AREA OF INTERVENTION

Palm Beach Island Resort and Spa is located on the island of Madhiriguraidhoo (5°28’13.08″N, 73°33’35.27″E ) in Lhaviyani Atoll.

It is the only island in the huge lagoon and it lays on the northeast rim of the atoll. The large reef system of this lagoon extends further North along the rim of the atoll. The island’s long stretch of reef is weel known for its beautiful diving sites all the way around the reef.

PROJECT OUTLINE

The three main components of the project are:

• Corals propagation, corals identification and fish identification.

• Monitoring of coral growth on different substrates while educating the staff to raise awareness about coral reefs and their threats.

• Relocating the corals on the reef substrates once grown into juvenile coral colonies (15 to 20 cm).

METHODOLOGY

The project involves researching coral growth and aims to link the research to finding practical ways to relocate corals on natural substrates once they are grown, using different coral restoration methods. The target was to maintain a small coral patch near the snorkelling area of the island and to sustain and assist the recovery of the reef.

All the coral fragments were collected from inside the lagoon. These fragments were broken off and fallen in the sand, which our team collected during snorkelling sessions. Before placing the fragments in the nurseries, the dead parts, sponges, algae and other organisms were removed.

For purposes of analysis, the corals have been classified according to the form of coral growth: branching, submissive and digitate. The measurements have been taken every week after attaching the corals to the frames, pods and lines. In total, 12 weeks of measurements have been collected.

Nursery A consists of different types of frames: one spider frame, two-tower frames, one pyramid frame, one blue bed made of PVC pipes (with cement bases) and a fishing line frame. All the frames, except for the PVC bed, are made of rebars.

The pyramid and the tower frames were the first to be installed. The coral fragments on the PVC bed were attached on 13th March 2018 and the corals tied on the lines were attached on 28th March 2018. This study focuses on the blue bed PVC frame and on the fishing line frame.

The nursery B consists of two kinds of frames: one pyramid close to the jetty and one fishing line frame located further at a depth of 5-6 m. All the frames are made of rebars. The fishing line frame was laid on the 28th of March 2018, while the pyramid was laid on the 8th of April 2018.

Two different areas from the east intertidal lagoon (NURSERY A) and the west side lagoon (NURSERY B) have been used to develop two coral nurseries. The east lagoon (NURSERY A) is relatively flat and shallow, with a varying depth of 2-3 m depending on the tide. In some areas, seagrass patches are found and the sandy bottom is interspersed with few rocks, rubbles and hard coral colonies. The area receives daily water exchange from the open ocean which generates the dynamic currents flowing around the island. Nursery A is located in the proximity of a pier where daily fish-feeding activities used to take place.

The west side (NURSERY B) is deeper with a 3-6 m depth depending on the tide and the location (two round pins on the map indicate two different sites). On the west of the Island, the lagoon bottom is completely sandy and the suspended particulate matter is strongly affected by the sea conditions. Due to the environmental conformation, this side was stronger affected by the currents and the weather, which made the activities in the nursery quite challenging.  

The location of the coral nursery is really important to ensure the healthy growth of corals. Ideally, a ‘hard coral’ nursery should have a good current flow (medium to strong), good water quality and sheltered from strong wave activities and must be easily accessible.

CORAL RESTORATION METHODS

Description and reference pictures for each of the experimented methodologies:

1- Corals attached on cement cylindrical pods, hold by a PVC frame (Nursery A, called: Blue Bed)

Number of coral fragments attached: 117

Bleached corals: 4

Number of corals recovered from Bleaching: 1

Disease corals: No diseases found

Lost corals: 3 corals got bleached and the recovery was slow. Algae grew over the corals and they did not survive.

Current status: 114 coral colonies growing

2- Coral fragments tied in fishing lines and coral plugs at the cement bases of the frame

MONITORING

Coral monitoring was carried out once a day for the first 12 months and the data are recorded on a weekly basis. During monitoring, any of the following activities may be carried out.

• Cleaning off overgrown algae from coral nursery (scrubbing the algae using brushes)

• Removing drupellas

• Measuring the corals with a calliper and recording on a slate

• Recording tide and temperature

• Removing dead corals

• Removing diseased corals

• Coral ID

• Fish ID

In Nursery A, during the first stages of the project, fish-feeding activity was carried out on the nearby pier. Due to this increment in nutrients in the water, we observed that algae grow very fast on the frames, overcoming the space needed for the corals’ growth. Nursery A needed to be cleaned of algae every day. After a couple of weeks, the fish-feeding activity was interrupted, and the algae growth rate decreased significantly. At this point, the herbivorous fishes grazing on algae were enough to keep them under control.  

The temperature at both the nursery areas was always between 30 and 31 C°, and the depth (with the low or high tide) was about 2-3 m in Nursery A, and 3-6 m in Nursery B.

AVERAGE CORAL GROWTH

Referring to the above tables we can observe the difference between the growth of branching corals and submassive corals.

The branching corals had a higher growth rate than the submassive ones.

Both branching and submassive corals resulted to grow better on the fishing line frames both in nursery A and B.

While the corals were growing, we observed the abundance of fishes growing with them, with a strong predominance of juvenile forms. This is particularly interesting because the coral nurseries resulted to be nurseries not only for corals but also for all the other organisms which live linked to them. We have started relocating corals to natural substrates after 1 year and 2 months of growth. All the corals attached to reef substrates were attached using marine epoxy (marine cement).

The corals are growing healthy after being attached to natural substrates.

AVERAGE TREND OF GROWTH OF BRANCHING CORALS

The analysis of corals growth shows that branching corals are the fastest-growing corals within the hard-coral species. The Acropora muricata resulted to be the fastest growing species among the other Acroporidae.

After attaching the fragments, it took almost a month for the corals to settle down and heal their tissue.

HARD CORAL SPECIES AND FISH SPECIES INHABITATING THE NURSERY

We were able to identify the corals in the nursery into 8 species of corals within 3 genera.

We have also identified 20 species of fish that have started to inhabit the corals in the nursery.

Hard Corals

• Acropora muricata

• Acropora humilis

• Acropora tenuis

• Acropora anthocercis

• Acropora pulchra

• Acropora gemifera

• Pocillopora meandrina

• Heliopora coerulea

Fish species

• Lutjanus Bangalensis – Bengal Snapper 

• Lutjanus Gibbus – Hump back Snapper

• Dasscullus aruanus – Humbug Damsel

• Neopomacentrus cyanomos – Regal Damsel

• Pomacentrus pavo – Azure Damsel

• Rhinecanthus aculeatus – Picasso Triggerfish

• Gymnothorax Fimbriatus – Spot face moray

• Thalassoma lunare – Moon wrasse

• Zebrasoma Scopas -Brown Tang

• Dascyllus trimaculatus – three spot humbug 

• Ctenochaetus binotatus – Two-spot bristletooth

• Pterois radiata- White line Lionfish

• Pterois volitans – Common Lionfish

• Acanthurus triostegus- Convict surgeonfish

• Hemitautoga scapularis – Zigzag wrasse

• Chaetodon kleinii – Brown butterfly fish

• Cirrhitichthys aprinus- Blotched hawkfish

• Chrysiptera biocelata – White saddled damsel 

• Labroides dimidiatus-  Blue steak cleaner wrassesCephalopholis argus- Peacock rock cod

CONCULSIONS

What we can conclude is that in this given context, the fishing line frame in nursery A allowed corals to grow faster and healthier when compared to the other methods. We have observed that in nursery A corals need more time to start growing and the pigmentation is also lower due to the sea surface temperature and the amount of nutrients in the water.

In nursery A, fish-feeding activity considerably increased the organic matter in the water speeding up the growth rate of algae which compete with corals for space. However, the conditions of water quality improved after fish feeding stopped, and the corals grew faster.

We were not able to check the acidification or test the water for other parameters (such as dissolved chemicals or heavy metals). It will be interesting to further develop this study by including water quality parameters and increasing the number of measurements.