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Two giant clams

The strange incident with the giant clam

Maria Dornelas

May 19, 2020

This stretch of the reef between South and Palfrey Islands feels like home. I have been coming here almost every year for the past 12 years. I can draw the contour of the reef crest with my eyes closed. I can tell you in excruciating detail how many species of coral there are here, and how rare or abundant they are. I mostly have my head in the coral when I am here, but I have seen sharks and turtles around. There are rumours of dugong sightings, and photographs of manta rays. But my favourite story about the reef we call Trimodal is about a giant clam. We started calling this reef Trimodal, because of the species abundance distribution of the corals on this reef crest. We counted over 42 thousand coral colonies there in 2005, and the SAD had a funny shape with three modes.

I can’t remember why exactly, but on this occasion we decided to park the boat in the lagoon area, at the back of the reef. We looked for a patch of sand and rubble and dropped anchor. We got our gear on and I braced myself for the swim across the reef flat towards the crest where we were more likely to find the species we were looking for. Because we were anchoring rather than using the mooring we normally used, we checked the anchor before we swam across. This is always a good idea, as coming back from a dive to find your boat gone is not much fun. Much to our surprise as we looked down, we saw that a giant clam had caught our anchor chain and closed up.

We tried to pull the chain out, with no success. I just sat at the surface having a giggling attack. I laughed and laughed and laughed picturing us explaining this to staff at the research station: we lost the anchor because a giant clam ate it. This would take “my dog ate my homework” to a whole different level. Laughing made my snorkeling mask fill up with water, which made me laugh even harder. We took photos and decided there was nothing we could do at this point.

The clam was not willing to let it go, so we decided to carry on with our job, and deal with the anchor on our return. At least the boat was definitely not going anywhere.

It was a beautiful sunny day, and I didn’t even complain much about the long swim. One of my legs is slightly longer than the other because of a motorcycle accident I had when I was 18. You probably won’t notice if you know me, and Ionly notice when I am swimming with my fins on. It makes long swims always interesting. In the British sense.

We got on with our job. Eventually, we were done for the day and headed back to the boat. By then the giant clam had decided the anchor chain was not tasty and had let it go. We headed back with a full day of data and an interesting story. In the literal sense.


Maria Dornelas
Maria is a Professor at the University of St Andrews. Her research focuses on quantifying biodiversity and understanding the processes that shape it.