Reproductive phenology of coralline algae Porolithon antillarum and Lithophyllum sp. under seasonal upwelling conditions, Colombian Caribbean

Crustose coralline algae are a group of calcified algae that has an important ecological role in coral reefs, such as cementation and stabilization of the reef framework, as well as providing habitat and food for different marine associates. Among the common genera, Lithophyllum and Porolithon (Corallinales) are conspicuous components of the Santa Marta reef communities in the Colombian Caribbean. From December to April, this area is influenced by seasonal trade winds, a phenomenon that is related to the upwelling of subsurface waters that causes a decrease in temperature from ∼29 °C to ∼22 °C and pH from ∼ 8.5 to ∼8.0. The aim of this study was to evaluate the effect of upwelling and non-upwelling (2017, 2018, and 2021) on the reproductive phenology of Lithophyllum sp. and Porolithon antillarum based on counts of superficial conceptacles per cm² and a determination of the reproductive stages of the algae collected in Tayrona National Natural Park and Punta Venado, Santa Marta. The algae presented the highest number of mature conceptacles during the upwelling period for P. antillarum and Lithophyllum sp. (46 and 27 conceptacles cm², respectively). Moreover, the tetrasporangial stage was the most frequent in all the thalli, thus indicating the predominance of this phase in the reproductive cycle of the algae studied. These results are important as they indicate the influence of seasonality on the reproductive stages of CCA and bring the need to do more research into the influence of the environment on the physiological mechanisms that determine the changes in the life cycle of these algae.