Experimental climate change weakens the insurance effect of biodiversity

Ecosystems are simultaneously affected by biodiversity loss and climate change, but we know little about how these factors interact. We predicted that climate warming and CO₂-enrichment should strengthen trophic cascades by reducing the relative efficiency of predation-resistant herbivores, if herbivore consumption rate trades off with predation resistance. This weakens the insurance effect of herbivore diversity. We tested this prediction using experimental ocean warming and acidification in seagrass mesocosms. Meta-analyses of published experiments first indicated that consumption rate trades off with predation resistance. The experiment then showed that three common herbivores together controlled macroalgae and facilitated seagrass dominance, regardless of climate change. When the predation-vulnerable herbivore was excluded in normal conditions, the two resistant herbivores maintained top-down control. Under warming, however, increased algal growth outstripped control by herbivores and the system became algal-dominated. Consequently, climate change can reduce the relative efficiency of resistant herbivores and weaken the insurance effect of biodiversity.

Juvenile growth of the tropical sea urchin Lytechinus variegatus exposed to near-future ocean acidification scenarios

To evaluate the effect of elevated pCO₂ exposure on the juvenile growth of the sea urchin Lytechinus variegatus, we reared individuals for 3 months in one of three target pCO₂ levels: ambient seawater (380 μatm) and two scenarios that are projected to occur by the middle (560 μatm) and end (800 μatm) of this century. At the end of 89 days, urchins reared at ambient pCO₂ weighed 12% more than those reared at 560 μatm and 28% more than those reared at 800 μatm. Skeletons were analyzed using scanning electron microscopy, revealing degradation of spines in urchins reared at elevated pCO₂ (800 μatm). Our results indicate that elevated pCO₂ levels projected to occur this century may adversely affect the development of juvenile sea urchins. Acidification-induced changes to juvenile urchin development would likely impair performance and functioning of juvenile stages with implications for adult populations.

Ce n’est pas la fête des mers (in French)

Surpêche, acidification sans précédent… A dix jours du sommet Rio +20, les océans sont au plus mal.

Ils recouvrent les deux tiers de la surface de la planète, abritent une diversité exceptionnelle et fournissent des ressources inestimables aux hommes. Ils régulent notre climat et ont un rôle capital dans les cycles biogéochimiques. Pour ces mêmes raisons, les océans sont mal en point. Dans ce monde bleu et silencieux, tous les voyants sont au rouge. Petit tour d’horizon à l’occasion de la Journée mondiale des océans.

Rio+20 Blueprint for the future we want: ocean acidificiation

What is ocean acidification?

The ocean absorbs approximately 26% of the CO2 added to the atmosphere from human activities each year, greatly reducing the impact of this greenhouse gas on the climate. When CO2 dissolves in seawater, carbonic acid is formed. It is this chemical reaction that leads to ocean acidification. Ocean acidity has increased by 30% since the beginning of the Industrial Revolution.

How is this threatening our Ocean?

Ocean acidity increases the amount of energy needed by many small ocean organisms in constructing their carbonate shells and structures, and in some places will make it impossible for these organisms to live. It causes seawater to become corrosive to the shells and skeletons of numerous marine organisms, affecting their reproduction and physiology. This will have impacts on ocean ecosystems that science is still examining.

Within decades, the chemistry of the tropical oceans will not sustain coral reef growth while large parts of the polar oceans will become corrosive to calcareous marine organisms.

UAF ocean acidification research expanding

The state of Alaska and the University of Alaska Fairbanks will be throwing a wider net to collect data on ocean acidification in the coming years. The state allocated $2.7 million in the UAF capital budget during the 2012 legislative session for expanded ocean acidification monitoring.

“This is a tremendous opportunity to improve our understanding of a problem that could have far-reaching implications for our state,” said assistant professor Jeremy Mathis, the director of the Ocean Acidification Research Center at UAF. “This infusion of funding will allow us to do things that we didn’t think were possible a couple of years ago.”

Mathis will use the new funding to build a network of ocean acidification buoys around the state that will provide real-time monitoring of changing conditions throughout some of the state’s most sensitive coastal areas.

Seasonal coupling and de-coupling of net calcification rates from coral reef metabolism and carbonate chemistry at Ningaloo Reef, Western Australia

Rates of net production, net calcification, and nutrient uptake were measured in a coral-dominated reef flat community on Ningaloo Reef in northwestern Australia under seasonally minimum and maximum light levels. Daily integrated light decreased twofold while water temperatures remained relatively constant increasing by only 1°C on average from summer to winter. Rates of daily community gross primary production (GPP) were only 33% ± 9% higher in summer than in winter (1400 ± 70 versus 1050 ± 60 mmol C m⁻² d⁻¹), far less than the twofold seasonal changes reported for most shallow reef communities. Rates of daily community net calcification (G_net) were not significantly different between seasons (190 ± 40 mmol CaCO₃ m⁻² d⁻¹ in summer versus 200 ± 10 mmol CaCO₃ m⁻² d⁻¹ in winter). The average rate of total nitrogen uptake (dissolved + particulate) was also not significantly different between summer and winter (8.3 ± 3.8 versus 6.6 ± 3.4 mmol N m⁻² d⁻¹, respectively), despite evidence of sporadically high nitrate uptake in both seasons. In summer, rates of hourly net calcification (g_net) were linearly correlated with diurnal changes in net production, pH, and aragonite saturation state (Ω_ar); and were mostly correlated with light except at mid-day under heavy cloud cover. However, in winter, g_net was independent of diurnal changes in light, net production, pH, and Ω_ar indicating that the reef flat community had possibly reached a threshold above which rates of net calcification were insensitive to diurnal changes in their environment.