"What this strongly suggested," says Dr Billett, "is that the 'Amperima Event' did not simply reflect localised, chance changes in the abundances of one or two species. Instead, changes in the whole deep-sea animal community were driven by environmental factors."
The animals living on the deep seafloor feed on organic matter in the form of phytodetritus the remains of tiny marine plants that once lived in the sunlit surface layer and which fall down through the water column and settle on the seabed. It seemed possible that an increase in the amount of this 'marine snow' might have driven the 'Amperima Event'.
From sediment trap measurements, a team led by Professor Richard Lampitt of the National Oceanography Centre has subsequently shown that variations in the supply of organic matter to the PAP can vary greatly between years. Indeed, a second sudden mass occurrence of Amperima in 2001 a possible second 'Amperima Event' may have been due to increased food availability.
Food quality may also be important. Dr Denise Smythe-Wright, also of the National Oceanography Centre and her colleagues have shown that the composition and potential nutrient quality of organic matter exported from the surface ocean depend on the species composition of the ocean phytoplankton community. This could favour the reproduction, recruitment and competitive ability of particular species.
For example, Amperima has a different requirement for certain carotenoid pigments than other species of sea cucumber. Carotenoids in shallow water are known to improve egg production and improve the chances of larvae in developing into juveniles. Carotenoids are used as feed in aquaculture to improve yields. In the food-limited deep sea, changes in the quantity and quality of the downward flux of carotenoids with season and
|Contact: Dr. Rory Howlett|
National Oceanography Centre, Southampton (UK)