Nicknamed “the Blob,” a large swath of abnormally warm water that covered part of the Pacific Ocean from 2014 to 2016 behaved much like a B horror movie, having a devastating impact on a wide variety of species.
A new study on the Santa Barbara Channel off the California coast shows how this environmental horror show continues to affect marine ecosystems.
At the time, the Blob caused significant shifts in aquatic ecosystems, particularly impacting sessile animals, animals that stayed in place like anemones. This latest research shows that six years later, the underwater populations that inhabit the kelp forest ecosystem have still not returned to where they were.
While levels of sessile invertebrates – filter feeders attached to reefs – have generally bounced back, numbers belonging to the invasive species Watersipora subatra (a recent arrival) and Bugula neritina (a long-term resident) have boomed. These are types of moss animals; small, colonial animals with tentacles that essentially work together in groups as a single organism.
“The groups of animals that seemed to be the winners, at least during the warm period, were longer-lived species, such as clams and sea anemones,” says ecologist Kristen Michaud of the University of California, Santa Barbara.
“But after the Blob, the story is a bit different. Bryozoan cover increased quite quickly and there are two types of invasive bryozoans that are much more abundant now.”
The number of sessile invertebrates saw an initial 71 percent drop in 2015 when the Blob took hold, as the warmer water meant that creatures such as anemones, tube worms and clams ran out of phytoplankton to feed on.
Plankton depend on nutrients supplied by colder water, which was limited due to the presence of warm water. The metabolism of these invertebrate invertebrates was also sped up by the heat, which meant they needed even more food that they weren’t getting.
Several causes may be responsible for the dominance of W. subatra and B. neritina, the researchers say: They include the ability to survive in higher temperatures and to compete more aggressively for space on reefs. In addition, the continued resilience of kelp forests in the region may have helped clear space for these bryozoans.
Another native sessile gastropod known as the scaly worm snail (Thylacodes pavement) has also done well, probably because it is better able to tolerate warmer water and because its food source options extend beyond plankton.
The problem with these changes is that the new arrivals do not play the same role in the ecosystem as the species they replaced. For example, the bryozoans are shorter-lived and fast-growing, and are not as adept at surviving the less intense but longer periods of warming 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 marine heat waves and continued warming.”
The water in the Santa Barbara Channel often undergoes 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, ripping out kelp forest covers, for example.
While the reefs have shown their ability to bounce back from these warmer spells, the Blob raised temperatures without sending the seas into a frenzy. That makes it a very interesting period for researchers to study, not least because ocean temperatures continue to rise due to global warming.
The region has been closely monitored for decades and that surveillance will continue. The researchers expect the lingering effects of the Blob to continue, including the ways 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,” said 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 true effect was.”
The research has been published in Communication Biology.