The Experiment

The reason I am here and my primary focus until September.

Why are copepods found in dense aggregations at certain depths?

 We have some understanding of the how; by swimming and the buoyancy of the lipid sacs many copepods contain they are able to maintain a certain depth even if there is strong upwelling/downwelling of the water in that area (giving some new meaning to the classification of copepods as plankton or 'drifters').

But what is the advantage? usually the reason for individuals to get together is for either food or sex (much like in humans) but but these aggregations are composed of many different species that cannot mate and their food supply is plankton that moves with the water current so it makes sense that the copepods should allow themselves to also move with this current and their food.

My role in this project is to determine the affect of pressure (as a proxy for depth) on the sinking rate (as a proxy for buoyancy).

To do this I must first determine the relative amount of fat or lipids the copepods contain. I measure the area of the oil sac and the area of the body (prosome) of the copepod using image analysis of each individual.

 After I have these measurements and I have removed the copepods antennae, I sink them.

I introduce the copepods gently into the top of the chamber and time them using a stop watch, recording the time as they pass every mark in order to later determine the sinking rate.

As the copepod reaches the halfway mark I introduce 3.5 atmospheres of pressure into the sinking chamber, this recreates the pressure the copepod would experience at 25 meters depth.

The hypothesis was that, because lipids are more compressible than water, the relative density of the copepod would increase and it would sink faster once the pressure is increased. However, in the 'fat' individuals especially, we have found the opposite.

Currently I have performed this experiment on 60 individuals and am now inputting the data into a spreadsheet  so that I can analyse the initial results.








Although this is my primary focus at the moment I am also carrying out a side project investigating any patterns in the visiting of the whale sharks that come here every year (more information in a future post).

As well as this I have also received the exciting news that I can start my very own project (with funding) once I return after this initial three month stay so now I have to come up with a relatively short research project that I can make my own.