//
you're reading...

Coastal Management

Slowing a Thorny Invasion – Managing for COTS with DNA

Kroon, F.J., Lefèvre, C.D., Doyle, J.R. et al. 2020. DNA-based identification of predators of the corallivorous Crown-of-Thorns Starfish (Acanthastser cf. solaris) from fish faeces and gut contents. Scientific Reports, 10, 8184. https://doi.org/10.1038/s41598-020-65136-4.

 

Australia is having a rough 2020. In addition to an historic wildfire season and a global pandemic to worry about, Crown-of-Thorns Starfish (COTS), Acanthaster spp., are once again causing major coral loss on the Great Barrier Reef (GBR). This is far from the first time this group of invertebrate predators has wreaked havoc on this ecosystem. While periodic outbreaks are common (indeed, almost half of the decline in coral cover on the GBR between 1985 and 2012 was attributed to COTS predation), this outbreak is largely affecting areas that were spared by recent bleaching, making mitigation particularly important. Lethal injection of COTS individuals, in combination with other larger scale management techniques, attempts to not only stop the direct predation, but more importantly lessen the total amount of larvae available to recruit back to the reefs. Research has also found connections between ecosystem-level management (e.g. Marine Protected Areas) and COTS levels: reefs with fishing prohibitions have fewer COTS, and outbreaks of lesser impact. Perhaps this indicates a higher level of predation on COTS when there’s more fish? One group out of Townsville, Australia attempted to find out.

Several COTS decimating a stony coral head. COTS are coral predators, eating the soft polyps of Scleractinian (stony) corals. Image from wikipedia

The theory: Predator Removal Hypothesis

The general idea here is not new. If you’ve taken ecology, or even just a unit during your high school biology class, you’ve probably seen a graph like this:

Example of a Lotka-Volterra model, from Wikipedia

One species (in red) preys directly on another (in black). The prey species is consumed by the prey, and so decreases in numbers. This removes a food source from the predator, so they in turn decrease in number (see figure above, displaying the Lotka-Volterra model.) Without predatory pressures, the prey species’ population can explode, providing so much food to the predatory species that its population grows again on a slight time lag and the cycle repeats. If we drill down on just one spike, we can see that when predation pressure is removed for reasons natural (as above) or artificial (anthropogenic hunting or fishing pressures, habitat degradation, disease, humans removing a predator because they’re anxious that coyotes will harm their pets—you name it) the prey population spikes. Maybe you’ve seen this when deer eat your hostas, or when rabbits overrun your garden. The theory’s actually been cited as the reason for It was suggested as a potential mechanism for COTS outbreaks back in 1969, albeit referring to a species of predatory gastropod (the Giant Triton – google it, it’s 2 feet long!).[1] Research has since identified more than 80 species that prey on COTS during its different life stages, which might explain why it takes protecting the whole reef to see a difference in COTS abundance. The Australian research team had seen modeling studies testing the predator removal theory on COTS, and decided to take it one step further, examining DNA taken from the gut contents and feces of reef fishes to better understand the real world dynamics of this potential predator-prey relationship.

Experimentation: Predator Dynamics IRL

Prepping for Study:

After collecting confirmed reports from the literature of reef fish known to have consumed COTS (either from field reports, laboratory feed experiments, or gut content/fecal analyses), the team ran two pilot studies to perfect the technique detecting Pacific COTS species (A. cf. solaris) in fecal samples. In the first, detections were successful up to 7 days post-feed in two out of the five pufferfish sampled. In the second, COTS spines were found in feces of two separate species of fish. Both of these pilot studies allowed the team to perfect preservation techniques before the full study.

Several fish species with positive COTS DNA detections. Images from wikipedia.

The Real Deal:

COTS DNA was eventually detected in 30 individuals from 18 different species of coral reef fish across eight different families, including six damselfish families. This includes several species of fish that had not previously been documented as COTS predators. One interesting question, given the fact that several of these ‘previously unknown’ predators also consume other fish species, is might that DNA have been transferred to them from a different meal rather than from direct predation on COTS (i.e. food web contamination.) The authors think not, noting that “the presence of COTS spines in some samples, combined with reported lethal predation on COTS gametes and larvae” suggest the likelihood that COTS predation is more common that previously thought.

Next Steps for COTS and Reef Management

This methodology is a step forward in COTS management: previous methods for gut content analysis is difficult as COTS remains are hard to identify and distinguish from other echinoderm remains. (This is probably why so few species had been previously identified as COTS predators.) Just as notably, the study supports the hypothesis that reef fish consume planktonic and benthic life stages of COTS on the reef, not just in the lab. Several species of fish that tested positive for COTS DNA are planktivorous feeders. In combination with the confirmed presence of COTS planktonic larvae at the reef sites where the damselfish were collected, this indicates that pelagic (meaning relating to the open waters of the sea as contrasted with waters close to structures, coasts, or bottom zones), planktonic feeding is highly probable. Damselfish are prevalent on healthy reefs. The authors suggest that damselfish, along with other planktivorous fish, could “markedly reduce the number of COTS larvae” as part of the larger goal of “lethal predation on the pelagic phase…and “predation on the settled phase” in combination with 1) reduced fisheries quotas on known COTS predators; 2) strategies to increase the abundance of fish species known to consume COTS; 3) temporal restrictions on fishing when outbreaks are predicted; and/or 4) establishing new no-take reserves at “outbreak initiation zones” and on other reefs known to have high larval connectivity. As we are always learning again and again, no species lives in a vacuum. The more we protect, the more we conserve.

[1] Endean R. Report on investigations made into aspects of the current Acanthaster planci (Crown of Thorns) infestations of certain reefs of the Great Barrier Reef. 35 (Queensland Department of Primary Industries (Fisheries Branch), Brisbane, Australia, 1969).

[1] De’ath, G., Fabricius, K., Sweatman, H. & Puotinen, M. The 27–year decline of coral cover on the Great Barrier Reef and its causes. Proc. Natl Acad. Sci. USA 109, 17995–17999 (2012).

Discussion

No comments yet.

Post a Comment

Instagram

  • by oceanbites 3 months ago
    Happy Earth Day! Take some time today to do something for the planet and appreciate the ocean, which covers 71% of the Earth’s surface.  #EarthDay   #OceanAppreciation   #Oceanbites   #CoastalVibes   #CoastalRI 
  • by oceanbites 4 months 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 5 months 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 6 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 7 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 7 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 7 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 8 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 8 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 8 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 8 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 9 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 9 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 10 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 10 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 11 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 11 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 12 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 12 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 1 year 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 
WP2Social Auto Publish Powered By : XYZScripts.com