Despite being found at depths of 2500 metres or more, the vents are subject to the same rhythm of tides that laps at our coastline. These tides may influence some of the animals living at the vents, such as the unusual shrimp that live at vents in the Atlantic. These shrimp appear to cultivate bacteria on their gills, harvesting them for food using a special appendage. The bacteria are nourished by chemicals in the vent water, so the shrimp need to bathe in this fluid to ensure a bumper crop. Using a time lapse video camera, we have seen the shrimp apparently shuffling around the sides of a vent as the tide changes, in order to stay in the fluids on the 'downwind' side.
Tides are the metronome of the oceans.
They provide a regular beat that some animals can use to synchronize their behaviour, particularly their reproduction. But reproduction at vents can be a complex affair. In the case of the shrimp, although there are literally millions swarming around the vents, only a handful of females carrying eggs on their legs have ever been found among the thousands that have been examined. It could be that we visit the vents at the wrong time of year, but this seems unlikely as there are always plenty of females seemingly just on the verge of laying their eggs. Carrying eggs in the scrum of shrimp around the vents, however, would be like putting your baby in a backpack and heading down to the front rows of a particularly rowdy rock concert.