Distribution of Atlantidae species (Gastropoda: Pterotracheoidea) during an El Niño event in the Southern California Current System (summer-fall 2015)

Atlantids are holoplanktonic gastropods present in tropical to sub-polar waters, and have gained an increasing interest due to their potential use as biological indicators of climate change and ocean acidification. However, there is a lack of information regarding their distribution for large areas of some oceans, particularly in the California Current System (CCS), which has been used as a model for many acidification studies and where intense warming events occur. The distribution patterns of 18 species of Atlantidae off the west coast of the Baja California Peninsula, Mexico, representing 90% of the atlantid species registered for the Pacific Ocean, were analyzed during a period of warm anomalies associated with the El Niño of 2015-2016 and the 2014-2016 marine heat wave (MHW). The species distribution showed 3 groups: 2 in the north (coastal and oceanic) and 1 in the south. The limit of distribution between these 3 groups was found in the vicinity of Punta Eugenia (PE). The southernmost community of atlantids was characterized by tropical and subtropical species that were transported northward due to coastal advection of warm waters associated with the El Niño of 2015-2016. North of PE, the warm-water affinity oceanic species Atlanta rosea and A. fragilis were found, evidencing the entrance of water from the Central Pacific related to MHW which affected the oceanic region off the coast of PE. The response of the distribution patterns proves that atlantids can be used as biological indicators, as they reflect the effect of environmental anomalies in the southern CCS.