ABSTRACT In warm monomictic volcanic lakes, annual cycles of water column stratification and mixing fundamentally regulate ecological processes by modulating oxygen and nutrient availability and heat distribution. However, their influence on the complex biological interactions between microbialites and freshwater sponges remains poorly understood. These interactions create a modern model of primordial benthic ecosystems. To elucidate the mechanisms sustaining this association in a warm monomictic lake, we assessed how environmental phases captured over a 10‐month period affected (i) the dissolved inorganic carbon system that regulates carbonate precipitation and microbialite growth and (ii) the population and reproductive dynamics of the freshwater sponge Ephydatia sp. Over a 10‐month period, we monitored the physicochemical dynamics of the water column, the characteristics of the microbialite reef, and the population dynamics of Ephydatia sp. The lake exhibited strong thermal stratification most of the year, punctuated by a brief winter mixing event. This physical regime was associated with pronounced fluctuations in oxygen concentrations and carbon cycling and sustained a microbialite growth rate of ≈0.0405 cm·year −1 by creating favourable conditions for microbialite productivity and carbonate deposition. Ephydatia sp. displayed a marked dependence on microbialites as its primary substrate and exhibited rapid population expansion and sexual reproduction following the winter mixing phase, a period characterized by increased nutrient concentrations and temperature. These dynamics reinforce the role of microbialites as ecosystem engineers and highlight the contribution of Ephydatia sp. to trophic complexity through the support of diverse invertebrate infauna.
Nava et al. (Mon,) studied this question.