Climate Change Challenges in the Corinthian Gulf

As we embark on a new journey aboard a fish harvesting vessel, gliding over the shimmering blue waters of the Corinthian Gulf, it’s hard to fathom the extent to which this serene coastline is being impacted by climate change. The reality becomes evident when we check a thermometer, revealing alarming signs of rapid warming in these waters, much like the broader trends observed throughout the eastern Mediterranean.

“The temperature is at 25.5°C for this time of year, which is unprecedented,” remarks George Tstatsos, the Operations Director at Kefalonia Fisheries, as he reads the sensor on an early October morning. Earlier this summer, temperatures soared to a staggering 29.5°C, and just last year, they recorded temperatures exceeding 30 degrees Celsius for three consecutive days. These figures are extraordinary for fish farmers, who traditionally anticipated summer highs around 26 to 27 degrees Celsius.

According to the latest findings from the Copernicus Climate Change Service, September 2024 was marked as the second warmest September globally, with temperatures averaging 0.7 degrees Celsius above the 1991-2020 baseline. The data indicates that numerous regions across the Mediterranean experienced their highest sea surface temperatures ever this past summer.

In response to these escalating challenges, Tstatsos and his dedicated team are working diligently to adapt to the new realities brought about by climate change. The increase in water temperature has led to reduced oxygen levels, which in turn hampers fish growth and encourages the proliferation of harmful pathogens. In an effort to counteract these effects, the team has relocated their fish cages further offshore, seeking areas with stronger currents and better oxygen availability. However, positioning their operations half a kilometer or more from the shore exposes them to the risks posed by increasingly severe storms that have become more frequent in recent years.

The sea bass farm is nestled in a secluded bay within the Corinthian Gulf. Another significant adjustment they have made pertains to stocking densities. “We have reduced the number of fish in each cage,” Tstatsos explains, “to ensure that our fish receive access to cleaner water, which translates to increased oxygen levels.” The nets themselves are being redesigned to accommodate these changes, featuring larger openings to facilitate improved water flow.

Moreover, the feeding regimen is undergoing modifications, with fish now being fed twice daily to allow for more effective digestion, given the available oxygen levels.

In Greece, there are currently 65 companies operating 328 fish farms, all grappling with similar challenges as they cultivate species such as sea bass for both local and international markets. To aid these farmers in navigating short-term management and long-term planning, scientists at the Hellenic Centre for Marine Research have been conducting studies on fish under controlled conditions at their facilities in Crete.

According to Nikos Papandroulakis, who leads the research efforts, various indoor recirculating aquaculture systems have been employed to monitor sea bass growth at temperatures of 26, 28, and 30 degrees Celsius. “When the temperature hovers around 28-29°C, the fish exhibit diminished growth rates,” he explains. “Additionally, they struggle to convert feed into biomass efficiently.”

“At temperatures exceeding 33-34°C, the fish experience a near-total psychological collapse, rendering them unable to grow or consume food,” he adds, emphasizing the critical impact of temperature on fish health and productivity.

This research, part of the EU’s Climefish project, aims to achieve three primary objectives: to collect comprehensive data on how climate change-related factors such as temperature, oxygen levels, and acidification affect fish physiology and performance; to model fish responses under varying climate scenarios; and to develop decision-making tools for farmers.

The outcome of this initiative includes two innovative applications: one utilizes satellite data and predictive models to forecast the oxygen needs of fish several days in advance, facilitating optimal feeding strategies, while the other enables fish farmers to evaluate different species and locations against long-term climate trends.

“Providing farmers with the right tools to adapt to current challenges and plan for the future is essential,” Papandroulakis concludes, highlighting the importance of proactive measures in the face of an uncertain climate.