To find out how these animals are affected by the boost of food, the researchers sent a Remotely Operated Vehicle (ROV) equipped with video and sampling equipment to the base of the canyon. Piloted from a control room onboard a ship at the ocean surface, the ROV dove more than a mile to the canyon floor. As the ROV crept across the seafloor sediment, it video recorded everything in its path and pushed plastic tubes into the mud, pulling up cores of and animals and silt.
When they brought the samples back to the surface, they found nearly 200 species in the sediment. But as they sampled closer to the canyon walls, they were surprised to find that despite the extra food and nutrients, the small sediment-dwellers (0.25 to 25 mm in size) became even smaller and less diverse. Why might this be?
A closer look at the video footage suggests the answer lies not in the sediment, but just above. As the ROV approached the canyon walls, the researchers noticed swarms of bigger, mobile animals crabs, starfish, urchins, sea cucumbers and other seafloor scavengers crawling on the sediment surface. Normally few and far between, these animals sense that food has arrived and converge at the base of the cliffs, the researchers explained. "The cliff face becomes a smorgasbord for larger animals," said McClain.
Ironically, more food for big, mobile animals on the sediment surface is bad news for smaller sediment-dwellers buried below. The larger animals devour all the food in their path as they plow across the canyon floor, wrecking habitat and leaving little for other animals to feed on. "Larger organisms come in and they churn up the sediment and eat all the food. That has big consequences for smaller animals that live there," McClain explained.
"The number of species near the cliff face was reduced by half compared to the middle of the canyon,"
|Contact: Robin Ann Smith|
National Evolutionary Synthesis Center (NESCent)