Ostracods response to environmental anthropogenic disruption in a neotropical karstic lake in southern Mexico

Abstract

Ostracods are highly sensitive to environmental changes and represent a powerful tool to assess anthropogenic impact. In this work we present ostracod and ephippium records of Lake San Lorenzo sediments dating from 1956 to 2013. Diatom and geochemical data presented by Caballero et al. (2022) are also considered for the discussion. The ostracod assemblage consists of Darwinula stevensoni, Cypridopsis okeechobei, Cytheridella ilosvayi and two unidentified species. We suggest that one of them could be a variant of C. okeechobei with different ornamentation developed as a response of increasing salinity caused by anthropogenic catchment disruption around 1981. The second unidentified species (Unknown 2) could belong to the Subfamily Cypridopsinae Kaufmann, 1900. This species rapidly adapted to the new environmental conditions of enhanced salinity, high nutrients level and variable oxygen, whereas the other ostracods were absent in the sediments dating from 1982 to 1992. Overall, D. stevensoni, C. okeechobei and C. ilosvayi are benthic species that occur in shallow waters or littoral zones with rich vegetation. However, we suggest C. ilosvayi was the most sensitive to oxygen variations as it is only present in the record in 1978. The lack of ostracod preservation in the sedimentary record, especially during 1995–2013 could be result of anoxic lake bottom conditions or dissolution caused by high organic matter content during periods of anthropogenic catchment disturbance, from 1970–1985 and from 1990–2000. Finally, we suggest analysis of C. okeechobei in natural populations and laboratory studies need to be assessed to determine if this species develops ornamentation changes when salinity conditions increase. Moreover, analysis and description of soft parts and live specimens of Unknown 2 will be necessary to determine this species.