Earlier today Isis provided us with a glimpse of what lives on a seamount located just a few miles from the SE Station. Estimates inferred through remotely-sensed altimetry data suggest that about 100,000 seamounts with an elevation higher than 1000m are spread throughout the world’s oceans. Because they are topographically isolated features, and are often associated with particular hydrographic processes that promote larval retention, it is believed that seamounts play a pivotal role in evolutionary divergence and speciation of deep-sea benthic fauna, contradicting the early view that they could increase connectivity by acting as stepping-stones for dispersal. Evidence, however, is not consistent across regions and taxa, which calls for further surveys to obtain a clearer picture of biogeographical patterns.
The seamount we visited rises from the abyssal plain at 4000m and has its summit around 700m below the surface. Due to time restrictions, the plan was to perform one video transect up a slope between 1050m and 850m depth, obtain high-definition video footage of benthic fauna and collect voucher specimens of the most representative species. The later part of the dive was to be devoted to finding and, if possible, retrieving an accoustic lander that had been lost during a previous cruise.
The diversity and abundance of benthic fauna were staggering. The more gentle slopes were mostly covered with gorgonian and sponge gardens with a diverse associated fauna including brittle-stars, crinoids and squat lobsters. Another significant feature of these areas was the presence of extensive layers of coral rubble (fragments of dead scleractinian corals which accumulate over hundreds of years or more).
Steeper slopes and vertical walls were densely inhabited by sponges, Gorgonocephalus sea stars, anemones, gorgonians, sea-pens and a few black corals. There were also numerous small colonies of reef-building scleractinian corals, probably Lophelia pertusa or Solenosmilia variabilis (not easy to distinguish through video). A closer look at the rock walls revealed a myriad of solitary scleractinian corals, as well as countless small sea stars and brittle stars.
So much to explore and so little time available. After a brief, yet fruitful, period spent at collecting specimens, we headed for the waypoint where the accoustic lander (hopefully) was. It showed up on screen, not far from its suspected location, turned upside down with a few floats missing, presumably because they have imploded. Unfortunately it was too risky to retrieve it during the night, and dawn was still a few hours away. Because the cruise runs on a tight schedule we could not afford waiting for suitable conditions so it was decided to leave the lander for now and come back for it later.
The last week of science has just begun. There’s still a lot to explore at the southeast station, so stay tuned for more news!