Baku, September 24, AZERTAC
In an exclusive interview with AZERTAC on the World Maritime Day, Ronny Berndtsson, Professor of water resources engineering at Sweden’s Lund University and Director of the Centre for Advanced Middle Eastern Studies, highlighted what needs to be done to preserve marine ecosystems; how increasing sea temperature affect coastal ecosystems and global sea levels; and if humanity could face a seafood storage.
- What needs to be done first and foremost to preserve marine ecosystems?
- In my view, the priority has to be reducing the multiple pressures on the ocean simultaneously, with climate change at the center.
The ocean is remarkably resilient, but resilience has limits. A coral reef, seagrass meadow, mangrove or fish population that is exposed simultaneously to warming, acidification, overfishing, nutrient pollution, plastics and habitat destruction has much less capacity to recover from any individual disturbance.
Therefore, I would put the priorities in this order:
1. Reduce greenhouse-gas emissions. This is fundamental because ocean warming and acidification are ultimately driven by the accumulation of atmospheric greenhouse gases.
2. Stop overexploitation of marine resources. Fisheries need to be managed according to changing ecosystem conditions rather than historical assumptions about where and how much fish will be available.
3. Protect and restore critical coastal habitats, coral reefs, mangroves, seagrass beds, salt marshes and kelp forests. These ecosystems provide nursery grounds, carbon storage, coastal protection and food.
4. Reduce land-based pollution, particularly nutrients, untreated wastewater, plastics and agricultural chemicals entering rivers and ultimately the sea.
5. Make international agreements enforceable in practice. This is where this year's World Maritime Day theme is particularly appropriate: the gap between international commitments and implementation needs to be closed. The IMO itself emphasizes translating regulations into national legislation, enforcement, training and practical action.
Marine protected areas are an important tool, but protection on paper is not enough. UNEP estimates that ocean coverage would have to increase substantially to meet the global 30%-by-2030 conservation target, while effective management remains a major challenge.
- How does increasing sea temperature affect coastal ecosystems and global sea levels?
- For coastal ecosystems, warmer water pushes species beyond their physiological limits. Coral reefs are perhaps the clearest example. Persistent temperatures only about 1–2°C above the normal range can trigger mass coral bleaching and mortality. Once reefs are degraded, their ability to support biodiversity and protect coastlines from waves and storms is also reduced.
Warming also changes where species can live. Many marine species are moving toward higher latitudes or deeper, cooler water. This changes food webs and can fundamentally alter the composition of coastal ecosystems. At the same time, warmer water holds less oxygen and increases stratification, making it more difficult for oxygen to reach deeper waters.
There is then a direct physical connection with sea-level rise. Warmer seawater expands—known as thermal expansion—and therefore raises sea level. The other major contribution is melting of land-based glaciers and ice sheets. IPCC estimates indicate that thermal expansion accounted for about half of global sea-level rise during 1971–2018, while melting land ice contributed most of the remainder.
This creates feedback of sorts for coastal societies: warmer seas damage natural coastal protection while rising seas increase the pressure on those same ecosystems and communities.
- What happens to commercial fish stocks, and could we face a seafood shortage?
-There is a serious future food-security risk, but I would not describe the future simply as “the oceans will run out of fish.”
Climate change changes where fish are found, how fast they grow, when they reproduce and how productive different ecosystems are. The IPCC reports that warming and changes in primary production are already affecting fisheries catches and their composition in many regions.
Fish species generally respond by moving toward cooler waters. This can produce winners and losers geographically: northern fisheries may temporarily gain access to species moving poleward, while tropical and subtropical fisheries can experience substantial losses. This is particularly serious for countries and coastal communities whose diets and economies depend heavily on local fisheries.
The chemical changes in seawater add another problem. Increasing atmospheric CO₂ is absorbed by the ocean, lowering pH and reducing carbonate-ion availability. This makes it more difficult for oysters, mussels, corals and other calcifying organisms to build shells or skeletons. These organisms are also part of larger marine food webs, so the consequences can extend beyond shellfish themselves.
There is encouraging evidence that good fisheries management can substantially improve resilience. The latest FAO assessment reports that global aquatic-animal production reached a record level, with aquaculture exceeding 100 million tons for the first time in 2024. At the same time, FAO stresses that sustainability and equity remain major challenges.
But climate change makes that task harder. FAO's 2026 assessment notes that if warming continues at the current rate, the amount of fish that fisheries can sustainably catch could decline by more than 10% by 2050 in several regions. More than 3.1 billion people currently obtain at least 20% of their animal protein from aquatic foods, so this is not simply an environmental issue—it is a food-security and social issue.