PRE2019 3 Group17

Group

Team Members

Name	ID	Email	Major
Amit Gelbhart	1055213	a.gelbhart@student.tue.nl	Sustainable Innovation
Marleen Luijten	1326732	m.luijten2@student.tue.nl	Industrial Design
Myrthe Spronck	1330268	m.s.c.spronck@student.tue.nl	Computer Science
Ilvy Stoots	1329707	i.n.j.stoots@student.tue.nl	Industrial Design
Linda Tawafra	0941352	l.tawafra@student.tue.nl	Industrial Design

Time Sheets

Peer Review

Will be added later

Project Goal

The Problem

One of the great benefits of the coral reef is that in case of natural hazards, such as coastal storms, the reef on average can reduce the wave energies by 97% (Ferrario, 2014). Meaning that it can prevent storms and flooding and thus protect the coastal inhabitants. Since roughly 40% of the world’s population is located within a range of 100 km from the coast (Ferrario, 2014), protecting the coral reef will result in a reduction of a great amount of damage. This would not only be in regard to human lives but also to environmental destruction. In the case of these natural hazards, it is the government that will be imputable for the caused devastation. Sadly, the coral reefs have been degrading for a long time, and their recovery is lacking.

Due to the acidification and warming of oceans due to climate change, pollution and destructive fishing practices (Ateweberhan et al., 2013) the amount of coral reefs is declining. One of the factors that could prevent the downgrading of a reef, is the resistance of a reef, its ability to prevent permanent phase-shifts; and the resilience of a reef, its ability to bounce back from phase-shifts (Nyström et al., 2008). These phase-shifts are undesirable because the reef ends up in a state where it can no longer return to a coral-dominated state (Hughes et al., 2010). If the reef has better resilience, it will be able to bounce back quicker. One of the ways to improve the resilience of the reef is increasing the species richness and abundance through the use of acoustics (Gordon, et al., 2019), which improves the reef’s resilience by giving it protection from macroalgae (Burkepile and Hay, 2008). For a coral reef to flourish, a wide biodiversity of animals is needed. Fish that lay their larvae on corals are one of the essential components in a healthy reef ecosystem. However, once corals are dying, the fish do not use them for their larvae and the whole system ends up in a negative cycle. By playing sounds, with different frequencies, fish are tricked into believing that the corals are alive and come back with their larvae. This attracts other marine animals, which causes the entire system to flourish again (Gordon, et al., 2019).

A robot could be used to place these speakers, or a robot could function as a speaker itself. However, this is not the only way in which robots can help the reefs. Robots could be created to replace labor and time-intensive work, as well as support scientists, researches and rescue organizations. Acoustic enrichment is one application, but consider also researching the current state of the coral reef by monitoring sound instead (Lammers et al., 2008), or removing the dangerous crown-of-thorns starfish (Endean, 1982), or any other number of applications. The goal for this projects is to design a robot that can safely move through coral reefs. Because the coral reefs and ocean are sensitive, a robot that operates there needs to have some alterations in order to not risk damaging the reefs. The reefs are already endangered, any tool that is send down there to help them recover must be absolutely safe, and this will require some specialization.

In this project we will consider current robots that have been used in a number of environments, from land robots to robots used in the general deep sea, and even robots currently used in coral reefs. We will consider their benefits and drawbacks and discuss how their design could support a specialized coral reef robot.

The User

Our user will be researchers who could use our robot to research coral reefs, interact with them and support them. We have made contact with one researcher at a university, but we are still in discussion with him. He informed us his department recently ordered a drone for research, so we hope to get many useful insights from him. We will have a meeting, during which we intent to discuss the following questions:

• What are issues you are facing while studying/ managing/ maintaining coral reefs?
  • How do you deal with them now?
  • How could a robot help?
  • Is a underwater robot which is specialized for coral reefs relevant?
• Would this/ our robot be suitable?
  • Why?/ Why not?
  • What can be improved?
  • What is the most important aspect of the design which we need to consider?
• Do you like the robot you bought lately?
  • Why?/ Why not?
  • Which aspects should our robot also have and what can be optimized?
  • Is it easy to control the robot? Does it have a good user interface?
• If a specialized robot was available for a reasonable price, what applications would you like to use it for?
• What qualities would a drone need to be reef safe?
  • Certain chemicals to avoid specifically?
  • What do you find concerning about your current drone in this area?

Due to scheduling issues and later the COVID-19 "lockdown" it has been hard to get this meeting, but we do have multiple contacts now so we hope to have some online meetings soon. However, these delays mean we had to do a lot of our work without direct user input.

Objectives

The main objective of our project is to design a robot that can safely move through the coral reefs. Our robot needs to be able to move and be stationary on the bottom of the ocean. The robot needs to navigate through the corals without bumping into it since this could damage the reefs. The robot design should not pollute the ocean. There should not be any big risk for the ocean. So the risk of things like battery leakage or losing the robot (which would cause it to become waste inside the ocean) should be minimalized. Additionally, the materials should be chosen right. The robot needs to be nigh unbreakable so no parts will get loose and float away. However, it should also not be too hard, as that would create too great a risk of damage to the reefs. The robot has to have a tele-operating system that makes sense to the user. The user needs a way to let the robot do what they want. This can be by preprogramming or with a tele-operating system that is adapted to the needs of the user. The robot needs to not disturb the life that is in the coral. Fish should not see the robot as food or as predator. Finally, the chemical components of the robot's coating should be considered, it should not cause coral bleaching or poison any fish.

Deliverables

(Needs further updating since our project goal shifted after the review session)

• An in-depth exploration of current robots like our objective and an assessment of how suitable they are for coral reefs.
• A suggestion or several suggestions, based on our research, of how to design a specialized coral reef robot.
• A report on what coral reef researchers desire and how our suggested designs could meet those desired applications.

Connection to the Larger Problem

This robot can be used to further research coral reefs more easily and it can be outfitted with various components to help improve the reefs. For instance, it could be outfitted with speakers for acoustic enrichment, so that people do not need to dive down to place them. (To be added: more detailed examination of use cases)

The Robot - to be moved

Coral Reef Considerations

Risks by direct contact with coral:

• Coral breaking when bumping into coral. Especially branching corals are the most vulnerable since they are fragile because of their growth form (Hawking and roberts, 1997).
• Coral breaking when getting stuck in the propeller.
• Anchoring can break the coral.
• When not capable of handling strong currents, the robot could damage the coral by being pushed to the coral with great force.

Risks by indirect contact with coral:

• Sedimentation/turbidity caused by the propellor, which can lead to mortality of coral species as it reduces the light penetration. If sedimentation or turbidity persists for too long the coral reef’s diversity can change, where the tolerant species replace the sensitive coral species(PIANC, 2010).
• Plastic can seal light and oxygen from the corals and can release toxins, which can increase the chance of coral becoming ill (Plastic Soup Foundation, 2018).
• Bacteria can travel on plastic. When pathogenic bacteria reach the coral, nothing can be done to fix it (Plastic Soup Foundation, 2018).
• Anti-fouling paint can damage coral (PIANC, 2010)

Information on the different kinds of reefs and where they grow. Coral needs warm, well lit water as well as solid surfaces to settle on. There are 5 types of reef (mentioned in order of distance from the coast): fringing, patch, barrier, atoll and bank or platform reef, which are all explained in the paper. Per region/oceans over the world the area of reef in km2 is given. Also species diversity in coral reef over the world is given. Spalding, M. D., Green, E. P., & Ravilious, C. (2001). World Atlas of Coral Reefs (1st edition). Berkeley, Los Angeles, London: University of California Press.

Requirements, Preferences and Constraints

(Table still needs to be made, but for consideration:)

(In order to prevent further downgrading and instead increase the growth of the reef, large biodiversity of animals is required. It is therefore important that the robot can navigate through the water to guide the fish towards the reef. For this, the robot should firstly be able to detect where fish should be guided and then maneuver in the ocean without damaging any of the already existing reefs. Establishing which parts of the reef need to be tackled can be done by scanning the reef by means of taking pictures and comparing them to a database full of images of coral reef. A camera that operates well underwater is, therefore, a must. This camera will also be used in combination with a filter to navigate the robot in the water.

Since fish can be tricked in believing the coral is still alive through sounds of different frequencies, the robot will have to be capable of creating these sounds underwater. To achieve this, an underwater sound system is needing to be implemented inside the robot. Research done by Enger, Karlsen, Knudsen, and Sand (1993) shows that there is a wide range in frequency of what fish can hear. In this research, tests were done on different fish which resulted in hearing thresholds differing between the species. To know what frequency to send out at what moment, the robot will have to know what kind of fish are around and adjust its emitting sound. A database of the types of fish is needed to compare the with the camera detected fish.

Currently, the work that is needing to be done to make sure the coral reef is either still intact or regrowing, requires divers to go down in the ocean to explore and help out. Since the robot is going to replace these divers, they will have to be able to do exactly what the divers already can. This means that the robot should not solely be capable of helping the coral grow back, but also be able to communicate the current state of the ocean back to researchers. For this reason, underwater wireless communication should be possible. For to robot to be moving around in the water and going fairly deep, it should contain a battery that can last long enough for the robot to go down explore the area and lure fish long enough to an area that they will migrate there. However, implementing a system inside the robot that will generate energy, would increase the robot's functionality. This way the robot can be used more effectively over greater distances.)

State of the Art and Literature Study - Potentially Scrapped

(This is left over from when we were still going to design our own robot from scratch. This research still can be used so it will be left here, though it will be reformatted or removed for the final delivery.)

Movement

• Options to move left and right:
  • Servo motors (or stepper) can be used to turn the tail → need to research the difference and see which one is easier and better to use
  • The rotor itself can turn → does this exist?
• Options to move up and down:
  • Regulate the density by sucking water in or out a water tank
  • Use a servo or stepper motor to tilt a tail up and down (which causes it to move up or down) → need to prototype to find out whether it works
• The robot can move down to the reef and be navigated to a spot where it can stay stationary. Two clips will grab a piece of rock to attach it to the ground
• Waterproof/ materials/ making process:
  • To 3D print it, is not the most viable option as it has to be printed in multiple parts and a 3D print needs a coating to make it waterproof. It is also a challenge to make a waterproof system which clicks into each other so that the prototype can be opened up for testing and maintenance
  • We could use a mold and make it from rubber or silicone. These parts can easily be screwed together as they are less rigid than 3D printed plastic. Through tests we need to find out whether this is waterproof
  • We could also put all the electronics in a bottle or waterproof bag so that they will not get damaged if the casing leaks

Sensors

• https://backend.orbit.dtu.dk/ws/portalfiles/portal/112200773/ChristensenPAAR2015.pdf
• https://www.sciencedaily.com/releases/2010/11/101123121105.htm

Fraunhofer-Gesellschaft. (2010, November 23). Underwater robots on course to the deep sea. ScienceDaily. Retrieved February 8, 2020 from www.sciencedaily.com/releases/2010/11/101123121105.htm

• “ The engineers from Fraunhofer Institute for Optronics, System Technologies and Image Exploitation in Karlsruhe, Germany are working on the "eyes" for underwater robots. Optical perception is based on a special exposure and analysis technology which even permits orientation in turbid water as well. First of all, it determines the distance to the object, and then the camera emits a laser impulse which is reflected by the object, such as a wall. Microseconds before the reflected light flash arrives, the camera opens the aperture and the sensors capture the incident light pulses.”
• “The powerful but lightweight lithium batteries”

User Interaction and Communication

Different underwater communication technologies are mentioned. Each technology has its own benefits and downsides. This paper explains how each works and what the speed, distance, power etc. it needed or can be reached.

Kaushal, H., & Kaddoum, G. (2016). Underwater Optical Wireless Communication. IEEE Access, 4, 1518–1547. https://doi.org/10.1109/access.2016.2552538

• Our implementation needs to be long-range
• Our implementation should not bother the fish or reefs
• We should consider/mention having some basic autonomous movement in case the wireless connection is disrupted. Also, in case of interference the robot should reject command it believes will damage the coral reefs (probably, the risk there is that it will misunderstand its environment and overrule the commands it receives and damage the coral reefs as a result)
• The kind of systems for telecommunication used to reach the depth of the ocean will be too expensive in our example case. We will probably use a way cheaper module in our example case and mention what could be used in the final product.
• Best currently available to normal people: http://www.top10drone.com/best-underwater-drones/
  • First, third and fourth ones uses wi-fi (fourth mentions having a wifi module inside the robot itself, but it is intended for close-to-civilization work)
  • Second one is connected to a cord but also has bluetooth functionality
  • Note: these all seem to go at most 100m deeps, whereas corals can be 400-6000m deep (https://ocean.si.edu/ocean-life/invertebrates/corals-and-coral-reefs). But there are also shallow water coral reefs that are as high as 15m below the surface, so we should be good. But we could look into what coral reefs we can reach with our modules. (Amit has a source that says up to 70m deep is fine)
• Options for real deep sea:
  • Bluetooth
  • Wifi (previously mentioned drones mention interference when using wifi, https://www.powervision.me/en/product/powerdolphin/specs mentions using wifi to connect to a mobile device on the shore, assume there is no interference)
  • Ultrasound (will it interfere with the fish? They are bothered more by low-frequency sounds than high-frequency sounds but is it completely safe? I can’t quickly find sources that say it’s no problem at all but a lot of researches have suggested using ultrasound to research coral reefs so it is likely fine) (we should also consider if it is a reliable way of doing things, since the soundwaves could bounce off of the corals, which would cause a lot of interference)
  • Worst case option is using a tether - but that could cause damage or be damaged
  • We don’t really have to worry about the water-air barrier, we can use buoy with signal receiver underwater to avoid interference. https://www.oceantechnologysystems.com/store/ffm-buddy-phone-packages/interspiro-aga-mkii-ffm-buddy-phone-package/ example of underwater communication between divers - ultrasonic
• Options for prototype: we can just use a cheap wifi module or ultrasound or something. It can be quite weak since we will be prototyping it in clear, shallow water.

Components

• “The most prolific reefs occupy depths of 18–27 m (60–90 ft), though many of these shallow reefs have been degraded.” - Biology of Corals | Coral Reef Systems
• Building an Arduino-powered underwater ROV - could be useful to see the software and component selection process
• Arduino-Based Submersible Robot Maps the Threatened Coral Reefs
• Underwater robot control system based on Arduino platform and robot vision module

• Motors
  • Waterproof Servos
• Camera
  • Arduino designed VS external camera
• Arduino based
• Wireless communication module (Wi-Fi?)
  • Arduino and HC-12 Long Range Wireless Communication Module
• Power source
• Weights?
  • We need to calculate the density it needs to navigate based on the motor
• Sensors
  • Location
  • Pressure
  • Gyro / accelerometer

Research into Current Underwater Drones

Scubo / Scubolino

https://tethys-robotics.ch/index.php/robots/ https://blog.arduino.cc/2016/06/13/scubo-is-an-omnidirectional-robot-for-underwater-exploration/

Scubo is an ROV built by Tethys Robotics, a robotics team from ETH Zurich. (https://tethys-robotics.ch/index.php/robots/). Scubo's defining feature is its omnidirectional movement, as well as its modularity. Scubo uses 8 propellers that extrude from its main body in order to allow the tethered robot to move with extreme agility underwater. The robot is made out of a carbon cuboid, which features a hole throughout the middle for better water flow and also cooling of the electronic components. It is constructed to be neutrally buoyant, allowing depth control through natural movement through the 8 propellers. On its body, there are 5 universal ports for modularity. The robot’s tether provides power for the onboard batteries, as well as allow direct control from a computer outside the water. It is controlled with a SpaceMouse Joystick. For processing, Tethys say they use an Arduino Due for the hard, real-time tasks, and an Intel NUC for high-performance calculations. (https://blog.arduino.cc/2016/06/13/scubo-is-an-omnidirectional-robot-for-underwater-exploration/)

LarvalBot / RangerBot

The RangerBot robot swimming above the a coral reef.

Description

Initially, the Queensland University of Technology (QUT) designed the COTBot to deal with the dangerous crown-of-thorns starfish that threatens coral reefs. This design got improved quite a bit (most importantly, it was reduced in size and cost) to make the RangerBot, which has the same purpose as the COTBot. This design then got shifted around a bit to make the LarvalBot, which is extremely similar to the RangerBot, but instead of killing starfish this robot is used to deliver coral larvae to promote the growth of new coral. All three of the robot designs were specifically for coral reefs. Most sources on the robots focus on the video analysis capabilities most of all, so that seems to be where the innovation of this robot lies, not the coral reef application. The RangerBot has some extra features as well, such as water quality sensors and the ability to collect water samples (Braun, 2018).

Movement

Both RangerBot and LarvalBot have 6 thrusters (Zeldovich, 2018) that allow full six degrees-of-freedom control, including hover capabilities (Dunabin et al., 2019). Both are controlled with an app that, according to the creators, takes just 15 minutes to learn (Dunabin, August 2018). The LarvalBot follows only preselected paths at a constant altitude, with the release of the larvae being controlled by user input (Dunabin, November 2018), it is unclear if the RangerBot also follows a pre-selected path, but it is likely since it operates fully automatically to dispatch the crown-of-thorns starfish, and there is no mention of automatic pathfinding in any of the report.

Collision Detection

RangerBot and LarvalBot have 2 stereo cameras (Zeldovich, 2018). The RangerBot uses these for obstacle avoidance amongst other functions, it is not specified if the LarvalBot has obstacle avoidance (Dunabin, August 2018). RangerBot uses video for obstacle avoidance because the usual method, sonar, does not work in coral reef environments. Unwater use of sonar and ultrasound is difficult either way, but the degree of complexity in coral reefs makes it manageable. Video is usually not used for this purpose because deep in the water it quickly gets dark and murky. However, coral reefs are quite close to the surface (or at least, the coral reefs we are concerned with are) and they are in clear water, so this environment is uniquely suited for cameras as a sensor (Dunabin et al., 2019).

Design, Materials, and Shape

RangerBot weighs 15 kg and is 75 cm long (Dunabin, August 2018), the LarvalBot will be bigger because it has the larvae on board, but the base robot has the same size. The RangerBot floats above the reefs and can only reach the easy-to-reach crown-of-thorns starfish (Zeldovich, 2018), that is why it can have the slightly bulky shape and can have the handle at the top without bumping into the reefs being a concern. There is unfortunately no information available online on what materials the robot was made out of.

Power Source

RangerBot and LarvalBot can both be untethered. However, the current version of LarvalBot is still tethered (Dunabin, December 2018). It is not mentioned in the report why, but I would assume this is because you need reliably real-time video to be able to tell the LarvalBot to drop the larvae at the right time. When without a tether, the robot can last 8 hours and it has rechargeable batteries (Queensland University of Technology, 2018).

Ocean One

Movement

The robot is designed for research purposes. Due to its design, the robot can take over tasks from human divers such as exploring archaeological sites or collecting a specimen. Moreover, it can excess places where human divers cannot go, such as places below 50 meters deep.

The robot has a high level of autonomy and is controlled via an intuitive, haptic interface. The interface “provides visual and haptic feedback together with a user command center (UCC) that displays data from other sensors and sources” (Khatib et al., 2016, p.21) . There are two haptic devices (sigma.7), a 3D display, foot pedals, and a graphical UCC. A relay station, which is connected to the controller, allows the robot to function without a tether.

“The body is actuated by eight thrusters, four on each side of the body. Four thrusters control the yaw motion and planar translations, while four others control the vertical translation, pitch, and roll. This thruster redundancy allows full maneuverability in the event of a single thruster failure” (Khatib et al., 2016, p.21).

Design, Material, and Shape

The robot has an anthropomorphic shape as it should have the same capabilities as human divers. The design of the robot’s hands allow “delicate handling of samples, artifacts, and other irregularly-shaped objects” (Khatib et al., 2016, p.21). “The lower body is designed for efficient underwater navigation, while the upper body is conceived in an anthropomorphic form that offers a transparent embodiment of the human’s interactions with the environment through the haptic-visual interface” (Khatib et al., 2016, p.21).

Power Source

The relay station can be used as a nearby charging station.

Collision Detection

In the paper, the authors seem to hint that the robot is equipped with a collision detection system. The hard- and software behind it is not explained.

OpenROV v2.8

Movement

The purpose of the robot kit is to bring an affordable underwater drone to the market. It costs about 800 euro to buy the kit and 1300 euro to buy the assembled robot (OpenROV, n.d.). The user is challenged to correctly assemble the robot, a fun and rewarding experience. Once the robot is made, the user is free to decide where and how to use the robot. The most common use is exploring the underwater world and making underwater videos.

The robot is remotely controlled and has a thin tether. Via a software program, which is provided and can be installed on a computer, the user is able to control the robot. The camera on the robot provides live feedback on the robots’ surroundings and the way it reacts to direction changes.

Two horizontal and one vertical motor allow the robot to smoothly move through the water. When assembling the robot, one should pay special attention to the pitch direction of the propellers on the horizontal motors. As the horizontal motors are counter rotating, the pitch direction of the propeller differs.

Other crucial parts are a Genius WideCam F100 camera, a BeagleBone Black processor, an Arduino, a tether, lithium batteries and extra weights.

Design/ material/ shape

All the components are held in place by a frame and stored in waterproof casings. The frame and multiple casings are made from laser cutted acrylic parts. The acrylic parts are glued together with either acrylic cement or super glue. When wires are soldered together, heat shrinks are used to secure a waterproof connection. Epoxy is used to fill up areas between wires to prevent leakage.

The design of the robot does not look very streamlined but moves surprisingly smooth. A drawback of the design is that the lower part, which contains the batteries, is always visible on the camera feed. This can be annoying when watching the video.

The robot is relatively small and can be compared to the size of a toaster. This is ideal for moving through places such as shipwrecks and coral reefs.

Power source

The robot uses 26650 (26.5mm × 65.4mm) Lithium batteries. The batteries need to be charged beforehand. The guide warns the user that the batteries could be dangerous and must be charged with the correct amount of voltage, which is 3V.

M-AUE

Current Use

Answering questions about plankton in the ocean. The M-AUEs study environmental processes in the ocean (Reisewitz, 2017).

Movement

The idea of the M-AUEs is that they move just like planktons in the ocean, by adjusting their buoyancy (through programming) going up and down while drifting with the current (Reisewitz, 2017). The author continues stating that the M-AUEs are moving vertically against the currents that are caused by the internal waves; they do this by repeatedly changing the buoyancy.

“The big engineering breakthroughs were to make the M-AUEs small, inexpensive, and able to be tracked continuously underwater,” said Jaffe (inventor of the M-AUEs) in Reisewitz (2017).

Control

The M-AUEs are designed to not go as deep to a point that they would be coming close to the seafloor. This will mean that in case of being used for coral research they will not maneuver through the coral, but instead hover above them. The M-AUEs are preprogrammed with a PID control algorithm, meaning that they will sense the actual depth that they are currently in and adjust the settings to the desired depth that they want to be at.

Localizing

According to Reisewitz (2017), acoustic signals are used to keep track of the M-AUEs while submerging, since GPS does not work under water. Receiving three-dimensional information on the location every 12 seconds, showed where exactly the M-AUEs are inside the ocean. Augliere (2019), says that GPS equipped moorings (which float on the surface of the ocean) are being used to send out sonar pings in those 12 seconds. These pings are then received by the hydrophones of the M-AUEs (which are located around 50 meters deep from the surface), giving data which researchers can use to localize them.

Battery

As stated by Augliere (2019), the M-AUEs have batteries with power to last for several days and also data storage that can last that long. “The system is powered by a battery pack made from 6 Tenergy 1.2 V, 5000, mA hour NiMH cells in a series configuration. The battery pack is fused with a 2 A fuse and is recharged at an optimal rate of 600 mA” (Jaffe et al., 2017)

Design and Material

The size of the M-AUEs is to be compared with the size of a grapefruit. It exists out of 2 shells that are concentric and made out of syntactic foam (Jaffe et al., 2017) which slide on top of each other. Inside these shells the batteries, a piston and an antenna are positioned and on the bottom, on the outside of the shell, multiple sensors are placed.

Possible Future Work

Reisewitz (2017) states that adding a camera to the M-AUEs will provide images of the state of the ocean, resulting in enabling to map the coral habitats and the movement of larvae or to do further research on the creatures in the ocean such as the planktons. Enhancing the robot with audio recording devices (hydrophones), will let the M-AUEs function as an ‘ear’ by being able to keep track of the sounds in the ocean.

Research Conclusion

From the conducted research can be concluded that a considerable amount of underwater robots are currently being developed and already brought to the market. Some of the robots are specialized for operating in specific environments, such as, coral reefs. Looking at the state-of-the-art provides insights and inspiration for the design of our robot.

References

Ateweberhan, M., Feary, D. A., Keshavmurthy, S., Chen, A., Schleyer, M. H., Sheppard, C. R. C. (2013). Climate change impacts on coral reefs: Synergies with local effects, possibilities for acclimation, and management implications. Marine Pollution Bulletin, Volume 74, Issue 2, pages 526-539. Retrieved from http://www.sciencedirect.com/science/article/pii/S0025326X13003020

Burkepile, D. E., Hay, M. E. (2008). Herbivore species richness and feeding complementarity affect community structure and function on a coral reef. Proceedings of the National Academy of Sciences, Volume 105, Issue 42, pages 16201-16206. Retrieved from https://www.pnas.org/content/105/42/16201

Endean, R. (1982). Crown-of-thorns starfish on the great barrier reef. Endeavour, Volume 6, Issue 1, pages 10-14. Retrieved from http://www.sciencedirect.com/science/article/pii/0160932782900047

Enger, P. S., Karlsen, H. E., Knudsen, F. R., & Sand, O. (1993). Detection and reaction of fish to infrasound. ICES mar. Sei. Symp., 196, 108–112. Retrieved from https://pdfs.semanticscholar.org/7491/2a618da033b24796f48e88e71eaa00a9b57d.pdf

Ferrario, F., Beck, M. W., Storlazzi, C. D., Micheli, F., Shepard, C. C., & Airoldi, L. (2014). The effectiveness of coral reefs for coastal hazard risk reduction and adaptation. Nature Communications, 5(1). https://doi.org/10.1038/ncomms4794

Gordon, T. A. C., Radford, A. N., Davidson, I. K., Barnes, K., Mccloskey, K., Nedelec, S. L., … Simpson, S. D. (2019). Acoustic enrichment can enhance fish community development on degraded coral reef habitat. Nature Communications, 10(1). doi: 10.1038/s41467-019-13186-2

Hawkins, J.P., Roberts, C.M., 1997. Estimating the carrying capacity of coral reefs for SCUBA diving. In: Proceedings of the 8th International Coral Reef Symposium, vol. 2, pp. 1923–1926.

Hughes, T. P, Graham, N. A. J, Jackson, J. B. C., Mumby, P. J., Steneck, R. S. (2010). Rising to the challenge of sustaining coral reef resilience. Trends in Ecology & Evolution, Volume 25, Issue 11, pages 633-642. Retrieved from http://www.sciencedirect.com/science/article/pii/S0169534710001825

Kaushal, H., & Kaddoum, G. (2016). Underwater Optical Wireless Communication. IEEE Access, 4, 1518–1547. From https://doi.org/10.1109/access.2016.2552538

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