Home Institution: University of Swansea in Wales
Sam is a recipient of a Munson Foundation award for coral reef research as well as being a graduate intern at BBSR.
I study at the University of Swansea in Wales which is part of the United Kingdom. I first came to Bermuda in the summer of 1995 to carry out the research for my university undergraduate project. I worked here for 3 months and in that time I designed, constructed and built traps to attempt to catch coral larvae out on the coral reefs. Coral larvae are baby corals and are the product of sexual reproduction. Reproduction is important as it is the way in which corals can settle and live in new areas. In other words, the larvae are the only way in which these animals can move as the adults are fixed to the bottom. The larvae drift in the water before they find an available and also suitable place in which they want to live. Space on the bottom is scarce on the reef, like a crowded neighborhood where there is no room to build a house. Animals like corals that live on the bottom (benthic animals) compete to push each other off space and to settle onto open space before other animals do. When corals die, either due to human impacts or naturally due to hurricanes, we need to understand what controls the resettlement of the larve to the reef to better plan how to sustain reefs.
My trap was designed to catch the larve as they began to settle to the bottom and look for a place to live. The number of larvae that I caught was then compared with another study that was measuring the number of larvae that actually settle on the reef. Settlement is the final stage of the baby coral's journey and involves the larvae attaching itself to the bottom (on a piece of stone or old coral for example) and transforming into a polyp (this is called metamorphosis and is similar to what happens with tadpoles to frogs or moths to butterflies). This polyp will then grow by copying itself to form new individuals anda colony is formed. It was interesting to see that the number of baby coral larvae that I caught in my traps was a lot greater than the number of larvae that were found settled on the bottom. This is because coral larvae are very tasty to many of the reef animals such as zooplankton (Link to Astrids page) and so are eaten before the can settle. Other larvae may never find a suitable place to live before they run out of energy and so they die. Because of all of these dangers, an adult must produce many baby coral larvae so at least some of them will survive to start a new coral colony.
After doing this initial study, I became fascinated with the life of these coral larvae that have such a hard time in the water finding somewhere to live and have to avoid lots of hungry predators. Various coral species have different methods, or strategies, forproducing these larvae. Some corals will reproduce by the production of larvae over many months of the year. Others will reproduce for only limited periods. Different coral colonies of the same species will reproduce over precise days of the month and even at specific times. The corals coordinate this by the phase of the moon and by amounts of light.
I returned back here to Bermuda in April 1998 to carry out postgraduate research for my Ph.D. I will spend some of my time at my home University of Swansea in Wales. However, most of my time will be spent here in Bermuda. Whilst I am no longer using my traps to try and catch the coral larvae, I am still investigating coral reproduction and the production of larvae. I mentioned how it is important that we know how corals reproduce. But for some species this is not known, or is not known in very much detail. Part of my job is to find out about the reproduction of these mysterious species. The second part of my job is to see if and how the reproductive cycle of some corals is different depending on where the coral colony lives. Here in Bermuda, some of the coral reefs are deeper than others. Some coral reefs are in areas of clear water while other corals live in murky waters that have a lot of sediment. These are examples of the different environmental conditions that corals can be exposed to.
I have chosen to study 2 different animals from 3 different groups of coral. The first group is not really true corals. They are called Zoanthids. These animals belong to the same overall class as the corals but are in a separate group, as they look very different. There are not as many different types of zoanthids as there are true corals but these animals can occur in large numbers on the reefs. The species that I am studying are
The other animals that I study are true corals. There are 2 major groups of true corals. These are the hard, stony corals (that are called scleractinians) and the soft corals (which are also called gorgonians or octocorals). The stony corals have hard skeletons made out of calcium carbonate whereas the soft corals have a flexible skeleton made out of a substance called gorgonin.[Link to coral biology section].
One of the hard corals that I am studying is called Madracis mirabilisand is a branching coral. This species is very common here in Bermuda, especially close to the shore. However, very little is known in detail of how and when it reproduces. The second hard coral species that I am investigating is Porites asteroides. This species is very common on a wide variety of reefs here in Bermuda. We already know about the reproduction of this species. But since it is an important member of the reef animals, it has been chosen as a species to use to see whether there are any differences in it's reproduction depending on where it lives. In other words, whether the environmental differences, that I mentioned between the reefs, have caused there to be a variation in the way in which this species reproduces. To find out more about coral biologyclick here.
In general, much less is known of the reproductive biology of the soft corals. The species that I am studying are both very common here in Bermuda and are known as sea rods. They are Pseudoplexaura porosa (that's it on the left) and Plexaura homomalla.
The methods that I use to study the reproductive cycles of these species is to collect samples from the corals every other week by SCUBA diving and cut them up to see whether there are any female eggs or male spermaries (sacs of sperm) in the polyps. I will also be placing nets over the colonies underwater on the reefs to catch the larvae as they are released from the adult colonies. This will show me exactly when the species release the larvae. Also, I will take whole colonies from the reef and put them in tanks here in the lab in order to watch them more closely. I have sites set up on reefs all around Bermuda that vary in their environmental conditions.