Warming oceans decimated sea parasites to damage environment

By Gwyn Wright via SWNS

Warming oceans have decimated sea parasites - but that is still damaging to the overall environment, warns a new study.

Scientists have found fish parasite populations plummeted in the Puget Sound estuary in the U.S. state of Washington between 1880 and 2018, while sea temperatures rose significantly.

However, this is still worrying because parasites help push energy through food webs and support predators at the top of the food chain.

Lead study author Professor Chelsea Wood from the University of Washington in Seattle said: “While parasites inspire fear or disgust — especially for people who associate them with illness in themselves, their kids or their pets — the result is worrying news for ecosystems.

“People generally think that climate change will cause parasites to thrive, that we will see an increase in parasite outbreaks as the world warms.

“For some parasite species, that may be true, but parasites depend on hosts, and that makes them particularly vulnerable in a changing world where the fate of hosts is being reshuffled.”

Some parasites have a single host species but many of them travel between host species.

Eggs are carried in one host species before the larvae emerge and infect another host.
The adult may reach maturity in a third host before laying eggs.

The number of parasites in Puget Sound fish that rely on three or more hosts during their life declined by 11 percent every decade on average.

Of 10 parasite species that had disappeared completely by 1980, nine relied on three or more hosts.

The researchers called the decline in such parasite species “severe," and added that it would trigger calls for better conservation if it had occurred in “species people care about” such as mammals and birds.

In contrast, the number of parasite species that rely on just one or two host species remained fairly constant.

For the study, the team used a new method for resurrecting information about historic parasite populations.

While mammals and birds are preserved with taxidermy, which retains parasites only on skin, feathers or fur- fish, reptile and amphibian specimens are preserved in fluid, which also preserves any parasites living inside the animal at the time it died.

The study focused on eight species of fish that are common in the behind-the-scenes collections of natural history museums.

Most came from the University of Washington Fish Collection at the Burke Museum of Natural History and Culture in Seattle.

The team carefully sliced up the fish specimens and manually counted how many parasites they found inside before returning them to museums.

In total, they counted 17,259 parasites of 85 types from 699 fish specimens.

Among the parasites they found were animals with an outside skeleton as well as crustaceans and tapeworms called the trypanorhyncha, whose heads are armed with hook-covered tentacles.

The team considered the abundance of host species in Puget Sound, pollution levels and rising temperatures as possible causes, but found the latter was the most likely cause of the decline.

Sea temperatures in Puget Sound rose by one degree Celsius between 1950 and 2019.

Wood added: “This study demonstrates that major parasite declines have happened in Puget Sound.

“If this can happen unnoticed in an ecosystem as well studied as this one, where else might it be happening?”

“I hope our work inspires other ecologists to think about their own focal ecosystems, identify the right museum specimens, and see whether these trends are unique to Puget Sound, or something that is occurring in other places as well.

“Our result draws attention to the fact that parasitic species might be in real danger.

“That could mean bad stuff for us — not just fewer worms, but less of the parasite-driven ecosystem services that we’ve come to depend on.”

The findings were published in the journal Proceedings of the National Academy of Sciences.