Haemolymph inorganic ion composition, physiology and behaviour dependent on temperature and magnesium in adult Paralomis granulosa (Decapoda, Anomura, Lithodidae)

A low capacity for regulation of extracellular Mg2+ has been proposed to exclude reptant marine decapod crustaceans from temperatures below 0°C and thus to exclude them from the high Antarctic. To test this hypothesis and to elaborate the underlying mechanisms in the most cold-tolerant reptant decapod family of the sub-Antarctic, the Lithodidae, thermal tolerance was determined in the crab Paralomis granulosa (Decapoda, Anomura, Lithodidae) using an acute stepwise temperature protocol (-1°, 1°, 4°, 7°, 10°, and 13°C). Arterial and venous oxygen partial pressures (Po2) in hemolymph, heartbeat and ventilation beat frequencies, and hemolymph cation composition were measured at rest and after a forced activity (righting) trial. Scopes for heartbeat and ventilation beat frequencies and intermittent heartbeat and scaphognathite beat rates at rest were evaluated. Hemolymph [Mg2+] was experimentally reduced from 30 mmol/L to a level naturally observed in Antarctic caridean shrimps (12 mmol/L) to investigate whether the animals remain more active and tolerant to cold (-1°, 1°, and 4°C). In natural seawater, righting speed was significantly slower at -1° and 13°C, compared with acclimation temperature (4°C). Arterial and venous hemolymph Po2 increased in response to cooling even though heartbeat and ventilation beat frequencies as well as scopes decreased. At rest, ionic composition of the hemolymph was not affected by temperature. Activity induced a significant increase in hemolymph [K+] at -1° and 1°C. Reduction of hemolymph [Mg2+] did not result in an increase in activity, an increase in heartbeat and ventilation beat frequencies, or a shift in thermal tolerance to lower temperatures. In conclusion, oxygen delivery in this cold-water crustacean was not acutely limiting cold tolerance, and animals may have been constrained more by their functional capacity and motility. In contrast to earlier findings in temperate and subpolar brachyuran crabs, these constraints remained insensitive to changing Mg2+ levels.

Seawater carbonate chemistry, thickness and carbonate elemental composition of the test of juvenile sea urchins in a laboratory experiment

Ocean surface CO2 levels are increasing in line with rising atmospheric CO2 and could exceed 900 µatm by year 2100, with extremes above 2000 µatm in some coastal habitats. The imminent increase in ocean pCO2 is predicted to have negative consequences for marine fishes, including reduced aerobic performance, but variability among species could be expected. Understanding interspecific responses to ocean acidification is important for predicting the consequences of ocean acidification on communities and ecosystems. In the present study, the effects of exposure to near-future seawater CO2 (860 µatm) on resting (M O2rest) and maximum (M O2max) oxygen consumption rates were determined for three tropical coral reef fish species interlinked through predator-prey relationships: juvenile Pomacentrus moluccensis and Pomacentrus amboinensis, and one of their predators: adult Pseudochromis fuscus. Contrary to predictions, one of the prey species, P. amboinensis, displayed a 28-39% increase in M O2max after both an acute and four-day exposure to near-future CO2 seawater, while maintaining M O2rest. By contrast, the same treatment had no significant effects on M O2rest or M O2max of the other two species. However, acute exposure of P. amboinensis to 1400 and 2400 µatm CO2 resulted in M O2max returning to control values. Overall, the findings suggest that: (1) the metabolic costs of living in a near-future CO2 seawater environment were insignificant for the species examined at rest; (2) the M O2max response of tropical reef species to near-future CO2 seawater can be dependent on the severity of external hypercapnia; and (3) near-future ocean pCO2 may not be detrimental to aerobic scope of all fish species and it may even augment aerobic scope of some species. The present results also highlight that close phylogenetic relatedness and living in the same environment, does not necessarily imply similar physiological responses to near-future CO2.

Morphometric measurements throughout ontogeny of selected planktic foraminiferal test species

Development plays an important part in shaping adult morphology and morphological disparity, yet its influence on evolutionary processes is seldom explored because of a lack of preservation of ontogenetic stages in the fossil record. By preserving their entire ontogenetic history within their test, and with the advent of high-resolution imaging techniques, planktic foraminifera allow us to investigate the influence of developmental constraints on disparity. Using Synchrotron radiation X-ray tomographic microscopy (SRXTM), we reconstruct the ontogenetic progression of seven species across several of the major morphotypic groups of planktic foraminifera, including morphotypes of a species exhibiting high phenotypic plasticity and closely related pseudo-cryptic sister-taxa. We show differences in growth patterns between the globigerinid species, which appear more tightly regulated within the framework of isometry from the neanic stage, and the globorotaliid species, whose adult stages present allometric trends. Morphological change through ontogeny results in a change in surface area to volume ratios. Different metabolic processes therefore dominate at different stages of ontogeny, changing the vulnerability of the organism to environmental influences over growth, from factors affecting diffusion rates in the juvenile to those affecting energy supply in the adult. These findings identify some of the parameters within which evolutionary mechanisms have to act.