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%).
Harvested fragments
Fragments cut to 5cm length
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.
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.
PCL on PCY
REC on ADI
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.
AHY REC good attachment
PCY PLA continued necrosis
Observations Month #4
Health of the 48 fragments – AMU and MFO corals, and the BIO tie all had the highest growth rate this month (0.6mm since November). PCY coral showed least growth (0.1 mm).
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.
Example of our results, looking at growth/health/attachment of various coral fragments, using different cable ties
Further Reading & References
The art of sticking: attaching methods affect transplantation success – A. Garcia-Baciero, et al.
DOI: https://doi.org/10.21203/rs.3.rs-2871191/v1
This experiment aimed to test the efficiency of different fasteners in attaching loose coral fragments to artificial substrates and assess their self-attachment and detachment rates within 90 days. The study transplanted 515 coral fragments from 8 species onto two substrates (glass bottles and iron rebar) using three fasteners (nylon cable tie, metal wire, and hemp rope).
The effectiveness of the fasteners was monitored every ten days for three months, recording data on self-attachment, detachment, and mortality rates. The coral fragments were checked for the growth of new tissue over the substrate and their stability. Algae and other organisms growing over the structures were removed weekly to prevent inhibiting coral growth.
The results showed that the type of fastener, substrate, and their interactions were the main determinants of coral self-attachment and detachment. In conclusion, the experiment demonstrated that cable ties were the most efficient fasteners for attaching loose coral fragments to artificial substrates. They resulted in lower detachment rates and higher self-attachment and growth rates compared to metal wire and hemp rope.
– detachment rates: cable ties (4%), metal wire (25%), hemp rope (69%).
– self-attachment/encrusting rates: cable ties (73%), metal wire (57%), hemp rope (30%).
Wire Coral Frame Trials 2023
July 2023
We have restarted our research into methods of attaching coral fragments onto our Reefscapers frames, with a new series of experiments. Seven different species of Acropora fragments were attached onto our test frame using three different materials (copper wire, fishing line, organic thread). This frame was then planted onto the House Reef, and monitoring photos were taken.
Our aim is to determine if the coral fragments can self-attach onto the frame as successfully as with plastic cable ties (our current preferred method), and to assess the practicality of each method. We noted that using wire was far more time-consuming, which limits its wide-scale use; however, the coral fragments are attaching and growing well after one month. Fishing line is proving successful, but the organic thread has already started to degrade.
To date, all fragments are self-attaching and growing over the wire. The organic thread has been overgrown by algae, but the wire and fishing line methods are working well so far. We continue to monitor health and growth of all the test fragments.
September 2023
All of the test coral fragments transplanted using the copper wire and the fishing line have encrusted well and self-attached firmly to the frame. By contrast, the fragments transplanted using the organic thread did not self-attach, and the thread is now degrading, causing the fragments to fall off.
Biodegradable Cable Ties with Chestnut Biopolymers (2022 – ongoing)
March 2025
Since 2022, we have been working with Chestnut Biopolymers (a UK-based manufacturing company) aiming to eliminate single-use plastic by offering biodegradable alternatives. This month, after receiving an updated prototype, we began a new batch of experiments with their biodegradable cable ties on 19 March.
For the experiment, we proceded to suspend four separate bags of ties under frames at different depths. These will be removed at three-month intervals to assess biodegradation. We hope the ties will remain intact long enough for coral fragments to attach, followed by complete decomposition.
If successful, biodegradable ties will be adopted across our restoration projects. We will provide updates at quarterly intervals.
Chestnut Biopolymers post on LinkedIn
May 2025
In addition to our ongoing biodegradable cable tie experiment, we have transplanted 3 small frames (pictured) with spare cable ties. The experiment itself is monitoring how far the cable ties biodegrade at different time intervals while suspended in the water column. To assess how well these cable ties work compared to our current stock, a frame of branching, plating, and digitate corals has been built for each growth form to assess attachment success. So far, we have found that the cable ties are more fragile than the ones we currently use, meaning attachment of corals has to be done with more care to avoid breaking the cable tie.
June Updates
After 3 months, it was time to remove the first batch of biodegradable cable ties from the test sites. One cylinder from each of the sites was removed, packaged and sent to the lab for analysis. The mesh at the shallowest site (<2m) was torn and empty (likely due to stormy seas during May).
In addition, we unfortunately found that the cable ties were too fragile to attach corals securely without breaking. Ties that did not initially break were found to have snapped within one week. Despite the current unsuitability of these ties, we hope our results will aid the development of a suitable replacement for traditional plastic ties in the future.
October Updates
This month, we removed the second batch of biodegradable cable ties. We found that all the ties had broken down into very small fragments and were no longer attached to the clear pipe. We collected some of the fragments and packaged them for lab analysis. Although the ties have clearly degraded and previous findings showed their unsuitability for securing coral onto frames, we will continue monitoring them until full decomposition. We hope this data will help inform the development of a suitable alternative to plastic cable ties in the future.
