While some parts of B.C.’s coast are seeing a decline in the floating kelp forests that support marine life, others are proving resilient, according to a new paper by University of Victoria researchers. Understanding why could help with restoration efforts of the species.
Bull kelp covers much of the coastline of Vancouver Island and B.C., said Maycira Costa, the lead scientist on the paper and a professor in the geography department at UVic.
In B.C., where the shore drops steeply into the ocean, kelp can only grow close to the coast. It attaches to rocks on the seafloor, like roots in a tree, and grows quickly toward the surface, where it can receive sunlight to complete photosynthesis, Costa said.
In some areas, such as around the Gulf Islands, it’s struggling, and in California, off-shore kelp beds are disappearing. But around Victoria, Esquimalt and Sooke, kelp is proving resilient, she said.
The team sought to understand why kelp is resilient in some areas to determine if those lessons could help to recover lost kelp habitats. Led by postdoctoral researcher Alejandra Mora-Soto, the team compared historic and current satellite aerial imagery to analyze the kelp cover and determine what areas are showing resilience and what areas are seeing a decline.
They found areas more exposed to open ocean, wind and currents have cooler water and healthy kelp that can withstand heat waves, Costa said. But around the Gulf Islands, water temperatures can rise so drastically during marine heatwaves that kelp can no longer survive, she said.
“The question is, is there a solution to recover some of these habitats?” Costa said. “And maybe it’s possible to restore in some areas, but maybe it’s not possible to restore anymore in other areas due to the environmental conditions.”
Kelp is considered an indicator of ecosystem health.
“If it’s inhospitable to kelp, it’s probably not OK for other species, either,” said Sarah Schroeder, a research assistant on the project.
It provides habitat in the ocean much in the way a forest does on land, Schroeder said, acting as home to small fish at the bottom of the food web, such as juvenile salmon and juvenile herring.
If we lose habitat for small, young fish, the issues travel up the food web, leaving the animals that rely on those smaller fish with less food to eat, she said.
The paper, looking at southern Vancouver Island, is part of a larger project examining the entire B.C. coast.
Further north along the coast, in the central Strait of Georgia from Nanaimo to Quadra Island, they found a more significant decline in kelp and much warmer summer ocean temperatures, Schroeder said.
“You can put spores out there and it will start growing but by mid-summer, the water is so warm that it will actually start to disintegrate,” she said.
There might be other factors at play in the decline of kelp, Costa cautioned. In the Johnstone Strait, on the northeast coast of the Island, kelp is not doing well despite relatively cool water temperatures and active currents, she said.
That decline could be related to sea urchins, which eat kelp, and appear to be growing in population in the area, Costa said.
The work was funded by the Natural Sciences and Engineering Research Council and Pacific Salmon Foundation.
