Glacier silt inhibiting kelp affects larger ecosystem

Photo courtesy of Sarah Traiger. Kim Powell replaces tubes on a sediment trap to measure silt in Kachemak Bay.

Photo courtesy of Sarah Traiger. Kim Powell replaces tubes on a sediment trap to measure silt in Kachemak Bay.

By Carey Restino

Homer Tribune

Old-timers will tell you that, back in the day, the glaciers of Kachemak Bay stretched across far more domain than now. Today, many are receding at a rapid rate, in pace with large ice fields worldwide said to be responding to temperature increases.

The increased glacier silt from all that melting ice is causing problems for at least one species in Kachemak Bay — kelp.

A recent study by the University of Alaska Fairbanks found that increased silt may be making it difficult for kelp to attach to underwater rocks. In addition, the silt in the water may be blocking sunlight to the bottom layers of the bay, limiting kelp’s ability to photosynthesize.

Brenda Konar, a professor at the University of Alaska Fairbanks School of Fisheries and Ocean Sciences, is working with doctoral student Sarah Traiger to study the effects of glacier melt on kelp reproductive cells’ ability to travel, settle and grow in Kachemak Bay.

The Harding Icefield has shrunk by 3 percent over the past 16 years, the National Park Service reports, resulting in more glacial silt in the water.

“As glaciers on the Harding Icefield continue to melt, we need to understand how communities and ecosystems are likely to change,” Konar said.

Konar and Traiger did much of their work, which was funded by Alaska Sea Grant, the university’s Center for Global Change and the Robert Byrd competition, during the summers of 2013 and 2014. They studied not only areas where glacier melt was expected to be an influence, but also areas in outer Kachemak Bay, where it was not expected to be much of an influence.

The two placed flat rocks at each of the study sites and measured the species that settled and grew on each rock. According to the researchers, grazing animals, such as sea urchins, were the biggest factor in reducing early kelp growth. But as sediment built up on the rocks, silt became the primary preventer of growth.

Kelp forests are important to coastal areas for a variety of reasons. They act as a nursery for fish and invertebrates, and prevent coastal erosion. They also provide habitat for chitons and crabs and are even a source of food for some residents near Kachemak Bay.

This isn’t the first study to warn of the impacts of glacial silt on marine organisms.

According to media reports, scientists say high glacier melt rates in Antarctica have impacted a wide variety of animals that eat tiny material suspended in water. Too much sediment is difficult for the creatures to filter out.

“This research gives us a baseline understanding of what we should monitor to determine what is changing and what is likely to change in the future,” Konar said. “It allows us to evaluate what might happen to populations downstream if glacier melt continues to increase over time.”

Konar said the results will help managers and decision-makers predict and prepare in advance for changes.

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Filed under ecology, glaciers, Kachemak Bay

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