Rays of hope for kelp and climate in south Salish Sea

It’s not all doom and gloom for the rich underwater kelp forests in the southern Salish Sea struggling to weather increasingly warm oceans.

Some pockets of bull kelp vital for sea life off southern Vancouver Island and B.C.’s Gulf Islands are proving to be resilient to rising sea temperatures and marine heat waves, a new University of Victoria study has found.

Global warming and extreme ocean temperature events like “The Blob” — a massive, prolonged marine heat wave that had cascading impacts on the marine ecosystem between 2014 and 2019 — have caused kelp to wither across the West Coast.

But it wasn’t clear what local effects climate stress was having on bull kelp fringing different kinds of shorelines in the region, according to lead researcher Alejandra Mora-Soto of UVic’s SPECTRAL Lab.

Diving into satellite imagery to analyze kelp cover and data on environmental conditions in the region from 2005 to 2022 — and even further back to 1972 at a site on Ella Beach — Mora-Soto determined kelp had the ability to bounce back in certain areas after being stressed by heat.

“The coasts in the Strait of Juan de Fuca are still within the optimal temperature range for kelp growth,” explains Mora-Soto. “We hypothesize that the summer winds in the Strait of Juan de Fuca increase water motion, an effect that favours canopy growth and the health of the kelp in general.”

However, kelp has declined along the more sheltered east coasts of Mayne, Saturna and Galiano islands in the Strait of Georgia, an area with higher water temperatures.

Given the expectation that spring and summer sea temperatures will continue to increase over time, there are increasing risks for these forests, which are hot spots of marine biodiversity, she added.

The largest species of brown algae, the fast-growing annual Nereocystis lutkeana (named for the Greek word meaning “mermaid’s bladder”), features a distinctive floating bulb and long stem resembling a bullwhip that often washes ashore during winter storms as it dies off.

Preferring cooler water temperatures between 4 C and 15 C, the bull kelp form large blades and an extensive canopy that provides food and shelter for many important fish species, seals, urchins, otters and crustaceans, said researcher Sarah Schroeder, who participated in the study.

The SPECTRAL Lab is doing a number of studies on kelp along B.C.’s entire coast, but one aspect of the recent study is to develop a better understanding of the seaweed’s importance to juvenile chinook salmon that use the seaweed corridors to move around, feed and stay safe from predators in the summer months before heading out to sea, said Schroeder.

Understanding how best to keep kelp healthy can, in turn, help protect the salmon, which are also threatened and a key food for endangered southern resident killer whales.

Bull kelp likes it rough

The study looked at four kelp clusters along the shores of southern Vancouver Island and the Gulf Islands and found the kelp canopy flourished and returned best along shorelines with cooler water exposed to open ocean or waves and wind that helped stir up needed nutrients.

The kelp on islands’ coastlines in the Strait of Juan de Fuca and certain areas of the Haro Strait did significantly better than canopies in the calmer, warmer waters of the Georgia Strait’s inside passage.

If waters in these areas warm too much during summer, that can limit kelp growth and their ability to reproduce, she said.

Additionally, these warm temperatures seem to be increasing a kind of small, white coral-like crustaceans that attach to kelp and possibly affect their health.

But the fact some kelp populations seem fairly stable is good news and offers hope moving forward because it helps pinpoint which seaweed beds need to be targeted for conservation or further study and perhaps inform kelp reforestation efforts elsewhere, she said.

“Protecting these resilient beds and having them as that [climate] refugia for marine life and to potentially restore and seed other areas is key,” Schroeder said.

Rochelle Baker / Local Journalism Initiative / Canada’s National Observer