OCEANS

Mediterranean region struggles with warming, acidification and jellyfish blooms

Mediterranean beach vacationers may again find themselves sticking to the sand rather than swimming in the sea this summer as fears of jellyfish stings return.

Others may opt to forgo the beach entirely, resulting in an economic loss of tourism dollars to the region. On the Israeli coast, for example, jellyfish outbreaks could potentially reduce the number of beach trips between 3 and 10.5 percent, which corresponds to an annual monetary loss in the range of €2.4 million to €6.2 million ($3.3 million to 8.4 million), according to the European Commission on the health of the sea.

Loss of tourism as a result of degradation to marine ecosystems, such as local jellyfish blooms, was one of the 10 top problems in the Mediterranean announced this month at a conference highlighting the conclusions of a 3 ½-year study funded by the commission.

And while jellyfish seem to be swarming more than ever, the exact cause of their abundance varies depending on the location. Warmer water allows for some species to breed more rapidly and provides an opportunity for invasive species to relocate from the southeastern shores to the north. But on a local level, a bloom can also come from changes to the ecosystem that allow for jellyfish domination, including pollution, runoff and overfishing.

And it is at this local level that the European Mediterranean Sea Acidification (MedSeA) initiative is investigating the effects of climate change across the entire Mediterranean Basin. "MedSeA is the first of its kind," said chemical oceanographer Sarah Cooley, a member of the international advisory panel for the initiative. "We have such a long history of settlement and use, but when it comes to data on climate change in the Mediterranean, we don't have very much data."

Global lack of local data

Warming and more acidic oceanic conditions as a result of rising CO2 in the atmosphere are a global concern, as discussed at the recent "Our Ocean" conference in Washington, D.C. (ClimateWire, June 18).

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Alexis Valauri-Orton, who spoke at the conference and is working now with the Ocean Conservancy in Washington, traveled to Norway, Hong Kong, Thailand, New Zealand, the Cook Islands and Peru last year on a Thomas J. Watson Fellowship, visiting local fisher and shellfish communities. "The big problem is there is no data in almost all of these places to demonstrate what the current situation is and few scientists working on it locally," she said by phone.

"In each place I visited, I was shocked by how few people had heard of ocean acidification. Those who have the most to lose have no idea what they're up against. If these communities don't understand this impending crisis, there's no way they can adapt or survive," she said during her talk at the conference. "Even in countries with excellent scientific research on ocean acidification, those dependent on marine resources had minimal knowledge and access to data. In most cases, no local scientists had even looked at how ocean acidification might affect the very resources those nearby depended on."

The MedSeA initiative is working to solve this discrepancy at least for the Mediterranean.

"It's the first cut at learning some interdisciplinary truth," Cooley, who is also with the Ocean Conservancy, said in an interview. The Mediterranean, she added, is "one of the most heavily used or depended-on bodies of water that we have, and has such iconic species that we absolutely have to think holistically when planning for the future. To make room for everyone, we have to commit to studies like this one."

Warming vs. acidification

Seawater acts as a sponge absorbing CO2 directly from the atmosphere. This lowers the pH, which is around 8.1 for the ocean in general. But similar to warming, the effects vary from place to place. Off the French coasts of the western Mediterranean basin, periodic measurements reported that "between 2007 and 2013, the averaged surface pH decreased constantly from about 8.100 to about 8.085," said Michaël Grelaud of the Universitat Autònoma de Barcelona, who is the data manager for MedSeA.

Bleached coral reefs are a sign that an area has suffered from a hot spell. The reef-building organisms die when the water gets too warm.

"The Mediterranean Sea has shown an average temperature increase of 0.67 °C over the last 25 years," noted the MedSeA study.

If carbon emission reduction measures are not implemented, atmospheric CO2 expected could reach 550 parts per million by 2050, and "there is a high level of certainty that this change to the atmosphere will lead to an average surface warming from 1 to 1.5 °C in the Eastern Mediterranean, Aegean and Adriatic Sea between 2000 and 2050. In summer, the average surface temperature is very likely to constantly exceed 29 °C in the South Eastern Mediterranean," according to the study.

And while many species have evolved in the Mediterranean to withstand warmer conditions, some are already showing signs of distress with the increased heat. "During summer heat waves, mussels, oysters and seagrasses already experience increased mortality," Grelaud said. "According to the projections, the amplitude and the duration of heat waves will increase due to global warming, leading to a functional extinction of Posidonia oceanica (seagrass) meadows by the middle of the 21st century (year 2049 ± 10 years) even under a relatively mild greenhouse-gas emissions scenario," he wrote by email.

But when it comes to acidification, the fear is that for some areas there will be no reef left at all. Reef-building organisms, many species of plankton and shellfish rely on calcite and aragonite minerals (CaCO3) in building their skeletal structures and shells. Coral reefs exist in our oceans thanks in part to the saturation of calcium carbonate ions in the water. The animals take up the ions as juveniles and turn them into the minerals they need to build their shells.

Calcium carbonate also acts as a buffer to the naturally slightly acidic seawater. But with the addition of CO2, additional carbonic acid attacks the carbonate ions, leaving shellfish and reef-building organisms suffering from a marine version of osteoporosis. They simply can't build the calcium carbonate mineral densities they need, because the dissolved calcium carbonate ions in the water have been taken up chemically by reactions with CO2.

"The few, available data sets from the Northwestern Mediterranean Sea indicate that in the 18-year period 1995-2013 alone, acidity has already increased more than 10 percent," the MedSeA study concluded. "Projections of CO2 emissions indicate a sustained uptake of anthropogenic carbon in the ocean and a 30 percent increase in acidification between years 2010 and 2050 if we continue to emit CO2 at the same rate. This implies, since the industrial revolution and within only a few decades, acidification of the Mediterranean Sea is likely to increase by 60 percent, and by 150 percent at the end of the century."

One small indicator that the local effects of warming and acidification are not always in tune with each other is that certain jellyfish that may thrive in the warmer waters also struggle in lower pH or higher acidic conditions. "The evidence is mixed," Cooley said.

Ultimately, acidification and warming are two different stressors and the ecosystem reacts to them in different ways, with some organisms profiting and some losing in different combinations. The local effect of these global pressures "is more of a mosaic," she added.

Communities can help to reduce the negative impacts of these stressors by regulating fishing practices, nutrient runoff and changes to freshwater flow from streams, rivers and drainage systems -- all of which can change the local biological and chemical conditions of the sea. "They need to look at how they are influencing the Mediterranean from a watershed perspective," she said.

Twitter: @seagirlreed | Email: seagirlreed@gmail.com

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