Key Physico-Chemical Factors Impacting Coastal Fisheries

Coastal fisheries are under growing pressure from shifting environmental conditions. The ocean’s physical and chemical properties-temperature, pH, sea level, and weather patterns-directly shape where fish live, how they reproduce, and whether shellfish can build their shells. Understanding these physico-chemical factors is essential for managing coastal fisheries and preparing communities that depend on them.

Sea level rise and coastal vulnerability
Regional variations complicate planning
Sea surface temperature trends
Species shifts in Korean and East Asian waters
Implications for fishing communities
Coastal acidification and pH changes
Economic stakes for shellfish industries
Coral reefs and broader ecosystem effects
Extreme weather events
El Niño impacts on key fisheries
Storms, floods, and infrastructure damage
The interconnected challenge

Sea level rise and coastal vulnerability

Rising sea levels pose one of the most significant long-term threats to coastal fishing communities. According to NOAA, global average sea level has risen 21-24 centimetres since 1880, with the rate of increase more than doubling from 1.4 mm per year throughout most of the twentieth century to 3.6 mm per year between 2006 and 2015. This acceleration is driven by two primary mechanisms: thermal expansion of warming ocean water and the melting of glaciers and ice sheets.

For fisheries, this translates into direct habitat disruption. Rising seas create stress on coastal ecosystems that provide crucial habitat for fish, wildlife, and commercially valuable species. Saltwater intrusion into freshwater aquifers contaminates the water supplies that sustain both agricultural and natural ecosystems. This salinisation affects freshwater aquaculture facilities, rice cultivation areas, and the delicate balance of estuarine nursery habitats where many fish species begin their lives.

Regional variations complicate planning

Sea level rise is not uniform across the globe, which creates particular challenges for fisheries management. In the United States, the fastest rates occur in the Gulf of Mexico from the Mississippi’s mouth westward, followed by the mid-Atlantic coast. Only Alaska and a few Pacific Northwest locations currently experience falling sea levels-a trend expected to reverse under high-emission scenarios.

Small island nations face existential risks. The Maldives could see fisheries decline by nearly 100 percent by the end of the century under high-emission scenarios, according to World Bank analysis. The combination of rising seas, warming waters, and coral reef degradation threatens both the nation’s fishing industry and the tourism sector that depends on healthy marine ecosystems.

For coastal communities worldwide, the economic consequences are substantial. Communities relying on coastal tourism, fisheries, and shipping may feel the impacts most deeply. High-tide flooding is already occurring at twice the rate it was two decades ago along U.S. coastlines, damaging infrastructure and disrupting fishing operations.

Sea surface temperature trends

Warming ocean temperatures are reshaping where fish species can survive and thrive. Warming oceans, rising seas, melting sea ice, and increasing acidification are affecting ecosystem structure and the distribution and abundance of marine species across many regions. Coastal waters often warm faster than the open ocean due to their shallower depths and proximity to warming landmasses.

The consequences for fish populations are dramatic. Marine species are highly sensitive to temperature changes and respond by shifting their distributions toward cooler waters-typically northward in the Northern Hemisphere or into deeper offshore areas. The Northeast U.S. Shelf Ecosystem has experienced long-term warming trends that continue across all ecoregions, with winter-spring temperatures appearing to have undergone a step change around 2010, increasing mean temperature by about 1°C.

Species shifts in Korean and East Asian waters

Korean coastal waters provide a well-documented example of temperature-driven species redistribution. Research has documented climatic regime shifts that affected the dynamics of marine ecosystems and fisheries resources. Following a shift from cooling to warming in the late 1980s, warm-water species like Japanese anchovy, common squid, yellowtail, and tunas increased markedly in catches during the 1990s compared to the early-mid 1980s.

Conversely, cold-water species such as walleye pollock and Pacific cod decreased in abundance, with the regions where they remained most plentiful becoming greatly reduced in extent. Warm-water species expanded their range northward while cold-water demersal species retreated. This pattern of replacement-where dominant fish species shift from sardine and filefish to chub mackerel and squid-demonstrates how warming fundamentally reorganises coastal fish communities.

Similar shifts have been documented in the Bering Sea, where ocean surface warming corresponds with more northerly distributions for capelin and juvenile sockeye salmon. During warm periods, capelin biomass decreased while herring, age-0 pollock, and juvenile sockeye salmon biomass increased, illustrating how warming creates winners and losers among fish populations.

Implications for fishing communities

These distribution shifts create practical challenges. Fishermen face a choice: follow the schools northward or pursue different species. Larger-scale, well-financed fishing operations have advantages in adapting to shifting stocks, while small-scale fishers working hand-to-mouth struggle to relocate or change their gear. The warming also drives up animals’ metabolic rates, forcing them to use more oxygen while simultaneously reducing oxygen availability in warmer waters-a double burden that can cause species to lose significant portions of their habitat.

Coastal acidification and pH changes

The ocean absorbs roughly a quarter of the carbon dioxide humans release into the atmosphere. While this provides a buffer against even more rapid climate warming, it comes at a cost: ocean acidification is literally causing a sea change that threatens the fundamental chemical balance of ocean and coastal waters worldwide.

The consequences for shell-building organisms are severe. Changing ocean chemistry could hinder shell-building, as the calcium carbonate building blocks shellfish need become less abundant and surrounding seawater grows more corrosive. The process also affects shellfish metabolism, including feeding and respiration rates. Research at NOAA’s Milford Lab has found that shell weight is significantly lower in oysters raised in low-pH conditions compared to those kept at typical pH levels.

Economic stakes for shellfish industries

The shellfish industry faces mounting pressure from acidification. The Pacific Northwest, Long Island Sound, Narragansett Bay, Chesapeake Bay, Gulf of Mexico, and areas off Maine and Massachusetts have been identified as hotspots where the billion-dollar U.S. shellfish industry is particularly vulnerable. Alaska’s fisheries, which account for nearly 60 percent of U.S. commercial fish catch and support more than 100,000 jobs, are also at significant risk.

Recent estimates suggest ocean acidification has cost the Pacific Northwest aquaculture industry $110 million and approximately 3,200 industry-related jobs. Coastal areas along acidification hotspots-where factors like nutrient runoff, pollutants, and coastal upwelling push pH to relatively extreme lows-face compounded challenges.

The U.S. Pacific shellfish industry experienced a crisis beginning around 2007 when oyster larvae began dying in massive numbers at coastal hatcheries. It took months to discover the true culprit: the ocean water being pumped into tanks had become more acidic due to the overlap of human-caused CO₂ emissions and seasonal upwelling. The low pH and saturation state made shell production too energetically costly for the shellfish to survive.

Coral reefs and broader ecosystem effects

Acidification extends beyond shellfish to affect entire marine ecosystems. Coral reefs are weakening in the Caribbean and cold-water reefs off Scotland and Norway. Living corals on the Great Barrier Reef have declined by half over the past three decades, reducing habitat for fish and undermining the resilience of the entire reef system.

Oysters form the foundation of delicate ecosystems that provide billions of dollars in value through shoreline stabilisation, water filtration, and habitat creation. Research in Alabama showed that even loose-shell oyster reefs can reduce shoreline retreat by over 40 percent while increasing populations of species like blue crab by 297 percent and flounder by 79 percent. When acidification weakens these foundation species, the ripple effects extend throughout coastal ecosystems.

Extreme weather events

Climate change is intensifying the frequency and severity of extreme weather events that directly impact coastal fisheries. El Niño events bring marine heatwaves-periods of extreme warm ocean temperatures that can severely disrupt ocean ecosystems. With climate change, these marine heatwaves are becoming more frequent, intense, and persistent.

The El Niño-Southern Oscillation (ENSO) pattern fundamentally alters conditions for coastal fisheries. El Niño events are associated with physical and biological changes that affect fish distribution, including altered sea-surface temperatures, changes in the ocean’s thermal structure, and disrupted coastal upwelling currents. In the Northern Hemisphere, El Niño typically causes tropical warm-water species to extend their range northward while cold-water species move north or into deeper water, restricting their ranges.

El Niño impacts on key fisheries

The consequences for specific fisheries can be devastating. During the 2023-2024 El Niño, the Peruvian anchoveta fishery-the world’s largest single-species fishery, typically yielding 4.4 million tonnes annually-experienced significantly reduced habitat and food availability. The warm conditions affected anchoveta distribution, reproduction, and recruitment, with biomass reductions that can extend beyond the event itself.

The 2023-2024 El Niño also increased coral bleaching risk across the Pacific, threatening species that depend on reef habitats. The California Current ecosystem experienced both positive and negative conditions, with warm ocean waters mixing with nutrient-rich upwelling to produce intense harmful algal blooms that caused shellfish fishery closures and marine mammal strandings along the Pacific coast.

A major consequence of El Niño is the loss of commercially important species where they traditionally occur. Market squid move to cooler waters northward, away from established California fisheries. Many rockfish species relocate from nearshore areas to deeper or more northerly waters. Pacific whiting shift their spawning and feeding grounds. Pacific salmon populations experience increased mortality and reduced growth after El Niño events.

Storms, floods, and infrastructure damage

Beyond ENSO cycles, tropical cyclones and severe storms pose direct threats to fishing communities. Along the California coast, El Niño conditions shift storm trajectories, redirect precipitation patterns, and temporarily increase sea levels. When warm water floats over cooler water, it blocks upwelling processes that deliver essential nutrients to coastal ecosystems, disrupting the food web that supports fisheries.

As global warming continues, both the frequency and intensity of these events are expected to change. Marine heatwaves along the seafloor can be more intense and persistent than surface heatwaves, seriously impacting fish populations. The Bering Sea snow crab population declined by 90 percent following an intense heatwave in 2018. Marine heatwaves also increase the likelihood of harmful algal blooms, which produce toxins affecting shellfish, seabirds, and other wildlife while depleting oxygen as they decompose.

Coastal communities dependent on fisheries face compound risks. Infrastructure damage from storms affects fishing vessels, processing facilities, and ports. Erosion reshapes coastlines and destroys habitats. Flooding contaminates aquaculture operations. Estuaries become siltier, tidal patterns change, and storm surges push seawater upstream, increasing salinity in areas that previously supported freshwater-dependent species.

The interconnected challenge

None of these physico-chemical factors operates in isolation. Sea level rise compounds the damage from storms. Warming temperatures accelerate acidification rates in some regions. El Niño events temporarily intensify all these stressors simultaneously. For fishing communities, this means adapting not to a single change but to a shifting combination of pressures.

U.S. marine ecosystems annually contribute over $210 billion and 1.7 million jobs while providing vital services including recreation and coastal storm protection. Protecting these benefits requires understanding how warming, acidification, sea level rise, and extreme weather interact to reshape coastal fisheries. The communities that have traditionally depended on predictable fish populations and stable coastal conditions face an uncertain future that demands both scientific understanding and adaptive management strategies.

What do you think? How should coastal fishing communities balance the need for immediate livelihoods with long-term adaptation to changing ocean conditions? What role should governments play in supporting fishers who must relocate or shift to different species as traditional stocks move or decline?

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References

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Table of Contents

Sea level rise and coastal vulnerability 🔗

Regional variations complicate planning 🔗

Sea surface temperature trends 🔗

Species shifts in Korean and East Asian waters 🔗

Implications for fishing communities 🔗

Coastal acidification and pH changes 🔗

Economic stakes for shellfish industries 🔗

Coral reefs and broader ecosystem effects 🔗

Extreme weather events 🔗

El Niño impacts on key fisheries 🔗

Storms, floods, and infrastructure damage 🔗

The interconnected challenge 🔗