By Milliam Murigi
Every Monday, scientists set out from Narragansett Bay, Rhode Island, USA aboard a research vessel.
Each team pursues a different study but shares a common mission: to understand how a warming ocean is changing marine life.
One team hauls trawl nets through the water to monitor fish and invertebrates while another collects bottles of seawater teeming with microscopic plankton invisible to the naked eye.
Together, their work is documenting a quiet but profound transformation unfolding beneath the waves, one that is changing the ocean from its tiniest organisms to its largest fisheries.
“For more than six decades, researchers at the University of Rhode Island’s Graduate School of Oceanography have monitored this bay, creating one of the world’s longest-running marine time series,” says Alex Rubin, a graduate assistant working on the Rhode Island university’s fish trawl survey.
Their findings reveal that climate change is not only shifting where marine species live but also altering the delicate food web that supports life in the ocean.
From microscopic plankton to prized lobster, climate change is reshaping life beneath the waves, forcing fisheries to adapt while exposing new risks to food security, coastal livelihoods and human health.
“Over the past 65 to 66 years, we’ve seen a considerable change in the fisheries community,” Rubin says. “Back in the 1950s, 1960s and 1970s, the community was mostly dominated by bottom-dwelling fish and invertebrates. Today, we’re seeing more mid-water and pelagic species.”
The shift reflects a broader trend occurring in oceans around the world. As waters warm, species that thrive in cooler temperatures are moving northward or into deeper waters, while warm-water species expand into areas that were once too cold to support them.
Among the clearest examples in Rhode Island is squid. Once uncommon in Narragansett Bay, squid have become increasingly abundant over the past three to four decades and are now a familiar sight throughout spring, summer and early autumn.
The changing waters have also transformed the state’s once-thriving lobster industry. As temperatures have climbed, lobster populations have steadily migrated north into the cooler waters of the Gulf of Maine, forcing many fishers to abandon traditional fishing grounds and target different species instead.
“Changing your target species often means changing your gear, and that comes with significant costs,” Rubin explains. “Fortunately, Rhode Island fishers have shown remarkable adaptability because their livelihoods depend on responding to these changes.”
Thousands of kilometres away, coastal communities in Kenya are beginning to face similar realities, although in different ways. Along Kenya’s coastline, artisanal fishers rely heavily on coral reefs, seagrass meadows and mangrove ecosystems for fish such as snapper, octopus and lobster among others.
As sea temperatures continue to rise and coral reefs come under increasing stress, fish are becoming less abundant in some traditional fishing grounds, forcing fishers to travel farther offshore, spend more time at sea and incur higher operating costs.
Scientists warn that coral reefs, which serve as breeding, nursery and feeding grounds for many commercially important fish species, are particularly vulnerable to rising ocean temperatures. Repeated coral bleaching events will reduce reef biodiversity and ultimately affect fish populations that millions of coastal residents depend on for food and income.
While shifting fish populations are the most visible sign of a warming ocean, scientists say the story begins much deeper in the food web. Alyssa Tsukada, a PhD student in Biological Oceanography at the University of Rhode Island’s Graduate School of Oceanography, says warming waters are altering the foundation of the marine food web by changing the abundance and composition of microscopic plankton, organisms that sustain nearly all marine life.
“Phytoplankton form the base of the marine food chain. They not only provide food for everything from tiny zooplankton to commercially valuable fish species, but they also remove carbon dioxide from the atmosphere through photosynthesis, making them critical in regulating Earth’s climate,” Tsukada says.
Warming waters are also favouring smaller phytoplankton cells. While the difference may seem insignificant, it ripples throughout the marine food web because fish must consume much larger quantities to obtain the same amount of energy.
The same process has important implications for Kenya’s Blue Economy. Phytoplankton also form the base of the marine ecosystem that supports fish harvested along the Kenyan coast. Changes in their abundance or composition can cascade through the food chain, affecting fish populations, seafood availability and the livelihoods of coastal communities.
Although inland fisheries contribute the largest share of Kenya’s fish production, marine fisheries remain a vital source of food, employment and income for thousands of households in Mombasa, Kilifi, Kwale, Lamu and Tana River counties.
Scientists have also observed another subtle but significant change. As ocean temperatures rise, certain harmful algal blooms are flourishing and outcompeting other phytoplankton. Some harmful algae produce toxins that accumulate in shellfish and other seafood. When contaminated seafood is eaten, those toxins can cause serious illnesses, including amnesic shellfish poisoning.
“The warmer the water becomes, the more opportunities some harmful algal bloom species have to outcompete other phytoplankton. That creates risks not only for marine ecosystems but also for fisheries and public health,” Tsukada says.
The impacts are already visible across Narragansett Bay, which has warmed by nearly three degrees over recent decades. Some fish populations have shifted toward the mouth of the bay where cooler but rougher waters make fishing more challenging. Similar changes are increasingly being reported across the globe as marine species follow temperatures suitable for their survival.
Along Kenya’s coast, scientists are also recording above-average sea surface temperatures that increase the risk of coral bleaching and other climate-related impacts on marine ecosystems. These changes threaten not only biodiversity but also food security and the country’s ambitions of growing a sustainable blue economy.
The consequences extend far beyond fisheries. Harmful algal blooms can force beach closures, degrade water quality, kill marine life by reducing oxygen levels and damage tourism and coastal economies that depend on healthy oceans.
As climate change accelerates, Rubin says investing in marine science has become more urgent than ever, enabling scientists to better understand rapidly changing oceans and help communities prepare for the future. He adds that seafood remains a major contributor to both food security and national economies, making investment in marine science increasingly important.
“The ocean covers about 70 percent of the Earth’s surface and plays a major role in global weather patterns, biodiversity and food production. The more we understand how the ocean is changing, the better prepared we will be to respond and build resilience,” he says.
For Tsukada, sustained investment in marine research is essential because the world’s oceans are deeply interconnected, meaning environmental changes in one region can have ripple effects on ecosystems thousands of kilometres away.
She says continuous scientific monitoring helps researchers detect emerging threats early, understand how marine ecosystems are responding to climate change and provide governments and coastal communities with the evidence needed to protect fisheries, safeguard public health and develop effective adaptation strategies.
“Understanding our oceans is much more than science. It’s about protecting human health, supporting fisheries, sustaining coastal economies and preserving ecosystems for future generations,” she says.
While scientists acknowledge uncertainty in predicting exactly what marine ecosystems will look like in the coming decades, Rubin says current trends provide a clear indication of where the future is heading.
“We’ll likely continue seeing changes in the timing of biological events such as fish and squid spawning,” he says. “Species that prefer cooler waters will continue moving north, while warm-water species will keep expanding into areas that were once too cold for them.”
