HOLO- AND MEROPLANKTON COMMUNITIES IN SURF ZONE WATERS OF A SOUTHWESTERN ATLANTIC SANDY BEACH (MONTE HERMOSO, ARGENTINA)

MARIA CLARA MENENDEZ; VITALE, ALEJANDRO JOSÉ; DELGADO, ANA LAURA

Simposio; VIII International Symposium on Marine Sciences 2022 (ISMS); 2022

In this study, we aimed to answer the following questions: (i) which taxa makeup and can be considered as descriptors within surf zone holo- and meroplankton in Monte Hermoso sandy beach, Argentina?, (ii) what environmental factors control their seasonal variations?, and (iii) is it possible to define a typical surf zooplankton community for this coastal ecosystem?. Zooplankton samples were collected at one fixed station twice per season during two annual cycles (2009-10, 2015-16), using a 300 µm mesh size conical net. A set of environmental variables were measured in situ and water samples were collected to determine chlorophyll and suspended sediments concentrations. Holoplankton was very abundant (13.52-11070.4 ind. m-3) and showed a strong seasonality, mainly related to the specific pattern of the two most abundant species: the copepods Acartia tonsa (>late summer-spring) and Paracalanus parvus (>winter). This community was affected not only by changes in water temperature and salinity but also by variations in the velocity of littoral currents, which evidenced that hydrodynamic forces were more significant in a short-term time scale than seasonal. Meroplankton abundances (1.3-48.05 ind. m-3) were significantly lower than those registered for the holoplankton. Medusae and larvae of Bivalvia and Grapsidae mainly dominated this community. This fraction also exhibited a seasonal pattern (>abundances in summer), mainly guided by the temporal changes in water temperature. The present results showed that in the surf waters, estuarine and neritic species coexists, evidencing the connection between near coastal ecosystems. These species can be recognized as residents or non-residents species, according to the description proposed by McLachlan and Defeo (2018). The abundances of the main surf zone zooplanktonic taxa were high and constant, emphasizing not only the importance of these waters as regular habitats (well-established communities) rather than transient ones but also the ecological role of coastal waters in planktonic life.