Monitoring coral settlers requires special techniques because these young corals are small and hard to see by eye for up to a year. Examining the substrate can also involve disturbing it, so there is a tradeoff between information to be gained from monitoring and disturbing small and vulnerable recruits. Thus, a monitoring program should be carefully considered and should align with the goals and objectives of the project. One strategy is to monitor corals after one year when the recruits have grown to a visible size. Alternatively, if finer resolution of survivorship information is needed, a blue UV light can aid detection of small corals, but is not completely reliable because some corals do not fluoresce consistently over time and some small non-coral organisms do.
If using a blue light, a ‘dark box’ is needed to enclose the substrate for examination as fluorescence is most effectively seen in a dark environment. Depending on the means of attachment, it may or may not be possible to pick up settlement substrates for examination, in which case a large-bore PVC elbow can serve as a handy ‘dark box’. High mortality is common in the first few months after outplanting. However, if high mortality rates continue as corals grow to larger sizes, monitoring can be an effective way to determine causes and possible adaptations needed to outplanting methodology or site selection.
- Coral recruits are very small, thus fundamentally difficult to see and count.
- Monitoring small corals on the seafloor includes some degree of disturbance, which should be considered as a tradeoff with the information to be obtained from monitoring.