Description: Glass sponges (Porifera: Hexactinellida) are important structuring elements in many Antarctic shelf communities. Despite many years of research on their ecology, species identification in the common genus Rossella and distinction against the well-studied species Anoxycalyx (Scolymastra) joubini remain problematic. The two main problems are: (1) the unresolved taxonomy of the genus Rossella which is in dire need of revision, and (2) the high morphological variability of some species. Some of the confusion is due to the fact that early species descriptions are partly based on very small individuals or just fragments and are often not comprehensive or clear enough. They usually focus on the spicules and include little information on the general external morphology of the species. However, with the increasing use of non-invasive techniques, such as Remotely Operated Vehicles (ROVs) and other camera systems, researchers have to rely on macroscopic features to identify species, and a working concept to this effect is required right away. We found that it is possible to reliably identify some common Antarctic sponge species based on macroscopic characteristics. This Data Collection contains a wide range of images of the currently well-established species of Antarctic Rossellidae, showing the macroscopic features typical for each species and morphological differences between similar species according to our current understanding. It includes photographs of freshly collected and dried specimens, as well as in situ images recorded by ROVs. We provide a large number of images to showcase the morphological variability and show with detailed images that the same macroscopic characteristics can be observed in collected specimens and in situ. For identification and description of Antarctic glass sponges, it is important to take into consideration not only the spicules and molecular data, but the outer morphology, as well. Therefore, we encourage everybody to use the images provided in this Data Collection as reference material.

Description: Coccolithophores are a group of unicellular phytoplankton species whose ability to calcify has a profound influence on biogeochemical element cycling. Calcification rates are controlled by a large variety of biotic and abiotic factors. Among these factors, carbonate chemistry has gained considerable attention during the last years as coccolithophores have been identified to be particularly sensitive to ocean acidification. Despite intense research in this area, a general concept harmonizing the numerous and sometimes (seemingly) contradictory responses of coccolithophores to changing carbonate chemistry is still lacking to date. Here, we present the "substrate-inhibitor concept" which describes the dependence of calcification rates on carbonate chemistry speciation. It is based on observations that calcification rate scales positively with bicarbonate (HCO3-), the primary substrate for calcification, and carbon dioxide (CO2), which can limit cell growth, whereas it is inhibited by protons (H+). This concept was implemented in a model equation, tested against experimental data, and then applied to understand and reconcile the diverging responses of coccolithophorid calcification rates to ocean acidification obtained in culture experiments. Furthermore, we (i) discuss how other important calcification-influencing factors (e.g. temperature and light) could be implemented in our concept and (ii) embed it in Hutchinson's niche theory, thereby providing a framework for how carbonate chemistry-induced changes in calcification rates could be linked with changing coccolithophore abundance in the oceans. Our results suggest that the projected increase of H+ in the near future (next couple of thousand years), paralleled by only a minor increase of inorganic carbon substrate, could impede calcification rates if coccolithophores are unable to fully adapt. However, if calcium carbonate (CaCO3) sediment dissolution and terrestrial weathering begin to increase the oceans' HCO3- and decrease its H+ concentrations in the far future (10 -100 kyears), coccolithophores could find themselves in carbonate chemistry conditions which may be more favorable for calcification than they were before the Anthropocene.