How will sea life adapt to climate change? Grunion might show us clues, says new CSU Long Beach study

AP Photo/Gary Florin, Cabrillo Marine Aquarium

Grunion, the little fish that come to shore to spawn along Southern California beaches, may hold clues as to how sea life will adapt to the effects of climate change on the ocean, according to a new study from California State University, Long Beach.

Researcher Darren Johnson conducted a series of experiments with grunion caught in Seal Beach. He found some families of grunion seemed better able to adapt to ocean acidification.

Grunion — unique little fish found only in Southern California and down south in Baja — mate on the sand when the waves wash them to shore. Grunion running season attracts droves of people who show up at beaches in the dark of night to wait and watch, some ready with buckets to collect the fish to eat when catching is allowed.

The grunion model

Johnson, an assistant professor for biological sciences, studied more than 300 grunion alongside then-graduate student Alexander Tasoff.

“Because of how grunions spawn, it was easier to track the genetic lineages of fish from particular groups of eggs,” according to a CSU Long Beach news release.

Each female lays 2,000 to 3,000 eggs. They have a short life — only about five years max — and grow to about six inches long. The females bury themselves up to the fins and lay their eggs, and the males deposit their milt, or seminal fluid, on top.

Waves then bury the eggs under sand, where they stay for 10 to 14 days before the baby grunion hatch.

The grunion in the experiment, collected while spawning during late-night hours in Seal Beach, were eventually released back into the ocean.

Grunion also share life cycle traits with other fish that live close to the shore, making them a convenient model species for studying how such fish might adapt to changes in seawater chemistry, according to the paper.

Acidifying ocean

Carbon dioxide is a greenhouse gas that contributes to climate change. Over time, the ocean becomes more acidic as it absorbs and reacts with carbon dioxide in the atmosphere.

Ocean acidification can reduce the growth and survival of marine species during their larval stages, according to the study.

Johnson tested different groups of grunion by putting them in water with varying levels of carbon dioxide, attempting to mimic the conditions of ocean acidification.

Test results showed that more acidic conditions increased the death rates of grunion larvae, but did not have a significant impact on the growth of the surviving larvae into mature grunion.

In fact, some families of grunion might be better adapted to survive ocean acidification.

“Despite the overall increase in mortality with low pH, different groups of larvae (each of which was a full sibling family) varied widely with respect to differences in mortality between the pH treatments,” the study reads.

But it was tricky to replicate natural ocean variations in the lab, according to the study: “For example, water temperature and food availability are dynamic in nearshore waters, and the females used in this experiment would have developed their eggs under different sets of ocean conditions.”

Since experiments were conducted over 14 days, the study also called for further research over longer periods of time.

“Understanding whether fish populations can adapt over time and become at least somewhat more tolerant of changes in seawater chemistry will help us anticipate more accurately the long-term effects of ocean acidification,” Johnson said in the news release.

The research paper will be printed in the March issue of Evolutionary Applications.

Laylan Connelly, Press-Telegram, 13 February 2019. Article.

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