Benthic marine calcifiers coexist with CaCO3-undersaturated seawater worldwide

Ocean acidification and decreasing seawater saturation state with respect to calcium carbonate (CaCO3) minerals have raised concerns about the consequences to marine organisms, especially those building structures made of CaCO3. A large proportion of benthic marine calcifiers incorporate Mg2+ into their calcareous structures (i.e., Mg-calcite) which, in general, reduces mineral stability. The vulnerability of some marine calcifiers to ocean acidification is related to the solubility of their calcareous structures, but not all marine organisms conform to this because of sophisticated biological and physiological mechanisms to construct and maintain CaCO3 structures. Few studies have considered seawater saturation state with respect to species-specific mineralogy in evaluating the effect of ocean acidification on marine organisms. Here, a global dataset of skeletal mol % MgCO3 of benthic calcifiers and in situ environmental conditions (temperature, salinity, pressure, and [CO32-]) spanning a depth range of 0 m (subtidal/neritic) to 5500 m (abyssal) was assembled to calculate in situ seawater saturation states with respect to species-specific Mg-calcite mineral compositions (?Mg-x). Up to 20% of all studied calcifiers at depths 1200 m currently experience seawater mineral undersaturation with respect to their skeletal mineral phase (?Mg-x1200 m) of all studied calcifying species to seawater undersaturation. These observations underscore concerns over the ability of marine benthic calcifiers to continue to construct and maintain their calcareous structures under these conditions. We advocate that ocean acidification tipping points can only be understood by assessing species-specific responses, and because of different seawater ?Mg-x present in all marine ecosystems

Benthic marine calcifiers coexist with CaCO3-undersaturated seawater worldwide

Ocean acidification and decreasing seawater saturation state with respect to calcium carbonate (CaCO3) minerals have raised concerns about the consequences to marine organisms, especially those building structures made of CaCO3. A large proportion of benthic marine calcifiers incorporate Mg2+ into their calcareous structures (i.e., Mg-calcite) which, in general, reduces mineral stability. The vulnerability of some marine calcifiers to ocean acidification is related to the solubility of their calcareous structures, but not all marine organisms conform to this because of sophisticated biological and physiological mechanisms to construct and maintain CaCO3 structures. Few studies have considered seawater saturation state with respect to species-specific mineralogy in evaluating the effect of ocean acidification on marine organisms. Here, a global dataset of skeletal mol % MgCO3 of benthic calcifiers and in situ environmental conditions (temperature, salinity, pressure, and [CO32-]) spanning a depth range of 0 m (subtidal/neritic) to 5500 m (abyssal) was assembled to calculate in situ seawater saturation states with respect to species-specific Mg-calcite mineral compositions (?Mg-x). Up to 20% of all studied calcifiers at depths <1200 m and approximately 90% of calcifiers at depths >1200 m currently experience seawater mineral undersaturation with respect to their skeletal mineral phase (?Mg-x<1). We conclude that as a result of predicted anthropogenic ocean acidification over the next 150 years, the predicted decrease in seawater mineral saturation, will expose approximately 50% (<1200 m) and 100% (>1200 m) of all studied calcifying species to seawater undersaturation. These observations underscore concerns over the ability of marine benthic calcifiers to continue to construct and maintain their calcareous structures under these conditions. We advocate that ocean acidification tipping points can only be understood by assessing species-specific responses, and because of different seawater ?Mg-x present in all marine ecosystems

Spatial variation in parasite-induced mortality in an amphipod: shore height versus exposure history

Characterizing the causes of spatial and temporal variation in parasite-induced mortality under natural conditions is crucial to better understanding the factors driving host population dynamics. Our goal was to quantify this variation in the amphipod Paracalliope novizealandiae, a second intermediate host of the trematode, Maritrema novaezealandensis. If infection and development of trematode metacercariae are benign, we expected mature metacercariae to accumulate within amphipods inhabiting high infestation areas. In field samples, intensity levels of mature metacercariae decreased linearly when amphipods harbored >5 immature metacercariae. This finding is consistent with the hypothesis that the parasite can be detrimental at high intensities of infection. Short-term field experiments showed that host survival also declines with the intensity of new infections and drops below 80% when early stage metacercariae reach 10 amphipod?1. However, parasite effects varied over space and time. High-shore amphipods suffered an increased risk of infection in the summer and a lower likelihood of survival: there was a 10–30% decrease in survivorship for any given infection intensity at high- versus low-shore locations. We also tested for differences in the susceptibility of naive and exposed populations using transplant experiments, and found that naive amphipods acquired greater parasite loads (on average, 4.7 vs. 2.8 metacercariae amphipod?1). Because survival decreases rapidly with infection intensity of both early- and late-stage metacercariae, naive populations would suffer considerably if the parasite were to increase its range. Our results indicate that trematode infections cause high mortality in amphipods during summer months under natural conditions, and emphasize that the effects of parasitism vary at local spatial scales and with exposure history

The impact of atmospheric mineral aerosol deposition on the albedo of snow & sea ice: are snow and sea ice optical properties more important than mineral aerosol optical properties?

Knowledge of the albedo of polar regions is crucial for understanding a range of climatic processes that have an impact on a global scale. Light-absorbing impurities in atmospheric aerosols deposited on snow and sea ice by aeolian transport absorb solar radiation, reducing albedo. Here, the effects of five mineral aerosol deposits reducing the albedo of polar snow and sea ice are considered. Calculations employing a coupled atmospheric and snow/sea ice radiative-transfer model (TUV-snow) show that the effects of mineral aerosol deposits are strongly dependent on the snow or sea ice type rather than the differences between the aerosol optical characteristics. The change in albedo between five different mineral aerosol deposits with refractive indices varying by a factor of 2 reaches a maximum of 0.0788, whereas the difference between cold polar snow and melting sea ice is 0.8893 for the same mineral loading. Surprisingly, the thickness of a surface layer of snow or sea ice loaded with the same mass ratio of mineral dust has little effect on albedo. On the contrary, the surface albedo of two snowpacks of equal depth, containing the same mineral aerosol mass ratio, is similar, whether the loading is uniformly distributed or concentrated in multiple layers, regardless of their position or spacing. The impact of mineral aerosol deposits is much larger on melting sea ice than on other types of snow and sea ice. Therefore, the higher input of shortwave radiation during the summer melt cycle associated with melting sea ice accelerates the melt process

Water stratification in the marine biome restricts vertical environmental DNA (eDNA) signal dispersal

Background: The utility of environmental DNA (eDNA) metabarcoding surveys to accurately detect species depends on the degree of DNA dispersal. Multiple marine studies have observed only minimal eDNA transport by horizontal water movement across small spatial scales, leading to the conclusion that spatially specific eDNA signals accurately resemble in-field species assemblages along a horizontal axis. Marine communities, however, are also structured vertically according to depth. In marine environments displaying permanent water stratification, vertical zonation patterns may be more apparent and present on smaller spatial scales (i.e., meters) than horizontal community structuring. The scale at which eDNA signals differ along a vertical transect and the accuracy of eDNA metabarcoding in revealing naturally stratified communities have yet to be assessed. Methods and results: In this study, we determined the ability of eDNA metabarcoding surveys to distinguish vertically localized community assemblages. To test this, we sampled three vertical transects along a steep rock wall at three depths (0 m, 4 m, 15 m), covering two distinct communities that were separated by near-permanent water column stratification in the form of a strong halocline at ~3 m. Using three metabarcoding assays, our eDNA metabarcoding survey detected 54 taxa, across 46 families and 7 phyla, including 19 fish, 15 crustacean, and 8 echinoderm species. Ordination and cluster analyses show distinct eDNA signals across the halocline for all three replicate transects, suggesting that vertical dispersal of eDNA between communities was limited. Furthermore, eDNA signals of individual taxa were only retrieved within their observed vertical distribution, providing biological validation for the obtained results. Our results demonstrate, for the first time, the need to take into consideration oceanographic (e.g. water column stratification) and biological processes (e.g. vertical community structuring) when designing sampling strategies for marine eDNA metabarcoding surveys

Species-level biodiversity assessment using marine environmental DNA metabarcoding requires protocol optimization and standardization

DNA extraction from environmental samples (environmental DNA; eDNA) for metabarcoding-based biodiversity studies is gaining popularity as a noninvasive, time-efficient, and cost-effective monitoring tool. The potential benefits are promising for marine conservation, as the marine biome is frequently under-surveyed due to its inaccessibility and the consequent high costs involved. With increasing numbers of eDNA-related publications have come a wide array of capture and extraction methods. Without visual species confirmation, inconsistent use of laboratory protocols hinders comparability between studies because the efficiency of target DNA isolation may vary. We determined an optimal protocol (capture and extraction) for marine eDNA research based on total DNA yield measurements by comparing commonly employed methods of seawater filtering and DNA isolation. We compared metabarcoding results of both targeted (small taxonomic group with species-level assignment) and universal (broad taxonomic group with genus/family-level assignment) approaches obtained from replicates treated with the optimal and a low-performance capture and extraction protocol to determine the impact of protocol choice and DNA yield on biodiversity detection. Filtration through cellulose-nitrate membranes and extraction with Qiagen's DNeasy Blood & Tissue Kit outperformed other combinations of capture and extraction methods, showing a ninefold improvement in DNA yield over the poorest performing methods. Use of optimized protocols resulted in a significant increase in OTU and species richness for targeted metabarcoding assays. However, changing protocols made little difference to the OTU and taxon richness obtained using universal metabarcoding assays. Our results demonstrate an increased risk of false-negative species detection for targeted eDNA approaches when protocols with poor DNA isolation efficacy are employed. Appropriate optimization is therefore essential for eDNA monitoring to remain a powerful, efficient, and relatively cheap method for biodiversity assessments. For seawater, we advocate filtration through cellulose-nitrate membranes and extraction with Qiagen's DNeasy Blood & Tissue Kit or phenol-chloroform-isoamyl for successful implementation of eDNA multi-marker metabarcoding surveys

A unique temperate rocky coastal hydrothermal vent system (Whakaari-White Island, Bay of Plenty, New Zealand): constraints for ocean acidification studies

In situ effects of ocean acidification are increasingly studied at submarine CO2 vents. Here we present a preliminary investigation into the water chemistry and biology of cool temperate CO₂ vents near Whakaari–White Island, New Zealand. Water samples were collected inside three vent shafts, within vents at a distance of 2 m from the shaft and at control sites. Vent samples contained both seawater pH on the total scale (pHT) and carbonate saturation states that were severely reduced, creating conditions as predicted for beyond the year 2100. Vent samples showed lower salinities, higher temperatures and greater nutrient concentrations. Sulfide levels were elevated and mercury levels were at concentrations considered toxic at all vent and control sites, but stable organic and inorganic ligands were present, as deduced from Cu speciation data, potentially mediating harmful effects on local organisms. The biological investigations focused on phytoplankton, zooplankton and macroalgae. Interestingly, we found lower abundances but higher diversity of phytoplankton and zooplankton at sites in the direct vicinity of Whakaari. Follow-up studies will need a combination of methods and approaches to attribute observations to specific drivers. The Whakaari vents represent a unique ecosystem with considerable biogeochemical complexity, which, like many other vent systems globally, require care in their use as a model of ‘future oceans’.R. Zitoun, S. D. Connell, C. E. Cornwall, K. I. Currie, K. Fabricius E , L. J. Hoffmann ... et al