Sediment biogeochemistry at CO2 vents off Papua-New Guinea (2013, 2014)

Measurement of biogeochemical parameters in coral reef sediments at carbon dioxide vents off Upa-Upasina (Normandy Island, Papua-New Guinea). The data includes in-situ micro/minisensor profiles, sediment characteristics, microbial and meiofauna abundances of vent sediments and reference sites without vent influence.

Primary production of phytoplankton and chlorophyll a in the southeast Barents Sea in August-September 1998

A study was performed from August 11 to September 3, 1998 in the Pechora Sea, which covered the shallow-water southeastern Barents Sea. Chlorophyll a concentration in the surface layer (C_chls) ranged from 0.08 to 1.15 mg/m**3, while primary production in the water column (C_phs) Varied from 17 to 170 mg C/m**2/day, aver. 75 mg C/m**2/day. Transition from central deep-water (60-190 m) parts of the sea to coastal shallow-water (15-30 m) parts was accompanied by increase of average C_chls values 2.4 times (from 0.21 to 0.51 mg/m**3) and decrease in average C_phs 1.6 times (from 95 to 58 mg C/m**2/day); the latter, in turn, resulted from decrease in thickness of the photosynthetic layer (H_ph) from 55 to 12 m and its relative transparency (H) from 17 to 4 m. This sharp change in H value and absence of a positive feedback between C_chls and C_phs were most probably related to rapid increase in the role of yellow substance and suspended matter in absorption of solar radiation in coastal waters. In sea areas with depths greater than 30 m a deep chlorophyll maximum was observed; at most of stations it located in the 20-35 m deep layer during illumination in photosynthetic active radiation range comprising 0.8-1.5% of its surface value. Parameters of photosynthetic light curves in these regions indicate participation of shade-adapted flora in formation of the deep chlorophyll maximum. In coastal waters characterized by a relatively uniform chlorophyll distribution over the water column no light adaptation of phytoplankton to efficient utilization of low irradiation for photosynthesis was encountered. Thus, a conclusion was made that combination of extremely low values of C_phs and H_ph makes the pelagic ecosystem of the Pechora Sea coastal regions very sensitive to anthropogenic impacts that may increase water turbidity.

Spatial community shift from hard to soft corals in acidified water

Anthropogenic increases in the partial pressure of CO2 (pCO2) cause ocean acidification, declining calcium carbonate saturation states, reduced coral reef calcification and changes in the compositions of marine communities. Most projected community changes due to ocean acidification describe transitions from hard coral to non-calcifying macroalgal communities; other organisms have received less attention, despite the biotic diversity of coral reef communities. We show that the spatial distributions of both hard and soft coral communities in volcanically acidified, semi-enclosed waters off Iwotorishima Island, Japan, are related to pCO2 levels. Hard corals are restricted to non-acidified low- pCO2 (225 µatm) zones, dense populations of the soft coral Sarcophyton elegans dominate medium- pCO2 (831 µatm) zones, and both hard and soft corals are absent from the highest- pCO2 (1,465 µatm) zone. In CO2-enriched culture experiments, high- pCO2 conditions benefited Sarcophyton elegans by enhancing photosynthesis rates and did not affect light calcification, but dark decalcification (negative net calcification) increased with increasing pCO2. These results suggest that reef communities may shift from reef-building hard corals to non-reef-building soft corals under pCO2 levels (550-970 µatm) predicted by the end of this century, and that higher pCO2 levels would challenge the survival of some reef organisms.

Dolomite-rich coralline algae in reefs resist dissolution in acidified conditions

Coral reef ecosystems develop best in high-flow environments but their fragile frameworks are also vulnerable to high wave energy. Wave-resistant algal rims, predominantly made up of the crustose coralline algae (CCA) Porolithon onkodes and P. pachydermum, are therefore critical structural elements for the survival of many shallow coral reefs. Concerns are growing about the susceptibility of CCA to ocean acidification because CCA Mg-calcite skeletons are more susceptible to dissolution under low pH conditions than coral aragonite skeletons. However, the recent discovery of dolomite (Mg0.5Ca0.5(CO3)), a stable carbonate, in P. onkodes cells necessitates a reappraisal of the impacts of ocean acidification on these CCA. Here we show, using a dissolution experiment, that dried dolomite-rich CCA have 6-10 times lower rates of dissolution than predominantly Mg-calcite CCA in both high-CO2 (~ 700 ppm) and control (~ 380 ppm) environments, respectively. We reveal this stabilizing mechanism to be a combination of reduced porosity due to dolomite infilling and selective dissolution of other carbonate minerals. Physical break-up proceeds by dissolution of Mg-calcite walls until the dolomitized cell eventually drops out intact. Dolomite-rich CCA frameworks are common in shallow coral reefs globally and our results suggest that it is likely that they will continue to provide protection and stability for coral reef frameworks as CO2 rises.

Selective mortality associated with variation in CO2 tolerance in a marine fish

Predicted future CO2 levels can affect reproduction, growth, and behaviour of many marine organisms. However, the capacity of species to adapt to predicted changes in ocean chemistry is largely unknown. We used a unique field-based experiment to test for differential survival associated with variation in CO2 tolerance in a wild population of coral-reef fishes. Juvenile damselfish exhibited variation in their response to elevated (700 µatm) CO2 when tested in the laboratory and this influenced their behaviour and risk of mortality in the wild. Individuals that were sensitive to elevated CO2 were more active and move further from shelter in natural coral reef habitat and, as a result, mortality from predation was significantly higher compared with individuals from the same treatment that were tolerant of elevated CO2. If individual variation in CO2 tolerance is heritable, this selection of phenotypes tolerant to elevated CO2 could potentially help mitigate the effects of ocean acidification.