Modelling environmental drivers of population dynamics in the salp Thalia democratica from in situ, short-term observations

Abstract

Blooms of the salp Thalia democratica are a recurrent feature in many coastal areas where they have significant ecological and societal impacts. To understand the environmental drivers of those blooms in the Catalan Sea, we conducted 8 sampling surveys of T. democratica populations at contrasting seasonal, temperature and chlorophyll conditions. During each survey we used a drifting buoy to track a salp population which we sampled every 30 minutes during a period of three hours, and determined short term variations in the abundances of the different stages. We built a set of different stage-classified population matrix models, each one representing different assumptions about the influence of temperature and chlorophyll on the different stages. The best model was one where only the females were affected by temperature, while matrix elements for the other stages were fixed. Elasticity analysis indicates that females drive the population dynamics through arrested reproduction at high temperatures. Whether this is a direct influence of temperature, or an indirect effect reflecting low food availability remains to be solved. In contrast to previous ideas, our results suggest that it is the female, and not the asexual oozooid, that is responsible for latency periods in salp populations