Luke and I have been in Dauin for a few days now. We are here to investigate the recruitment of cryptobenthic fish. If you’ve read this blog before, you’ll know that I am interested in camouflaged, small critters that live on the seafloor (=cryptobenthic). You might not, however, have heard about “recruitment”. This is the term used to describe the process of larval fish (which usually swim in the open ocean) “settling down” on the reef. When fish larvae settle, they change rapidly from small, transparent, weird oddballs to colourful reef fish. Or in the case of the critters I study, to camouflaged weird oddballs.
There are many reasons why I would like to know more the recruitment of the species I study. The most important one is that nobody really knows why some of these baby fishes show up where they do. If you don’t know this information, it is really hard to protect the right places that would be a suitable habitat for baby fish. Another reason is that this process is vastly different from anything we see on land, making it fun and challenging to try and figure out what is going on.
So how does one best study tiny baby fish? In the case of my critters, looking for the small adults is already hard, so how do you even begin to try and find the even tinier versions? The slightly disappointing answer is: “We don’t really know”. There are multiple techniques to find new recruits or larvae that are about to settle down (light traps, visual surveys, crest nets, …). But most of those don’t seem to be very effective for camouflaged critters. One method did show promise in a study in the Caribbean, the benthic “SMURF”. If at this moment you are imaging little blue creatures with scuba tanks, catching baby fish with lassos and you don’t want to spoil that mental picture, please stop reading now.
Since you’re still reading, I can now disappoint you about my SMURFs, they are not the ones you have seen on tv (no ethics clearance possible). SMURF stand for “Standard Monitoring Unit for Recruitment of Fishes”. It is a mesh-basket you fill with any substrate you want (pebbles, sand, coral rubble, plastic,…) which you then place in the ocean for a set time. After that time you collect the basket and see how many baby fish were attracted to your unit. Not quite the blue man-option, but you are the one who kept reading.
Luke and me made a whole bunch of units, which we deployed around Dauin. To deploy the units we had the help from my supervisor Euan Harvey, who decided to drop by to see what we are up to in Philippines. Euan is an expert in remote sampling using video cameras, but he definitely seemed to enjoy setting up experiments on baby critters as well. This could be due to the fact that on his very first muck dive here, we found Flamboyant cuttlefish, Blue-ringed octopus, a bunch of Frogfish, Ghostpipefishes, Seahorses and loads more critters.
This is the second time I am trying this experiment, the first attempt was thwarted by the ocean. Conditions are looking better now, so with some luck the units will survive the next weeks. By the end of the SMURF-project, we will hopefully know if this method works well for the species I study. With some luck, I will even be able to tell you if baby cryptic fish prefer sand, pebbles, or rubbish. The method can then be used in the future for other people wanting to study the recruitment of cryptic species, so we can start to unravel some of the bigger questions about these poorly studied animals.