Galatheid crabs feast opportunistically on a pelagic catch. The largest crab individuals were feeding directly on the catch, whereas the smaller crabs waited their turn to on the outskirts of the group. Video captured by the Little Hercules ROV on a site referred to as "Zona Senja" on August 2, 2010. Video courtesy of NOAA Okeanos Explorer Program, INDEX-SATAL 2010. Download (mp4, 20.6 MB)
Dive number 10 took place in an area recently mapped by the Indonesian Research Vessel Baruna Jaya IV. The dive site is referred to as “Zona Senja”, or “Twilight zone” as the depth range resides in the transition zone between the photic zone and deep-sea. We started at the base of a wall at 323 meters depth, and climbed along the northeastern wall to a depth of 270m. We then moved laterally to the east on this same depth contour. After that we continued upslope toward the south along the eastern edge of the ridge top until reaching a summit at 250m. From there we moved east down slope until we reached the end of bottom time. Impressive assemblages of rich communities were observed. Fauna was different from what we have seen so far in the deeper sites explored during this expedition this site. Big fragments of basalt were covered with high abundances of suspension feeders. Sessile fauna also densely populated terraces of cemented sand. At 286-300m we experienced strong shimmering in the water related to a marked thermocline. No significant changes in faunal composition were detected with this change in temperature. The seafloor became predominantly clay-carbonate (pyroclastic tuff) with rounded cobbles dispersed along the margins and in depressions as we moved shallower. Not much sessile fauna was seen on it. However, high abundances of mobile fauna and burrowing fauna were observed. No significant change in faunal composition was observed along the depth/temperature gradient. The observed changes in the abundances of sessile fauna seemed related to hard substrate availability.