Amperima rosea

Background

Amperima rosea is a small detritivore that feeds on phytodetritus—remains of phytoplankton from shallow waters that drift or sink to the sea floor. It breeds at any time of year, producing small eggs (less than 200 μm) with little yolk, suggesting planktonic larval development. The species shows high fecundity, and mass spawning may follow an external stimulus such as a sudden increase in food supply.

In the mid-1990s, on the Porcupine Abyssal Plain, its density surged from two or three individuals per hectare to over six thousand per hectare, a phenomenon called the 'Amperima event.' This high level persisted in subsequent years. During the same period, other sea cucumber species also increased in number but decreased in average size, and the brittle star Ophiocten hastatum experienced an explosive population increase. The rate of seabed surface turnover accelerated from two and a half years to six weeks.

The population increase has been linked to a greater abundance of phytodetritus, possibly due to higher surface water temperatures caused by climate change. The rapid rise in sea cucumber numbers may have reduced the build-up of organic materials in the sediment that would otherwise have occurred.