Waters off California have been unusually warm the last couple years, making conditions great for swimmers and surfers.
It's also changing the sorts of microscopic marine plants that thrive there, according to a new study from UC Irvine.
The researchers analyzed samples of phytoplankton, organisms that are often the first link in the ocean food chain.
They noted that typically there are seasonal changes in the distribution of these phytoplankton. In winter, Southern California waters are full of larger species of phytoplankton like diatoms. In summer, smaller types take over.
However, during the three-year course of study, average temperatures off the coast climbed about two degrees Celsius.
This had a “tremendous impact on our coastal ocean,” said researcher Adam Martiny, associate professor at UC Irvine.
Specifically, he said there were more small phytoplankton year round and fewer larger ones even in winter. Since phytoplankton are the base of the food chain, such a change has likely sent ripples through the ecosystem.
"This I would imagine would end up having tremendous influence on the types of fish that can live here," Martiny said. He thinks the influx of rare tropical fish in local waters might be related to this change in phytoplankton.
"It also has a big impact on the chemistry of the ocean as well," he said.
That's because phytoplankton take in carbon, nitrogen and phosphorus, but different varieties take in different amounts.
The small ones are great at absorbing lots of carbon for photosynthesis but don't need much nitrogen and phosphorus. Large phytoplankton fix less carbon but can use more of the other chemical elements.
So a change in phytoplankton populations can impact not just the carbon cycle, but the chemical make-up of coastal waters as well.
The current jump in ocean temperatures is probably due to natural climate patterns like El Niño, and things will likely return to normal, Martiny said.
But he said warmer sea temperatures under climate change scenarios change could eventually make year-round presence of smaller phytoplankton a permanent feature of the waters off Southern California. It's unclear what that would mean for the ecosystem at large, but Martiny said the past few years might be a preview of what is to come.