Marine biology: watch the first video of a possible rare sponge reef discovered near California

Vast mounds of sponges spanning hundreds of meters have been discovered 600 meters deep near the Channel Islands off California

Environment


March 3, 2022


Vast mounds of glass sponge skeletons have been discovered 600 meters deep on the seabed of the Channel Islands National Marine Sanctuary off California. The mounds are unlike anything previously found in the area and may be examples of a very rare habitat type known as a sponge reef.

The reef-like mounds were first spotted by researchers in 2020, during a dive by a remotely operated vehicle (ROV) from the EV Nautilus research vessel.

“We’ve started to see patches of dead sponges,” said Abigail Powell, a contractor with the U.S. National Oceanic and Atmospheric Administration, during a virtual talk at the 2022 Ocean Sciences Meeting. It got denser and denser, and soon we were climbing big mounds.

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The area is relatively well explored, so the discovery came as a surprise. “There have been many dives here over the years, but never on this particular track,” Powell said.

The mounds are mostly made of silica skeletons of dead glass sponges, browned by a layer of sediment. However, many other species live on and in the mounds, including fish, clams, and sponges of both reef-building and non-reef-building types.

In 2021 the ship returned to the sponge mound site and an ROV zigzagged over two of the mounds. This revealed that the largest mound was over a kilometer long, 500 meters wide and at least several meters thick in some places.

“The continuous extent of the patches over hundreds of meters is unlike anything we’ve encountered before,” Powell said.

A funnel-shaped sponge (Heterochone calyx) growing above sponge mounds

NOAA/NWFSC Fisheries

Sponge reefs were common in the age of the dinosaurs, but were thought to have completely disappeared from modern oceans. Then, in the 1980s, live sponge reefs were discovered off the coast of British Columbia in Canada, and a few more were discovered elsewhere.

“Filter sponge reefs are spectacular, yet fragile, ecosystems,” Powell said.

However, she is hesitant to call the mounds California sponge reefs until acoustic scans reveal their deeper structure.

“We need to know if the mounds are made up of sponge skeletons or if we’re looking at a relatively thin layer of sponges growing on rocky ridges,” Powell said. new scientist.

“I think ‘reef-like’ would be a good way to describe what we found until we know more.”

What is clear is that the proportion of living reef-building sponges on the surface of the mounds is much lower than on the reefs off Canada.

It is unclear if this is a natural phenomenon explained by local environmental differences between the two sites, or if something killed large numbers of reef-building sponges in the Channel Islands National Marine Sanctuary. Normans.

“There are still a lot of unanswered questions,” Powell said.

While trawling is permitted in some parts of the sanctuary, the sponge mounds are in a no-go zone and should therefore be protected from all types of fishing.

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