Built over millennia, but now threatened by a changing climate, will these glass sponge reefs be able to persist?

Hidden in the cold, dark depths of the Northeast Pacific lies a city like no other: a metropolis not of steel and concrete, but of living sponges made mostly of glass. Layer by layer, generation after generation, the sponges grow atop the structures built by their ancestors. These extraordinary reefs rise above the seafloor and can stretch for kilometres. Their living architecture provides a home to a rich and diverse underwater community of fishes and invertebrates, including species of commercial importance and conservation concern like rockfishes.

 

Rockfish schooling above a glass sponge reef. © Adam Taylor, Marine Life Sanctuaries Society

 

Among the many services glass sponge reefs provide to ecosystems and society, they process considerable volumes of water, twice as fast as mussel beds which are the next most intense suspension feeding community in the ocean. The 19 documented glass sponge reefs in the Salish Sea, for example, collectively filter the equivalent of 1% of the total water volume in this water body daily. By doing so, they remove up to 90% of bacteria from the water and sequester large amounts of carbon. 

Built by three species of reef-forming glass sponges, these reefs are found nowhere else in the world in this form. They have persisted for millenia under the distinctive oceanographic and geochemical conditions found along the coast from British Columbia, Canada, to southeast Alaska, US, giving them a unique and geographically restricted distribution. But this ancient underwater world is increasingly under threat. A new assessment, Glass Sponge Reefs of the Northeast Pacific - Status and Vulnerability, published in the IUCN Red List of Ecosystems, classifies the ecosystem as Vulnerable (VU). Evidence of damage from fishing gear, combined with growing threats from ocean warming and marine heatwaves, identifies the risk of further reef decline in the decades ahead. Conservation measures were enacted for the reefs in Hecate Strait and Queen Charlotte Sound, Strait of Georgia, and Howe Sound in British Columbia in 2017-2022 (1, 2). The assessment highlights the need for sustained protection and climate-informed management to safeguard these reefs and the biodiversity they support.

 

Diver Glen Dennison above glass sponges in Howe Sound, British Columbia. © Adam Taylor, Marine Life Sanctuaries Society

Written by: Angela Stevenson - University of Plymouth & GEOMAR Helmholtz Centre for Ocean Research Kiel; Melanie Warren & Adam Taylor - Marine Life Sanctuaries Society; Lily Burke & Anya Dunham - Fisheries and Oceans Canada