Coral Attachment Experiments

Reefscapers cable tie experiments coral species

Study Into Sustainable Cable Ties

The Background

Since inception, we have been using standard plastic cable ties to attach coral fragments onto our Reefscapers frames. This has proved to be very effective, attaching the corals securely to give them time to grow over the ties and encrust onto the bars. Over the years, we have experimented with different methods, giving various degrees of success, but we have always reverted to plastic ties for their reliability and durability (they do not disintegrate into microplastics, so their pollution impact is low).

The Preliminaries

Over the last few weeks, we have been researching new products made from eco-materials, and ordering samples from various global companies for testing purposes. We contacted six different suppliers that sell cable ties made from sustainable materials, and we are also working closely with one company to create our own formula of biopolymers.

During August, we started our new study to find the best alternative to plastic without compromising the efficiency and results of our current coral propagation techniques.

The Site

We chose Kuda Huraa’s Water Villas site (easily accessible, strong ocean currents), at depths of 0.4m (low tide) to 1.5m (high tide). Annual average temperature is 29.5°C (daily minimum 27.3°C; daily maximum 31.7°C in April).
Our temperature logger has been deployed at this site and is recording hourly.

Reefscapers ocean temperature Maldives (2021-22)
The Coral Species

We selected six coral species that we commonly select for propagation. All the fragments have the same or similar genotype.

  • ADI Acropora digitifera, AMU Acropora muricata, AHY Acropora hyacinthus.
  • PVE Pocillopora verrucosa, MFO Montipora foliosa, PCY Porites cylindrica.
Reefscapers cable tie experiments coral species
The Experimental Methods
  • Eight single coral fragments were cut to 5cm length.
  • Two fragments of each species were used to test each of the four types of cable ties, and attached to a flat table-shaped coral frame (RK0124) divided into four sections.
  • The fragments will be monitored and photographed each month to test the resistance of the cable ties, and to record any visible effects on coral growth and health.
  • Attachment: record the number days taken for each fragment to successfully encrust to the tie.
  • Growth: mm of growth (length) for each fragment.
  • Health categories (percentage alive): Good (80-100%); Fair (40-80%); Bad (1-40%); Dead / Fallen (0%).
Reefscapers cable tie experiments fragments

Harvested fragments

Reefscapers cable tie experiments 5cm

Fragments cut to 5cm length

Reefscapers cable tie experiments attachment

Coral fragment securely attached

The Cable Ties – Initial Observations 
  • BIO – “bioplastic i-tie”, biodegradable, reusable, releasable, polyester/starch (30% renewable) [6x360mm].
    Broke easily in use, therefore requiring a greater number of ties. Difficult to tighten effectively around the fragments. One coral fragment (MFO) was broken.
  • PCL – “PCL cable tie”, intrinsically biodegradable, non-releasable, polycaprolactone [6x150mm / 8x300mm].
    Thick and inflexible, difficult to tighten around the fragments. The available lengths are not ideal for our requirements (short length is too short, long length produces extra waste).
  • REC – “1030 extra stretchy”, reusable, non-releasable, soft polyurethane [10x300mm].
    Elastic and adjustable, so comfortable and easy to use efficiently. Each tie is reusable and can be cut to attach up to three fragments, minimising waste significantly.
  • PLA – “classic plastic tie”, non-releasable, polyurethane [various sizes].
    Flexible, useful lengths, easy to use efficiently. But non-recyclable and produces waste.
Reefscapers cable tie experiments RAPSTRAP
Reefscapers cable tie experiments frame
Observations Month #2
  • BIO – “bioplastic i-tie”, biodegradable, reusable, releasable, polyester/starch (30% renewable) [6x360mm].
  • PCL – “PCL cable tie”, intrinsically biodegradable, non-releasable, polycaprolactone [6x150mm / 8x300mm].
  • REC – “1030 extra stretchy”, reusable, non-releasable, soft polyurethane [10x300mm].
  • PLA – “classic plastic tie”, non-releasable, polyurethane [various sizes] – Two ties broke.
  • BESE – sample quantity and not part of the full study. Thick and inflexible. Most ties broke, as it proved impossible to securely tighten without breaking. Only three cable ties remain.
Attachment

  • Ties – best overall attachment is REC (followed by PLA & PCL); worst is BIO.
  • Corals – fastest encrusting rate in ADI & AHY; fragments of PVE or PCY have yet to encrust.
Health & Growth of Coral Fragments

  • 42 healthy, 4 fallen, 1 fair (PCL with PCY has a localised dead zone).
  • Overall average growth is 0.4mm by the end of Month 1.
  • No differences in growth between cable ties.
  • Corals – AMU shows most growth (10mm average); PCY zero growth.
Reefscapers cable tie experiment PCL on PCY

PCL on PCY

Reefscapers cable tie experiment REC on ADI

REC on ADI

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