Tags

 

Introduction

In the Maldives due to global and local pressures, reefs have been strongly threatened, leading to a high decrease in coral cover. Due to the growth of tourism and the development of the islands in the last few years, the pressures of local human activities are increasing. Furthermore, coastal development acts synergistically with global warming, worsening the status of coral reefs and affecting corals’ resilience.

The project began on 5th February 2018. This coral conservation project aims to study coral growth and to distinguish the variation in growth rates using 4 different coral rearing methods on different substrates. This study investigates also the fish community attracted by the coral nursery, identifying the different fish species.

Furthermore, the project contributes to finding a practical method to re-attach the corals to natural substrates, after growing the fragments in the nursery, once they are grown into juvenile corals of 15 to 20 cm.

Aim and Objectives

The primary objective of this project is to research and find a practical method to re-attach corals on natural substrates. This could possibly support and help the recovery of damaged coral reefs.

Below are the objectives we followed in this project.

  • Establish a cultured coral nursery using different coral rearing methods.
  • Follow up by cleaning the substrates and taking care of the coral fragments.
  • Monitor the corals’ growth with a calliper and register the measurements. 
  • Identify coral species.
  • Identify the fish species attracted to the corals in the nursery. 
  • Engage the staff of the resort in coral conservation workshops to educate and to enhance their knowledge of corals reefs. Involve them in the project while assisting in monitoring the corals.

Palm Beach Island Resort and Spa is located in the island of Madhiriguraidhoo (5°28’13.08″N, 73°33’35.27″E ) in Lhaviyani Atoll. It is the only island in the lagoon and is located in the north-east rim of the atoll and the large reef system of this island extends further north along the rim of the atoll. The island’s long stretch of reef has hypnotic diving sites all the way around the reef.

Project site plan

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. The 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 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, this made the activities in the nursery quite challenging.  

The location of the coral nursery is really important to ensure 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. After collecting data, we focused our efforts and resources on nursery A.

Project Outline

Project Components

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 its threats. 
  • Re-attach the corals on the reef substrates once grown into juvenile coral colonies (15 to 20 cm).

Work Methodology

The project involves researching coral growth and aims to link the research to find practical ways to re-attach corals on natural substrates once they are grown, using different coral rearing methods. The target was to maintain a small coral patch near the snorkelling area of the island and, hopefully, 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 to the lagoon bottom and collected during snorkelling.

For purposes of analysis, the corals have been classified according to the form of coral growth: branching, submissive and digitate. The measurements were taken every week after attaching the corals on the frames, pods and lines. In total, 12 weeks of measurements have been collected. Before placing the fragments in the nurseries, the dead parts, sponges, algae and other organisms were removed.

The pyramid and the tower frames were installed earlier than the other frames. The coral fragments on the PVC bed nursery A were attached on 13th March 2018 and the corals tied on the lines which were attached on 28th March 2018. This study focuses on the blue bed PVC frame and on the fishing line frame.

The nursery A consists of dissimilar 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 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 March 2018, while the pyramid was laid on the 8th of April 2018.

Coral Rearing Methods

As mentioned earlier, here are the 4 different coral rearing methods utilised. Below they are highlighted with pictures for reference

Corals attached to plastic pods & corals attached on cement cylindrical pods (PVC tube filled with cement) Nursery A – 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 – 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

Coral fragments tied in fishing lines

Number of coral fragments attached: 32

Bleached corals: 1

Number of corals recovered from Bleaching: 1

Disease corals: No diseases found

Lost corals: 8.  all the corals attached on the cement base were affected by the moving sediment.

Current Status: 24 coral colonies growing.

Corals attached on metal frames using cable ties (spider like)

Number of corals fragments attached: 43

Bleached corals: 2

Number of corals recovered from Bleaching: 2

Disease corals: No diseases found

Lost corals: 1.  Current Status: 42 coral colonies growing

Corals attached to natural substrates using epoxy

Number of coral colony attached: 14

Bleached corals: 2

Number of corals recovered from Bleaching: 2

Disease corals: No diseases found

Lost corals: 0 

Current Status: 14 coral colonies growing

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 weekly
  • Recording tide and temperature
  • Removing dead corals
  • Removing diseased corals
  • Count the corals to identify lost corals.
  • Coral ID
  • Fish ID

In the nursery A, at the time of starting the nursery, fish feeding was carried out on the nearby pier. We observed that algaes have grown on the base of the nursery frame and over coral pods occupying the space that the coral fragments can grow onto. We cleaned the nursery from algae every day. We suspected the fish feeding considerably increased the organic matter in the water and speeded up the growth rate of algae. After a couple of weeks since the fish feeding was stopped, we noticed the growth rate of algae had reduced, and we rarely had to clean the nursery, instead, the herbivorous fishes grazing on algae was enough to keep them in check.  

The temperatures at the nursery area were always recorded as 30/31 degrees Celsius. The water temperature, on both sides, was usually the same and the depth (with low or high tide) is about 2-3 m in Nursery A, and 3-6 m in Nursery B.

Average Coral Growth

The average growth (cm) of corals on nursery A – cement pods on blue bed 

The average growth (cm) of corals on nursery A – fishing lines

The average growth (cm) of corals on nursery B – fishing lines

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

The measurements were taken every week in the nurseries for twelve weeks after the corals were attached. 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).

All the coral fragments were collected from the lagoon area. The corals have now been attached to natural substrates, inside the same lagoon where they have been growing, to observe their growth and survival rates.

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 to heal its tissue. As you can see in the above graph, in the first 30 days the growth was really slow. After about 36 days the corals started growing faster and after a week they grew to double their size.

Hard Coral Species And Fish Species Found In 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 who 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

Picture of Nursery A

Conclusion

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 considerably increased the organic matter in the water speeding up the growth rate of algae which compete with corals for the space. However, the conditions of water quality improved after fish feeding stopped, and the corals were observed to grow faster.

We were not able to check the acidification or test the water for various parameters. It will be interesting to further develop this study by including water quality parameters and increasing the number of measurements. Right now, due to the lockdown, there is no staff monitoring the coral nurseries. It is important to continue monitoring the corals reattached to the substrates.

There is a vast gap in local research on coral conservation projects in the Maldives. So, it will be good to have various studies to improve coral conservation methods to understand the growth of coral, their habitat and its resilience and the ability to adapt and to evolve to the changing environment.

 

Project report by Hassan Ahmed (Beybe) – Reef Check Instructor and the President of Save the Beach Maldives

Irene Pancrazi – Marine biologist

16th June 2020