The Seas Are Warming Too... And That Should Make Us Very Afraid

By Hanis Razalli, Prof. Dato’ Dr. Aileen Tan

April 2024 FEATURE
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PENANG IS SURROUNDED by a sea that protects us, provides food and—the island being small—moderates our climate. Now, imagine a world where our oceans are heating up, leading to a cascade of threats to marine life and coastal communities—sea levels rise, marine ecosystems crash and extreme weather events become more frequent.

This crisis goes beyond mere sunburns at the beach; it is about the survival of diverse marine ecosystems and maintaining the balances which nurture life. As global temperatures climb, the ocean currents that dictate our climate patterns change. Studies have shown that sea surface temperatures have risen by an average of 0.18°C per decade globally, with coastal waters experiencing a higher rate of increase compared to open oceans. [1] This accelerates coral bleaching and kills reefs—over 90% of the reefs in the Great Barrier Reef in Australia experienced unprecedented mass bleaching in 2016. [2] Malaysia has not been spared; many of the reefs in the Straits of Malacca and the South China Sea have been affected.

As our oceans warm, a ripple effect threatens the foundations of global fisheries and aquaculture—industries that millions rely on for livelihood and sustenance. Rising sea surface temperatures lead to longer, more severe marine heatwaves, disrupting marine ecosystems and causing fish habitats to change or disappear.

Here, this means that the whole seafood industry is at risk. A trawl survey in 2016 conducted by the Department of Fisheries Malaysia revealed a significant decline in the country’s demersal (bottom-living) fish populations, showing an 88% decrease in biomass and densities compared to original stock levels. [3] It highlights a concerning trend in catch volume— in 2016, a notably productive year, Malaysia’s total marine fish catch was 1.57 million tonnes. By 2022, this figure had fallen to 1.31 million tonnes, marking a substantial reduction of approximately 16.5% from the previous catch levels.

No wonder fish is now expensive.

The Science Behind the Warming Seas

Most of the extra heat from our carbon emissions end up in the ocean, causing not just surface warming but affecting the depths, altering the balance of marine life and the global climate. This increasing heating trend, driven by our carbon footprint, poses a significant challenge to many species on Earth, including us.

Imagine the ocean as the Earth’s thermostat, finely tuned to regulate the climate by absorbing heat from the sun and distributing it across the globe. The ocean’s surface, often referred to as Earth’s “skin layer”, absorbs about 90% of the solar radiation that reaches Earth. This not only warms the surface water but also, through processes like convection and oceanic currents, distributes heat to deeper ocean layers, illustrating the ocean’s capacity to serve as a critical climate regulator. But the whole ocean system is connected and what affects other oceans has dire implications on the seas around Penang.

As global warming reduces the Arctic Sea’s ice cover, we observe the “albedo effect” at play. With less ice to reflect sunlight, the darker ocean surface absorbs more solar energy, significantly accelerating ocean warming. This is not just about warmer waters; it is a fundamental shift affecting everything from the ocean’s depths to the polar ice cap and tropical marine ecosystems. For example, the warming sea has disrupted the breeding patterns of polar species such as the masses of krill Antarctic shrimps—a key species in the marine food web. Migratory species such whales and birds that are part of our tropical ecosystem are also affected.

Ocean currents, acting as nature’s conveyor belts, play a pivotal role in climate regulation by redistributing heat globally. The Thermohaline Circulation moves warm water from the equator towards the poles and cold water from the poles back to the equator—a critical process in stabilising the global climate. This intricate dance of warming waters and shifting currents highlights the ocean’s power in shaping our climate; a dance that is now out of step, as it were.

Heat and Its Impact on Marine Ecosystems

Rising sea temperatures have significant impacts on crucial marine habitats such as coral reefs and seagrass beds. Coral reefs—the rainforests of the sea—are particularly at risk of bleaching, which occurs when their life-giving algae partner is expelled from their tissues, causing them to bleach and making them vulnerable to disease and death. The algae also provide corals with essential nutrients in exchange for a home and protection. This coral-algae relationship is crucial for their survival.

Similarly, the growth, reproductive patterns and metabolic functions of seagrass beds and mangroves, which are crucial nurseries for many marine species, are also affected by warming waters. Increased sedimentation from these events restricts sunlight penetration essential for seagrass survival, affecting the habitat and food source for a variety of marine life.

As the ocean warms, a silent migration occurs beneath the waves; fish and marine creatures begin seeking refuge in cooler waters. This shift towards higher latitudes or deeper depths has led to tropical species appearing in temperate zones, such as the sighting of lionfish, a tropical predator, in the Mediterranean Sea. [4] Such refugees can drastically alter local marine biodiversity. Species once alien to certain areas are now becoming local, disrupting existing food webs and competing with native species for space and resources. This changes the composition and function of marine ecosystems and challenges fisheries, conservation strategies and the stability of marine habitats.

Furthermore, our oceans are not only warming but also becoming more acidic, which poses a threat to marine organisms worldwide. Oceans absorb approximately a quarter of the CO₂ emitted into the atmosphere annually. CO₂ levels rising leads to a decrease in the pH of water and, by nature, its chemistry. This gradual acidification affects calcium carbonate availability, something crucial for the skeletal structures of many marine organisms such as corals, molluscs and many planktons.

Beyond physical harm, ocean acidification disrupts the sensory systems of some fish, making it harder for them to detect predators or navigate to breeding grounds. Research has shown that increased CO₂ levels interfere with neurotransmitter functions, which are critical for these sensory processes. [5]

Moreover, ocean acidification can alter phytoplankton communities’ structure, which forms the base of the marine food web. These communities, small in size but huge in numbers, are primary producers, which means that their decline has cascading effects up the food chain. [6] The combined effects of ocean acidification and warming threatens to lead to habitat loss and shifts in entire marine ecosystems, affecting biodiversity and ecosystem functioning.

Effects on Coastal Fisheries

Studies reveal a concerning trend: as waters warm, fish catches become smaller, younger and less abundant. [7] This phenomenon is attributed to the increased metabolic demand in warmer waters, which limits energy available for growth and reproduction. This warming effect, coupled with fishing pressures, paint a grim picture for fish populations, threatening the collapse of fisheries and the communities that rely on them. Coastal cities like Penang are particularly vulnerable.

Fishermen around the globe are navigating the stormy seas of change, triggered by climate change, overfishing and environmental degradation. As fish populations shift in response to warming waters, fishermen are forced to venture further out, facing rising fuel costs and longer journeys that strain their daily life.

Addressing these issues requires a multifaceted approach, including implementing sustainable fishing quotas, protecting critical habitats and investing in aquaculture as an alternative source of fish protein.

For communities that have thrived on fishing for generations, these changes threaten their way of life. As the impacts of climate change deepen, the sustainability of fishing practices and the communities that depend on them hang in a precarious balance, making the need for adaptive strategies and sustainable management more urgent than ever.

The potential for job losses and economic turmoil is significant, particularly as fisheries management adapts to these environmental changes. Implementing catch limits to protect fish populations may initially reduce income for fishermen. However, these measures are crucial for long-term sustainability, with economic models suggesting that they could lead to more stable fisheries and, consequently, more reliable incomes in the future.

Encouragingly, some communities are pioneering adaptive strategies, such as diversifying income sources beyond fishing and adopting new technologies for sustainable harvests. These efforts showcase resilience and the potential for a harmonious balance that fishing communities can strike with the marine environment.

Aquaculture Challenges

Then comes the threat of diseases. Warmer temperatures create optimal conditions for pathogens to thrive—bacteria multiply and spread more quickly in elevated temperatures. This effect is especially pronounced during warmer months when water temperatures consistently exceed the normal range.

The challenge does not stop there; intensified farming practices amplify these risks, turning aquaculture into a tightrope walk between productivity and the outbreak of diseases. Adopting sustainable practices can mitigate these risks, such as reducing the density of fish stocks, which minimises stress and aggression among fish, lowering their vulnerability to infections. Similarly, enhancing water flow in farming pens improves oxygenation and waste removal, creating a less hospitable environment for pathogens.

Aquatic farming, from clam growth to plankton productivity, is acutely responsive to minor shifts in water temperature. Small shifts in water temperature can significantly disrupt the timing of critical lifecycle events such as spawning, migration and growth. A slight increase in temperature can accelerate growth rates but also shorten the lifespan of species like clam. This reduces the productivity of shellfish such as the blood cockles (ham), the Venus clam (lala) and other shellfish, both in the wild and in aquaculture systems. [8]

Increased temperature also translates to lowered capacity for water to hold oxygen, exacerbating the challenges in aquaculture by altering nutrient dynamics and microbial communities. This, disrupting the balance of microbial communities and favouring the growth of harmful algae over beneficial species, hinders the growth and health of farmed organisms and those in the wild.

This imbalance results in algal blooms, such as a red tide, which produce toxins harmful to marine life. As they consume vast amounts of oxygen, exacerbating deoxygenation, “dead zones” come into being which are so devoid of oxygen that most marine life cannot survive. This is already happening in Penang, as witnessed in the recent event at Teluk Bahang, where a significant loss of aquatic life had drastically impacted local aquaculture operations. [9]

Research demonstrates that clams and seaweed, integral components of aquaculture, play pivotal roles in enhancing ecosystem services. Bivalves, like oysters and mussels, naturally filter out pollutants, improving water quality in our seas, while seaweed acts as a carbon sink, absorbing CO₂ from the atmosphere and mitigating the effects of climate change. Adopting polyculture practices, where different aquatic species are farmed together, offers mutual benefits such as nutrient cycling and disease control. For example, combining seaweed with shellfish farming can enhance overall productivity and environmental health by utilising seaweed’s ability to absorb excess CO₂ and providing habitat for marine life.

Implementing low-impact farming techniques such as floating cages for shellfish that allow natural water flow and that reduce the need for feed, minimises the environmental footprint. These methods not only preserve water quality but also ensure the health and growth of farmed species without disrupting local ecosystems. The Japanese oyster industry, severely impacted by climate extremes, saw an alarming 90% mortality rate in 2020. [10] This devastating loss, attributed to unprecedented warming waters, underscores the vulnerability of aquaculture to climate variability and the urgent need for adaptive strategies. There is a critical need for strategic planning and site selection in aquaculture, emphasising environmental resilience and climate adaptability. Carefully choosing locations by evaluating factors such as water depth, temperature stability and protection against extreme weather is key to safeguarding the industry’s future and adapting to the unpredictable impacts of climate change.

In the face of warming seas, aquaculture, through a combination of cutting-edge science, innovative and resilient strategies, and mindful stewardship, is an answer offering sustainability and adaptability. One innovative response is the development of selective breeding programmes focused on creating heat-resistant breeds. By identifying and selecting genetic traits that confer temperature tolerance and disease resistance, researchers can produce parents that are better adapted to survive in warming waters. Genomic selection emerges as a powerful tool in this quest, honing in on disease resistance and other vital traits to secure the future of aquaculture species.

Beyond genetics, the blueprint for resilience includes revamping farm management—integrating advanced water circulation systems to stabilise temperature and oxygen levels and optimising nutrition to bolster fish health and growth. The health of our aquatic farms also hinges on our vigilant monitoring of water quality.

Beyond immediate farm productivity, embracing sustainable aquaculture practices plays a crucial role in environmental conservation. Techniques such as polyculture (raising different species together), using renewable energy sources and participating in habitat restoration projects not only reduce the industry’s environmental footprint but also contribute to the restoration of aquatic ecosystems.

Meeting the Challenges of a Warming Sea

We can alleviate pressure on the vulnerable marine ecosystems of Penang with the development of heat-resistant marine species, expanding protected areas, and embracing sustainable fishing and aquaculture. Community initiatives like beach clean-ups and mangrove reforestation, alongside global efforts to curb emissions, demonstrate the potential for collective action to foster change.

Adopting renewable energy and supporting conservation are also vital.

United in our efforts, we can preserve marine biodiversity, sustain fishing communities and secure food sources for us and future generations.

  • [1] Pachauri, Rajendra K., et al. Climate change 2014: synthesis report. Contribution of Working Groups I, II and III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. IPCC, 2014.
  • [2] Hughes, Terry P., et al. "Global warming and recurrent mass bleaching of corals". Nature, vol. 543, no. 7645, 2017, p. 373-377.
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  • [5] Munday, Philip, et al. "Ocean acidification impairs olfactory discrimination and homing ability of a marine fish". Proceedings of the National Academy of Sciences, vol. 106, no. 6, 2009, p. 1848-1852.
  • [6] Dutkiewicz, Stephanie, et al. "Impact of ocean acidification on the structure of future phytoplankton communities". Nature Climate Change, vol. 5, no. 11, 2015, p. 1002-1006.
  • [7] Dorst, Renee M., et al. "Warmer and browner waters decrease fish biomass production". Global Change Biology, vol. 25, no. 4, 2019, p. 1395-1408.
  • [8] Canu, Donata M., et al. "Effect of global change on bivalve rearing activity and the need for adaptive management". Climate Research, vol. 42, no. 1, 2010, p. 13-26.
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Hanis Razalli

is a Research Officer and consultant specialising in the marine environment. Her present research focuses on creating and maintaining marine reserves in a sustainable manner. She is currently working on Penang's islands and marine sanctuaries towards meeting the goals of SDG 2030.

Prof. Dato’ Dr. Aileen Tan

is the Director for the Centre for Marine and Coastal Studies, USM. Her experience on aquaculture helped develop several key national and international projects in this field.