When descriptive ecology meets physiology: a study in a South Atlantic rhodolith bed

Abstract

This study presents two years of characterization of a warm temperate rhodolith bed in order to analyse how certain environmental changes influence the community ecology. The biomass of rhodoliths and associated species were analysed during this period and in situ experiments were conducted to evaluate the primary production, calcification and respiration of the dominant species of rhodoliths and epiphytes. The highest total biomass of rhodoliths occurred during austral winter. Lithothamnion crispatum was the most abundant rhodolith species in austral summer. Epiphytic macroalgae occurred only in January 2015, with Padina gymnospora being the most abundant. Considering associated fauna, the biomass of Mollusca increased from February 2015 to February 2016. Population densities of key reef fish species inside and around the rhodolith beds showed significant variations in time. The densities of grouper (carnivores/piscivores) increased in time, especially from 2015 to 2016. On the other hand, grunts (macroinvertebrate feeders) had a modest decrease over time (from 2014 to 2016). Other parameters such as primary production and calcification of L. crispatum were higher under enhanced irradiance, yet decreased in the presence of P. gymnospora. Community structure and physiological responses can be explained by the interaction of abiotic and biotic factors, which are driven by environmental changes over time. Biomass changes can indicate that herbivores play a role in limiting the growth of epiphytes, and this is beneficial to the rhodoliths because it decreases competition for environmental resources with fleshy algae.

Rhodolith beds (Corallinaceae, Rhodophyta): An important marine ecosystem of the Saya de Malha and Nazareth Banks

“…RBs are however at risk from disturbances such as climate change, global warming, and associated ocean acidifi cation, as well as from other disturbances with anthropogenic sources such as sedimentation, and fi shery trawling (Foster et al, 2013;Harvey et al, 2017;Schubert et al, 2019). Rhodoliths grow only a few millimeters per year (Foster et al, 2013) and these disturbances aff ect their recruitment, development, health, and survival rate which may lead increased competition from space competitors such as fl eshy algae (Martin and Hall-Spencer, 2017;Carvalho et al, 2020) in shallower areas.…”