Seamounts, Cold-Water Corals, Hydrothermal Vents & Sponges

Seamounts

The rich source of food around seamounts makes them attractive locations for suspension feeders on the seafloor, such as corals.
Photo Credit: NOAA

Seamounts are underwater mountains, usually volcanic in origin, that reach heights of at least one kilometre but do not break the surface of the water. These structures create unique tides and water movement that encourage the growth of plankton. Plankton attracts large numbers of fish and marine mammals. The rich source of food around seamounts also encourages the growth of suspension feeders on the seafloor, such as corals.

The concentration of fish stocks around seamounts has made them attractive fishing grounds. Many of the fish species found around seamounts mature slowly and do not reproduce quickly, which makes them particularly vulnerable to overfishing and slow to recover from stock depletion. As well, fragile species found on seamounts, including cold-water corals, are particularly vulnerable to human activities such as bottom tending fishing gear.

• The Bowie Seamount has been designated a Marine Protected Area under Canada’s Oceans Act. Read about Canada’s Bowie Seamount, located west of the Queen Charlotte Islands, approximately 180 km offshore.

Cold-Water Corals

Several coral species attached to bedrock in the Atlantic Ocean, found on the southeast slope of Banquereau, Nova Scotia.
Photo Credit: DFO

Cold-water corals feed on microscopic animals in the water column and as a result are almost always found in areas with high currents where food is plentiful.

They can be found in shallow subtidal areas, on the continental shelf, seamounts, to mid-ocean ridges and down to the abyssal plains of the deep ocean. Cold-water corals generally grow very slowly and some can live for several hundred years.

There are over 30 species of coral in the waters of the Northwest Atlantic Ocean and over 80 species in Canada’s Northeast Pacific waters.

Some corals in Canada are rare reef-builders, such as Lophelia pertusa, and are protected by marine protected areas. Reef-building corals provide habitat for other marine life, thereby increasing biodiversity.

Hydrothermal Vents

Hydrothermal vents are seafloor geysers. The area surrounding them is usually densely populated with sea life.
Photo Credit: NOAA

On land, we know them as hot springs, fumaroles and geysers. The most famous is likely the Old Faithful geyser in Yellowstone National Park, which erupts several times a day, spouting water heated by volcanic rock deep within the Earth’s crust.

On the seafloor, they are called hydrothermal vents.

Hydrothermal vents continuously spew mineral-rich and geothermally heated water. Areas around hydrothermal vents are usually densely populated with sea life.

They are known to exist in the Pacific and Atlantic Oceans and most are found around two kilometres  below sea level, in areas of the seafloor along the Mid-Ocean Ridge system -- the underwater mountain chain that stretches around the globe.

The pressurized water discharging from these vents may reach 400 degrees Celsius. Hydrothermal vents are thought to have a significant effect upon temperature, chemistry, and water circulation patterns of the area around them.

• Found off the coast of British Columbia, the Endeavour Hydrothermal vents have been designated a Marine Protected Area under Canada’s Oceans Act. Read about Canada’s Endeavour Hydrothermal Vents.

Deep-Water Sponges

Sponges are aquatic animals that are multi-cellular but without tissues. This makes them fragile and susceptible to damage. Sponges are filter-feeders, extracting food particles and absorbing dissolved nutrients from the water. As larvae, they attach to firm surfaces, and typically stay their whole adult lives in one place, like a plant. They are found from shallow subtidal regions to eight kilometres below sea-level.

There are thousands of types of sponges. Some sponges reproduce sexually and asexually and can attach to one another, building large reefs. Deep-water sponge grounds can be hotspots of biodiversity, creating diverse habitats for many other types of marine life.

Unique glass sponge reefs that are thousands of years old, hundreds of square kilometres in size, and over six stories high were discovered in 1987 on the seafloor of Canada’s Western continental shelf by the Geological Survey of Canada. Until then, it had been thought that such towering glass sponge reefs had become extinct around the time of the dinosaurs. The only other location on earth with glass sponge reefs is in Antarctica.

Found in waters around the world, sponges are vulnerable to human activities. They are removed easily by bottom-tending fishing gear, and re-growth from damage can be slow – if it occurs at all. Clouds of sediment in the water, which occur when the sea bottom is disturbed, can also smother and kill sponges.

• Four deep-water sponge reef areas located in waters of the Eastern Queen Charlotte Sound and Hecate Strait are now closed to all bottom trawling. Read about the British Columbia sponge reefs of Hecate Strait.