The Influence of Summer Cyclonic Circulation in the Southern Gulf of California on Planktonic Copepod Communities

This study evaluated how the summer circulation pattern in the Southern Gulf of California influences copepod communities. The evaluation was based on hydrographic data and zooplankton samples collected during a multidisciplinary research cruise conducted in June and July of 2019. The results revealed the presence of a cyclonic circulation with a diameter of approximately 100 km, located near the entrance of the Gulf, affecting the upper 200 m layer. A total of 30 copepod species were identified, including 20 from the order Calanoida and 10 from Cyclopoida. The most abundant Calanoida species were <i>Canthocalanus pauper</i>, <i>Clausocalanus furcatus</i>, and <i>Subeucalanus subcrassus</i>, with respective densities of 2316.80, 1593.60, and 1584.64 ind m⁻³. The most abundant Cyclopoida species were <i>Oithona setigera</i>, <i>Dioithona rigida</i>, and <i>Oncaea venusta</i>, which had densities of 963.44, 290.56, and 235.52 ind m⁻³, respectively. The horizontal distribution of these species showed variations influenced by the cyclonic circulation. Specifically, low abundance values were observed at the center of cyclonic circulation, while higher values were found at its periphery. This pattern was consistent among the dominant species, indicating that they do not benefit from the cold subsurface waters induced by circulation. In fact, the distribution of some species was higher in a band of warm water located in the eastern portion of the study area. Overall, our findings shed light on how the summer cyclonic circulation in the Southern Gulf of California affects the copepod community, an aspect that has not been previously explored. This research enhances our understanding of the processes influencing this group of organisms in a highly dynamic environment.