should be considered in future monitoring activities. More particularly, the extremely high abundance of M. gregaria in Puyuhuapi Fjord should be considered in any rigorous protection measures planned for the fjord.