Patricia Greene, July 16, 2006

NOAA Teacher at Sea
Patricia Greene
Onboard NOAA Ship Hi’ialakai
June 26 – July 30, 2006

Mission: Ecosystem Survey
Geographical Area: Central Pacific Ocean, Hawaii
Date: July 16, 2006

The ornate butterflyfish (Chaetodon ornatissimus) is one type of butterflyfish that is also a coral predator.
The ornate butterflyfish (Chaetodon ornatissimus) is one type of butterflyfish that is also a coral predator.

Science and Technology Log

When you think of the Northwestern Hawaiian Islands and predators, the first thing that comes to mind may be the apex predators; tiger sharks, Galapagos sharks and species of huge fish such as the jacks. Corallivores (an animal that feeds on corals) may include fish, sea stars or mollusks.  Generally, two types are recognized; obligate corallivores; those that feed only on corals and facultative corallivores; which feed on corals, algae, sponges, and mollusks.However, while snorkeling the Kure Atoll, I was reminded that there is another group of predators here; the corallivores. I observed a crown of thorns that appeared to be feeding on the coral and upon further research I discovered and recognized a variety of Northwestern Hawaiian Islands creatures that I have seen that also specialize in feeding on corals.

The crown of thorns feeds by inverting its stomach through its mouth, and then digests the corals externally. Human attempts at controlling populations of crown of thorns have been relatively unsuccessful and causes of these population spikes or outbreaks have been a topic of debate. Some believe they are natural occurrences and occur in cycles while other scientists believe they are due to human causes such as increased sedimentation and pollution.The crown of thorns (Acanthaster planci) has cryptic coloration and toxin-filled spines.  It prefers to feed on rice corals (Montipora), lace corals (Pocillopora), and cauliflower corals (Acropora). Ironically, the crown of thorn eggs and larvae are often fed on by the stony corals. Other natural enemies of the crown of thorns is the harlequin shrimp and the fireworm. This little shrimp does not kill the crown of thorns, but merely creates a small, open wound. This is known as “facilitated predation.” The larvae of the fireworm then enter the cavity, reproduce, and the offspring eat the crown of thorns from the inside out; eventually causing death.

The crown of thorns (Acanthaster planci) is a major predator of coral reefs.
The crown of thorns (Acanthaster planci) is a major predator of coral reefs.

We have also observed a variety of butterflyfish on the reefs; all that are also coral predators. The ornate butterflyfish (Chaetodon ornatissimus), the oval butterflyfish (Chaetodon lunulatus), the fourspot butterflyfish (Chaetodon quadrimaculatus), and the multiband butterflyfish (Chaetodon multicinctus), are all obligate corallivores. Other butterflyfish that eat both corals and invertebrates include; the threadfin butterflyfish (Chaetodon auriga) and the teardrop butterflyfish (Chaetodon unimaculatus).

We have also identified the spotted pufferfish (Arothron meleagris) hiding in the corals of Kure Atoll’s lagoon. This unique creature has a beak-like mouth with sharp frontal teeth for removing pieces of substrate and flat teeth in the back for grinding. They feed on a variety of organisms, including the stony corals and calcareous algae. They have a unique adaptation that allows them to lodge their bodies into a crevice or hole and then puff up so it is impossible for a predator to dislodge them. Their tissue is relatively toxic to humans.The shortbodied blenny (Exallias brevis) is an obligate corallivore. It prefers the lobe (Porites lobata) and finger coral (Porites compressa). The spotted color of these fish blends nicely with the colonies of coral. Removing tiny bites these fish have little impact on the health of the corals. The coral colony is able to regenerate new polyps and fill in he bite marks.

The shortbodied blenny (Exallias brevis) is an obligate corallivore, which feeds on coral.
The shortbodied blenny is an obligate corallivore, which feeds on coral.

The blue-eye damselfish (Plectroglyphidodon johnstonianus) inhabits the Northwestern Hawaiian Islands coral reefs. It feeds only on coral, preferring the lace, antler, cauliflower, finger and lobe corals. These small fish are very territorial and will defend their nests, hiding in the corals that also serve as food. Most of the coral predators do not pose any major threats to the coral reefs. They are natural inhabitants of the reefs and do little damage. The crown of thorns can cause mass devastation; during major outbreaks at other Pacific Ocean locations the coral cover was reduced from 78% to 2%. In 1970, approximately 26,000 crown of thorns were destroyed off the southern coast of Moloka`i. However, during all of dives in the Northwestern Hawaiian Islands we only observed two crown of thorns, which is good news for this remote region.

Dena Deck, July 12, 2006

NOAA Teacher at Sea
Dena Deck
Onboard NOAA Ship Hi’ialakai
June 26 – July 30, 2006

Mission: Ecosystem Survey
Geographical Area: Central Pacific Ocean, Hawaii
Date: July 12, 2006

A map integrating backscatter map with bathymetry, showing the seafloor in rich detail
Integrating backscatter with bathymetry, showing the seafloor in rich detail

Science and Technology Log

When soldiers from Napoleon’s army found the Rosetta Stone, it was a breakthrough discovery. Carved in ancient Egypt, it contained pieces of a message in known languages and also a language that had been dead for centuries. Without any link to other known languages, historians had been unable to decipher this language until the stone was found, which provided the necessary clues to translate it. Modern day ocean mappers are looking for their own Rosetta Stone that will allow them to link backscatter data to other ecological information.

A backscatter map, indicating substrate characteristics. Dark areas represent a harder seafloor, while lighter areas are indicative of a soft, sandy bottom.
A backscatter map, indicating substrate characteristics. Dark areas represent a harder seafloor, while lighter areas are indicative of a soft, sandy bottom.

Our ship, the NOAA ship Hi`ialakai, has a set of three sonars that, when used in conjunction, can provide accurate data about the seafloor. When emitted by a sonar, a “ping” comes back bringing two pieces of information with it: travel time and strength. The two-way travel time (the time it took from emission, bouncing off the seafloor and return back to the ship), coupled with the measured velocity of sound in the specific water location where the ship is traveling in, gives mappers a bathymetric view of the seafloor, revealing the depth of each of its points. (See “Painting the Seafloor” article.)

A second piece of data obtained from each ping is the strength of the signal. When sound hits a surface, above water or below, some of it is absorbed and the rest bounces back in what we experience as an echo. The strength of this echo depends on the hardness of the material that the sound is bouncing from. This is a very convenient fact of nature that is used when mapping to compliment the bathymetric map that provides the depth. The acoustic hardness of a substrate, or ocean bottom, affects the strength of the ping coming back to the sonar. In a real sense, the loudness of the echo changes if it is bouncing off sand or rock. Sand, being soft and full of small holes in between grains, will absorb quite a bit of sound. A more solid surface like a rock will provide a bigger echo for each ping that hits it.

A diver armed with a camera is towed from a boat, obtaining many pictures that will be used to groundtruth mapping data.
A diver armed with a camera is towed from a boat, obtaining many pictures that will be used to groundtruth mapping data.

This strength of the signal coming back is called “backscatter” and provides mappers with a second view of the seafloor. While bathymetry is a measure of the depth, backscatter gives us a clue about the nature of the seafloor being mapped. Since coral reefs, with their calcium carbonate, provide a much harder surface than a sandy sea bottom, the two will appear differently in the backscatter map. Values of intensity range from low intensity, showing up as white and representing soft, sandy bottom, to high intensity, represented as dark areas for harder substrate in the backscatter gray scale map.

When the backscatter map shows up binary data – white and black – it is easy to infer on the type of substrate being mapped. The challenge is presented with all of the gray areas in the map. Does light gray represent coarse sand? Is dark gray indicative of sand over rocks, or thousands of coral polyps? Or maybe just rock covered by sand? Every shade of gray has a value that can indicate a type of substrate.

Mapping
Mapping

Backscatter alone cannot give you these answers. With so many variables present in the mapping process, data needs to go through a “ground-truthing” process, or compared to visual observations of the sites. To do this, researchers collect video, photographs and perform actual dive observations of many of the sites that are mapped. These video and images need to be analyzed by a person. It’s a tedious process that cannot be automated – it requires having a person able to classify types of substrate from watching hour after hour of video data or many photographs. And all of these data needs to be “geo-rectified,” or coupled with GIS information to know exactly where each video segment and photograph was taken. Sometimes the payoff for “groundtruthing” backscatter is unexpected: wrecks or rich coral beds can be discovered.

We do not have yet a backscatter “signature” for each type of substrate, or sea bottom, yet. This would be the Rosetta Stone of mapping, a development which will allow mappers to correctly identify some of the ecological characteristics of each area mapped. For instance, mappers are working towards refining their backscatter analysis to allow them to tell apart live coral from bleached ones.

The NOAA Coral Reef Conservation Program has built a pilot data set from the French Frigate Shoals, consisting of large amounts of video footage, observations, and other data. They are in the process of compiling all of this information with their backscatter maps they have for the area, and study how they relate, trying to find meaning to each gray area in these maps.

When mapping, additional and unexpected discoveries can take place. Sometimes what we think of as featureless terrains are revealed to have rich topographies. In 2004, an ocean area off the island of Oahu in Hawai`i, thought to be featureless and plain, was discovered to have sand dunes and ridges, providing important habitat to the marine fauna. Interpretation of backscatter data has improved in quality over the years, and when combined with videos and photographs, remote characterization of sea floor habitats becomes possible.

Dena Deck, July 11, 2006

NOAA Teacher at Sea
Dena Deck
Onboard NOAA Ship Hi’ialakai
June 26 – July 30, 2006

Mission: Ecosystem Survey
Geographical Area: Central Pacific Ocean, Hawaii
Date: July 2, 2006

A NOAA ship using the sonar system.
A NOAA ship using the sonar system.

Science and Technology Log

The first part in appreciating what we have is to know exactly what we have to begin with. Biologists conduct species census in both terrestrial and marine environments, and spend a great deal of time studying each species. But to gain a fuller understanding of an ecosystem, it is also necessary to know the physical characteristics of the environment that provides the foundation for these ecosystems. This is one of the main reasons why we map the seafloor.

The primary goal, as far as mapping is concerned, is to have 100% of all shallow coral reefs mapped. The group mapping the Northwestern Hawaiian Islands is a large team comprised of staff from NOAA Fisheries Coral Reef Ecosystem Division, and the University of Hawai`i. They have an exemplary set of tools at their disposal to do their work. Aboard the NOAA shipHi`ialakai, they employ two sonar systems. Used in conjunction, these sonar systems are slowly giving us a detailed account of the submerged geological features that make up the Hawaiian archipelago.

A bathymetry map showing a 15-meter drop off from several angles. Colors indicate relative depth
A bathymetry map showing a 15-meter drop off from several angles. Colors indicate relative depth

The primary objective of this mission is to produce benthic (sea bottom) habitat mapping of Kure and Pearl & Hermes Atolls. We are filling in a doughnut-shaped gap on both Kure and Pearl & Hermes Atolls, finishing a painting of the seafloor that started several expeditions ago. Coral reefs around the world are receiving increased attention because of the many threats that they face (coastal development, overfishing, climate change), and the U.S. Coral Reef Task Force has produced a number of goals and mandates relating to these ecosystems in America. Among these goals is a call for better management of these resources, and to learn more about them. Mapping all U.S. coral reefs puts Hawai`i at the center stage of this effort with its large chain of islands and atolls stretching across vast distances and volcanic islands found at every stage of geological development, from birth to eventual demise.

The research vessel Ahi operating in Kure atoll. Note the AC cabin to operate the computer equipment required for the sonar.
The research vessel operating in Kure atoll.

The two sonars that we have aboard the ship perform the same task, but each is best suited to work in different conditions. That is because they employ different frequencies which have different rates of penetration. Let’s go back to the analogy of painting a wall. If you have a large wall to paint, you can use a broad brush (or even better, a roller), to cover large areas at every stroke. But within this wall you also have edges that need to be painted more carefully. Let’s say there is a light switch placed in the middle of the wall. Using a painting roller will invariably leave white spaces in between (either that, or you end up also painting the light switch!). So for this light switch, you would use a smaller brush, allowing you to carefully get close to it, eventually covering the entire surface of the wall without painting over it. In this analogy, each light switch in the wall represents an atoll of the archipelago.When a ship maps the ocean floor, it needs to slowly cover swath areas under it. The process is very much like painting a wall with a brush. A wall cannot be painted all at once, of course. The painting is accomplished one stroke at a time, where each passing of the brush needs to slightly overlap the previous one, as to not leave any white spaces in between. When mapping the seafloor, the ship, with its sonar as a giant brush, needs to carefully cover every bit of seafloor surface, as to not leave any area between passes, or swaths, blank and unmapped.

A recently completed bathymetry map superimposed with satellite imagery of Kure atoll. Red indicates lowest depth, and blue deepest. Satellite image has white around edge indicating the exposed reef ring.
A completed bathymetry map superimposed with satellite imagery of Kure atoll. Red indicates lowest depth, and blue deepest. White indicates exposed reef ring.

I am going to use the example of sunlight traveling through water to illustrate the way that the ship’s sonar works, both light and sound are waves.  Sunlight has many frequencies, frequencies that readily break out into all colors by raindrops or a prism. Red color has the highest frequency and, much like the 3002 kHz sonar, is the first absorbed by water. The color red is the first one to disappear underwater. Take anything cherry-colored down a few meters of water, and it will quickly loose all its brilliance, turning into a dull-looking color, an effect that is magnified with the scarcity of light at nighttime. Fish also know this very well. Many fish which are active at night tend to have a red color. Soldierfish, with their large eyes and flame-red color, are perfectly suited for the night environment.Painting over a light switch would mean running the ship into the reef! So mappers have a set of “ paint brushes” in the form of three sonars that allow them to carefully map each area. There is one low-frequency sonar (using a 300 Kilohertz (kHz) frequency) that has a long wavelength that can map between 100 meters (about 328 feet) and 4,000 meters (about 13,421 feet) – this is the ship’s big roller. There is another, high-frequency sonar (using a frequency of 3002 kHz) that can map when the seafloor is less than 100 meters (about 300 feet) from the surface – this is like a mid-sized brush. There is a third sonar, mounted on a smaller, 25-foot research vessel Ahi (which stands for Acoustic Habitat Investigator), with a sonar working at an even higher frequency, which can get really close to the reef – up to places which are 10 meters in depth (quite shallow, at 30 feet). This little boat is like the small brush used to cover areas right at the edge of what needs to be mapped.

Blue, at the other end of the visible light spectrum, has a low frequency. Its large wavelength is the last one to be absorbed by particles in the water, and penetrates deep in the ocean. If you are able to go down deep enough, say 100 meters (328 feet), all around you will look blue. I once went on a submarine ride with my sister, and when we reached 45 meters (150 feet) in depth, the entire inside of the submarine was bathed by blue light. I took her picture and, with no camera tricks, it showed how everything had acquired a sapphire hue (see picture).

When the pings return back to the ship from their very quick trip to the ocean floor, the sonar measures (or “listens”) to how long it takes for them to return, and how strong their signals are. To do this accurately, there are over 100 arrays of receivers in the sonar on the bottom of the ship, each carefully calibrated to listen carefully to each echo of a new ping. The pings coming back carry with them two bits of important information: how long they take (known as the “Two-Way Travel Time”) and the strength of the signal. The time it takes for the ping to return depends on how far it needs to travel (of course!) and how fast sound is traveling in the water.Now, how exactly does sonar work? The sonar unit emits sound, actually given the descriptive term of “ping.” This ping can be at either the low or high frequency described above. After the ping is emitted the sonar unit “listens” for it to come back. Sonar, therefore, has two essential components: the first one that emits the ping, and the second one that listens for it coming back from the seafloor. This is because when sound hits a surface, some of it is absorbed while the rest bounces back. (If you have many large walls around you, you can hear almost all of your sound coming back at you, this is the echo you hear.) The denser, and flatter the surface, the more of the sound that bounces back.

Adding a bit of complexity to this process, the speed of sound is not immutable like the speed of light. In water, it depends on the temperature of the water, its salinity, and depth (all of them affecting the density of water), so careful and constant measurements need to be taken regularly. A large array of devices, collectively known as CTD, are routinely lowered from the main ship into the water. Armed with this information, and by carefully measuring the time it took for the ping to complete its travel, we can know how far each ping had to go. If you do this many times over, you have something called “bathymetry,” a picture of the seafloor.

Putting together shallow and deep water mapping, we soon end up with a seafloor that has been completely painted, full of colors representing depths. An accurate map is essential as a base layer upon which other information can be overlaid, such as bottom cover type – coral, rocks, sand, etc. Mapping, combined with bottom characterization allows us to monitor long-term trends and changes in the marine habitat. This long-term observation is an essential tool for management of the resources. It can serve as one of the indicators for the effectiveness of the conservation efforts, allowing us to make “sound” management decisions.

Patricia Greene, June 28, 2006

NOAA Teacher at Sea
Patricia Greene
Onboard NOAA Ship Hi’ialakai
June 26 – July 30, 2006

Mission: Ecosystem Survey
Geographical Area: Central Pacific Ocean, Hawaii
Date: June 28, 2006

Science and Technology Log

We awoke with anticipation at approximately 5:30 a.m.  Today we were scheduled to arrive at Kure Atoll and with any luck would have our first snorkel experience in the Northwestern Hawaiian Islands.  We have been in transit twenty-four hours a day for six days onboard the NOAA Ship Hi’ialakai.  We have covered a distance equal to traveling from Houston, Texas to Reno, Nevada.

Our snorkel gear is placed on deck near the loading area at 6:45 a.m. and after a quick breakfast we go up on deck with anticipation of our first view of Kure’s Green Island.  Two shade trees are in the middle of the island and appropriately a rainbow drapes the north end.  Birds; albatrosses, terns, and frigate birds fly out to greet us, while spinner dolphins play in the spray at the bow of our ship.  What an awesome welcome!

At last we are instructed to load and we pull away from the Hi’ialakai, excited and anxious to see this underwater realm that we have all been reading, researching and immersed in the last six days while transiting.At 7:30 a.m. the dive and snorkel team meet on the fantail and receive one last safety meeting from the Chief Boatswain and Dive Saftey Officer, Mark L. O’Conner.  Protocol on the ship is that the Maritime Archeology dive boat, the H1, is loaded first with supplies and people then lowered by crane into the ocean.  Next the research vessel Ahiwith the University of Hawaii and NOAA mapping crew will enter the water, also by hydraulics.  Lastly our snorkeling boat, an inflatable zodiac with a 50hp 4 stroke will be placed in the water.  The only difference is our boat is not loaded so therefore we pass supplies into the boat and then we will need to climb down a Jacob’s ladder on the side of the Hi’ialakai in order to enter the boat.

Our first reward is the sight of a Hawaiian monk seal on one of the sand spits.  Ordinary Seaman, Jason Kehn, our coxswain, is careful to take the boat far around the area so as to not disturb this rare, endangered species.  The monk seal is apparently oblivious to our presence and only when we see a flipper move and his head rise, are we sure he is not dead.

After last minute safety instructions and advice to “look predators in the eye,” we are ready to enter the reefs.  The water around us is a collage of vibrant shades of blue and turquoise.  We open our eyes and are surrounded immediately by a huge school of chubs; seemingly curious and unafraid of us.  The visibility is phenomenal, probably 80ft.; the water crystal clear with no turbidity.Jason competently maneuvers to our dive site; we are grateful that he knows the area because our GPS is telling us we are still 21 miles from the site! We tie up to a CREWS (Coral Reef Early Warning System) buoy; one that transmits temperature, turbidity, and other environmental data that can detect significant impacts to the coral reef ecosystem.

Fishes are numerous in Kure Atoll’s lagoon. Smaller species dominated our survey area. This may be explained by the coral reef habitat.  Coral cover was around 80 percent, with finger coral (Porites compressa) being the dominant species.  Living finger coral provides many hiding holes for the juveniles and adults of smaller species, and this may be the reason for the great abundance of smaller species of fish.

Ellyn, our naturalist from Hawai`i, observed that overall there is greater diversity in the fish species in the NWHI than on the main Hawaiian Islands, however, in general the fish were smaller in size for their species.  Patty, our Teacher-at-Sea from the Florida Keys noted that overall the coral appeared much healthier that many of the reefs in the keys and noted the absence of the soft corals and brain coral so common in the keys. Finger coral may be an endemic species and is quick growing, often out competing other coral species for space.  Massive continuous heads created yards of living reef on our survey site.  We observed that the sheer weight of the massive heads often forced large pieces of living reef to break off and form rubble fields below the living reef.  These rubble fields provide highly desirable substrate onto which other species of corals recruit and create many tiny hiding holes, very desirable homes for larval fish to recruit into from the water column.  Homes for the adults, homes for the recruiting juveniles…what a perfect place to live!

Chris Harvey, June 23, 2006

NOAA Teacher at Sea
Chris Harvey
Onboard NOAA Ship Oscar Elton Sette
June 5 – July 4, 2006

Mission: Lobster Survey
Geographical Area: Central Pacific Ocean, Hawaii
Date: June 23, 2006

Science and Technology Log 

“When both feet are planted firmly, you are stuck”

I can only think of one thing to write about today- or yesterday, or the day before, for that matter. That is, what day is today? Piglet would tell me that today is the day after yesterday, which does not help since I do not know what day yesterday is. And Pooh would tell me that today is the day before tomorrow, which makes more sense, but not enough. Eeyore would tell me that today is a bad day, while Rabbit would tell me that today is however many days past the first of the year it so happens to be (as he calculates how many days have passed since then!). Owl would tell me that today is just a state of pondering what today really means. And Christopher Robin would tell me that today is today, of course! I was thinking that today must be close to July. Days just seem to pass out here. And it seems we are much closer to being back in port than to being out to sea. And yet a container of milk said June 14 for the expiration date. So I think to myself, are we in some kind of time warp, or am I drinking milk that is two weeks past expiration? Pooh says expiration dates don’t matter anyway, as long as you put some honey in the milk. (Is it the sun, or salty air, or both that are getting to me?)

But low and behold, as I poured the crunchy ice-milk into my cup I realized that my rationality, what the sun and sea have not taken from me, had been undermined by a piece of modern technology called a freezer! God bless the freezer! We have been eating “fresh” fruit and vegetables for over twenty days now, and I have had no complaint on the freshness of the food. Scurvy has stayed clear of the Oscar Elton Sette!

Presently we are anchored off of Maro Reef, far enough out not to do damage to the reef, yet close enough that- with my mega ultra 17 X super zoom lens (it’s not really that great!)- I can see waves breaking on the reef. Our friendly albatross has multiplied during the day, and all but disappeared during the evening. Have I mentioned how amazing these creatures are?

In terms of work, yesterday we averaged nearly six lobsters per trap, which was a substantial increase over past days in the NWHI. However today was back to normal. We are in our last rotation of jobs this week, which is bittersweet in that by the end of the week we get another break. Only this time the break is for good. I can tell you that without a shadow of a doubt, I will not miss hauling and setting lobster traps.

However, having just observed the Pacific sunset (behind a big nasty storm, beautiful nonetheless) I am reminded of my joys while being here. And yes I still coo like a schoolgirl over her first crush when I see the stars at night. I’ve made it a point to spend several hours a night lying underneath them. I have come up with my own constellations, since the other ones seem to be rather old and archaic. There is the Hippopotamus, the Wishbone, the Giraffe, the Arrow, the Sun to name a few (Yes, I know the Sun already exists. But I have found another one, much brighter than our own, but further away…Have I told you of the sun and salty air and what it does to the mind?)

As for the quote of the day. When both feet are planted firmly, one would think they would be on stable ground. This is good for some, and bad for others. I am of the kind that likes to think that two feet planted implies immobility. Although it does not quite rule out two feet firmly planted while running in some direction. Still, I always think of my life- the few times I think of my life in terms of footsteps- as having one foot on the ground, and one foot in the clouds. But that might also be because the more I think about planting myself anywhere, the more I want to get up and go somewhere else. In fact, I think that at this very moment I shall quit my teaching job and find a job as a deckhand in Honolulu! (That is the foot in the clouds speaking!) Of course this is not sensible, but can you imagine the stories I would be able to tell you then!

My friends Pooh, Eeyore, Piglet, Rabbit, Owl, and Christopher Robin want me to mention that, if you get the chance, you should read The Tao of Pooh. For those of you who know me, you will find that the cover of the book somewhat resembles a piece of artwork tattooed to my right leg (or rather, the artwork on my right leg somewhat resembles the cover of the book). Either way, the book is wonderful in that it brings about a simpler perspective of life. I have been reading it in the time I have been out here, savoring the pages for the perspective that I gain from them.

Other than that, life goes on like Groundhog Day. Did I mention the effect of the sun and the salty air on the mind? Oh, thanks Pooh, I see that I have. Well it makes one love the sea and all of the Beautiful experiences that one experiences out here. Absolutely amazing!