The developmental stages of the sea louse Lepeophtheirus elegans (Copepoda: Caligidae) are described from material collected from marine ranched Korean rockfish, Sebastes schlegelii. In L. elegans, setal number on the proximal segment of the antennule increases from 3 in the copepodid to 27 in the adult. Using the number of setae as a stage marker supports the inference that the post-naupliar phase of the life cycle comprises six stages: copepodid, chalimus I, chalimus II, pre-adult I, pre-adult II, and the adult. We observed variation in body length in both of the chalimus stages which we consider represents an early expression of sexual size dimorphism. We interpret the larger specimens of chalimus I as putative females, and the smaller as putative males; similarly with chalimus II, larger specimens are putative females and the smaller are males. Two patterns of life cycle are currently recognized within the Caligidae but the evidence presented here reconciles the two. We conclude that the typical caligid life cycle comprises only eight stages: two naupliar, one copepodid, and four chalimus stages preceding the adult in Caligus, but with the four chalimus stages represented by two chalimus and two pre-adult stages in Lepeophtheirus. This is a profound change with significant implications for the aquaculture industry, given that lice monitoring protocols include counts of chalimus stages and use temperature to predict when they will moult into the more pathogenic, mobile pre-adults. Lice management strategies must be tailored to the precise life cycle of the parasite.

Mussels have the ability to control biomineral production and chemical composition, producing shells with a range of functions. In addition to biological control, the environment also seems to influence the process of biomineralization; thus, shells can be used as archives of ambient water parameters during the calcium carbonate deposition. Past and present environmental conditions are recorded in the shells in the form of various proxies including Mg/Ca or Sr/Ca ratios. For such proxies to be accurate and robust, the influence of biological effects including the size of studied organism must be examined and eliminated or minimized, so that the environmental signal can be efficiently extracted. This study considers mineralogy and elemental composition of shells representing four size classes of Mytilus trossulus from the Baltic Sea. Obtained results suggest that mineralogy and chemical composition change throughout the shell development due to most likely a combination of environmental and biological factors. The content of aragonite increases with increasing shell size, while the bulk concentrations of Na, Cd, Cu, U, V, Zn and Pb were found to decrease with increasing height of the shells. Therefore, using mussels for environmental monitoring requires analysis of individuals in the same size range.

The Southern Ocean is showing one of the most rapid responses to human‐induced global change, thus acting as a sentinel of the effects on marine species and ecosystems. Ocean warming and acidification are already impacting benthic species with carbonate skeletons, but the magnitude of these changes to species and ecosystems remains largely unknown. Here we provide the largest carbonate mineralogical dataset to date for Southern Ocean bryozoans, which are diverse, abundant and important as carbonate producers, thus making them excellent for monitoring the effects of ocean warming and acidification. To improve our understanding of how bryozoans might respond to ocean warming and acidification, we assess latitudinal and seafloor temperature patterns of skeletal mineralogy using bryozoan species occurrences together with temperature data for the first time. Our findings, combining new mineralogical data with published data from warmer regions, show that the proportions of high‐Mg calcite and bimineralic species increase significantly towards lower latitudes and with increasing seawater temperature. These patterns are consistent with the hypothesis that seawater temperature is likely a significant driver of variations in bryozoan mineralogy at a global scale.

Bryozoans represent an extremely diversified phylum in terms of biomineralogy. The mineral composition of the bryozoan skeleton is most likely controlled by the organism itself and to some degree by the ambient environmental conditions (e.g., pH, Mg/Ca ratio, temperature). The purpose of this study is to describe the mineral composition of nearly one-quarter of all Antarctic bryozoan species known to date and to discuss, locally and in a global context, the potential factors that control mineralization in bryozoan skeletons. Collections of bryozoans were gathered by divers and with van Veen grabs (0.1 m²) from depths of 6–300 m at King George Island, Antarctica, during the summer seasons of 1985, 2007, and 2011. An x-ray diffraction analysis of the skeletons indicated that all analyzed Antarctic bryozoans (256 individuals, 71 taxa) precipitated monomineral calcite skeletons. The magnesium content ranged from 0.2 to 10.1 mol% MgCO₃. Most of the studied species (76%) consisted of intermediate-magnesium calcite. Yet extreme variations in mol% MgCO₃ were found between individuals of the same species as well as between species and populations. The high variability found between specimens of the same species suggests that the mol% MgCO₃ could be determined by the biology or physiology of an individual. The magnesium content was equally distributed in each of three growth forms (e.g., erect flexible, erect rigid, and encrusting). The mean mol% MgCO₃ in Antarctic species was significantly lower than that in bryozoans from Mediterranean, Chile, and New Zealand but similar to that in Arctic bryozoans. This finding confirms the latitudinal-pattern hypothesis of a decreased Mg content toward polar regions.