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1999 Patton Seamount Expedition

[Bill Donaldson with Macroregonia macrochira, thwmac.jpg=10KB]


Scarlet king crab [thscar.jpg, 7KB]


[Galatheidea, thgalunk.jpg=6KB]
 

In July 1999, Dr. Bradley Stevens explored the Patton Seamount (54.66 N, 150.50 W) in the Gulf of Alaska with the DSV Alvin. The objective was to study the depth distribution of four commercially important deepwater crab species. During the study eight dives were completed to depths of 200-3000 meters. Several other crab species were observed that had previously not be known to exist in this area.

The giant spider crab (Macroregonia macrochira) was one of the surprising finds. They were observed from 1030 meters down to as deep as 3240 meters. It is the most abundant crab below 1000 meters, and virtually the only species of crab below 2000 meters. This crab was first described by Sakai (1978) from trawl sampling at depths of 800-1100 meters on the Emperor Seamounts north of Hawaii, at 42 degrees N. It has also been observed and collected from the Endeavor Ridge at 48 degrees N.

Two other unexpected species of crab were observed, Paralomis verrilli and Paralomis multispina. In an Arctic Science Journeys Radio Script (2001), Dr. Stevens says that the Paralomis crabs could not be distinquished from king crabs, but the difference was obvious once they were captured. P. verrilli was captured at 1074 meters and P. multispina at 915 meters.

Crabs such as Grooved Tanner (Chionoecetes tanneri) and golden king (Lithodes aequispina) were not surprising. Grooved Tanner crabs were captured from 620 to 850 meters and occurred on sandy and sedimented substrates, but were occasionally seen on rocks. This crab occurs from Kamchatka and the northwest Pacific Ocean, to waters off Cortez Bank, Mexico; and in depths from 29 to 1944 m. Golden king crab were abundant at the upper elevations of the Patton Seamount, generally above 500 m. Most of the adults were observed on rocky substrates, and grasping pairs were seen on several dives.

The scarlet king crab (Lithodes couesi), as shown in the photo above, were common at greater depths than golden king crab. The juveniles were captured down to 930 meters, and adults were common between 530 and 600 meters. They were commonly observed on or under rocks, but some were obseved on sand/gravel substrates.

Two different types of squat lobsters were also observed, Munidopsis albatrossae (Family Galatheidae) was usually seen below 1000 meters, and Chirostylus sp. (Family Chirostylidae) were observed above 500 meters. One Galatheid was collected at 2953 meters. Like the king crabs, the family Galatheidae are classified as Anomurans, or "asymmetrical tail" crabs. The family Chirostylidae are small red crabs with long chelipeds. These were abundant among the rocks and cobbles on the upper slope and flat top of Patton Seamount, and were commonly observed among the branchs of gorgonian soft corals, on the outer flank of the mountain.

More information can be found in the poster, Ecology of Deepwater crabs on a Gulf of Alaska Seamount Studied with the DS/V Alvin (250 KB.pdf) and in a 2005 publication, Faunal Assemblage Structure on the Patton Seamount (Gulf of Alaska, USA) (.pdf)by Gerald R>. Hoff (ADFG) and Dr. Bradley Stevens.


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