Dubbed “the Blob”, a large body of abnormally warm water covering part of the Pacific Ocean from 2014 to 2016 performed like a B-grade horror movie, having a devastating impact on a wide variety of species.
A new study of the Santa Barbara Channel off the coast of California highlights 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, those stranded like anemones. This latest research shows that six years later, the underwater populations inhabiting the kelp forest ecosystem have still not returned to where they were.
While levels of sessile invertebrates – reef-attached filter feeders – have globally rebounded, the number of invasive species Watersipora subatra (recent arrival) and Bugula neritina (a long-term resident) exploded. They are types of bryozoans; tiny, tentacled colonial animals that essentially act in groups as a single organism.
“The groups of animals that seemed to be the winners, at least during the warm period, were long-lived species, such as clams and sea anemones,” says ecologist Kristen Michaud, from the University of California to Santa Barbara.
“But after the Blob, the story is a bit different. Bryozoan cover has increased quite rapidly, and there are two invasive bryozoan species that are now much more abundant.”
Sessile invertebrate numbers saw an initial drop of 71% in 2015 when the Blob took hold, as warmer water meant critters like anemones, tubeworms and clams lacked phytoplankton to feed on. .
Plankton depend on nutrients brought by colder water, which was limited thanks to the presence of warm water. The metabolism of these sessile invertebrates was also increased by heat, meaning they needed even more food than they were getting.
Several causes may be responsible for the predominance of W.subatra and B.neritina, say the researchers: they include the ability to survive higher temperatures and compete more aggressively for space on reefs. Additionally, the continued resilience of kelp forests in the region may have helped clear space for these bryozoans.
Another native sessile gastropod known as the scale worm snail (Thylacodes squamigerous) is also doing well, probably because it is better able to tolerate warmer waters and because its food sources go beyond plankton.
The problem with these changes is that the newcomers do not play the same role in the ecosystem as the species they replaced. For example, bryozoans are shorter-lived and faster-growing, and are not as adept at surviving less intense but more prolonged periods of warming as the animals they replaced.
“This pattern in community structure persisted throughout the post-Blob period, suggesting that it may be more of a long-term shift in benthic animal assemblage,” Michaud says. “These communities may continue to change as we experience more marine heatwaves and continued warming.”
The water in the Santa Barbara Channel often experiences temperature fluctuations, such as those caused by El Niño events. However, unlike the Blob, these events are also accompanied by significant wave and storm action – which, for example, tears up kelp forest covers.
While the reefs have shown they are able to rebound from these warmer periods, the Blob has raised temperatures without whipping the seas into a frenzy. This makes it a very interesting time for researchers to study, especially because ocean temperatures continue to rise due to global warming.
The area has been carefully monitored for decades, and this monitoring will continue. Researchers expect the Blob’s ongoing effects to continue, including how it impacts marine species higher 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 were to react to such an event with new research, we would never know what the true effect was.”
The research has been published in Communications Biology.
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