Intro to Sampling Strategy

The sampling is ramping up here in Reunion, and the checkboxes are filling up next to target corals. In the last three days, we have collected samples from 27 corals, representing 22 species from 16 genera, 11 families, and 2 classes. Since the actual physical taking of a sample involves just rubbing a syringe against it and breaking off a tiny chunk, our number may not actually seem very high. However, there are a few things that make the process take longer than theory would predict. As Amelia mentioned in the last post, one thing that’s slowing us down is the environment. We’ve discovered before that working in shallow water is not easy. In the lagoon here on Reunion, the water is often so shallow that we are trying to spot live corals in ankle-deep water, then having to find a way to lie down to examine them without crushing the reef or sitting on a poisonous stonefish. In other places, the water is about waist-deep, and the huge waves breaking on the crest continue into the back-reef, sloshing us around amongst the sharp corals and stinging fire-corals, and making it very difficult to stay steady enough for photos and sampling. Plus, it’s winter here, and the water is ‘cold’. 76 degrees Fahrenheit seems warm at first, but after ~4 hours of being submersed in it, the water still saps out all of our body heat. We’re getting cold, sunburned, and beat up!


But if that was the only problem, I’d say we’d just have to suck it up and get the work done! But another, bigger problem is that we have to find the corals. Not just any, but a relatively specific list of coral types. We’re only planning to take a small number of samples from each type while we’re here, and I’d prefer not to take them all from the same location at the same time. I mentioned before that confounding factors can make it difficult to determine which variable is responsible for a given trend. If all we found on Day 1 were Porites and Acropora, and we immediately took all of the trip’s samples for those species, we would have confounded our species variable with time and location. Later, if we took all of our Fungia samples on a single, different day, it would be hard to be confident that differences in the microbes between our Porites and Fungia samples were actually attributable to host specificity. An equally good alternative explanation would be that microbes on corals on Day 1 were different than microbes on corals on Day 5, no matter which species we sampled on each day. This is likely to be true for many microbes due to differences in disease prevalence, tidal height, current direction, light level, etc. To be confident that differences are due to coral species, we need to have a clear sampling plan. A solution is to find and sample replicates from many different coral species on the same day. Differences among these samples would be more confidently attributable to individual colonies and, through replication, to coral species. So we are doing our best to find locations that have high levels of diversity. High diversity reefs were easy to find at Lizard Island and KAUST and made our sampling there go great!

We are not having problems finding Porites (massive) and Acropora (branching)...

We are not having problems finding Porites (massive) and Acropora (branching)…

This Fungia, however, is the only one we’ve found, so far.

The first couple of days that we were here in Reunion, we spent a lot of time exploring the lagoon just down the street from our rental house. We chose the house hoping that the majority of our sampling could be just a short walk and swim away. However, we weren’t finding much in those reefs. Of the ~16 families of corals that we hoped to find here, only 2 were common, and we only found 5 there in total. So after a weekend of exploring the island for fun (escaping the critical eyes of the heavy crowds at the beach), we began our sampling in the lagoon of Trou d’Eau, a short drive south of us. The reefs there were, if anything, less abundant and diverse than the ones here. We got samples from 5 families. So the next day we went even further south, to Saint-Leu, to see if our luck would be better. Indeed, we found a reef that had much more cover and much more diversity than those up north. We collected samples from 8 families, 5 of which were new! Still, with a total of 10 families, we were still missing a few that have been very common and conspicuous in other wide-ranging Indo-Pacific reefs that I have sampled. So we decided yesterday to try a different environment and brave the shark-infested fore-reefs via scuba. The day was great – I absolutely love the feeling of being on a boat in the tropics, and the feeling of breathing clean, cool air through a regulator while suspended underwater. Plus, the sampling is way easier while diving under the waves, and doesn’t tend to get us all beat up. But the reef wasn’t very diverse. We found 5 families of corals – only 1 of them new.


Ahh, I love being on the water!


Thought this was a Montipora – closer inspection reveals it’s just another species of Porites!


Weekend getaway


Cold mists of the volcano

As the trip reaches its half-way point, we are ready to buckle down and get going on replicates of what we already have. We’ll keep our eyes out for the missing coral families, but would be relatively satisfied with the current repertoire if it’s all we wind up finding. Today, we head south again, this time diving on the fore-reef, where we hope to find a beautiful combination of easy sampling and diverse corals.


Print Friendly, PDF & Email