Patterns of magnesium content in Arctic bryozoan skeletons along a depth gradient

A growing body of evidence suggests that ocean acidification acting synergistically with ocean warming alters carbonate biomineralization in a variety of marine biota. Magnesium often substitutes for Ca in the calcite skeletons of marine invertebrates, increasing their solubility. The spatio-environmental distribution of Mg in marine invertebrates has seldom been studied, despite its importance for assessing vulnerabilities to ocean acidification. Because pH decreases with water depth, it is predicted that levels of Mg in calcite skeletons should also decrease to counteract dissolution. Such a pattern has been suggested by evidence from echinoderms. Data on magnesium content and depth in Arctic bryozoans (52 species, 103 individuals, 150 samples) are here used to test this prediction, aided by comparison with six conceptual models explaining all possible scenarios. Analyses were based on a uniform dataset spanning more than 200 m of coastal water depth. No significant relationship was found between depth and Mg content; indeed, the highest Mg content among the analyzed taxa (8.7 % mol MgCO₃) was recorded from the deepest settings (>200 m). Our findings contrast with previously published results from echinoderms in which Mg was found to decrease with depth. The bryozoan results suggest that ocean acidification may have less impact on the studied bryozoans than is generally assumed. In the broad context, our study exemplifies quantitative testing of spatial patterns of skeletal geochemistry for predicting the biological effects of environmental change in the oceans.

Physical and biological controls on the carbonate chemistry of coral reef waters: effects of metabolism, wave forcing, sea level, and geomorphology

We present a three-dimensional hydrodynamic-biogeochemical model of a wave-driven coral-reef lagoon system using the circulation model ROMS (Regional Ocean Modeling System) coupled with the wave transformation model SWAN (Simulating WAves Nearshore). Simulations were used to explore the sensitivity of water column carbonate chemistry across the reef system to variations in benthic reef metabolism, wave forcing, sea level, and system geomorphology. Our results show that changes in reef-water carbonate chemistry depend primarily on the ratio of benthic metabolism to the square root of the onshore wave energy flux as well as on the length and depth of the reef flat; however, they are only weakly dependent on channel geometry and the total frictional resistance of the reef system. Diurnal variations in pCO₂, pH, and aragonite saturation state (Ω_ar) are primarily dependent on changes in net production and are relatively insensitive to changes in net calcification; however, net changes in pCO₂, pH, and Ω_ar are more strongly influenced by net calcification when averaged over 24 hours. We also demonstrate that a relatively simple one-dimensional analytical model can provide a good description of the functional dependence of reef-water carbonate chemistry on benthic metabolism, wave forcing, sea level, reef flat morphology, and total system frictional resistance. Importantly, our results indicate that any long-term (weeks to months) net offsets in reef-water pCO₂ relative to offshore values should be modest for reef systems with narrow and/or deep lagoons. Thus, the long-term evolution of water column pCO₂ in many reef environments remains intimately connected to the regional-scale oceanography of offshore waters and hence directly influenced by rapid anthropogenically driven increases in pCO₂.

PhD-student position in Neuroscience within the subject of ocean acidification and the effects of elevated pCO2 on fish behaviour

Uppsala University hereby declares the following position to be open for application:

PhD-student position in Neuroscience within the subject of ocean acidification and the effects of elevated pCO₂ on fish behaviour

at the Department of Neuroscience, Physiology Unit, Uppsala Biomedical Centre (BMC), Uppsala University, starting as soon as possible.

Ocean CO₂ levels increase in line with atmospheric CO₂ and recent studies showed that fish reared in high-CO₂ water (700 – 900 ppm which is predicted by IPPC for year 2050 and 2100) display drastic behavioural alterations. For instance, instead of the normal avoidance reaction, the smell of predatory fish attracted fish larvae raised in CO₂-acidified water. These behavioural effects of elevated pCO₂ seem to be mediated by effects on the central nervous system of the fish. The fact that these effects are observed in several species indicates that the scope of this problem is truly global. The project, which is funded by the Swedish Research Council (VR), is focused on the neural mechanisms mediating behavioral effects of elevated pCO₂.

Effects of ocean acidification on the embryos and larvae of red king crab, Paralithodes camtschaticus

The effects of the decline in ocean pH, known as ocean acidification, on marine species are not well understood. To test the effects on embryos and larvae of red king crab, Paralithodes camtschaticus, ovigerous crab and their larvae were held in CO₂-acidified (pH 7.7) and control (ambient; pH 8.0) seawater during development. Morphometrics, hatch duration, fecundity, survival, mineral content, and condition were measured. Acidified embryos had 4% larger eyes and 5% smaller yolks, while mean hatch duration was 33% longer and female fecundity was unaffected. Acidified embryos also resulted in 4% longer larvae while acidified larvae had lower survival. Calcium content of both larvae and female carapaces after molting increased by 5% and 19%, respectively. Although ocean acidification may increase larval size and calcium content, the implications of this are unclear and decreased survival is likely to harm red king crab populations.

Effect of increased pCO2 on early shell development in great scallop (Pecten maximus Lamarck) larvae

As a result of high anthropogenic emission of CO₂, partial pressure of carbon dioxide (pCO₂) in the oceans has increased causing a drop in pH, known as ocean acidification (OA). Numerous studies have shown negative effects on marine invertebrates, and that the early life stages are the most sensitive to OA. We studied the effects on embryo and larvae of great scallop (Pecten maximus L.), using mean pCO₂-levels of 477 (ambient), 821, 1184, and 1627 ppm. OA affected both survival and shell growth negatively after seven days. Growth was reduced with 5–10% when pCO₂ increased from ambient 477 ppm to 1627 ppm, and survival based on egg number was reduced from 40.4% in the ambient group to 10.7% in the highest pCO₂-group. Larvae/embryos stained with calcein one day after fertilization, showed fluorescence in the newly formed shell area indicating calcification of the shell already at the trochophore stage. Shell hinge deformities were observed at elevated pCO₂-levels in trochophore larvae after two days. After seven days, deformities in both shell hinge and shell edge were observed in veliger larvae at elevated pCO₂-levels. Although the growth showed a moderate reduction, survival rate and increased amount of deformed larvae indicates that P. Maximus larvae are affected by elevated pCO₂ levels within the range of what is projected for the next century.