Marie Meffre UMR Marine Biodiversity, Exploitation and Conservation (MARBEC), University of Montpellier, France
7th International Jellyfish Blooms Symposium (JBS7), November 21–24, 2023. Organized by University of Kerala and ICAR-CMFRI at Kovalam, Thiruvananthapuram, India: Plenary and oral presentations
Hello everyone I’m marim M and I will present you the Aral survey of a jellyfish bloom dynamic in a small Mediterranean Lagoon many jellyfish faces produce massive blooms their distribution is patchy and their burst and burn nature makes them difficult to monitor traditional servies using Nets and boats transects cannot cover the
Entire blue magnitude so how do we quantify the special temporal dynamic of a bloom well we need to take some altitude AR serves are adapted to jellyfish patchy distribution around 10 Studies have been using drones or planes to study jellyfish Blooms from the air these figures present the
Altitudes and flight time used for each species apart from wor studies only three other Studies have used planes to survey jellyish personel at all in 2000 to study Ora La labata Graham at Al in 2003 to study fla punata and hon at Al 200 2006 to study CIA capata and Rosa
Octopus most of the time ples are used to study big and very visible jellyfish the species we monitored is rulu the species has many assets for Arial survey this is one of the biggest jellyfish spes of the Mediterranean Sea and this spes swims near the surface rumu does its entire life cycle
In Bashan Lagoon B lagon is located in the south of oh sorry you don’t have the yeah that’s better okay um I’ll start again okay um result yeah bar is located in the south of France it’s a semi-enclosed shallow Lagoon with an area of 40 kilm square these characteristics makes it a natural
Mesocosm ideal for the study of jellyfish three cohorts have been identified in the lagoon to cover the cohorts and capture the special temporal dynamics of the of the entire Bloom we did three different flight okay so let’s move on to the image acquisition we used a small planes equipped with a high resolution
Camera the plane flew at an altitude between 300 and 600 M the entire Lagoon was covered three times once by each flight each flight lasted for three hours the path is looks like this each flight represents several thousand picture so we obtain um photos like this one the resolution is 10,328 for
7,660 uh pixels which means that if we zoom in zoom in again and zoom in a little bit we can different differentiate each jellyfish for the analysis we estimated that the minimum size for a jellyfish to be properly detected was 10 cm now let’s see how we um analyzed the
Picture so the first step is to remove all the elements ments that can be problematic for the jellyfish detection such as the coast the coast sorry you don’t hear the glare and the birds it looks like this once they are detected and then it looks like this it
Creates a binomial mask with the ConEd and the non-ed area the second step is the calculation of the area and centroid of the conted area here in Black then we detect the jellfish in this area for the anterior picture it looks like this so for each picture we obtain the total number of
Jellyfish sorry we obtain the total number of jellyfish that we can divide by the conted area to obtain the jellyfish density for each jellyfish we get the coordinates so okay the total length and the area so let’s move on to the results to this day we have only
Analyzed one out of four images for each flight they are represented here by the yellow dots on this map the lagoon area has been divided by a grid each case of the grid is four uh yeah 400 per 400 m then we calculate the average density of
Jellyfish per hectare for each case of the grid and to be able to interpret the map we use an interpolation model so here you can see the average jellyfish density per 100 m Square so one hect um in yellow it’s a high density it’s four 400 individuals per
Hectar and in blue is 50 individual or less per per hect um okay so these are the maps of the free of the three flights the bloom seems to start at three different spots in the west of the Lagoon then moves um then the jellyfish are gathered to the
West we think that can be trapped here by the current this create a huge Bloom patch of 4.8 kilm Square which means that the bloom of this Bloom patch of high density covers 12% of the Lagoon um during the last flight we can see that that this patch has been divided and mooves
South another interesting thing to notice is that um during the first flight we observe a huge density in the west at the free spots so that might be the polyps locations because that would be where the bloom begins it’s especially interesting because nonr popse has been found in the world
Yet to conclude um IRL monitoring is very complimentary to net or direct obser observations the main limits are the limited detection of small individuals misidentifications of jellyfish it’s a method that is very weather dependent and costly nevertheless this method allowed us to have the anterior distribution of the bloom and to
Um capture the bloom in its Anor spal temporal Dimension which uh which are data we couldn’t have otherwise um it’s also precise enough for cohort detection so the next step of this study will be to detect the cohorts thank you for your attention