Monitoring and Maintenance of Corals in the Nursery Copy

Tracking corals in the nursery is one of the most straightforward monitoring techniques described in this lesson and arguably the least important.

In the nurseries, we are usually not trying to optimize growth and prove that we can grow corals better than somebody else. Our goal is to restore the reef, so we are only concerned with monitoring corals in the nurseries as risk mitigation and knowing when to outplant the corals. Our time is instead spent ensuring the survival of a diverse range of coral genera for our restoration feedstock.

Mostly, local reef managers do not need to spend much time or energy collecting monitoring data at the nurseries. However, there are some instances when this may be called for, such as:

  • Projects that rely on funding cycles may have different goals and could want to show that the corals in their nursery grew some amount in a year to achieve grant deliverables.
  • Scientific studies being done by academics and researchers may need to know how many new branches the coral has grown or what the growth rates of the corals are when testing new techniques.
  • Advanced restoration projects that track coral genetics, such as in the case of many government-based programs or those responsible for endangered species.
  • Spawning programs involved in selective breeding, hybridization, or other such work where lineage tracing is important.

Rapid Collection of Monitoring Data

We recommend visiting in-water nurseries as often as possible, usually at least once weekly. Time is limited, and our primary goal is to maintain the nurseries. Monitoring should take no more than a few minutes.

This is often achieved through photographs. Photos can be quickly taken of nursery trays and compared from month to month to understand growth rates.

This can be a bit more complicated for corals growing on ropes and tree nurseries. Often, the most useful data is just counting the number of surviving fragments versus the number of fragments that have suffered partial or complete mortality.

During non-bleaching years, most corals in the nursery will survive and grow. If you start to notice a high increase in mortality from one week to the next, further investigations should be undertaken.

There will be times when you have students doing research projects, when you want to publish results in academic journals, or when you have other reasons to justify spending more time monitoring corals in the nurseries.

Some of the things you may want to track will be done so using the techniques you already learned in the EMP, such as:

  • Calculating coral diversity by recording the genera/species of corals present
  • Recording coral disease, bleaching, or other compromised health states
  • Recording predation by corallivorous fish or invertebrates
  • Measuring growth manually or through photos/ImageJ

In these cases, you will want to tag individuals. The objectives of your research project will dictate the sample population size necessary, but usually, it is not the entire stock of corals in the nursery.

This can be done with tags made of PVC, engraved stainless steel, cow tags, or other improvised methods based on available materials.

With the increasing availability of cheap underwater cameras, photos and photogrammetry should be a part of every visit to the nursery. Photos are valuable for showing progress to non-specialists and the general public, and you can learn to analyze them further.  

For post-analysis, use free software programs such as ImageJ or CPCE, which allow you to set a reference scale and then calculate lengths or areas.

There are also many free 3D photogrammetry programs online that you can use to create 3D models using video or photosets.

For all photos, you must have items in the picture of a known scale, usually a ruler or caliper. For table nurseries, meshing can also be helpful in top-down photographs. The reverence item should be in the same plane as the coral to reduce perspective issues when setting the scale in the computer software.

Maintenance of Coral Nurseries

Most of your time at in-water nurseries should be dedicated to maintenance. This will include different tasks depending on the day, the conditions, and the skill level of the volunteers or assistants you have on the dive.

The most crucial job is identifying threats to coral survival or growth. Most frequently, this will be fouling organisms such as sponges, macroalgae, colonial tunicates/ascidians, and cyanobacteria.

Cleaning Nurseries

All fouling organisms compete for space with corals and, in the artificial environment of a nursery, may have a competitive advantage due to a lack of predators or other factors.

At each visit, the nurseries should be inspected for issues, and divers should be equipped with brushes or other preferred tools to remove fouling organisms. Generally, it is not necessary or desirable to clean filamentous algae or attempt to clean the entire nursery as this may cause corals to become dislodged and could remove desirable organisms.

Beneficial organisms should be left on the nurseries, such as sea slugs which feed on some of the fouling organisms, or the hermit crabs that consume detritus.

Volunteers and assistants need to be thoroughly briefed on the organisms to look for, which to remove, and which to leave be.

Occasionally, corallivorous gastropods or echinoderms can make their way into the nurseries. In our experience, a single crown of thorns that finds its way onto a table nursery can decimate the entire feedstock in less than two weeks.

Volunteers should always be on the lookout for these organisms and know the proper safety procedures to remove and relocate them when necessary.

After the mortality and health data have been taken, any dead fragments should be removed, as there is no value in keeping them in the nurseries, and they may be harboring fouling organisms.

Volunteers should be briefed on how to identify a dead fragment and properly remove it from the nursery without disturbing the healthy corals around it.

Transplanting Mature Corals

The final reason to regularly maintain and monitor corals growing in the nurseries is to know when to transplant them back to the restoration site. This will be different for each genus of coral and each nursery type.

For the tray nursery, competition between corals is usually the deciding factor. Once the corals all start growing, they will fill the tray and may begin to compete with or abrade one another in waves or currents. Before they reach that point, the largest corals should be removed.

In the rope nurseries, it is generally when the ropes become too heavy for the floats, and the corals have all started to grow over the rope material, similar to the tree-style nurseries.

In all cases, we suggest moving corals out as they reach a large enough size and are healthy enough to do so.

In our experience, there is little value in setting arbitrary dates as may be required in projects that must adhere to funding cycles. The nurseries should be viewed as something ongoing, with corals being added and removed on every visit depending on the needs of each fragment or colony.

One of the major criticisms and observed failures of some restoration projects occurs by moving corals into areas that are not conducive to their growth and survival.

Failure often occurs when managers view reefs as purely stable ecosystems and attempt to replace historic species that may no longer be able to survive there. Loss is also likely when corals are moved great distances or even small distances if conditions are very different.

In our experience, no set rules can apply to all situations. However, some good considerations are to not move fragments or transplants too far from the location they were retrieved from (less than 300 m). If the reefs are so degraded that there is a need to move corals in from another area, this is most successfully done using larvae, colonies produced from cultured larvae, or through other means of increasing the natural recruitment of corals.

Already established corals moved into areas where their parent populations have already proven to be unsuccessful will generally led to project failure and have negative consequences for the donor reef.