//
you're reading...

Coastal Management

Lethal Injection: Crown of Thorns Edition

Paper:  Rivera-Posada, J., Pratchett, M.S., Aguilar C., Grand, A., Caballes, C.F., (2014). Bile salts and the single-shot lethal injection method for killing crown of thorns sea stars (Acanthaster planci). Ocean & Coastal Management., 102(A): 383-390.  doi:10.1016/j.ocecoaman.2014.08.014

 

Introduction

Outbreaks of crown of thorns sea star (Acanthaster planci)–see Figure 1, are one of the main causes of coral reef decline in the Indo-Pacific, including Australia’s Great Barrier Reef. Due to their voracious appetites and few predators, crown of thorns sea star, or COTS for short, can decimate large areas of live coral in a short period of time. Great efforts and resources are directed at reducing population outbreaks. However, given a limited understanding of why, when and where outbreaks occur, the most direct solution is to take ‘em out (not to a nice dinner, but to kill them). Death by injection of sodium bisulfate is the most commonly used method, but this requires COTS to be removed from the reef and injected many times.

Figure 1: Crown of thorns sea star (Image Credit: Chris Wilson, flickr Creative Commons)

Figure 1: Crown of thorns sea star (Image Credit: Chris Wilson, flickr Creative Commons)

Bile is a digestive liquid that is stored in the gallbladder of all vertebrates and can be collected from cows and sheep after they are slaughtered for the meat industry. Derivatives of bile such as oxgall (dehydrated bile) and Bile Salts No.3 (more refined) have been tested as an alternative substance to kill COTS in the Phillipines with promising results. In the Great Barrier Reef, COTS can reach huge, honkin’ sizes, up to 42 cm (16.5 in) in diameter! Rivera-Posada et al., wanted to assess the effectiveness of bile-derived injections in the Great Barrier Reef and hence, as a potential widespread control.  After all, being able to kill COTS in situ would be less labour intensive than lugging them out of the water, killing and disposing of them properly.

 

The study:

The location of Lizard Island is marked by the red bubble.

Figure 2: The location of Lizard Island is marked by the red bubble.

220 COTS ranging from 30-42cm (12-156.5 in) in diameter were collected around Lizard Island in the Great Barrier Reef—see Figure 2. The captured COTS were then transferred to tanks at the Lizard Island Research Station and acclimated. Different concentrations of oxgall (6 and 12 grams per litre (g/l)) and Bile Salts No.3 (4 and 8 g/l) were mixed with distilled water. Distilled water was used because bacteria in tap or seawater may break down the bile rendering the solution less effective.

Ten groups of five COTS were then injected with different concentrations of both oxgall and Bile Salts No.3 solutions in different sites of the body—See Figure 3.

Other marine life such as fish, corals and echinoderms were then collected and acclimated to assess any potential side effects of using the bile derivatives. Collected animals were placed in a control tank, or in the same tanks of injected COTS for 8 days. Another injected COTS individual was placed in the treatment tanks on the fourth day. Activities of all animals were recorded on video.

Figure 3

Figure 3: Left – Injection sites tested, Right – Injection guns tested. Taken from Rivera-Posada et al., 2014.

In the field, outbreak conditions of COTS were mimicked by placing 50 collected COTS each in two neighbouring, small patches of reefs. One hour of acclimation was given to the COTS, then divers were unleashed to administer a single 10 ml, 8 g/l injection of Bile Salts No.3 with the prototype gun at one reef.  At the other reef, divers administered six to fifteen 10ml, 140g/l injections of sodium bisulfate with the DuPont Velpar Spotgun (commonly used method), see Figure 3. Activity of injected COTS and surrounding marine life were recorded with strategically situated cameras and analyzed–See Figure 4.

field

Figure 4: B – diver injecting COTS during field studies. C: In-situ GoPro recording species interactions with COTS remains. Taken from Rivera-Posada et al., 2014.

Data from all parts of the study were then statistically tested for significant results.

 

Results:

100% of the COTS that were administered the Bile Salts No.3 (refined bile) died, significantly higher than the 80% mortality rate of COTS that were injected with the oxgall (dehydrated bile)–See Figure 5. The Bile Salts No.3 possesses sodium cholate and sodium deoxycholate that are known substances that cause cell membranes to rupture, so this result was not surprising. Doubling the concentration of both bile solutions decreased time between injection and death. Furthermore, it was found that the base of the arm was the most effective injection site since it had the shortest time to death after injection–See Figure 5.

Bile Salts vs oxgall

Figure 5: Comparison between Bile Salts No. 3 and Oxgall. Blue – Mortality rate, Orange – Time to death after injection. Taken from Rivera-Posada et al., 2014

Figure 6:  Wrasse picking at COTS remains in the field.

Figure 6: Wrasse picking at COTS remains in the field.

Reef fish, coral and echinoderms that were exposed to injected COTS did not show any signs of illness, even after some completely consumed COTS remains. It is likely that naturally occurring marine bacteria break down Bile Salts No.3, so that less is consumed by fish.

In the field, since only one injection was required with Bile Salts No. 3, it took around 12 minutes for divers to inject all found COTS, substantially less time than the 35 minutes it took to inject all COTS multiple times with the sodium bisulfate solution. One advantage of using the traditional bisulfate method was that it was obvious if the COTS had been properly injected as the COTS became immobile immediately.

COTS that were injected with Bile Salts No.3 were hyperactive for up to one hour. Interestingly, predation by pufferfishes and triggerfishes was common on COTS injected with sodium bisulfate, yet there was no direct consumption by the same fish on COTS injected with Bile Salts No.3, although other fish did pick at the remains—see Figure 6.

Significance:

Overall, Bile Salts No.3 is a more efficient and effective substance to elicit COTS mortality in the Great Barrier Reef.  Less of this solution is needed, and time to death after injection is shorter than other chemicals.  While this is a great step, Bile Salts No.3 still require treatment of individual COTS.  During an outbreak, COTS can reach densities of up to 156,000 per hectare,  so it is time consuming, very expensive and not feasible for large areas.  Thus, the importance of developing new and more effective control methods remains a top priority.  Rivera-Posada was able to classify the entire microbiome of COTS comparing healthy vs sick COTS last year.  The results from this mapping were 25 potential candidates to induce a COTS-specific disease.  Unfortunately funding is limited for continuing studies, so if there are any interested grad students or marine biologists reading this, get involved!  In the meantime, Bile Salts No.3 provides a great alternative to the current widespread method.  And when used in conjunction with management efforts to reduce nutrient influx, and supporting successful protected areas to bolster COTS predator populations, we can cheer on corals in their fight for survival!

Discussion

Trackbacks/Pingbacks

  1. […] arm to reach down and deliver a single injection of bile salts, which should kill the starfish without harming the surrounding reef’s fragile environment. The robot is designed to search the reef for up to eight hours at a time and can deliver more than […]

  2. […] arm to reach down and deliver a single injection of bile salts, which should kill the starfish without harming the surrounding reef’s fragile environment. The robot is designed to search the reef for up to eight hours at a time and can deliver more than […]

  3. […] arm to reach down and deliver a single injection of bile salts, which should kill the starfish without harming the surrounding reef’s fragile environment. The robot is designed to search the reef for up to eight hours at a time and can deliver more than […]

  4. […] arm to reach down and deliver a single injection of bile salts, which should kill the starfish without harming the surrounding reef’s fragile environment. The robot is designed to search the reef for up to eight hours at a time and can deliver more than […]

  5. […] arm to reach down and deliver a single injection of bile salts, which should kill the starfish without harming the surrounding reef’s fragile environment. The robot is designed to search the reef for up to eight hours at a time and can deliver more than […]

  6. […] arm to reach down and deliver a single injection of bile salts, which should kill the starfish without harming the surrounding reef’s fragile environment. The robot is designed to search the reef for up to eight hours at a time and can deliver more than […]

  7. […] arm to reach down and deliver a single injection of bile salts, which should kill the starfish without harming the surrounding reef’s fragile environment. The robot is designed to search the reef for up to eight hours at a time and can deliver more than […]

Post a Comment

Instagram

  • by oceanbites 2 weeks ago
    Not all outdoor science is fieldwork. Some of the best days in the lab can be setting up experiments, especially when you get to do it outdoors. It’s an exciting mix of problem solving, precision, preparation, and teamwork. Here is
  • by oceanbites 1 month ago
    Being on a research cruise is a unique experience with the open water, 12-hour working shifts, and close quarters, but there are some familiar practices too. Here Diana is filtering seawater to gather chlorophyll for analysis, the same process on
  • by oceanbites 2 months ago
    This week for  #WriterWednesday  on  #oceanbites  we are featuring Hannah Collins  @hannahh_irene  Hannah works with marine suspension feeding bivalves and microplastics, investigating whether ingesting microplastics causes changes to the gut microbial community or gut tissues. She hopes to keep working
  • by oceanbites 3 months ago
    Leveling up - did you know that crabs have a larval phase? These are both porcelain crabs, but the one on the right is the earlier stage. It’s massive spine makes it both difficult to eat and quite conspicuous in
  • by oceanbites 3 months ago
    This week for  #WriterWednesday  on  #Oceanbites  we are featuring Cierra Braga. Cierra works ultraviolet c (UVC) to discover how this light can be used to combat biofouling, or the growth of living things, on the hulls of ships. Here, you
  • by oceanbites 3 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Elena Gadoutsis  @haysailor  These photos feature her “favorite marine research so far: From surveying tropical coral reefs, photographing dolphins and whales, and growing my own algae to expose it to different
  • by oceanbites 4 months ago
    This week for  #WriterWednesday  on Oceanbites we are featuring Eliza Oldach. According to Ellie, “I study coastal communities, and try to understand the policies and decisions and interactions and adaptations that communities use to navigate an ever-changing world. Most of
  • by oceanbites 4 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Jiwoon Park with a little photographic help from Ryan Tabata at the University of Hawaii. When asked about her research, Jiwoon wrote “Just like we need vitamins and minerals to stay
  • by oceanbites 4 months ago
    This week for  #WriterWednesday  on  #Oceanbites  we are featuring  @riley_henning  According to Riley, ”I am interested in studying small things that make a big impact in the ocean. Right now for my master's research at the University of San Diego,
  • by oceanbites 5 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Gabby Stedman. Gabby is interested in interested in understanding how many species of small-bodied animals there are in the deep-sea and where they live so we can better protect them from
  • by oceanbites 5 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Shawn Wang! Shawn is “an oceanographer that studies ocean conditions of the past. I use everything from microfossils to complex computer models to understand how climate has changed in the past
  • by oceanbites 5 months ago
    Today we are highlighting some of our awesome new authors for  #WriterWednesday  Today we have Daniel Speer! He says, “I am driven to investigate the interface of biology, chemistry, and physics, asking questions about how organisms or biological systems respond
  • by oceanbites 6 months ago
    Here at Oceanbites we love long-term datasets. So much happens in the ocean that sometimes it can be hard to tell if a trend is a part of a natural cycle or actually an anomaly, but as we gather more
  • by oceanbites 6 months ago
    Have you ever seen a lobster molt? Because lobsters have exoskeletons, every time they grow they have to climb out of their old shell, leaving them soft and vulnerable for a few days until their new shell hardens. Young, small
  • by oceanbites 7 months ago
    A lot of zooplankton are translucent, making it much easier to hide from predators. This juvenile mantis shrimp was almost impossible to spot floating in the water, but under a dissecting scope it’s features really come into view. See the
  • by oceanbites 7 months ago
    This is a clump of Dead Man’s Fingers, scientific name Codium fragile. It’s native to the Pacific Ocean and is invasive where I found it on the east coast of the US. It’s a bit velvety, and the coolest thing
  • by oceanbites 8 months ago
    You’ve probably heard of jellyfish, but have you heard of salps? These gelatinous sea creatures band together to form long chains, but they can also fall apart and will wash up onshore like tiny gemstones that squish. Have you seen
  • by oceanbites 8 months ago
    Check out what’s happening on a cool summer research cruise! On the  #neslter  summer transect cruise, we deployed a tow sled called the In Situ Icthyoplankton Imaging System. This can take pictures of gelatinous zooplankton (like jellyfish) that would be
  • by oceanbites 9 months ago
    Did you know horseshoe crabs have more than just two eyes? In these juveniles you can see another set in the middle of the shell. Check out our website to learn about some awesome horseshoe crab research.  #oceanbites   #plankton   #horseshoecrabs 
  • by oceanbites 9 months ago
    Feeling a bit flattened by the week? So are these summer flounder larvae. Fun fact: flounder larvae start out with their eyes set like normal fish, but as they grow one of their eyes migrates to meet the other and
WP2Social Auto Publish Powered By : XYZScripts.com