Light Trapping

On the 18th January Anna and I joined Simon for the monthly marine team light trapping Plankton sampling at comfortless cove, which is also paired with day sampling and is the same idea as moth trapping but in the water.

Light trapping is used to Investigate the composition and abundance of zooplankton communities for ocean biomonitoring. This is because Zooplankton provide the foundation for all marine systems and are often described as “beacons of change”, as their composition shifts in the face of changing abiotic and biotic factors. 

Extended temporal sampling of populations is therefore essential to establishing baselines of expected community shifts in the wake of intra- and inter-annual variability. 

Light trapping also allows the collection of organisms which are often under sampled (larval forms) by attracting active swimming plankton and allows for collection areas where plankton nets may cause damage to sensitive habitats or be snagged on complex substrate e.g. rocky reefs. 

The light traps feature a cloverleaf shaped array (30 cm in diameter and 25 cm in height) with four entry slits (5 mm wide) and a central light tube for a glow stick to be placed in the center. With a detachable collection sieve, fitted with a 250 micron mesh size. 

Light trap deployments are conducted just after sunset during the two darkest nights of the lunar cycle at Comfortless Cove and English Bay. By sampling at fixed intervals across the lunar cycle a “blueprint” or snapshot of larval fish transport between two key recreational fishing sites and the marine biodiversity of typically under sampled taxa is hoped to be developed. 

Anna, Simon and I deployed one light trap at the surface and one at 4m below the surface, leaving it in the water for an hour before hoisting them back up and taking them to the fish lab to put the samples into alcohol to preserve them for identification later. On the 19th January Abi went with Marcos to do the same thing at Wigan Pier at English Bay.