Coral Attachment Experiments

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.

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.

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%).

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.

Observations Month #1

• 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, 5 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.

Observations Month #2

THE TIES

• BIO – “bioplastic i-tie”, one tie broken. Low attachment rate.
• PCL – “PCL cable tie”, high growth rate (1mm).
• REC – “1030 extra stretchy”, the most attached fragments, and high growth rate (1mm).
• PLA – “classic plastic tie”, low attachment rate.
• BESE – sample quantity and not part of the full study. 7 out of 10 ties broken.

THE CORALS

• ADI – average growth.
• AHY – average growth.
• AMU – high growth to date (1.7mm).
• MFO – high growth to date (1.7mm); increased attachment.
• PCY – least amount of growth to date (0.3mm); poor attachment; slight localised mortality around fragmentation site.
• PVE – increased attachment.

HEALTH & GROWTH Of CORAL FRAGMENTS

• Health of the 48 fragments – Good: 42, Fair: 1, Bad: 0, Fallen: 5

Observations Month #3

HEALTH & GROWTH Of CORAL FRAGMENTS

• Health of the 48 fragments – Good: 38, Fair: 5, Bad: 0, Fallen: 5

THE TIES

• BIO – “bioplastic i-tie” – fewest attached fragments.
• PCL – “PCL cable tie” – high growth rate (overall 1.5mm).
• REC – “1030 extra stretchy” – good attachment.
• PLA – “classic plastic tie” – zero breakage.
• BESE – sample quantity and not part of the full study.

THE CORALS

• ADI – average growth and attachment.
• AHY – good attachment and encrusting, with REC.
• AMU – high growth rate (2.2mm average).
• MFO – average growth and attachment.
• PCY – zero attachment and lowest growth (0.3mm); localised dead zones around the cable tie and/or the base of the coral (all tie groups).
• PVE – improved attachment and encrusting.

Observations Month #4

THE TIES

• BIO – “bioplastic i-tie” – 1.4cm.
• PCL – “PCL cable tie” – 2.0cm.
• REC – “1030 extra stretchy” – 1.8cm.
• PLA – “classic plastic tie”.
• BESE – out of study.

The Corals

• ADI – average attachment and growth rate (1.1cm).
• AHY – good attachment and encrusting; growth 1.6cm.
• AMU – high growth rate of 3.0cm.
• MFO – average attachment, good growth (2.8cm).
• PCY – zero attachment, low growth (0.6cm). In addition, 1 fragment (PCL attached) experienced tissue loss, and a second fragment (BIO attached) fell this month.
• PVE – 1 fragment attached via a REC tie has suffered extensive mortality, potentially due to algal competition. Low growth (1.0cm).

Observations Month #5

KEY FINDINGS FOR THE MONTH

• Zero new ties broke this month (4 have broken since the start).
• Health attachment growth – zero change this month (Fair: 5 / Bad: 1 / Fallen: 6).
• PCY attached to PLA. This species remains unattached to the other tie types.
• The tie group which exhibited the highest growth rates so far is PCL, with an overall growth average of 2.7mm
• The species with the highest growth rates continue to be AMU (4mm) and MFO (3.5mm). PCY has presented the least amount of growth (0.6mm).

Final Observations Month #6

Each fragment was monitored monthly for a total time of six months, to test the resistance of the different cable ties in a very dynamic marine environment, and to observe any visible effects in coral growth and health.

PLA was the best cable tie, and BIO was the worst. REC proved to be better than PCL in attachment, but not in health and growth (there is no evidence that these factors are directly related to the tie type). REC is easy to handle, making it the best sustainable alternative to the plastic tie.

THE TIES

• BIO – “bioplastic i-tie” – 1.4cm. They broke easily in use, and proved to be the least durable overall, with the most fallen fragments.
• PCL – “PCL cable tie” – 2.0cm. Hard, thick and not flexible. After 6 months, coral attachment rates and health were good, and growth rates were excellent.
• REC – “1030 extra stretchy” – 1.8cm. Elastic, adjustable, comfortable, efficient, easy to use. Good attachment rates.
• PLA – “classic plastic tie”. Flexible, appropriate size, efficient, easy to use, cheap. But non-recyclable and produces high amounts of waste. After 6 months, 100% durability and best rates of attachment and coral health.
• BESE – out of study.

THE CORALS

• ADI Acropora digitifera – average attachment and growth rate.
• AHY Acropora hyacinthus – good attachment and encrusting.
• AMU Acropora muricata – fastest growth rates.
• PVE Pocillopora verrucosa – one fragment of 100% dead tissue (on REC). Low growth.
• MFO Montipora foliosa – average attachment, good growth.
• PCY Porites cylindrica – overall, the lowest attachment, slowest growth rates, and lowest health (all with localised areas of dead tissue).

HEALTH

▪ 75% of the 48 fragments exhibited signs of good health (>90% alive tissue). Fair 10%, Bad 0%, Dead 2%, Fallen 13%.
▪ Coral health in relation to tie type: PCL and PLA had best health, BIO the worst.
▪ Most broken ties occurred within months 1 and 4, suggesting that coral fragments take 4 months to fully attach/encrust after transplantation.