Dive 19: Mendelssohn Seamount
September 25, 2017
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Dive 19: Old Growth Forest

Mendelssohn Seamount had some of the most high-density coral communities of any area that we have been to in the last three years. Amazingly large bamboo colonies were observed, along with corals that appear to be hundreds of years in age. Video courtesy of the NOAA Office of Ocean Exploration and Research, Deep-Sea Symphony: Exploring the Musicians Seamounts. Download (mp4, 28.8 MB)

The dive on Mendelssohn Seamount was the grand finale of our seamount exploration. Starting at nearly 1,800 meters (5,905 feet), we found a dense pink coral garden (Hemicorallium sp.) with exceptionally large colonies. As remotely operated vehicle Deep Discoverer (D2) moved upslope, the community became more diverse with corals including Chrysogorgidae, Hemicorallium sp., Isididae (bamboo), and possibly some primnoids. It became unclear at about 1,700 meters (5,577 feet) depth if the substrate was really featureless lava flows or tuff, given that this cone atop a guyot’s carbonate cap may be the result of secondary volcanism. We then entered a dense bamboo coral forest with colonies up to three meters (9.8 feet) tall, suggesting that both the corals and the community are very old. The slope decreased as D2 neared the summit, approximately 1,650 meters (5,413 feet), where more coral diversity was observed, including Iridigorgia and Hemicorallium (pink) corals, the latter with a six to eight-inch-wide base and covered with crinoids. More topographic relief was finally observed, in this case a talus chute running between elevated massive outcrops. The dive closed out in an area with more diversity, but similar density of old colonies, including several different species of bamboo corals, large Hemicorallium colonies and the first instance of a true Metalagorgia sp. coral on this expedition, followed by several other colonies.Throughout the dive, there were several instances of corals providing habitat for other organisms, such as crinoids, brittle stars, squat lobsters, and zoanthids. Other highlights included observations of a halosaur, sea spider, anemones, a spider crab, and a Bolosominae sponge.