Ocean acidification-induced food quality deterioration constrains trophic transfer

Our present understanding of ocean acidification (OA) impacts on marine organisms caused by rapidly rising atmospheric carbon dioxide (CO2) concentration is almost entirely limited to single species responses. OA consequences for food web interactions are, however, still unknown. Indirect OA effects can be expected for consumers by changing the nutritional quality of their prey. We used a laboratory experiment to test potential OA effects on algal fatty acid (FA) composition and resulting copepod growth. We show that elevated CO2 significantly changed the FA concentration and composition of the diatom Thalassiosira pseudonana, which constrained growth and reproduction of the copepod Acartia tonsa. A significant decline in both total FAs (28.1 to 17.4 fg cell−1) and the ratio of long-chain polyunsaturated to saturated fatty acids (PUFA:SFA) of food algae cultured under elevated (750 µatm) compared to present day (380 µatm) pCO2 was directly translated to copepods. The proportion of total essential FAs declined almost tenfold in copepods and the contribution of saturated fatty acids (SFAs) tripled at high CO2. This rapid and reversible CO2-dependent shift in FA concentration and composition caused a decrease in both copepod somatic growth and egg production from 34 to 5 eggs female−1 day−1. Because the diatom-copepod link supports some of the most productive ecosystems in the world, our study demonstrates that OA can have far-reaching consequences for ocean food webs by changing the nutritional quality of essential macromolecules in primary producers that cascade up the food web.

Non-calcifying larvae in a changing ocean: warming, not acidification/hypercapnia, is the dominant stressor on development of the sea star Meridiastra calcar

Climate change driven ocean warming and acidification is potentially detrimental to the sensitive planktonic life stages of benthic marine invertebrates. Research has focused on the effects of acidification on calcifying larvae with a paucity of data on species with alternate developmental strategies and on the interactive effects of warming and acidification. To determine the impact of climate change on a conspicuous component of the intertidal fauna of southeast Australia, the development of the non-calcifying lecithotrophic larvae of the sea star Meridiastra calcar was investigated in the setting of predicted ocean warming (+2-4°C) and acidification (-0.4-0.6 pH units) for 2100 and beyond in all combinations of stressors. Temperature and pH were monitored in the habitat of M. calcar to place experiments in context with current environmental conditions. There was no effect of temperature or pH on cleavage stage embryos but later development (gastrula-larvae) was negatively effected by a +2°-4°C warming and there was a negative effect of -0.6 pH units on embryos reaching the hatched gastrula stage. Mortality and abnormal development in larvae increased significantly even with +2°C warming and larval growth was impaired at +4°C. For the range of temperature and pH conditions tested, there were no interactive effects of stressors across all stages monitored. For M. calcar, warming not acidification was the dominant stressor. A regression model incorporating data from this study and projected increasing SST for the region suggests an increase in larval mortality to 70% for M. calcar by 2100 in the absence of acclimation and adaptation. The broad distribution of this species in eastern Australia encompassing subtropical to cold temperate thermal regimes provides the possibility that local M. calcar populations may be sustained in a warming world through poleward migration of thermotolerant propagules, facilitated by the strong southward flow of the East Australian Current.

Storm-induced upwelling of high pCO2 waters onto the continental shelf of the western Arctic Ocean and implications for carbonate mineral saturation states

The carbon system of the western Arctic Ocean is undergoing a rapid transition as sea ice extent and thickness decline. These processes are dynamically forcing the region, with unknown consequences for CO2 fluxes and carbonate mineral saturation states, particularly in the coastal regions where sensitive ecosystems are already under threat from multiple stressors. In October 2011, persistent wind-driven upwelling occurred in open water along the continental shelf of the Beaufort Sea in the western Arctic Ocean. During this time, cold (<−1.2°C), salty (>32.4) halocline water—supersaturated with respect to atmospheric CO2 (pCO2 > 550 μatm) and undersaturated in aragonite (Ωaragonite < 1.0) was transported onto the Beaufort shelf. A single 10-day event led to the outgassing of 0.18–0.54 Tg-C and caused aragonite undersaturations throughout the water column over the shelf. If we assume a conservative estimate of four such upwelling events each year, then the annual flux to the atmosphere would be 0.72–2.16 Tg-C, which is approximately the total annual sink of CO2 in the Beaufort Sea from primary production. Although a natural process, these upwelling events have likely been exacerbated in recent years by declining sea ice cover and changing atmospheric conditions in the region, and could have significant impacts on regional carbon budgets. As sea ice retreat continues and storms increase in frequency and intensity, further outgassing events and the expansion of waters that are undersaturated in carbonate minerals over the shelf are probable.

Elevated carbon dioxide differentially alters the photophysiology of Thalassiosira pseudonana (Bacillariophyceae) and Emiliania huxleyi (Haptophyta)

Increasing anthropogenic carbon dioxide is causing changes to ocean chemistry, which will continue in a predictable manner. Dissolution of additional atmospheric carbon dioxide leads to increased concentrations of dissolved carbon dioxide and bicarbonate and decreased pH in ocean water. The concomitant effects on phytoplankton ecophysiology, leading potentially to changes in community structure, are now a focus of concern. Therefore, we grew the coccolithophore Emiliania huxleyi (Lohmann) W. W. Hay et H. Mohler and the diatom strains Thalassiosira pseudonana (Hust.) Hasle et Heimdal CCMP 1014 and Thalassiosira pseudonana CCMP 1335 under low light in turbidostat photobioreactors bubbled with air containing 390 ppmv or 750 ppmv CO2. Increased pCO2 led to increased growth rates in all three strains. Additionally, protein levels of RUBISCO increased in the coastal strains of both species, showing a larger capacity for CO2 assimilation at 750 ppmv CO2. With increased pCO2, both T. pseudonana strains displayed an increased susceptibility to PSII photoinactivation, and to compensate, an augmented capacity for PSII repair. Consequently the cost of maintaining PSII function for the diatoms increased at increased pCO2. In E. huxleyi, PSII photoinactivation and the counter-acting repair, while both intrinsically larger than in T. pseudonana, did not change between the current and high-pCO2 treatments. The content of the photosynthetic electron transport intermediary Cytb6f complex increased significantly in the diatoms under elevated pCO2, suggesting changes in electron transport function.

Coral reefs – are they tough enough?

Whether you’ve been to the Chimneys dive site in Fiji or have never left your hometown of Chimney Rock, Wisconsin (population 276), you have undoubtedly heard of coral reefs. The structures are famous for their amazing beauty and richness of species. They provide many services to humans, including food, fisheries, coastal protection from storms and waves, recreational opportunities, tourism and species useful for medicine.

But corals are simple creatures with thin tissues spread over large surfaces; this makes them particularly sensitive to their environment. Coastal development and increased pollution, run-off from land, coral disease, habitat destruction and overfishing mean that nearly all coral reefs are in decline. With the additional impacts of sea-level rise, temperature increases, and ocean acidification, the world’s coral reefs face mounting threats; their future is a matter of much research and debate (Pandolfi et al. 2011a, Hoegh-Guldberg et al. 2011, Pandolfi et al. 2011b).

Ocean acidification gets deep in the Mediterranean Sea!

In recent years the issue of ocean acidification has moved rapidly up the political, economic and social agendas and is especially pertinent when combined with other pressures upon the marine environment, such as increased seawater warming and oxygen loss, overfishing and proliferation of invasive species. The Mediterranean Sea is of special interest to ocean acidification research as it is a complex, semi-enclosed body of water with high environmental variability and natural CO2 vents that may give scientists a window into a what a high CO2 ocean may look like in the future.

To discuss and share knowledge about ocean acidification and climate change impacts on this dynamic marine environment, over 60 scientists from 12 countries, mainly from the Mediterranean region, met in Rome on 4th and 5th March 2012 for the first Annual Science Meeting of the EU-funded Mediterranean Sea Acidification in a Changing Climate (MedSeA) project.

Why climate change might not spell death for the Reef

Rising ocean temperatures caused by climate change are unlikely to mean the end of the coral on the Great Barrier Reef, according to a new scientific study.

The Cell Press journal Current Biology this morning published what it says is the first large-scale investigation of climate effects on corals and found while some corals were dying, others were flourishing and adapting to the change in water temperatures.

Reef winners and losers in a warmer world

There are winners and losers among corals under the accumulating impacts of climate change, according to a new scientific study.

In the world’s first large-scale investigation of how climate affects the composition of coral reefs, an international team of marine scientists concludes that the picture is far more complicated than previously thought – but that total reef losses due to climate change are unlikely.

“Coral reefs are sometimes regarded as canaries in the global climate coal mine – but it is now very clear than not all reef species will be affected equally,” explains lead author Professor Terry Hughes, director of the ARC Centre of Excellence for Coral Reef Studies at James Cook University.

The emerging picture, he says, is one of ‘winners and losers’, with some corals succeeding at the expense of others. Rather than experiencing wholesale destruction, many coral reefs will survive climate change by changing the mix of coral species as the ocean warms and becomes more acidic.

Assembly rules of reef corals are flexible along a steep climatic gradient

Coral reefs, one of the world’s most complex and vulnerable ecosystems, face an uncertain future in coming decades as they continue to respond to anthropogenic climate change, overfishing, pollution, and other human impacts [[1] and [2]]. Traditionally, marine macroecology is based on presence/absence data from taxonomic checklists or geographic ranges, providing a qualitative overview of spatial shifts in species richness that treats rare and common species equally [[3] and [4]]. As a consequence, regional and long-term shifts in relative abundances of individual taxa are poorly understood. Here we apply a more rigorous quantitative approach to examine large-scale spatial variation in the species composition and abundance of corals on midshelf reefs along the length of Australia’s Great Barrier Reef, a biogeographic region where species richness is high and relatively homogeneous [5]. We demonstrate that important functional components of coral assemblages “sample” space differently at 132 sites separated by up to 1740 km, leading to complex latitudinal shifts in patterns of absolute and relative abundance. The flexibility in community composition that we document along latitudinal environmental gradients indicates that climate change is likely to result in a reassortment of coral reef taxa rather than wholesale loss of entire reef ecosystems.

Study links raised carbon dioxide levels to oyster die-offs

Oyster hatcheries along the Washington and Oregon coastlines began experiencing calamitous die-offs beginning in 2006. Scientists suspected they were because of increased carbon dioxide levels in the air that were causing ocean acidification. That theory has now proved out, according to a study just published by the journal Limnology and Oceanography.