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Seawater Mg:Ca and Sr:Ca ratios are biogeochemical parameters reflecting the Earth–ocean–atmosphere dynamic exchange of elements. The ratios’ dependence on the environment and organisms' biology facilitates their application in marine sciences. Here, we present a measured single-laboratory dataset, combined with previous data, to test the assumption of limited seawater Mg:Ca and Sr:Ca variability across marine environments globally. High variability was found in open-ocean upwelling and polar regions, shelves/neritic and river-influenced areas, where seawater Mg:Ca and Sr:Ca ratios range from ∼4.40 to 6.40 mmol:mol and ∼6.95 to 9.80 mmol:mol, respectively. Open-ocean seawater Mg:Ca is semiconservative (∼4.90 to 5.30 mol:mol), while Sr:Ca is more variable and nonconservative (∼7.70 to 8.80 mmol:mol); both ratios are nonconservative in coastal seas. Further, the Ca, Mg, and Sr elemental fluxes are connected to large total alkalinity deviations from International Association for the Physical Sciences of the Oceans (IAPSO) standard values. Because there is significant modern seawater Mg:Ca and Sr:Ca ratios variability across marine environments we cannot absolutely assume that fossil archives using taxa-specific proxies reflect true global seawater chemistry but rather taxa- and process-specific ecosystem variations, reflecting regional conditions. This variability could reconcile secular seawater Mg:Ca and Sr:Ca ratio reconstructions using different taxa and techniques by assuming an error of 1 to 1.50 mol:mol, and 1 to 1.90 mmol:mol, respectively. The modern ratios’ variability is similar to the reconstructed rise over 20 Ma (Neogene Period), nurturing the question of seminonconservative behavior of Ca, Mg, and Sr over modern Earth geological history with an overlooked environmental effect

Whole-body regeneration (WBR)—the formation of an entire adult from only a small fragment of its own tissue—is extremely rare among chordates. Exceptionally, in the colonial ascidian Botrylloides leachii (Savigny, 1816) a fully functional adult is formed from their common vascular system after ablation of all adults from the colony in just 10 d, thanks to their high blastogenetic potential. While previous studies have identified key genetic markers and morphological changes, no study has yet focused on the hematological aspects of regeneration despite the major involvement of the remaining vascular system and the contained hemocytes in this process. To dissect this process, we analyzed colony blood flow patterns using time-lapse microscopy to obtain a quantitative description of the velocity, reversal pattern, and average distance traveled by hemocytes. We also observed that flows present during regeneration are powered by temporally and spatially synchronized contractions of the terminal ampullae. In addition, we revised previous studies of B. leachii hematology as well as asexual development using histological sectioning and compared the role played by hemocytes during WBR. We found that regeneration starts with a rapid healing response characterized by hemocyte aggregation and infiltration of immunocytes, followed by increased activity of hemoblasts, recruitment of macrophage-like cells for clearing the tissues of debris, and their subsequent disappearance from the circulation concomitant with the maturation of a single regenerated adult. Overall, we provide a detailed account of the hematological properties of regenerating B. leachii colonies, providing novel lines of inquiry toward the decipherment of regeneration in chordates.

The non-Antarctic Notothenioidei families, Bovichtidae, Pseudaphritidae and Eleginopsidae, diverged early from the main notothenioid lineage. They are important in clarifying the early evolutionary processes that triggered notothenioid evolution in the Antarctic. The early-diverged group represents 8% of all notothenioid species and never established themselves on the Antarctic shelf. Most attention has been paid to the Antarctic notothenioids and their limited physiological tolerance to climate change and increased temperatures. In this review, we discuss key life history traits that are characteristic of the non-Antarctic early-diverged notothenioid taxa as well as the genetic resources and population differentiation information available for this group. We emphasise the population fitness and dynamics of these species and indicate how resource management and conservation of the group can be strengthened through an integrative approach. Both Antarctic waters and the non-Antarctic regions face rapid temperature rises combined with strong anthropogenic exploitation. While it is expected that early-diverged notothenioid species may have physiological advantages over high Antarctic species, it is difficult to predict how climate changes might alter the geographic range, behaviour, phenology and ultimately genetic variability of these species. It is possible, however, that their high degree of endemism and dependence on local environmental specificities to complete their life cycles might enhance their vulnerability.

As a response to ocean warming, shifts in fish species distribution and changes in production have been reported, that have been partly attributed to temperature effects on the physiology of animals. The Southern Ocean hosts some of the most rapidly warming regions on earth and Antarctic organisms are reported to be especially temperature sensitive. While cellular and molecular organismic levels appear to, at least partially, compensate for elevated temperatures, consequences of acclimation to elevated temperature for the whole organism are often less clear. Growth and reproduction are the driving factors for population structures and abundances. The aim of this study was to assess the effect of long-term acclimation to elevated temperature on energy budget parameters in the high Antarctic fish Trematomus bernacchii. Our results show a complete temperature compensation for routine metabolic costs after nine weeks of acclimation to 4°C. However, an up to 80% reduction in growth was measured at 2 and 4°C compared to the control group at 0°C. With regard to a predicted temperature increase of up to 1.4°C in the Ross Sea by 2200, such a significant reduction in growth is likely to affect population structures in nature e.g. by delaying sexual maturity and reducing production, with severe impacts on Antarctic fish communities and ecosystems.

Ocean acidification, or the lowering of seawater pH, is caused by sequestration of atmospheric CO2 into the oceans. This study investigated the effects of present-day pH 8.0, predicted ocean surface pH for the years 2100 and 2300 (pH 7.7 and pH 7.3, respectively) and an extreme pH (pH 7.0) on fertilisation and embryogenesis in the Antarctic nemertean worm Parborlasia corrugatus and sea urchin Sterechinus neumayeri. Fertilisation success was not affected by pH in P. corrugatus across a range of sperm concentrations. Fertilisation success in S. neumayeri declined significantly in pH 7.0 and 7.3 seawater, but only at a low sperm concentration. Seawater pH had no effect on the rate of egg cleavage in S. neumayeri, or the proportion of abnormal embryos 1-day post-fertilisation. P. corrugatus embryogenesis was also relatively robust to pH changes, with a significant effect detected only when the seawater pH was decreased to 7.0. While fertilisation and early cell division were relatively robust, later development through to the gastrula was sensitive to pH. In S. neumayeri, an effect of pH on development was evident by the gastrula stage, while there were significantly more abnormal P. corrugatus embryos in pH 7.0 up to the blastula stage, and in pH 7.0 and pH 7.3 at the coeloblastula stage. Our results are similar to the observations on other marine invertebrate species where fertilisation and early embryonic development are generally robust to lowered seawater pH, while the older coeloblastula and gastrula stages are more responsive. We also found no evidence to suggest that Antarctic species are more adversely affected by lower seawater pH compared with the findings for non-Antarctic counterparts. We conclude that in the two species we examined, near-future decreases in pH (decreases of a parts per thousand 0.3-0.5 pH units) may not have a significant effect on fertilisation and early embryogenesis, while predicted longer term decreases (decreases of a parts per thousa

Whole-body regeneration (WBR)—the formation of an entire adult from only a small fragment of its own tissue—is extremely rare among chordates. Exceptionally, in the colonial ascidian Botrylloides leachii (Savigny, 1816) a fully functional adult is formed from their common vascular system after ablation of all adults from the colony in just 10 d, thanks to their high blastogenetic potential. While previous studies have identified key genetic markers and morphological changes, no study has yet focused on the hematological aspects of regeneration despite the major involvement of the remaining vascular system and the contained hemocytes in this process. To dissect this process, we analyzed colony blood flow patterns using time-lapse microscopy to obtain a quantitative description of the velocity, reversal pattern, and average distance traveled by hemocytes. We also observed that flows present during regeneration are powered by temporally and spatially synchronized contractions of the terminal ampullae. In addition, we revised previous studies of B. leachii hematology as well as asexual development using histological sectioning and compared the role played by hemocytes during WBR. We found that regeneration starts with a rapid healing response characterized by hemocyte aggregation and infiltration of immunocytes, followed by increased activity of hemoblasts, recruitment of macrophage-like cells for clearing the tissues of debris, and their subsequent disappearance from the circulation concomitant with the maturation of a single regenerated adult. Overall, we provide a detailed account of the hematological properties of regenerating B. leachii colonies, providing novel lines of inquiry toward the decipherment of regeneration in chordates.