Woolly sculpin struggling in acidic ocean waters.

Ocean Acidification: How It's Affecting Fish and What It Means for Us

Elliot Brynn in Climate & Environment August 2025 • 4 min read.

"New research reveals the surprising ways ocean acidification impacts fish, challenging previous assumptions and raising concerns about marine ecosystems."

Our oceans are facing a silent but potent threat: ocean acidification. As we pump more and more carbon dioxide into the atmosphere, a significant portion is absorbed by the seas, leading to a decrease in pH levels. This change in ocean chemistry has far-reaching implications for marine life, especially for creatures living in already challenging environments.

For years, scientists believed that teleost fish, a group that includes most of the fish we eat, were relatively resilient to these changes due to their well-developed acid-base regulatory systems. However, emerging research is painting a more complex and concerning picture. A recent study published in Conservation Physiology sheds light on how ocean acidification is affecting the woolly sculpin (Clinocottus analis), a small fish inhabiting the rocky intertidal zones of the California coast.

The study reveals that ocean acidification isn't just a looming threat, but an active stressor reshaping the physiological capabilities of marine life, with consequences that ripple through the food web and potentially impact us all.

The Hidden Costs of Acidity: What the Woolly Sculpin Reveals

Woolly sculpin struggling in acidic ocean waters.

The woolly sculpin, like many intertidal organisms, is accustomed to harsh conditions: fluctuating temperatures, salinity, and oxygen levels. Researchers Joshua R. Hancock and Sean P. Place from Sonoma State University sought to understand how ocean acidification might compound these existing stresses, particularly in relation to hypoxia, or low oxygen conditions. They exposed sculpins to both current and projected future ocean pH levels and meticulously examined their metabolic rates, hypoxia tolerance, and acid-base regulatory capacity.

What they discovered challenges the assumption that teleost fish are impervious to ocean acidification. The researchers found that sculpins acclimated to more acidic conditions exhibited elevated routine metabolic rates (RMR). This means they were burning more energy just to maintain basic bodily functions. This increased energy expenditure has significant knock-on effects. Think of it like this: imagine your car suddenly needing more fuel to travel the same distance. That extra fuel has to come from somewhere, potentially impacting other aspects of your life.

The study's key findings highlight these critical trade-offs:

Increased Metabolic Rate: Sculpins in acidified water worked harder to maintain internal balance.
Decreased Hypoxia Tolerance: The increased energy demand reduced their ability to cope with low oxygen conditions.
Acid-Base Regulation: Their bodies ramped up acid-base regulatory capacity (Na+,K+-ATPase activity) to maintain cellular function

The researchers also investigated whether ocean acidification affected the sculpins' reliance on facultative aerial respiration – their ability to breathe air when oxygen levels in the water are low. Surprisingly, even when exposed to severe anoxia, the sculpins did not display aerial respiration.. This lack of behavioural adaptation suggests that the treatments created a metabolic cost, which was high enough to affect the fish significantly.

The Bigger Picture: What This Means for Our Oceans

This research underscores that the impact of ocean acidification on marine ecosystems is more nuanced and potentially more severe than previously thought. Even fish with robust regulatory systems can face significant physiological challenges, leading to trade-offs that affect their survival and behavior. As ocean acidification continues, these subtle shifts in the physiology of key species can have cascading effects throughout the food web, impacting biodiversity, fisheries, and the overall health of our oceans. Understanding these complex interactions is crucial for developing effective conservation strategies and mitigating the impacts of climate change.

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This article is based on research published under:

DOI-LINK: 10.1093/conphys/cow040, Alternate LINK

Title: Impact Of Ocean Acidification On The Hypoxia Tolerance Of The Woolly Sculpin,Clinocottus Analis

Subject: Management, Monitoring, Policy and Law

Journal: Conservation Physiology

Publisher: Oxford University Press (OUP)

Authors: Joshua R. Hancock, Sean P. Place

Published: 2016-01-01

Everything You Need To Know

What is ocean acidification, and how does it occur?

Ocean acidification refers to the ongoing decrease in the pH of the Earth's oceans, caused by the uptake of carbon dioxide (CO2) from the atmosphere. As the ocean absorbs CO2, it leads to a series of chemical reactions that increase the concentration of hydrogen ions, making the ocean more acidic. This process impacts marine organisms, particularly those with calcium carbonate shells and skeletons, and can have cascading effects throughout marine ecosystems.

Which specific fish species and publication was the focus of the research highlighted, and what parameters were studied?

The *Conservation Physiology* study focused on the woolly sculpin (*Clinocottus analis*), a small fish living in the intertidal zones of the California coast. Researchers Joshua R. Hancock and Sean P. Place exposed these sculpins to current and projected future ocean pH levels and analyzed their metabolic rates, hypoxia tolerance, and acid-base regulatory capacity to understand how ocean acidification affects them, especially when combined with low oxygen conditions.

What were the key physiological findings of the study regarding how ocean acidification affects the Woolly Sculpin?

The study revealed that woolly sculpins exposed to acidified water exhibited increased routine metabolic rates (RMR), meaning they burned more energy to maintain basic bodily functions. This higher energy expenditure reduced their tolerance to hypoxia (low oxygen conditions) and increased their acid-base regulatory capacity (Na+,K+-ATPase activity) as their bodies worked harder to maintain cellular function. These findings challenge the assumption that teleost fish are unaffected by ocean acidification.

The research mentioned that ocean acidification affected the sculpins' reliance on aerial respiration; what was observed and why is it important?

While the study did not find evidence of aerial respiration in woolly sculpins under severe anoxia, this absence is significant. Aerial respiration is a coping mechanism for fish in low-oxygen environments. The fact that ocean acidification appears to inhibit this behavior suggests that the metabolic cost imposed by the more acidic conditions leaves the sculpins with insufficient energy to engage in this adaptive response. It indicates a critical constraint on their ability to cope with environmental stress.

What are the broader ecological implications of the physiological changes observed in the Woolly Sculpin due to ocean acidification?

The observed physiological changes in woolly sculpins due to ocean acidification can have far-reaching ecological consequences. Increased metabolic rates and reduced hypoxia tolerance can affect their growth, reproduction, and survival. These changes can cascade through the food web, impacting predators that rely on sculpins as a food source and potentially altering the structure and function of the entire intertidal ecosystem. Ultimately, these effects can threaten biodiversity, fisheries, and the overall health of our oceans.