Four species of crown-of-thorns

I wanted to toss up a quick post to clear up something we were talking about earlier in our trip.  We had several conversations earlier regarding the challenges of crown-of-thorn starfish (Acanthaster planci; often called simply “COTS”) surrounding their purported colonial nature.  This was a misconception.  The original stepping off point was the comment that this corallivorous echinoderm that has been decimating coral reefs across the Pacific for at least 70 years might indeed be some sort of amalgamation of four different organism.  The confusion spurred much debate while we were on Aitutaki and needs to be set straight.  It is not that a given individual is composed of four separate critters.  Rather, that what we have traditionally considered to be a single species is apparently four separate, identical-looking species.

COTS on a reef in Aitutaki Lagoon, August 2015

COTS on a reef in Aitutaki Lagoon, August 2015

Dead and desiccating crown-of-thron starfish at our Base 1 beach on Aitutaki.  July 29, 2015.  Killing individuals underwater can release larvae that bolster the population so the only sure way of killing these guys is to haul them up onto dry land and let them dry out in the air and sun.

Dead and desiccating crown-of-thorn starfish at our Base 1 beach on Aitutaki on July 29, 2015. Killing individuals underwater can release larvae that bolster the population. Hence the only sure way of killing these guys is to haul them up onto dry land and let them dry out in the war air and tropical sun.

See Vogler et al (2008) for the genetic data, but here is the upshot:

The distribution of four identified crown-of-thorns starfish species based on genetic markers (barcoding).  Figure from Vogler et al. 2008.

The distribution of four identified crown-of-thorns starfish species based on genetic markers (barcoding). Figure from Vogler et al. 2008.

From Vogler et al. 2008’s Introduction:

Coral reefs, the most species-rich marine ecosystems, are subjected to growing anthropogenic pressure, limiting their resilience to natural threats such as corallivorous predators (Bellwood et al. 2004).  Among those, the crown-of-thorns starfish (COTS) Acanthaster planci is infamous for its dramatic population explosions (called outbreaks) that have devastated coral reefs throughout the Indo-Pacific for decades, making it a major management issue (Birkeland & Lucas 1990Veron 2008).  But despite extensive research into COTS biology, the causes of outbreaks are still not clear; they probably involve a variable set of interacting natural and anthropogenic factors that lead to increased recruitment (Engelhardt & Lassig 1997).  An important consideration in both COTS research and management is that A. planci has been regarded as a single species throughout its distribution, and therefore the same ecological and behavioural traits are assumed worldwide.

Acanthaster planci‘s long-lived pelagic larva—surviving from three to four weeks in normal conditions (Yamaguchi 1973) to about seven weeks in marginal food regimes as found in oceanic conditions (Lucas 1982)—would be expected to promote genetic homogeneity.  But this species appears to be highly structured (Benzie 1999), in line with other recent studies of widespread marine invertebrates (e.g. Becker et al. 2007).  Using sequences of the mitochondrial cytochrome oxidase subunit I gene (COI) from samples covering its entire distribution, we show that A. planci consists of four deeply diverged clades that form a pan-Indo-Pacific species complex (as identified by DNA taxonomy; Vogler & Monaghan 2007).

And from their discussion:

Our discovery of four highly differentiated clades in one of the world’s most destructive coral predators has significant conservation implications.  Identifying cryptic speciation is essential to adequately study and contain species that require management (Bickford et al. 2007).  Although the status of A. planci is relatively poorly documented from the Indian Ocean and the Red Sea, outbreaks there do not appear to be as massive and widespread as in the Pacific (Zann 2000), suggesting that outbreak patterns might vary between the different sibling species.  Up to now, however, the overwhelming majority of COTS research has been performed in the Pacific.  Failure to recognize the existence of the sibling species could have contributed to a lack of understanding of the processes that lead to outbreaks in the different COTS lineages, by extrapolating results obtained from the Pacific studies to A. planci‘s entire distribution for both research and management purposes.

Future research will be required to investigate whether the life history, behavioural patterns and/or ecological requirements that may affect the outbreak dynamics of these four independent evolutionary COTS lineages have diverged sufficiently to necessitate lineage-specific management.  This could prove to be crucial for the design of appropriate management strategies to minimize the impact of future catastrophic COTS outbreaks in different regions of the world.

While still interesting, they are no chimera.

Remotely Operated Vehicle Reef Surveys

Today the AARR team set out to conduct the first reef surveys using ROVs on Aitutaki. The beginning of the day started out a little rough with one of the ROVs flooding which forced the team to return to base to grab the back up unit. Once back underway, a total of five surveys were successfully completed, four of which were within the lagoon and one outside along the edge. Average transect length was 35 m with the duration of the surveys lasting approximately 2 minutes. Depth, water temperature, and heading of transects were recorded with an onboard inertial measurement unit (IMU). Average depth of the surveys was 3.64 m, average temperature was 23.9 Celsius, and average heading was to the North (with the current). Surveys were conducted on all sides of the island (north, south, east, and west) to determine if there is a difference in fish abundance and species richness.


A preliminary analysis of the videos showed the reef area outside of the lagoon had the highest fish abundance and potentially the highest species richness. Also, the surveys on the east side of the island appeared to have the lowest abundance and richness overall. However, a more thorough examination of the videos followed by a statistical analysis is required to confirm these assertions.


The unit that flooded was flushed with freshwater to remove salt from the electronics and dried the rest of the day. This evening we put it back together to see if it would turn on, which luckily it did! The unit was outfitted with the bio-fluorescent sensory package once again will be launched to look for fluorescing coral later tonight.East side Lagoon Forward

Rarotonga Snorkeling

One thing I wish I got the chance to do more of was snorkeling while we were in Rarotonga.  The lagoon tour that we did was really quite amazing.  The water was light blue and unbelievably clear; it is the kind of water I never thought I would see in person let alone snorkel in.  The creatures in the water were another amazing site to see. I feel like I saw more fish during this snorkeling session than I have in my whole twenty-three years leading up to this trip.  In addition, I saw a small eel that traveled from one rock to another, as well as Roger (a giant moray eel).  I could not believe how huge Roger looked when a crew member from the lagoon tour pulled the eel out and up from his hiding spot in the rocks!  Another thing I recall seeing was the coral garden in the lagoon.  This is where a metal grate/structure is placed on the sea floor and pieces of coral are attached to the top and grow with less space restrictions than on the coral reef itself.  It was really cool to be able to see a protective environmental measure that I have learned about in school while I was out in the lagoon; I was glad to see that the locals put forth those efforts and were educating other people and tourists about what they are doing to enhance their coral reefs.

The Red-Tailed Tropic Bird

On one of our last days of research on the motus of Aitutaki, the sandy beach crew sampled the motu of Maina.  To our surprise, this motu turned out to be a nesting site for red-tailed tropic birds (Phaethon rubricauda) and we were sampling during breeding season.  Like other seabird species, tropic birds make very simple nests called scrapes.  These scrapes are just small depressions on the back beach made by parents scraping the sand away.  I was able to get close to a few nests without disturbing the birds and took some great pictures.  It was nice to see the beginning of life take place for these beautiful birds in such a wonderful place.  This seemed a nice symbol for our overall trip; this research trip could be the beginning of our lives as naturalists helping out different parts of the world.




Sandy Beaches of the Motus

The sandy beach crew sampled beaches at two different motus yesterday and found some interesting results.  Because sandy beaches tend to be low in diversity on their beach face, we changed our protocol for the Cooks to take more cores in the sand submerged in water than is our norm.  As a consequence, we found multiple species of tube worms, horn snails and crabs. One of the larger motus, Motukititu, was naturally built on uplifted coral and had the highest biodiversity of the motus we have sampled.  Honeymoon Island (also a motu) had the lowest diversity, although more studies need be conducted to make a clear connection between the structure/geomorphology of an island or given beach and its associated biodiversity.
Another interesting observation we have made about these moths revolves around the imprints in the sand.  In California, we are so used to seeing every beach filled with divots made with footsteps, we have assumed this look to be normal.  On the nearly untouched motus of Aitutaki, the beaches lack such ubiquitous divots, but do have hundreds of hermit crab tracks, shells, and pristine, smooth sand.


Motu, Bommie, Patch Reef & Sandy Beach Surveys

On Thursday we left with the sun starting to peak across the water to do a full day of surveying in the lagoon surrounding the main part of Aitutaki.  We left the dock and zipped across the clear turquoise water to see the amazing coral reefs in the lagoon.  As the boat stopped we were greeted by a giant trivially (Caranx ignobilis) and crystal visibility.

We found flame tail snappers (Lutjanus fulvus), honeycomb groupers (Epinephelus merra) and Vanessa spotted a scribbled pipefish (Corythoichthys intestinalis)!   With the help of the awesome Dr.Steele we were actually able to learn what all these pretty reef fish were as scientists instead of a typical tourist simply glimpsing them on a short snorkel.

As we ventured along the white sandy-bottomed lagoon, large piles of corals called bommie’s, would appear like mountains under the sea.  Villages of fish and coral species were mystical to see.

We stopped on Barefoot island, a bit of a tourist spot to get our passports stamped as a special Cook Islands treat!

Once we were on the far motu, a small island on the outer edge, Dr. Anderson helped us identify awesome invertebrates and some cool worms we haven’t even identified yet!
This day was magical.  We learned so much and are so greatful for this amazing opportunity!

Clam Hatchery 

A couple days ago we visited the Marine Research Center and looked at the clam hatchery. Charlie Waters, a specialist regarding clams, gave us a thorough explanation about the reasons for low spawning success and the purpose of his research. Charlie explained that low reproduction was due to the distance between individuals. Each species of clam are too far away from each other to spawn, those species include; genera tridacnidae maxima, tridacnidae gigas, tridacnidae derasa and the genera hippopus.  

In the 20th century, many areas in the Cook Islands relied on clams as a food source, and therefore many clams were removed from the population overtime causing a decrease in the abundance of clams. Clams are significant to the reefs as they are coral reef filter feeders and food for the octopus as well as other marine life. When they are spread to thin, the cannot reproduce. This could easily offset the balance of marine environments.

With the current ciguatera research in place my assumption is that with the lack of clams, increase in tourism, the previous banana exportation, and chemical runoff the reefs and lagoons are less viable to fighting off the neurotoxin. It may also be that the potentially ciguatoxic coral is spread when large storms come through, causing unsettled ocean water and debris.

Sunset wrasse 

Ciguatera has been an emerging problem within the last four or five years on Rarotonga and a few other nearby islands, such as Aitutaki. Although many people rely on reef fish populations as a food source, the sunset wrasse is untouched as it is not a public interest.  

These fish feed mainly on small invertebrates. Small snails and brittle stars are their favorite prey. Sunset wrasse are characterized as having a pink-striped head with green bands and a blue and green forebody. Their pharyngeal jaw allows them to extend their mouth widely and grind up their dinner, which sometimes could be up to half their size. They usually are present in small groups near seaward reefs and coral patches. They can be seen down to 30 meters. Incredible in many ways and my favorite fish so far!