6 years later, marine life still hasn't recovered from the ocean's monstrous heat

6 years later, marine life still hasn’t recovered from the ocean’s monstrous heat

Nicknamed “The Blob,” a large patch of unusually warm water that covered a stretch of the Pacific Ocean from 2014 to 2016 behaved like a B-grade horror movie, wreaking havoc on a variety of species.

A new study of the Santa Barbara Channel off the California coast shows how this environmental horror show continues to affect marine ecosystems.

The blob caused significant changes in aquatic ecosystems at the time, particularly affecting sessile animals that were stuck in place like anemones. This latest research shows that six years later, the underwater populations that inhabit the kelp forest ecosystem are still not where they were.

While the numbers of sessile invertebrates — filter feeders attached to reefs — have recovered overall, numbers of invasive species have declined Watersipora subatra (a newcomer) and Bugula neritina (a long-term resident) have experienced a boom. These are species of bryozoans; tiny, colonial, tentacled animals that essentially work together in groups as a single organism.

“The animal groups that seemed to be the winners, at least during the warm period, were longer-lived species like mussels and sea anemones,” says ecologist Kristen Michaud of the University of California, Santa Barbara.

“But after the blob, the story is a little different. Bryozoan coverage increased fairly quickly, and there are two types of invasive bryozoans that are much more common now.”

Sessile invertebrate numbers initially declined 71 percent in 2015 when the blob took hold, as warmer water meant creatures like anemones, tubeworms and clams ran out of phytoplankton to feed on.

Plankton depend on nutrients brought up by colder water that was limited thanks to the warm water’s presence. The metabolism of these sedentary invertebrates was also boosted by the heat, meaning they needed even more of the food they couldn’t get.

Several causes could account for the dominance of W.subatra and B. neritina, the researchers say: This includes the ability to survive at higher temperatures and compete more aggressively for space on reefs. Additionally, the continued resilience of the kelp forests in the region may have helped make room for these bryozoans.

Another native sessile gastropod known as the scale snail (Thylacodes scaly) has also done well, most likely because it tolerates warmer waters better and because its food sources extend beyond plankton.

The problem with these changes is that the newcomers don’t play the same role in the ecosystem as the species they replaced. For example, the bryozoans are short-lived and fast-growing, and are not as adept at surviving the less intense but longer-lasting warming periods as the animals they replaced.

“This pattern in community structure has persisted throughout the post-blob period, suggesting that this may be more of a long-term shift in benthic aggregation,” says Michaud. “These communities may continue to change as we experience more ocean heatwaves and sustained warming.”

The water in the Santa Barbara Channel is often subject to temperature fluctuations, such as those caused by El Niño events. However, unlike the blob, these events are also accompanied by significant wave and storm movement, tearing out kelp forest covers, for example.

While reefs have shown they can recover from these warmer periods, the blob has raised temperatures without sending the seas into a frenzy. That makes it a very interesting time to study for researchers, not least because ocean temperatures continue to rise due to global warming.

The region has been carefully monitored for decades, and this monitoring continues. Researchers anticipate the blob’s lingering effects will continue, including the way it affects marine species further up the food chain.

“The blob is exactly the kind of event that shows why long-term research is so valuable,” says marine ecologist Bob Miller of the University of California, Santa Barbara. “If we had to respond to such an event with new research, we would never know what the real effect was.”

The research was published in communication biology.

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