by Evgeni Matveev
Why do we spend our time, energy, and taxpayer money to go to a remote part of Canada and study sea sponges? An important question, no doubt. Right off the coast of Canada are the largest and only known sponge reefs in the world; despite this there is very little known about this unique ecosystem.
The reefs were discovered by Kim Conway's team on accident in the late 80s, during side-sonar mapping of the sea floor. When they sent cameras down they saw expanses of glass sponges on an unforeseen scale. Glass sponges have a rigid scaffolding made of silica, and they have flagella that filter thousands of liters of water per day. By definition, a reef means that young sponges are growing on dead sponges, so this ecosystem has been in existence for thousands of years - some were estimated to be 6000-8000 years old.
Because we know so little about such an enormous and long-lived structure it’s crucial that we assess the role of the reefs in the Canadian Pacific ecosystem and determine the risk human activity poses to their survival. Data collected by us could be used used in the future for environmental policy design.
Like coral reefs, sponge reefs provide structure for other animals to live on. Sponge reefs teem with halibut, rockfish, squat lobsters, shrimp, and many other ocean creatures. The crevices of sponge exhalent openings and grooves of their body wall provide a refuge for small animals. A barren sea floor, conversely, exposes the little creatures to predation risk. Stephanie Archer, Anya Dunham, and Mary Thiess from the Department of Fisheries and Oceans (DFO) are on this expedition to research the role of sponge reefs as habitat for other animals. They brought hydrophones (underwater microphones) to listen to the chatter on the reef and compare it to the noise levels off reef.
Video transects will then be analysed to get a measure of biodiversity, and compared to the audio recordings. The idea is to determine whether hydrophones are a viable option for quantifying the number of animals that live on and off reef. Eventually this will allow us to assess to what animals are living on the reef even when we can't be there with the ROV.
Additionally the DFO team is trying to determine what role sponges play in the reef food web. By analyzing carbon and nitrogen isotopes of various animals they're hoping to build a food web structure and establish where sponges fit in. In an on board experiment, they'll also try to chemically label sponge excrement and see if any animals eat it to determine how important sponges are in the food web of the reef.
Lauren Law from the Leys lab is also here to study a reef community structure but in a addition to how many, she asks what animals are present on the reefs. This question involves looking at video transects, and doing a meticulous analysis of the relationship between sponge cover and abundance of various macro-fauna. She is also looking at the diversity of sponges that make up the reefs by doing DNA barcoding. This is an important question because the community structure and biodiversity can give us an indication of how resilient this ecosystem is to environmental change.
Sponge reefs are key to the biodiversity we see throughout the Canadian Pacific, but they’re at risk from human activity. Sponges in the Hecate Strait are very delicate, and live in relatively nutrient poor waters. This means any disturbance will have profound effects on sponge health. Our preliminary results from the cruise in 2015 suggest that the sponges rely on the flow around them to alleviate the cost of pumping water through their filtering mechanism.
This year Sally Leys and Evgeni Matveev are interested in confirming these results by looking at the relationship of sponge pumping rate and oxygen consumption with surrounding flow. It could be that these sponges are so abundant in this area because tidal cycles along the continental shelf provide enough surrounding flow for the sponges to survive on little food.