Bryozoan biomineralization in the Future Ocean

Marine bryozoans have the physiological ability to produce biomineralized skeletons with functional roles that have been shaped by natural selection for almost 500 million years. Calcareous skeletons have been acquired independently in two bryozoan clades, once in the Ordovician and again in the Jurassic, thus providing an evolutionary replicate. Bryozoan colonies are today important bioconstructors in some shallow-water marine environments and, being able to respond to environmental changes physiologically and morphologically, they are good candidates for testing the effects of global changes.

The aim of this contribution is to highlight the importance of bryozoans as biomineralizers by describing basic structures (zooidal skeletal structure, ultrastructure, mineralogy and geochemistry), the roles and function of organic components, and the impacts of contemporary global changes, especially ocean acidification, on biomineralization processes.

Bryozoan skeletal wall ultrastructures are diverse, their mineralogy can be calcitic, aragonitic or bimineralic, and the geochemistry of the calcite component varies from low- through mid- to high-Mg calcite. Results of laboratory studies of different living bryozoan species performed in an area of natural CO₂ vents area and of laboratory studies of bryozoans cultured at low pH levels are presented. These show that ocean acidification combined with global warming are likely to have detrimental effects on calcification, growth rate and production of polymorphic zooids for defence and reproduction, although some species exhibit a degree of resilience through reallocating energy resources from biomineralization.

Preliminary results of a pilot study that aims to show the presence and distribution of calcium carbonate associated with organic components in a Mediterranean bioconstructional bryozoan are reported, adding information on biomineralizational patterns and processes that are still poorly understood among bryozoans.