Dubbed the ‘Blob’, the extremely warm water that covered the Pacific Ocean from 2014 to 2016 was like a B-grade horror movie, which had a huge impact on various species.
A new study on the Santa Barbara Channel off the coast of California shows how this dangerous environmental phenomenon continues to affect marine ecosystems.
The Blob caused a huge change in marine life at the time, especially affecting the permanent, marine animals like the anemone. A recent study shows that six years later, the underwater inhabitants of the kelp forest have not returned to where they were.
While the number of sessile invertebrates – filter feeders attached to reefs – has rebounded, the numbers of invasive species have declined. Watersipora subatra (latest arrival) and Bugula neritina (long time residents) were impressed. These are types of bryozoans; small, colonial, small animals that work together in groups as a single organism.
“The groups of animals that seemed to be the most successful, especially in the warmer climates, were long-lived organisms, such as crabs and sea anemones,” said biologist Kristen Michaud, of the University of California, Santa Barbara.
“But after the Blob, the story is a little different. Bryozoan cover increased very quickly, and there are two types of destructive bryozoans that are now very abundant.”
Numbers of sessile invertebrates dropped by 71 percent in 2015 when the Blob took hold, as warmer waters meant creatures like anemones, tubeworms, and clams emerged from the phytoplankton to eat.
Plankton depend on food brought in by cold water, which was scarce due to the availability of warm water. The digestive system of these ruminants was also enhanced by the heat, meaning they needed more food than they were getting.
Several factors may be responsible for the control of W. subatra and B. retina, the researchers say: include the ability to survive at high temperatures, and intense competition for space on reefs. In addition, the density of kelp forests in the area may have helped clear the habitat for bryozoans.
A type of sessile gastropod called the scaled worm snail (Thylacodes are dangerous) has also been doing well, mainly because it can tolerate warmer water, and because the nutrients it provides go beyond plankton.
The problem with this change is that the new arrivals do not have the same share of the species as the species they have changed. For example, bryozoans are short-lived and grow rapidly, and cannot survive as hot climates as the animals they replaced.
“This trend in community groups has persisted throughout the Blob’s time, suggesting that this may be a long-term change in the population of native animals,” says Michaud. “These areas may continue to change as we experience ocean heat waves and continue to warm.”
Water in the Santa Barbara Channel often fluctuates in temperature, such as those caused by El Niño. However, unlike the Blob, these events are also accompanied by large waves and storms – which, for example, tear apart kelp forests.
Although reefs have shown they can bounce back this summer, the Blob added to the heat without whipping the ocean into a frenzy. This makes it a very interesting time for researchers to study, not least because sea temperatures continue to rise due to global warming.
The area has been closely monitored for many years, and monitoring will continue. The researchers hope that the Blob’s effects will continue, including how it affects marine life raising food.
“The Blob is exactly the case that shows why long-term research is so important,” says marine biologist Bob Miller, of the University of California, Santa Barbara. “If we had to act on such cases with new research, we would not know what the consequences were.”
Research has been published in Communications Biology.
