Creature Feature: The Mosaic Boxer Crab Lybia tesselata

by Kerry Grimshaw and Annette DesRochers

One of the participants on this cruise is Steve McKagan, a fisheries biologist and NOAA partner from the Pacific Islands Regional Office (PIRO) located in Saipan. While Steve's role on this mission is with the Fish REA team, he has also taken an interest in the ARMS project. He is working with local agencies in Saipan to start up a Biosecurity (i.e., marine invasive species) project and is considering using ARMS methods and materials to establish a baseline for the harbors of Saipan, Tinian, and Rota. As such, he spent a day at Maug with the ARMS team to learn how ARMS are deployed in the field and how they are processed, which was a win-win situation for both sides as he captured some excellent photographs while observing the activities.

Taking advantage of the opportunity, following are some of Steve's photos capturing a bit of the ARMS recovery process followed by Kerry's writeup on one of the creatures that he found most intriguing. As an honorary ARMS team member—Data Managers serve dual roles on RAMP missions by helping to process the ARMS once they have been recovered—I too am enamored with these critters.

ARMS team member Russell Reardon recovering an ARMS unit at Maug. NOAA photo by Steve McKagan.

Transiting a recovered ARMS unit on the small boat back to the ship to be processed. NOAA photo by Steve McKagan.

Russell Reardon, hard at work in the ARMS "office". NOAA photo by Steve McKagan.

ARMS team members Kerry Grimshaw and Russell Reardon begin processing an ARMS unit. NOAA photo by Steve McKagan.

As the ARMS are processed, crabs are separated out to be photo documented and for taxonomic identification. NOAA photo by Steve McKagan.

As Kerry explains, one of the characters we have seen often in the ARMS on this cruise has been the Mosaic Boxer Crab, Lybia tesselata.  While many of the crabs that are collected are unique and dare I say beautiful, this little guy highlighted below tends to stand out from the others.

Mosaic Boxer Crab, Lybia tesselata.  NOAA photo by Kerry Grimshaw.

These small crabs, commonly known as pom-pom crabs for the small anemones they hold in their pincers, have a mutualistic symbiotic relationship with anemones.  The boxer crab’s pincers are small and are so well adapted to holding their anemones that they are rendered nearly useless for defense, yet they are able to take advantage of the anemones to serve this purpose. The stinging anemones act as a deterrent to predators by giving an extra punch to the crab's defense tactics; it advertises its weapons by waving its pincers with the anemones in the direction of any potential predator as if it’s shadowboxing.

The Boxer Crab versus the fish. Source: YouTube.  

Possessing such a pair of specialized pincers can be beneficial and has proven useful as there are a number of different species of Lybia that carry anemones; however, there are disadvantages too. Having such small pincers with only a few grippers unfortunately means the crab's pincers aren’t strong enough to tear up food as other crabs do. To overcome this boxer crabs have adapted to using their second pair of legs for this purpose by tearing food into small pieces and then moving it towards its mouth.  Another way that boxer crabs have been observed to feed is by using the anemones as “mops” which are swiped along the substrate to collect food particles on the tentacles of the anemone which can then be removed by the crab’s mouthparts.

The Mosaic Boxer Crab in action. Source: YouTube.

The boxer crabs can put their anemones down, but doing this would make them very vulnerable to predation. However they must do such a risky thing when molting their exoskeleton.  The crabs will place each anemone in turn in a safe place and then as quickly as possible free itself of its old exoskeleton. Then it quickly grasps its anemones in its pincers before quickly retreating to a safe place where it can allow its new body to harden.

There's even a YouTube video showing a Boxer Crab molting. This one takes a little more patience, it's not quite 5 minutes long, though it's not really worthwhile to watch until about 3:30.

And yet another video showing the Boxer Crab that just molted recovering its pom poms!

The Makings of a Marine National Monument

by Jake Asher and Annette DesRochers

Farallon de Pajaros (FDP), also known as Uracas, was our northernmost stop of this cruise.  Once known by the pseudonym, “Lighthouse of the Western Pacific”, FDP’s last known eruption was back in 1967. Even after 44 years, the landscape above the shoreline remains largely barren.

The Hi’ialakai positioned in front of FDP to recover dive teams. 
NOAA photo by Edmund Coccagna.

In stark contrast, the Islands of Maug crater—there are three small islands all together with a submerged caldera in the center—are lush with vegetation compared to FDP. As a former Geographic Information Systems Specialist, Maug happens to be one of my favorite places in the Pacific to map because of its unique horseshoe-shaped topography with a subsurface pinnacle rising from the depths in the middle.

 Maug bathymetry (seafloor) map.
Source: Pacific Islands Benthic Habitat Mapping Center.

One of the small boats, HI-1, returning to the Ship with the islands of Maug in the background. NOAA photo by Annette DesRochers.

FDP, Maug, and Asuncion (highlighted earlier this week), make up the “Islands Unit” of the Marianas Trench Marine National Monument. The other two Units of the Monument are the Marianas Trench itself and the Volcanic Unit which includes the numerous submerged volcanoes and hydrothermal vents along the Mariana Arc (click here to see a map). Supply Reef, also one of the places surveyed during this mission, is one of the undersea volcanoes that are protected by the Monument designation under the Volcanic Unit.

Abundant marine life can be found throughout the Marianas Trench Marine National Monument. NOAA photo by Edmund Coccagna.

Declared in early 2009, the Monument seeks to protect the biologically diverse and abundant marine life found in the waters of these islands, seamounts, and hydrothermal vents.  These unique habitats are home to one of the most diverse collections of corals found in the Western Pacific, and also support some of the largest biomass of reef fishes found in the region.

Large schools of bigeye jack (Caranx sexfasciatus) present at both FDP and Maug, providing divers with an eyeful. NOAA photo by Jake Asher.

Maug, in addition to having a diverse and abundant benthic environment, is of particular scientific interest due to its underwater vents.  Hydrothermal vents within the caldera seep hot (60^oC), acidic water into the environment around it and provide a unique platform for researchers to study the effects of highly acidic water in a coral reef environment. This is of particular interest as the pH of the world's ocean water appears to be lowering due to the uptake of anthropogenic CO₂. This ‘acidification’ of the water is reducing the availability of bicarbonate in the oceans, which is the main building block for calcifying animals, such as corals, to grow and survive.

REA fish diver Marie Ferguson takes advantage of the warmth emitted by the hydrothermal vents at Maug. NOAA photo by Jill Zamzow.

In close proximity to the vents are some of the most impressive Porites rus stands that divers on this cruise have ever seen.   NOAA photo by Jeff Anderson.

Both the REA benthic and fish teams surveyed the areas near the vents, and the oceanography team used an auto-sampler to take water samples at a high frequency.  The hourly samples will be analyzed for dissolved inorganic carbon and total alkalinity and from these the aragonite saturation levels in the water can be determined.  The saturation level of aragonite determines the amount of the ion that is available for corals to use as building blocks for their structure.  Theoretically, the more acidic the water, the less aragonite ion is available in the water for corals to use for growth.  Salinity, temperature and current flow was also measured using additional instruments in the area.  These data will help us understand more about a natural coral reef environment under highly acidic conditions.

A remote access sampler (RAS) was deployed near a vent site inside the caldera at Maug for two days in order to collect hourly water samples over a 48 hour period. NOAA photo by Jake Asher.

Maug just might be considered the “crown jewel” of the Monument.  Listening to divers recount the highlights from their surveys at Maug certainly substantiates that notion. With astounding coral cover reaching up to 75% in some places, the benthos teems with life, keeping scientists on both the benthic REA and towed-diver teams occupied.

A diver photo-documenting the unique habitat and organisms found in the Monument. NOAA photo by Edmund Coccagna.

While the benthic environment at FDP is largely depauparate in places, likely the result of ‘recent’ geologic activity, it too has its gems. That being said, some of the most spectacular views during our short time at FDP happened to be topside.

Sunrise over Farallon de Pajaros. NOAA photo by Jake Asher.

Moonrise over Farallon de Pajaros. NOAA photo by Jake Asher.

A day of rest

by Jake Asher

Supply Reef, an active submarine volcano, was mostly a rest day for all teams, except for one.  The oceanography team set out at Supply Reef to recover a salinity and temperature recorder, along with an old wave and tide recorder anchor.  While shark sightings have been uncommon at all our other stops aside from the occasional whitetip reef shark (Triaenodon obesus) and small grey reef shark (Carcharhinus amblyrhynchos), Supply had a few greys that were larger than what we had seen to date.

A grey reef shark, Carcharhinus amblyrhynchos, at home amongst a school of Caesio teres. NOAA photo by Oliver Vetter.

Including some that were more “friendly” than others!

A grey reef shark, Carcharhinus amblyrhynchos, getting up close and personal!  NOAA photo by Oliver Vetter.

Needless to say, divers recovered their equipment, snapped photos, paid respects to the locals, and completed their operations safely.

A barred filefish (Cantherhines dumerilii). NOAA photo by Oliver Vetter.

Meanwhile, the rest of the scientific staff enjoyed a much needed day off after 10 straight days in a row of dive operations. Not to worry though, the oceanography team, while they were busy prepping for ops at Supply, still enjoyed a day off from dive operations on the previous day. The favorite activity aboard the ship on days off?  Trying to make up for all those lost zzz's.

Next stop, Asuncion

by Jake Asher and Annette DesRochers



Asuncion Island. NOAA photo by Annette DesRochers.



Asuncion was our first stop inside of the Marine National Monument. Spectacular as its appearance may be topside, with its iconic, conical shape, the underwater environs were equally, if not more, amazing.


ARMS team member Russell Reardon, normally busy recovering or deploying ARMS underwater, takes a few moments to enjoy the underwater scenery at Asuncion. The coral Pocillopora sp. can be seen in the foreground of this benthic habitat. NOAA photo by Russell Reardon.

A spectacular picture of the bubble coral, Plerogyra sinuosa. NOAA photo by Paula Ayotte.

Another beautiful species of coral, Euphyllia ancora. NOAA photo by Jake Asher.

High relief basaltic and rock boulder reefs were framed with a living veneer of coral cover showing an amazing level of diversity in some places, while large predatory fish like the dogtooth tuna patrolled along its perimeter.

A large dogtooth tuna (Gymnosarda unicolor) cruises past divers. Note the scars and missing section of the pre-opercular plate. NOAA photo by Jake Asher.

One of the most unique aspects of Asuncion’s underwater habitat compared to all the other places across the Pacific where CRED conducts research is that it contains one of the few, if not only, vertical REA survey sites.

The vertical benthic REA site at Asuncion. NOAA photo by Russell Reardon.

In addition to the variety of coral and fish species that have been observed, we have seen many other types of organisms as well.

Usually our towed divers are ‘flying’ over the reef recording broad-scale observations of the habitat below, but every now and then, they get to observe the reef up close and personal, where they can observe some of the more conspicuous creatures such as this banded coral shrimp, Stenopus hispidus. NOAA photo by Jake Asher.

A pink whipray, Himantura fai, that is either expressing aggressive behavior towards the photographer or it wants to mate with him! NOAA photo by Kevin Lino.

Throughout the Marianas Archipelago, ARMS have only been deployed at some of the islands; Asuncion currently does not have any ARMS deployed. At islands where there are no ARMS units to recover and/or deploy, the ARMS team, when it's logistically feasible, will conduct non-coral marine invertebrate surveys instead. It's a real treat to observe some of  these cryptic species in their home environment as opposed to in the lab while processing the ARMS.

An octopus spotted in the field, looking very conspicuous indeed. NOAA photo by Paula Ayotte.

And an octopus collected from an ARMS. NOAA photo by Kerry Grimshaw.

It's amazing that such a vast ocean contains such wonderfully small and beautiful creatures hidden in the tiniest of nooks and crannies.

This coral crab, Trapezia sp., spotted by one of the benthic divers during a marine invertebrate survey, is hiding out in his favorite coral, Stylophora sp. NOAA photo by Kerry Grimshaw.

A persian carpet worm, Pseudobiceros bedfordi. NOAA photo by Paula Ayotte.

Eight is enough

by Steve McKagan

Working primarily with the Fish REA team, I'm used to having up to four people at most in the water at a given time during a survey.  The reason is fairly simple, fish don’t like being disturbed.  Today was a markedly different experience as I jumped aboard the biggest field boat on board the Hi’ialakai, HI-1, and went on a documentary dive with the benthic, oceanography, and ARMS teams.

ARMS team member Kerry Grimshaw securing lines to an ARMS unit to be recovered. Her team member is in the distance doing the same. During a typical recovery, three ARMS units in all are recovered from a site and are then brought back to the Hi`ialakai to be processed. NOAA photo by Steve McKagan.

It isn’t just the sheer number of people on an HI-1 dive that differs from a regular day out with the Fish REA team; it is also what they are doing.  To successfully establish fish counts, divers hover quietly several feet above the bottom watching and noting the behavior of their subjects.  In contrast, today the ARMS team was both deploying new settling plates and collecting baseline units which were stationed at this site two years ago, just after the Marine National Monument designation took place (http://www.fws.gov/marianastrenchmarinemonument/).

It's hammer time as ARMS team member (and Operations lead) Russell Reardon pounds stakes into the substrate that secure the ARMS units in place for ~2 years. NOAA photo by Steve McKagan.

The Fish REA team does its best to blend in with the surroundings bringing minimal gear; today a single oceanography diver brought more equipment to the bottom than could possibly be carried once filled, more than doubling his size and weight.

At depth, Chis Sullivan fills three twenty-liter bottles with seawater to later be used for metagenomic analysis to determine the microbial composition of the seawater. NOAA photo by Steve McKagan.

Yes it is true, Fish REA folks can sometimes be seen looking down into a hole trying to identify a camouflaged fish or eel, but when one dive buddy is looking down the other is most likely looking up and around.   In contrast, I couldn’t get a single member of the benthic, oceanography or ARMS teams to look up for this photograph.

Six members of the Benthic, Oceanography, and ARMS teams busily working away on the reef conducting benthic surveys, collecting water samples, and deploying ARMS units. Can you spot them all??  NOAA photo by Steve McKagan.

In the end I learned that you don’t absolutely need to have a lot of big fish around to have an enjoyable and educational dive, especially when algae experts are willing to show you what it would look like if a barracuda in the vicinity decided to charge the oceanography samples.

Benthic team member Ryan Okana demonstrates barracuda-like behavior as Chris Sullivan slowly surfaces with his water samples in hand. NOAA photo by Steve McKagan.

Thanks to everyone for another great day on Leg 2 of MARAMP.

Beyond Sarigan....

by Annette DesRochers

As Edmund promised, our expedition through the Northern Mariana Islands has indeed been a mystical journey. Setting sail from Sarigan, we have stopped at and passed by many a volcanic peak along the way. From dawn till dusk, the views from topside have been nothing short of spectacular. While this is true for many of the places where our research takes us, it seems especially true in this part of the world.

Sunset over the two stratovolcanoes of Pagan. NOAA photo by Jake Asher.

Our first stop after Sarigan was the island of Pagan, one of the larger islands in the Northern Marianas. Not only is the shape of the island unique compared to the singular cone-shape of the other islands in the northern part of chain, but it is also one of the most geologically active. Just this past year, a U.S. Fish and Wildlife Service research camp left the island due to increased volcanic activity. The largest eruption in recent history was in 1981—the few remaining residents on the island had to be evacuated—though it has erupted several times since then with one relatively minor event in late 2006 just months before CRED’s 2007 research cruise to the region.

The view from the Hi’ialakai of Mount Pagan. NOAA photo by Annette DesRochers.

Despite the obvious beauty of the island, I for one have been partly disappointed since we arrived. Everyone that has been to this region talks about seeing Mount Pagan, the northern volcano on the island, steaming in the distance. As you see in the picture above, not a speck of smoke to be seen; nothing but blue skies and white fluffy clouds. I guess it could be worse.

Early morning launch near the northeast side of Pagan where large rock formations jut out from the sea. NOAA photo by Jake Asher.

It's business as usual as the dive teams set out for a day of operations. That being said, I don’t think any of the divers, even those who are now on their fifth research cruise to the region, ever tire of the sites above or below the sea surface. One of the REA fish divers was sharing her photos with me from her surveys here at Pagan, and even she can’t get enough of some of the species they find here such as the variations of anemonefish in the pictures below.

Clark's anemonefish (Amphiprion clarkii). NOAA photo by Paula Ayotte.

Pink anemonefish (Amphiprion perideraion). NOAA photo by Paula Ayotte.

And the oceanography team, normally busy underwater deploying and recovering various oceanographic instruments, took time out to enjoy some of the spectacular corals that are found here.

A mushroom coral (Fungia sp.). NOAA photo by Oceanography team.

Previous RAMP surveys have noted a number of underwater stressors to the coral reef habitats here at Pagan, from a large increase in cyanobacteria cover (i.e., blue-green algae) seen island-wide in 2009, to persistent Acanthaster plancii (crown-of-thorns) populations. Thankfully, our recent surveys revealed that neither appear to be currently causing stress to the benthic environment here.

Peering through the rock formations, you can see a glimpse of the volcano in the background. NOAA photo by Paula Ayotte.

At the end of a long day, the divers’ route back to the ship takes them around the north side of the island past the amazing rock formations, but their work is not yet done. It takes several players to safely deliver the small boats back into their cradles on the Hi’ialakai. We're well into the second leg of this cruise, and yet, no matter how tired or routine it might seem, safety always comes first.

Chief Scientist Jake Asher snaps his camera just in time to show AB Carmen Greto throwing the lines to one of the divers on HI-2. NOAA photo by Jake Asher.

After three days of surveys here at Pagan Island, it's time to move on to our next destination. Next stop on our journey, Asuncion Island.

Measuring Fish while Flying

by Jacob Asher and Danny Merritt

This year a pilot project has been implemented by CRED’s fish team using a stereo-video system on the fish-towboard to improve the team’s ability to precisely measure fish and benthic features, and to accurately define the size of the area surveyed. This project is being done in collaboration with the Harvey Lab at the University of Western Australia. Dr. Euan Harvey and his lab have been using stereo-video systems for both diver surveys and on baited camera systems [a method to attract fish or other animals into the field of view of a camera using bait] for a number of years, including the use of baited cameras (BRUVS) around Guam and the CNMI. The use of such a system on a towboard, however, is a novel technique.

Noah Pomeroy flying the stereo-video fish towboard at Pagan Island. NOAA photo by Jacob Asher.

Overall the implementation during this cruise, while it is still preliminary, has been successful despite a few challenges. During a towed-diver survey, the fish diver tries to ‘aim’ the towboard to ensure that fish pass by the field of view of both cameras. It has taken some time for the divers to become accustomed to the new cameras that are mounted on the towboards because they’re bulkier and harder to maneuver.  Also, the post-processing of the video files at the end of the day has been a challenge because of the volume of data that is collected. On a typical day of operations, the tow team collects approximately 6 hours of high-definition video on 2 cameras. The result? Huge videos that must be downloaded, converted to a usable format, and organized so that the videos can be analyzed later on.

Measuring Fish with Cameras
Stereo-photogrammetry (or stereo-video) is a technique CRED uses for sizing and ranging objects, such as fish, seen in video or still images. The method uses two images taken at the same time of an object from 2 different perspectives. If the relative orientation of both images is known, it is then possible to measure the distance from the camera to the point seen in the images. This is the same process by which people are able to judge distances with our two eyes. By knowing the location of 2 points on an object, such as the head and tail of a fish, the distance between the points (e.g. fish length) can also be calculated.

Above is an example of stereo-photogrammetry software being used to measure fish captured from BotCam video. In this case, two pink snapper have been measured.

CRED has been using stereo-video systems for baited camera systems for a number of years. An example from BotCam video (a deep baited camera system) of stereo-photogrammetry software is shown above.

Heading north....

by Edmund Coccagna

We have left the populated southern islands of the CNMI behind and have entered the area of the Northern Mariana Islands.  The region is somewhat of a mystical place where volcanoes rise sharply out of the sea, forming perfectly cylindrical cones.  Some of the islands have been inhabited by lush vegetation, while others were left with nothing but bare ash and rock.  Historically, these islands have been marked by violent volcanic eruptions caused by their geographic location on one of the earth’s major subduction zones along the Marianas Trench.  Over time they have developed and in turn eroded into what we now see, which is quite the spectacle of where land meets the sea.

The safeboat tucks inside of a cliff side cave with a view of the ship in the background. NOAA photo by Jason Helyer.

Our first stop in the region was at the small island of Sarigan.  The appearance of Sarigan is much like the others, with dramatic rock features created by the island’s violent past, both above and below the surface of the water.  The terrestrial habitat of Sarigan is marked by vegetation on the western side and sheer basaltic rock on the eastern side with many tremendous formations.  People have inhabited the island at different times in the past, but currently no one currently resides on the island, except for birds and insects.  Below the surface, the majority of the reef habitat is formed of large boulders or basaltic rock with low to moderate levels of coral cover.  Sarigan does host the greatest populations of large bodied reef fish that we have encountered on this trip yet.  Divers on the fish teams reported sightings of three different types of sharks, including white tip reef sharks, grey reef sharks, and Tawny nurse sharks, large Napoleon wrasses, and large schools of jacks, barracudas and rainbow runners.

Area of Porties rus. NOAA photo by Jacob Asher.

Sarigan is one of only two islands that the US Geological Survey (USGS) actively monitors.  The current status of the advisory is safe with no alerts, which was good news for the small boats working in the vicinity of the island.  Although the date of the last eruption on Sarigan is unknown, a seamount seven miles to the south experienced an explosive eruption in late May of 2010, which caused the USGS to close access to the nearby islands in the chain, including Sarigan.  The submarine volcano reportedly blasted ash 49,000 feet into the atmosphere!  That is incredibly impressive considering the origin of the blast occurred well below the surface of the water.   

The island of Sarigan, Northern Mariana Islands. NOAA photo by Annette DesRochers.

We only spend one day at Sarigan due to its small size and then head north to Pagan.  Many other volcanoes rising from the water await and there are many more stories to come.