Salish Sea reefs in need of serious protection
Over the past few years, measures have been taken to protect B.C.’s rare glass sponge reefs from damage by humans. Marine protected areas and marine refuge areas now offer some protection to 21 reefs on the central and south coast.
However, new research shows that a far more invidious and insidious threat endangers these vital ecosystems.
In laboratory studies at the University of British Columbia, researchers placed glass sponges in warmer and more acidic water to mimic future projected ocean conditions, then measured how the critters’ pumping capacity, body condition and skeletal strength changed.
Within a month, the sponges’ pumping capacity fell by more than 50 per cent and they lost 10 to 25 per cent of their tissues, which could starve the sponges. Their bodies also lost half their strength. Weakened skeletons could prevent reefs from forming as the region’s ocean warms. It could also cause reefs to collapse under the weight of growing sponges or animals walking and swimming among them.
Long thought to be extinct, living glass-sponge reefs were discovered in the deep waters of Hecate Strait and Queen Charlotte Sound in the late-1980s. Scientists have since located similar reefs in shallower waters in Howe Sound, off Tsawassen and Parksville, by Bowen, Mayne, Galliano and Gabriola islands, and elsewhere along the coast.
Research has shown that glass sponge reefs provide natural services that are critical to our ocean environment, our economy, and our health.
The reefs act as kidneys for the region’s lush and productive ocean system by filtering microbes and cycling nutrients through food chains. The sponges that live on the reefs feed by pumping sea water through their bodies, filtering almost 80 per cent of microbes and particles, sequestering carbon from seawater, and expelling clean water.
According to University of British Columbia research estimates, the 19 known reefs in the Salish Sea can filter 100 billion litres of water every day, equivalent to one per cent of the total water volume in the Strait of Georgia and Howe Sound combined.
The reefs also provide critical habitat for many fish and invertebrates, including economically important species such as rockfish, spot prawns, herring, and halibut. In addition, the nitrogen waste that the sponges excrete fertilizes plankton, which many fish and shellfish feed on.
But by their very nature, the reefs are fragile. Glass sponges absorb silica from the water to form their glass skeletons, giving them hard bodies, but making them brittle. Built up over thousands of years by generations of fragile glass sponges settling atop the fused dead skeletons of their predecessors, the reefs themselves are made largely of glass.
Cables, crab pots, and fishing lines dropped or dragged across them can destroy them, shattering the intricate, towering structures and communities.
Sediment suffocates them. Sponges breathe by absorbing oxygen from the water that they pump through their bodies. When a sponge detects sediment, it stops pumping. With no water pumping through, breathing also stops. This can last from two to 10 minutes, but when sediment hangs about in the water for longer periods, the sponges repeat the process several times, starting up to see if the water is clear enough to breathe and feed. Some sensitive species stop pumping for as long as six hours when there’s too much sediment.
No creature does well if they can’t breathe or eat for extended periods of time.
Since 2015, the reefs have been seeing increased protection. Bottom-contact fishing closures in marine refuge areas help to protect nine reefs in Georgia Strait. Fishing is banned outright in a 2,000-square-kilometre marine conservation area around four reefs in Hecate Strait and Queen Charlotte Sound. And last year, eight new marine refuge areas, totalling 32.6 square kilometres, were created to protect nine shallow glass sponge reefs in Howe Sound.
A number of scientists and organizations are pushing for stronger protections for the Salish Sea reefs. Marine protected areas, such as those around the Haida Gwaii-area reefs, provide greater protection throughout the entire water column. They’re also seeking to extend the buffers around the southern reefs to forestall damage from drifting sediment plumes.
However, faced with the more serious effects of climate change on the reefs, these protections are paltry and insufficient. If we cannot keep our coastal waters from warming and becoming more acid, we will lose the reefs and the natural cleaning, carbon storing and fisheries nursing that they provide.