Assessing the role of tidal cycle, waves, and wind as drivers of surf zone zooplankton on a temperate sandy beach

Abstract

The surf zone is strongly affected by tides, waves, and winds. However, there are still a lack of knowledge about the response of the zooplankton community to these physical factors in the surf area, with a particular emphasis on tidal effects. The aim of this study was to conduct a preliminary assessment of two distinct tidal cycles, encompassing fluctuations in on-offshore currents, waves, and wind and their influence on the surf zooplankton community of Pehuen Co (PC) sandy beach, Argentina. The study involved field sampling at a single station in the surf zone on September 4th, 2018, and May 20th, 2019. The sampling covered four tidal phases at 3-hour intervals, when water and zooplankton samples were collected for analysis. Environmental variables, such as current velocities, water level, and wind data, among others, were also registered. The results indicated that the abundance of surf zooplankton was significantly influenced by physical forces, resulting in distinct impacts. During the Sept 2018 tidal cycle (calm conditions), an on-offshore current emerged as the primary driving force, resulting in the highest abundance of zooplankton being observed at low tide. In contrast, during the May 2019 tidal cycle (southern winds), strong winds intensified the offshore current velocities and wave height, affecting the zooplankton abundance. High velocities of on-offshore currents corresponded to lower abundance of zooplankton at low tide. This situation introduced an extra physical force -the wind- playing a significant role in restructuring the dynamic of the zooplankton community. The preliminary analysis suggests that the relationship between environmental and biological data is complex and varies depending on the physical factors involved. Notably, in rough conditions, south winds can restructure zooplankton dynamics, influenced by strong winds. This work emphasizes the importance of the surf zone waters of sandy beaches and are useful for future research or monitoring programmes of similar high-energy ecosystems.