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Currents
Question number: 30 Posted: 25 Nov 2004 10:18
Topic: Fish ecology Creator: Bente Lorentzen
Status: Answered Scientist: Odd Aksel Bergstad
Written by: Bente Lorentzen 25 Nov 2004 10:18

How does the current affect the spreading of fish larvae and eggs? Are the populations around the Mid- Atlantic ridge isolated from populations ashore?

Written by: Odd Aksel Bergstad 25 Nov 2004 11:08

Most fish eggs and larvae are small and have limited ability to control their position in the water, hence their movements in space and time are determined by their buoyancy and the vertical and horizontal flow of the water. Bouancy depend on the denisty of the organism in relation to the density of the water, and ifferent watermasses have different densities depending mainly on salinity and temperature.

Ocean currents can concentrate or spread eggs and larvae. Concentration is usually beneficial, and so is flow into more productive areas. The latter is waht happens when eggs and larvae drift from spawning areas into nursery areas where the food production is favourable.

In mid.ocean areas we know little about how eggs and larvae are spread or retained in certain areas. Around seamounts therea are currents that sometimes act as traps for egges and larvae, but a fraction will always be lost because currents carry them away from the only inhabitable area, i.e. the seamount.

We don't know if the populatuons around the Mid-Atlantic Ridge are isolated from those along the continental margins. Probably there is limited exchange of eggs and larvae across the deep-sea basins. We are investigating this issue using genetical techniques based on DNA-analyses.This can tell us if and for how long populations have been separated, in evolutionary terms.

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