Community Research and Development Information Service - CORDIS

A simple videorecording system for estimating the abundance, distribution and population structure of jellyfish in surface waters

The study of abundance and distribution of jellyfishes is difficult because usually had a very aggregated distribution. We have developed a simple and relatively economic system to study the structure and distribution of megaplanckton organisms. For this, a underwater camcorder was placed in a steel structure and towed from a boat to a depth of 1,5 meters. In this structure of pyramidal design the camera was oriented filming the square base. All the structure oriented as well in the direction of advance of the boat. Next to the camera we towed a CTD and temperature and salinity data were stored. The camcorder and the CTD were synchronous with the clock of a GPS that registered and sent to a notebook the position every second. We tried to evaluate the abundance and distribution of three species of medusas (Cotylorhiza tuberculata, Rhizostoma pulmo and Aurelia aurita) in a shallow coastal lagoon (Mar Menor, SE of Spain).

We covered all the area with a route in zigzag. After the sampling, in the laboratory we digitalized the videotapes. Taking a minute of film like a transect we counted the medusae that crossed the frame, the density of jellyfishes was calculated with the sailed distance, and temperature and salinity averages of all the data stored in that route was calculated too. This values was assigned to a position and maps of distribution, abundances and hydrographics dates were made. In the process of to see the films we captured the images when a jellyfish crossed near the steel frame and with analysis of image software we measured it. (we used the freeware Image Tools)

This method allow us to obtain higher number of samples and the amount of this is bigger than the obtained with others methods. With this method we obtain less variances in the results of abundance. On the other hand the number of measured individuals were higher too. Also is possible the study of size distributions in different areas of the lagoon. All software used: 1.- Capture and compression of video with VirtualDub 1.6.10 (freeware) 2.- Processing CTD data. SeaBird software. (freeware) 3.- GPS Mapping software. OziExplorer. (low cost of purchase) 4.- Image analysis with UTHSCSA ImageTool v 3.0 --Results--> During years 2003 and 2004 this method for the study of the populations was used in the Mar Menor (SE of Spain). This method was very useful for the study of Cotylorhiza tuberculata and Rhizostoma pulmo in the years of more abundance.

For Aurelia aurita was a bad method because this specie is almost transparent being difficult of count and measured it. The population dynamics and the distribution were studied. We made relationships between the medusae distribution and the hidrology characteristics of the water. Improvements of the system for the future. The use of this method with more precision and try to study the different levels of aggregation.

Capturing the data each second and positioning each individual medusae perhaps we observe differences in this scale and we could explain why are jellyfish in this scale of aggregation. The use of specific software that applies different treatments of colour to the images perhaps allows us to recount and to measure the individuals of Aurelia aurita too.

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Reported by

Instituto Español de Oceanografía
Magallanes 2
30740 San Pedro del Pinatar
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