Physical-Biological Variability Analysis of a Pacific Coast Lagoon (Ojo de Liebre) Through a Hydrodynamic-NPZD Coupled Numerical Ocean Model

Gabriela Reséndiz Colorado and David Rivas, CICESE, Biological Oceanography, Ensenada, Baja California, BJ, Mexico
Ojo de Liebre lagoon (LOL, by its acronym in spanish), located at the Pacific Coast roughly in the middle of Baja California Peninsula and connected with Vizcaíno Bay, is of paramount ecological importance mainly because it is a refuge zone for the gray whale during winter. In this season, gray whales arrive in this lagoon to mate and to give birth their calves, therefore this lagoon is a national protected area and it is considered as World Heritage by the UNESCO. In spite of these aspects, its dynamics is still poorly understood, which makes difficult its management and long-term protection. In order to fill knowledge gaps about LOL's physical and biogeochemical variability, a high-resolution hydrodynamic model, coupled to a Nitrate-Phytoplankton-Zooplankton-Detritus (NPZD) ecological model, was implemented. The preliminary analysis of a multi-year simulation shows vigorous tidal-driven water exchanges across the lagoon's mouth, while the lagoon's interior has a weaker circulation. Combination of the circulation and the bathymetry variations produces marked horizontal gradients in temperature and salinity along the lagoon, where these variables increase 2 C and 3 psu to the interior, respectively. Moderate levels of dissolved nitrogen (nitrate) are available throughout the year in all the lagoon, with its maximum in June (0.2 mmolN m) and its minimum in September (0.01 mmolN m). On the other hand, phytoplankton is present mostly in the lagoon’s mouth, clearly influenced by the exchanges with shelf waters; in the lagoon’s interior the phytoplankton levels are generally lower with small increments in the central zone from August to September. These results are a first approach to the understanding of the main processes that control the ecosystem dynamics, specifically the lower trophic levels, as a first step to understand the dynamics of the species that live and arrive in the lagoon.