Prof. Christopher McQuaid1
1Rhodes University, South Africa, Grahamstown, South Africa
Microscopic organisms on rocky shores generally tend to be viewed as food for larger organisms, but endolithic cyanobacteria that attack calcareous substrates can have far-reaching community-level effects. This topic was explored using field experiments and modelling. The distribution of endolithic cyanobacteria is shaped by substrate type and biogeography and involves succession on new substrates. Cyanobacteria have direct physiological effects that are generally negative, reducing scope for growth as host energy is re-directed to shell repair, indicating a parasitic relationship. They also have physical effects that influence species interactions; their presence on mussels makes epibiosis more likely, while they damage the host shell, increasing its roughness and thus rates of microplastic trapping. Endolithic cyanobacteria can, however, have unexpected positive effects on the host. By enhancing erosion of the periostracum and depositing calcium on the outside of mussel shells, they alter the host’s albedo. This increases sunlight reflection, significantly reducing body temperatures and even reducing mortality rates under heat stress. The cooling effect even extends to neighbouring mussels that are not infested and results in reduced interstitial temperatures within the mussel bed, with consequences for the many organisms dependent on mussel beds as habitat. The effect is strongest where and when heat stress is greatest, suggesting that, under warming climate conditions, the relationship between mussels and cyanobacteria could become mutualistic. Importantly, this also indicates that the vulnerability of a species to global warming can be powerfully modified by species interactions.
Biography:
Christopher McQuaid is recently retired having explored marine biology in two fields: Southern Ocean ecology and the ecology of rocky shores. Intertidally, he is interested in how larval dispersal, physiology and species interactions shape communities and often uses mussels as a model system. He has over 330 publications.
