A novel μCT analysis reveals different responses of bioerosion and secondary accretion to environmental variability

Corals build reefs through accretion of calcium carbonate (CaCO3) skeletons, but net reef growth also depends on bioerosion by grazers and borers and on secondary calcification by crustose coralline algae and other calcifying invertebrates. However, traditional field methods for quantifying secondary accretion and bioerosion confound both processes, do not measure them on the same time-scale, or are restricted to 2D methods. In a prior study, we compared multiple environmental drivers of net erosion using pre- and post-deployment micro-computed tomography scans (μCT; calculated as the % change in volume of experimental CaCO3 blocks) and found a shift from net accretion to net erosion with increasing ocean acidity. Here, we present a novel μCT method and detail a procedure that aligns and digitally subtracts pre- and post-deployment μCT scans and measures the simultaneous response of secondary accretion and bioerosion on blocks exposed to the same environmental variation over the same time-scale. We tested our method on a dataset from a prior study and show that it can be used to uncover information previously unattainable using traditional methods. We demonstrated that secondary accretion and bioerosion are driven by different environmental parameters, bioerosion is more sensitive to ocean acidity than secondary accretion, and net erosion is driven more by changes in bioerosion than secondary accretion

Spondylus crassisquama Lamarck, 1819 as a microecosystem and the effects of associated macrofauna on its shell integrity: isles of biodiversity or sleeping with the enemy?

In May 2009, we studied the bivalve Spondylus crassisquama and its relevance for macrobenthic biodiversity off the north Ecuadorian coast. We found that the large and heavy shells offer an exclusive substrate for numerous epibiont species and highly specialized carbonate-drilling endobiont species (71 species in total), which is a distinctly different and much more diverse habitat than the surrounding sandy bottoms (13 species, 4 of them found in both habitats). This is reflected by a Bray–Curtis dissimilarity index of 0.88. We discuss in detail the live habits of all 9 species of drilling endobionts that we found, and conclude that these can be seen as true mutualists, with the exception of boring sipunculids and bivalves. To further illustrate this complex co-existence, we visualize and quantify for the first time the tremendous effects of boring organisms on the shell structure of S. crassisquama by means of magnetic resonance imaging and a video appendix is provided

Fauna living in colonies of Mussismilia hispida (Verrill) (Cnidaria: Scleractinia) in four South-eastern Brazil islands

Colonies of Mussismilia hispida were collected in four south-eastern Brazil islands and fixed in formalin. Volume, living and basal areas of each coral head were measured. Animals found over, under and inside the corals were sorted, resulting in 9657 specimens belonging to more than 130 taxa. The underside of the colonies was occupied by bivalves and colonial forms of sponges, bryozoans and ascidians. On the living surface, barnacles and cryptochiridean crabs were detected. The endolithic animals included polychaetes, bivalves and sipunculid worms. Most of the animals collected were vagile microcrustaceans. In general, the corals in this ecosystem: (1) act as a nursery place for the community; (2) provide protection for many species also found in other habitats; (3) support a community mainly omnivorous and detritivorous; (4) are initially colonised randomly.<br>Colônias de Mussismilia hispida foram coletadas em quatro ilhas do sudeste brasileiro e fixadas em formalina. Depois de medidos o volume e as areas vivas e da base de cada coral, os animais encontrados sobre, dentro e sob as colônias foram triados, resultando em 9657 espécimes, pertencentes a cerca de 130 espécies. As bases das colônias encontravam-se ocupadas por bivalves e colônias de esponjas, briozoários e ascídias; na superfície viva, cirripédios e "caranguejos-galha" se fizeram presentes; a fauna endolítica incluiu poliquetas, bivalves e sipúnculos. Crustáceos vágeis, tais como copépodes, isópodes, anfípodes, tanaidáceos e ostrácodes responderam pela maioria dos animais encontrados. De maneira geral, pode-se dizer que os corais neste ambientes: (1) atuam como um local protegido para a reprodução das espécies associadas; (2) fornecem abrigo a muitas espécies também encontradas em outros ambientes; (3) sustentam uma comunidade que se alimenta principalmente de bactérias, detritos e do muco dos corais; (4) são inicialmente colonizados ao acaso