Investigating Coral Reef Acoustics to Aid Reef Restoration

Words by Ben Williams, 2019 BioScience Graduate

Most people are aware coral reefs throughout the world are struggling one way or another. A range
of issues are responsible including overfishing, pollution and climate change induced bleaching to
name a few. However, coral reef communities provide valuable ecosystem services to a vast number
of individuals, it’s estimated One Billion people have some degree of dependence on these
ecosystems. With much of the world’s reefs degraded or lost it makes conserving those that remain
vital, and restoration of former reefs an important endeavour to many individuals.

The Marine Bioacoustics group in Exeter focuses much of their efforts on understanding the
soundscapes of coral reefs. These soundscapes encompass the entirety of the sound that can be
heard on particular spots of the reef and can be collected using underwater microphones we call
hydrophones. Emerging research suggests a lot can be determined about a reef from a few key
parameters within its soundscape which could be used to indicate the health of the surrounding
reef. A great example is shown in the spectrograms below, where you can hear an audible difference
between the soundscape of a healthy reef and that of a degraded reef:

This short acoustic clip first plays us the buzz of a healthy reef, followed by the quieter setting heard on a degraded reef

A group of us from Exeter’s Marine Bioacoustics group are currently out in Indonesia exploring reef
acoustics further. We’re collaborating with a project set up by Mars™, who have been working on an
intuitive way to restore the reefs in South Sulawesi. They use two key methods in doing so, the first
is coral propagation, where small samples of coral are clipped off live colonies and transported
somewhere new where they grow back at a faster rate than if left on their original colony. The next
step is to attach these to a skeleton system they call ‘Spiders’, which provide a substrate for new
corals to colonise and elevate them slightly above the reef bottom to provide the water flow needed
to bring nutrients to the growing coral. The Mars™ project has implemented large areas of these
spiders around two islands off Makassar with an impressive degree of success in their ability to
restore the reef.

This photo shows some of the several month old spiders placed by the Mars™  team which are showing an impressive rate of growth.

Our team from Exeter is particularly interested in the difference between the soundscapes of healthy and degraded reefs. We’re visiting the Mars™ restoration efforts to help explore the differences in soundscapes between their restored sites, degraded sites and baseline healthy sites. The hope is that in the future we will be able to show restored sites match the soundscape of healthy sites, and a quantifiable difference between the restored sites and degraded sites will be observable. We’re trialing this out using hydrophones which we’ve been placing daily on different sites within the reefs to determine whether this is a feasible methodology in comparing the reef soundscape.

Ellie May deploying a GoPro to film our quadrat used for the underwater playback test.

We’re also exploring the possibility of using ‘soundscape enhancement’ to help fine tune the ecology of the reef at a local scale to bring about restorative impacts. This is a highly innovative approach in which submersible loudspeakers are placed on patches of degraded reefs where they play recordings that may help recovery of the reef. A proof of concept of this was only recently provided in a 2018 study authored by Tim Gordon, who is now leading the expedition out here in Indonesia, and other members of the
Marine Bioacoustics group. The study found that larval and juvenile recruitment was greater at sites where healthy reef noise was played compared to sites where degraded reef noise was played. The use of soundscape enhancement is therefore of a great interest to restoration programmes like Mars™ in Indonesia, and we’re also out here to help them investigate whether this could be a potentially useful tool for their restoration. This time we’re trialing playback methods that could be used to affect the ecology of adult fish within the reef, primarily regarding their grazing behaviour which is a key process in controlling algae overgrowth at degraded sites.

 

#ExeterMarine is an interdisciplinary group of marine related researchers with capabilities across the scientific, biological,  medical, engineering, humanities and social science fields.

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A Day in the Life of a Marine Bioacoustics Intern

Words by Ellie May and Ben Williams, ExeterMarine Undergraduate Students

 

Hi there, this is Ellie May and Ben Williams giving you an update on our current trip to the Indonesian island of Sulawesi to assist Tim Gordon and Lucille Chapius in looking at the soundscapes of healthy and degraded reefs. We are currently based in the city of Makassar, where we take one of MARS symbioscience’s boat out to the islands of Bontasua and Badi to measure the acoustic complexity, richness and invertebrate snap rates of different spots around the reef. Our first day out on the islands consisted of observing and understanding the scale of restoration provided by MARS via their spider systems, in which they attach fragments of healthy reef colonies to a metal spider structure in order to promote growth in degraded areas. Our interest is understanding whether adult fish respond to the soundscapes of different reefs, and whether playing recordings of healthy soundscapes will increase not only the abundance of fish but also their rate of grazing.

The spider structures used by MARS to promote coral growth.

A typical dive day consists of being up at 7.30am to prepare our equipment and make any final adjustments before we head out to the islands at 9am. A member of the MARS team will take us to the relevant reef spot, where we deploy hydrophones to sample the baseline of the reef at various times of the day. GoPro’s are set up adjacent to the hydrophones in order to test the quality of sound they record in comparison to the hydrophones. Both Ben and I have our own side projects we are working on throughout the duration of our time here. I’m trying to prove that GoPro’s can be just as useful as hydrophones in recording reef soundscapes, which then allows any individual with access to a GoPro and free coding applications to discriminate between key components of sound, massively increasing the data sets researchers can use to measure reef health.

Our daily commute!

 

During our first week, our time was split between days in the water and daily trips to the local hardware stores in order to find extra bits of equipment we needed, and safe to say we had to be pretty inventive! However, as the days pass, we’re all getting into the swing of things and learning which tasks need prioritising and where we individually fit in to the project. During our days in the water we are constantly moving between locations to record as much as possible, as well as setting up quadrats to measure fish grazing rate in response to healthy reef sound played through our underwater speaker.

Part of our Speaker system that needs to stay dry!

 

We usually return to Makassar’s port by 5pm, cram all our equipment into a ‘Grab’ taxi and head back to our accommodation for a debrief and evening plan. Luckily as food is so cheap we tend to go out for dinner every night, and try to sample a mix of local Indonesian food as well as a few more Western cuisines. Gado-Gado is our favourite local dish and we have a tally of how many our team can eat within the approximate month we are all staying here, as this is the only vegetarian Indonesian dish we have found as of yet!

Ben setting up our hydrophone and GoPro system.

 

After supper and a debrief we get on with preparing everything for the next day in the field, whether that be making slight adjustments to the equipment to decrease set up time or cutting and editing our audio recordings to make the data analysis in the future a lot less time consuming. We tend to get relatively early nights here as everyone is usually shattered after a long day that is both mentally and physically taxing! Often in the evenings Ben and I reflect on how truly privileged we are to be able to learn about bioacoustics on such beautiful and diverse reefs, and be able to have a first-hand insight into the incredible work MARS are doing on coral restoration. To be able to see both the logistical planning and fieldwork skills it takes to organise and run such a project is amazing, especially as a current undergraduate. Observing the differences between the restored and untouched reefs really consolidates how important restoration projects are, and hopefully there is a much wider community finally realising that big changes are needed in order to save the biodiversity of our reefs.

#ExeterMarine is an interdisciplinary group of marine related researchers with capabilities across the scientific, biological,  medical, engineering, humanities and social science fields.

Find us on: Facebook : Twitter : Instagram : LinkedIn  

If you are interested in working with our researchers or students, contact Michael Hanley or visit our website!

Scientists at Sea Podcast – Climate Change, Turtles, and Bivalves

Show Notes

In this episode Ethan and Ben discuss the latest Climate Change Report released by the IPCC (Intergovernmental Panel on Climate Change), with Professor Annette Broderick and Dr. Paul Butler. As well as covering key points of the report, Annette and Paul tell us about how climate change is a significant aspect of their current research.

 

About our guests:

Annette Broderick – Professor of Marine Conservation

Profile

Annette’s research investigates the exploitation of marine vertebrates, with a primary focus on marine turtles. The thermal environment is particularly important for turtles, so the potential effects of climate change could have a big impact on these populations. Listen to the episode to find out more.

If you’re interested in turtle conservation, Annette runs a long-term field study in northern Cyprus which takes on volunteers each year, you can find out more here

 

“The most biodiverse habitats in the world that we have are on the reefs, we’re going to lost those systems undoubtedly I think by 2040/2050 we’ll be talking about corals reefs and how beautiful they were.”

 

 

 

Dr. Paul Butler – Honorary Senior Research Fellow

Profile

Paul’s research is in the field of sclerochronology, focusing in particular on the use of shells from long-lived bivalve molluscs to study the history of the marine environment. Essentially, these molluscs deposit annual increments in their shells (like rings on a tree stump). If a bivalve shell has a known date of death, a timeline of environmental variables can be investigated from that one shell, including seawater temperature and the origin of water masses. This can be of particular interest when studying climate change. Have a listen to the episode and take a look at Paul’s profile for more information.

 

 

Want to know more about sclerochronology and some intriguing clam facts? Sarah Holmes, PhD Researcher, wrote an excellent blog about this a few months ago, you can read it in full here.

 

 

Arctica islandica, one of Paul’s study species
Photo – Hans Hillewaert

 

 

Our longest chronology, which goes for 1300 years, is for waters of the north coast of Iceland… essentially we’ve got a temperature record… over the past 1000 years it shows a declining temperature up to about 150 years ago and then it shows a rapid increase

 

 

What is the IPCC?

The IPCC was established 30 years ago by the United Nations Environment Programme (UNEP) and the World Meteorological Organization (WMO) to provide a scientific view of climate change and its potential environmental and socio-economic impacts.

What is the IPCC Climate Change Report?

In December 2015 the Paris climate agreement was signed whereupon countries agreed that they would keep global temperatures “well below two degrees C above pre-industrial levels and to pursue efforts to limit the temperature increase even further to 1.5 degrees C”. The UN asked the IPCC to produce a special report to assess the feasibility of keeping global temperature rises to a maximum of 1.5C.

Scientists are nominated by governments and international institutions. In this particular report there we 91 lead authors from 40 countries which reviewed 6,000 references. This work is unpaid.

Where do we stand right now?

Currently we are on track to reach 1.5C warming between 2030 and 2052, and 3C by 2100.

If we hit just 2C warming, this could have serious impacts, here are just a handful:

  • Almost all coral reefs will be destroyed.
  • The arctic will have summers with no ice at least once a decade.
  • Huge numbers of animals and plants will become extinct.
  • Low-lying coastal regions, such as Bangladesh, will suffer from sea level rise.

 

“One of the key messages that comes out very strongly from this report is that we are already seeing the consequences of 1°C of global warming through more extreme weather, rising sea levels and diminishing Arctic sea ice, among other changes,” said Panmao Zhai, Co-Chair of IPCC Working Group I. – IPCC Press Release

 

There has been extensive coral bleaching already due to sea temperature rise
Photo – Acropora

Can we avoid this?

Yes, but we have just 12 years to turn it around and serious change is required. You can read more about that here.

The report finds that limiting global warming to 1.5°C would require “rapid and far-reaching” transitions in land, energy, industry, buildings, transport, and cities. Global net human-caused emissions of carbon dioxide (CO2) would need to fall by about 45 percent from 2010 levels by 2030, reaching ‘net zero’ around 2050. This means that any remaining emissions would need to be balanced by removing CO2 from the air.

“Limiting warming to 1.5°C is possible within the laws of chemistry and physics but doing so would require unprecedented changes,” said Jim Skea, Co-Chair of IPCC Working Group III. – IPCC Press Release

You can read the IPCC Climate Change Press Release in full here.

 

Hosted by Ethan Wrigglesworth

Episode and show notes produced by Ben Toulson

#ExeterMarine is an interdisciplinary group of marine related researchers with capabilities across the scientific, medical, engineering, humanities and social science fields. If you are interested in working with our researchers or students, contact Michael Hanley or visit our website!

 

It’s Stressful Being a Coral! Declining Coral Cover on the Great Barrier Reef

Author: Jennifer McWhorter

Jennifer McWhorter is pursuing her PhD in a joint program between the Universities of Exeter and Queensland. Using various climate and ecological modelling techniques, Jen hopes to improve our spatial knowledge of coral reef stressors.

 

The above diagram describes the process of coral bleaching followed by mortality. Source: Great Barrier Reef Marine Park Authority (GBRMPA)

 

Similar to humans experiencing a fever, coral reefs undergo similar stress. The more frequent the fever and the longer the fever lasts, the more life threatening it becomes. Sea surface temperatures in the ocean are increasing at an alarming rate due to human inputs of carbon dioxide into the atmosphere (Ekwurzel et al., 2017). In 2016/2017, the Great Barrier Reef (GBR) experienced two back-to-back severe warming events that caused widespread coral bleaching[1]. According to the Australia Institute of Marine Science, hard coral cover on the GBR has declined at a rate that has never been recorded.

 

Figure 2. “Large-scale spatial patterns in change in coral cover and in heat exposure on the Great Barrier Reef, Australia. A, Change in coral cover between March and November 2016. b, Heat exposure, measured in DHW (in degree C-weeks) in the summer of 2016. Map template is provided by Geoscience Australia (Commonwealth of Australia (Geoscience Australia) 2018).” Source: Hughes, T. P., et al., 2018

 

In addition to coral bleaching, cyclones and crown-of-thorns sea star outbreaks have been the main cause of decline in coral cover on the GBR within the past four years. The northern area of the GBR is expected to have lost about half of its’ coral cover. This estimate reflects the impacts of two episodes of severe coral bleaching from 2014-2017 and two cyclones.  The central reef has experienced a decline in coral cover from 22% in 2016 to 14% in 2018 due to coral bleaching and the ongoing southward spread of the crown-of-thorns sea star. Even though the southern portion of the GBR was not exposed to the 2016/2017 warming events, coral cover has dropped from 33% in 2017 to 25% in 2018. On the southern reefs, the crown-of-thorns sea star outbreaks appear to be the main cause for the most recent decline.

 

During my last trip to Australia, I assisted in injecting vinegar into the crown-of-thorns sea stars at Lodestone Reef on the GBR. The vinegar kills the sea star within 24 hours potentially reducing their threat to hard, or stony corals. Photo Credit: Chris Jones

 

“Clearly the reef is struggling with multiple impacts,” says Prof. Terry Hughes, Director of the ARC Centre of Excellence for Coral Reef Studies. “Without a doubt the most pressing of these is global warming. As temperatures continue to rise the corals will experience more and more of these events: 1°C of warming so far has already caused four events in the past 19 years.”

“Ultimately, we need to cut carbon emissions, and the window to do so is rapidly closing.”

 

 

[1] Coral bleaching – Coral bleaching occurs when the relationship between the coral host and zooxanthellae (photosynthetic algae, NOAA), which give coral much of their colour, breaks down. Without the zooxanthellae, the tissue of the coral animal appears transparent and the coral’s bright white skeleton is revealed. Corals begin to starve once they bleach. (GBRMPA)

 

Additional Resources:

Ekwurzel, B., Boneham, J., Dalton, M. W., Heede, R., Mera, R. J., Allen, M. R., & Frumhoff, P. C. (2017). The rise in global atmospheric CO2, surface temperature, and sea level from emissions traced to major carbon producers. Climatic Change144(4), 579-590.

Hughes, T.P. & Kerry, J.T. Back-to-back bleaching has now hit two-thirds of the Great Barrier Reef. The Conversation https://theconversation.com/back-to-back-bleaching-has-now-hit-two-thirds-of-the-great-barrier-reef-76092 (2017)

Hughes, T. P., Kerry, J. T., Baird, A. H., Connolly, S. R., Dietzel, A., Eakin, C. M., … & McWilliam, M. J. (2018). Global warming transforms coral reef assemblages. Nature556(7702), 492.

Media Release: Two Thirds of the Great Barrier Reef hit by back-to-back mass coral bleaching

Long-term Reef Monitoring Program – Annual Summary Report on coral reef condition for 2017/2018

 

#ExeterMarine is an interdisciplinary group of marine related researchers with capabilities across the scientific, medical, engineering, humanities and social science fields. If you are interested in working with our researchers or students, contact Michael Hanley or visit our website!