Does Sand Kill Corals?

Depending on the scenario, sand can hurt corals … but corals have also developed ways to protect themselves from sand or sedimentation.  Sand can affect corals in a number of ways:

• When there are a lot of waves, sand particles can become suspended in the water column and as the waves move the water back and forth, these particles can scour the reef (and corals) like a slow but steady sand blaster.
  
• When there is a lot of sand in the water, the visibility (how far you can see) and the amount of sunlight reaching the bottom is decreased.  Since corals use sunlight for energy(by way of their symbiotic zooxanthellae) this can reduce the rate at which the corals grow and in extreme cases can cause bleaching or even kill the coral.
  
• Even in calmer areas, where there are not as many waves, sand can sometimes land on corals. If too much sand lands on a coral it can be smothered and killed.  ... but many corals have a way to rid themselves of this “unwanted sand.”  They can secrete a mucous layer which acts as a protective shield.  When sand lands on the coral, it gets stuck in the mucous layer and then when water motion increases, the coral sheds the mucous layer – and all the sand that was stuck to it.

Hearing the Reef with our "EARs"

Scientists deploy an EAR on a nearby reef

Recently we have had several questions about the EARs or "Ecological Acoustic Recorders" we are deploying at various islands and reef to monitor sounds in the shallow water areas during the year or two between expeditions.

Mr. Hill's period 2 class asks: "What type of fish can you hear with the EAR or what was the most exciting thing you have heard on the EAR?"

The Ecological Acoustic Recorder can record a variety of sounds. We often listen to whales, dolphins, snapping shrimp and of course fish. Some of the most common fish sounds that we have identified are the domino damsel fish Dascyllus albisella (a purr), the soldierfish Myrispristis sp. (drum sound) and the butterfly fish Chaetodon sp.  Many of the fish sounds we listen to have not yet been linked to a particular species and we are collaborating with the University of Hawaii and Dr. Tim Tricas to identify fish and sounds they produce.

One of the most exciting findings the EARs have provided is the discovery of Humpback whales using the Northwestern Hawaiian Islands (NWHI) as a winter habitat, just as they do in the main Hawaiian Islands.  It was commonly thought that Humpbacks only transited through the NWHI.  EARs in the NWHI have recorded Humpback whale song, indicating the use of the area as a breeding site.

We have had an occasion where some unknown sounds on one of our EARs puzzled us for a couple of days.  We would only hear snippets of what sounded like human voice.  But the dates of occurrence of these sounds did not correspond with our deployment or retrieval of the device, so it could have not been from our divers, not to mention the fact that humans cannot usually make comprehensible sound underwater.  In the end, it turned out to be a filming crew who was getting underwater footage and we suppose they had underwater speakers.  The first full recording that we got of it said "ACTION, Action ... Follow the diver to the left..."

Who knows what we will hear next ...

A deployed EAR listens and waits ...

Fish and How we Count Them

Orangepeel Angelfish (Centropyge shepardi)

Fish are some of the most conspicuous residents of the coral reef environment and, along with corals, tend to get the majority of the attention.  These communities also tend to be the ones we get the most questions about.  Recently we received some excellent questions from Mr. Hill's period 2, 5 and 6 classes.  They ask the following:

• "Have any of the scientists on your team ever discovered a new species of fish?"
• "Do you search for particular species of fish on your dives or do you simple count and measure all the fish that you come across."
• "What type of sharks have you identified on your trip to date? What was the biggest fish that you have seen on your trip to date?"

Ornate Butterflyfish (Chaetodon ornatissimus)

We have three teams of scientists whose job it is to assess the overall condition of the reef fish community at each of the islands we visit.  While we haven't yet discovered any new species of fish on this expedition, one of our scientists may have discovered on on an expedition a few years ago.  The process of discovering a new species is more complicated than you might imagine.  You may find something you don't recognize, but that doesn't mean that NO ONE has ever seen it before.  If you find something you can't identify you have just started down a very long but exciting path.  First you have to do quite a lot of research to make sure you really are the first person to see and describe your particular fish.  You look through all your fish guides and all the scientific papers you can find, consult regional and local experts and taxonomist at universities and museums to see if ANYONE has ever seen the fish you found.  If you really are the first person to see it you then need to describe it and publish your findings in the scientific literature to let other scientists know of your find.  You describe in extreme detail what the fish looks like so that other scientists can compare fish they may find to your notes.  You describe what color it is, how big it is, what shape it is, how many scales it has along its lateral line, how many fin rays or spines it has in each of its fins, you may even take a sample for genetic analysis so that the DNA sequence of your fish can go into a taxonomic gene bank.  This process can take years but it is very exciting.  When all is said and done, you get to name your fish!

Saddled Butterflyfish (Chaetodon ephippium)

So ... Do we count all fish we encounter? That’s an excellent question. We do count every single fish we encounter in our survey area. Of course, we know very well that we are missing some, especially the ones that are hiding deep inside the recesses of the reef, but we do the best we can.  Often we are not as much trying to get an accurate count of the total number of fish in a particular area, but more how a given site compares to other sites we visit.  For this purpose, as long as we are making our counts in the same way at each site, we are likely missing the same things each time so our counts are comparable.  The more counts we make, the more accurate we are.  Although we pay special attention to the typical “food” fishes, we also want to understand what is happening to the entire fish community and how it is changing through time.  Are we seeing different species now compared to what we saw in the past?  Is the total number of species or species diversity changing from site to site or over time?

Pyramid Butterflyfish (Hemitaurichthys polylepis)

So how do we count all those hundreds of fish belonging to various species swirling around us?  We use a variety of different methods al of which involve SCUBA.  For many of the smaller fishes: we stay at the center of our survey area, take 5 minutes to establish a species presence list, and than proceed to enumerate and size all the fish in this list, one species at a time.  It's a little tricky, but you get the hang of it and get better the more times you do it.  There is a lot of training involved.

Divers counting small fish along transects

For some of the larger species we use what we call a towed-diver or towboard method.  These large fishes tend to exist in very low densities, that is to say, we don't find very many of them in a given area.  So, you have to cover a lot of area in order to get a good idea of how many there are at a given island.  The scientists who study these fish use dive planes which are towed behind a small boat along the coral reef for distances of up to a mile or more.

A towboarder flying over the reef

We fly these dive planes at a depth of about 50 feet and count all of the large fishes we come across during a 50 minute survey.  We don't count as many fish, but the ones we see tend to be bigger.  We see a whole variety of species including a lot of sharks.  On this expedition most of the sharks we have seen have been white-tip reef sharks (Triaenodon obesus) but we have also seen a few gray reef sharks (Carcharhinus amblyrhynchos) and tawny nurse sharks (Nebrius ferrugineus).  What is the biggest fish we have seen so far?  Definitely one of the nurse sharks which was about 6 feet long.  We have also seen some big dogtooth tuna (Gymnosarda unicolor).

Blackfin Barracuda (Sphyraena qenie)

Dogtooth tuna (Gymnosarda unicolor)

Small but Colorful

photo by Cristi Richards

A nudibranch (Chromodoris elisabethina) crawling along the reef

While many of the animals that people think of when someone mentions coral reefs are large or conspicuous like turtles, fish, and even the coral itself, other residents of the reef are small and easily missed. One such creature is the nudibranch.  Nudibranch literally means 'Naked Gills' which is appropriate because it breathes through a set of bushy external appendages on its back, sort of like wearing your lungs on your back. Nudibranchs, also sometimes called sea slugs, are a group of shell-less snails that live in all oceans of the world and at almost every depth. They are often very colorful but are easily overlooked because they are usually less than an inch long. They tend to be carnivorous, feeding on sponges, anemones, or other sea slugs and the 'horns' that you see at the front are actually sensory organs used for touch, taste and smell. They defend themselves either by blending into the algae or coral around them or by using bright colors to indicate that they are poisonous.  If you look closely, you may be lucky enough to spy one crawling along the reef.

A little more about corals

by Jean Kenyon, photo by Cristi Richards

While on the expedition we have received some excellent questions from students following the expedition.  From time-to-time we will try our best to answer as many of your questions as we can.  For Mr. Hill's period one class, here is a brief discussion on corals by Dr. Jean Kenyon:

Corals can reproduce in two major ways. One is by "sexual reproduction" in which an egg is fertilized by a sperm, which then develops over a period of time into an adult coral. Another way used by some, but not all, types of coral is "asexual reproduction", which usually involves a piece of the adult colony breaking off, becoming re-attached to the bottom, and continuing to grow. Sexual reproduction produces a genetically distinct individual, while asexual reproduction produces offspring that are identifical genetic copies of the parent.

More than 200 species of corals are known from Guam. Wake has been less well studied, but at least 80 species have been documented.

Corals get their color from two sources. Some of the color actually comes from colored pigment in microscopic algae (zooxanthellae) that live inside their tissue. Some, but not all, corals, have additional colored pigment inside their own cells.

For more information on corals, you might want to head over to this coral biology page put together by the Bermuda Biological Station for Research.  Corals exist all around the world in warm tropical waters and while the BBSR deals mainly with Atlantic corals, the basic biology remains the same.

Last days at Tinian

We finished surveys around Tinian a few days ago and it was one of the first really spectacular weather days we've had. We were treated to sunny skies and calm water with not a swell or white cap in site.  We were also treated to some amazing scenery ... as the last few islands we have explored (Guam, Rota, Aguijan, and Tinian) have all been composed of limestone that has dissolved through the years from the pounding of waves and rain. These combined forces have created some amazing caves and overhangs. Some of the caves are at the water's edge while others are half way up the cliff face. It has made for some dramatic transits between survey sites.

Unfortunately, one of our small boats (HI-1) wasn't having quite as good of a day as we were. It has been having intermittent transmission troubles for the last few days which clear up every time we bring the engineers out to take a look (kind of like when you take your car to the mechanic). On their last dive, while on the bottom, the REA team could hear the boat overhead and a rhythmic knocking as if there was tribal music playing.  Then everything went quiet and as they were swimming back to the boat, they noticed that the anchor line was out - not a good sign. The boat had evidently stopped working all together and a tow boat from the ship was on the way to bring them home. It was a very quiet, slow ride back with plenty of time to consider the luxury of such a large diving platform versus the inflatable Avon that they will be using until HI-1 is up and running again. So begins our adventures aboard Avons! Wish us luck ...

Plectroglyphidodon imparipennis

What is that? It's this guy:

How do you say it? Your guess is as good as mine.

Plectroglyphidodon imparipennis is the scientific name for the bright-eyed damselfish. So why can’t we just call it that? Common names for fish vary widely. Scientific names are more specific, and are used world-wide. Here at CRED, the fish team has come up with four-letter codes to make data recording a little easier. We usually use the first two letters of the genus, and the first two letters of the species name. So Plectroglyphidodon imparipennis would simply be PLIM. This is much easier to write underwater when you see many fish at once. It’s easier for our brains to say, “hmm, that’s 4 PLIM at 5 cm, 1 EPPO at 45 cm, and 4 GNAU at 22 cm.” Instead of writing down:
4 Plectroglyphidodon imparipennis’ at 5 cm, 1 Epinephelus polyphekadion at 45 cm, and 4 Gnathodentex aureolineatus’ at 22 cm. Here’s some interesting species we’ve seen so far:

Hoplolatilus starcki, or HOST, the starks tilefish

Triaenodon obesus, or TROB, a whitetip reef shark

Exallias brevis, or EXBR, the leopard blenny

Cirrhitichthys falco, or CIFL, the dwarf hawkfish

Here's Paula Ayotte pausing to write down some species codes during a survey:

and here's what a data sheet looks like after a survey:

If you are lucky and discover a new species, you get to name it. I think the species name kaylynii sounds great. Keep that in mind, all of you aspiring fish biologists.

Finished at Guam & moving on

We’ve spent the past 4 days (4/5-4/8) working in the waters surrounding Guam. Our scientific party conducted an impressive 204 dives in those 4 days. Twenty-five REA (Rapid Ecological Assessment) sites were surveyed for fish and benthic communities. The Fish and Benthic Tow-Board teams completed 23 towed-dives covering an astounding 46.8 km! In addition to all of those surveys, the Oceanography team successfully deployed/recovered a number of moored instruments and conducted CTD casts and water sampling. We have been busy!


Today we surveyed along the south side of the island of Rota. We have one more day here before heading to north to Aguijan and then Tinian.

Oceanography Update!

During our 5 days in port I had the opportunity to speak to some great people from Guam's 'Lets Do Science', about oceanography and the instruments we're putting in around Guam. We've got instruments to measure sea surface temperature, subsurface temperature and the sound of the reef.

Sea Surface Temperature Buoy

Temperature is important to know because, just like you and me, corals can only survive in the right temperatures -not too hot and not too cold.

We also put out an instrument that measures the sounds of the reef.

Acoustic Recorder
This gives us data on how noisy the reef is which gives us an idea of how healthy it is with animals, as they make noises going about their everyday business. We can also listen to how many boats there are in the area.

Today was our 3rd day at Guam and we have been roasted by the sun and thrown about by the waves, especially on the east side.
We've put in all our instruments now and seen amazing things around Guam.

Tomorrow is our last day, and we'll be doing water samples and measuring the temperature and salinity (how salty the water is) using an instrument called a CTD.

Feel free to send us any of your oceanography, cruise or any other questions and we'll do our best to answer them!

BYE!

You don't have to go far

Guam is littered with history and one needn't go very far to find it.  For the past few days we have been tied up at one of the piers at the US Navy base in Apra Harbor, Guam.  Leaving the ship one is greeted by a huge anchor, originally belonging to a Japanese ship sunk off of Saipan and recently brought to Guam.
Not too far down the road is an anti-aircraft gun emplacement still waiting for incoming planes.  While many of the artifacts have been moved from their original positions, a few can still be found where they have stood for the past 60 years.  A harsh reminder of turbulent times.
Unfortunately WWII also served to obliterate much of Guam's prior history with entire towns wiped off the map either by the occupation or by the shelling and bombing which proceeded the recapture of the island.  Near the eastern end of the naval base, a partial cemetery with broken headstones is all that remains of Sumay town.Guam was also a way station for the original trans-pacific cable line linking the US mainland to her interests in the far east.  The relay station at Sumay was a prime target during the Japanese invasion, and the ruins are still pockmarked with bullet holes and mortar damage. For many of us, our knowledge of this era is limited by the black-and-white footage and photographs of the war years and it is sobering and yet beautiful to see these monuments set against the brilliant colors of the tropical pacific.