Day
16 - La Perouse Pinnacle
October 23, 2006
By Andy Collins,
NOAA, NOS, NWHIMNM -
Education and Outreach Specialist
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La
Perouse Pinnacle
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The most obvious feature of French Frigate Shoals is La Perouse Pinnacle, a single basalt stack with a smaller basalt outcropping to the West that rises out of central part of the atoll’s lagoon. It is like the last act of defiance of the sinking and eroding volcano that once rose high above the surface, like the main Hawaiian Islands, but is now completely submerged and covered with a thick layer of coralline skeleton, all but La Perouse. At night the pinnacle has been said to take on the appearance of a sailing ship, and in the whaling days of the 1800s, when ships transited the Northwestern Hawaiian Islands to reach the Japan whaling grounds far to the West, several tried to approach the mistaken pinnacle and foundered on the reefs that surround it. The near vertical slopes of La Perouse, despite being basalt, are painted a dull white from seabird guano deposited over countless years and this may have contributed to its mistaken identity in the past, appearing as the main mast sails of a sailing ship. The guano certainly contributes to the teeming diversity of life below the surface, and the survey team had an extremely productive day there yesterday, finding many species not found from other habitats around the atoll.
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La Perouse Canyons |
Since La Perouse is the only rock substrate found in the atoll it provides a unique habitat for organisms that need or prefer a non-corraline surface to attach to. Several species of algae not found elsewhere were found here, and the enriched water from the bird guano may also provide additional nutrients that fuel the species diversity. The undersea surface surrounding the pinnacle is also quite diverse in three-dimensional structure, with rock canyons, boulders, and a cave that forms a tunnel through the pinnacle. There are several other caves and ledge features as well, and these provide unique habitats where the scientists collected sponges and ascidians not found anywhere else in the atoll. In addition to providing many unique micro-habitats for organisms, the pinnacle also appears to be a favored congregating spot for large schools of fishes, ulua, a monk seal or two, reef
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Ulua |
sharks, and turtles. The tunnel that goes through the pinnacle is particularly
exciting since strong currents surge through it and scuba divers, and whatever
else is around the entrance, get sucked into it like a giant vacuum. On our second
dive I was nearing the entrance of the tunnel when I saw Jim Maragos and John
Starmer hurled backwards out of the tunnel, as if swimming frantically away from
a large shark. It was not until I verified that they were okay, and approached
the tunnel myself, that I realized what was going on and got sucked through myself,
along with a big ulua who seemed to be playing in the surge.
As with my few other dives on this expedition I tried to keep my eyes trained on the bottom, on the lookout for the tiny and strange. Many of the organisms collected during this expedition are so tiny you need a microscope to identify them, and are frequently collected by methods other than hand collection – they are sucked up through the underwater vacuum, or brushed off a piece of coralline rubble and trapped by a fine mesh net, some are brought onto the ship encased in their rubble pieces, only to be discovered when the rubble is broken apart. At night a loud banging permeates through the floor of the room I work in, as safety goggle-clad biologists crack the rubble with hammer and chisel. The other day I was watching this and a four-inch long stomatopod called a mantis shrimp popped out of what appeared to be solid rock (actually coral skeleton, but hard as rock!).
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Blue
Dragon Nudibranch.
Photo:
Andy Collins.
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I am not one of
the critter collectors, but merely the outreach guy, so when I am with the field
teams I stick to observation, and trying to figure out just how in the heck these
scientists see these tiny critters moving on the surface when I can barely see
them even isolated in small plastic cups in the lab. Anyway I try, but at La
Perouse I have to admit almost complete failure since I was utterly entranced
by the HUNDREDS of large blue dragon nudibranchs, Pteraeolidia ianthina (Angas,
1864). It was like a nudibranch NASCAR event down there. Everywhere I looked,
dragon nudibranchs. I must have taken 80 pictures of these marvelous critters,
one curled on top of an orange sponge, one luxuriantly spread across a patch
of deep red corraline algae, another resting in the shade of the even more abundant
limu kohu, Asparagopsis taxiformis. (I only know the genus and species of that
last seaweed because my friend Sabra Kauka, a teacher, and a Native Hawaiian
from Kauai, nearly lost all her saliva staring at these beautiful red marine
plants last year when she snorkeled at La Perouse as part of the Boatload of
Educators cruise. Limu kohu is a favored food seaweed of Hawaiians, and sadly
is not seen in such abundance in the main Hawaiian Islands as it used to be.)
Blue dragon nudibranchs feed on hydroids which are a type of cnidarian, like corals, that have stinging cells and catch their prey from the water column and kill or stun them with venom. Blue dragons also have zooxanthellae (algae) in their tissues, like corals, and the food (carbohydrates) they produce from photosynthesizing help to sustain the nudibranch. This symbiotic relationship between the nudibranch and the algae may also be a reason why this particular critter is so readily spotted, since it needs to be out in the open for enough sunlight to reach its tissues and the zooxanthellae within. I also learned from Cory Pittman, our resident nudibranch expert, that blue dragon nudibranchs like exposed basalt rock and areas with a lot of water movement, like at La Perouse, and this may be another reason why they were so abundant.
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Yellow sponge. Photo: Andy Collins. |
After nearly wasting my camera battery taking pictures of the little blue
dragons I moved on to the corals, the sponges, and the algae. I saw odd yellow
sponges like hairy tubes, and flat orange sponges, black sponges like the surface
of the moon, and this neat purple sponge that we collected at other locations,
and we collected it here because it may tell an interesting story. Leslie Harris,
our polycheate (worm) expert has been looking closely at all the sponges we have
been collecting since she found some interesting worms in the sponges that a
few of the homolid (collector) crabs brought up with them in our deepwater traps.
The homolid crabs have a specialized pair of clasping rear appendages that they
use to hold a piece of sponge, or even deepwater coral, above their body, either
for protection, camouflage, or for some other reason we don’t know. Anyway,
these crabs came up with pieces of sponge that we rudely took away from them
and examined under the microscope, and Leslie found species of worms, including
one with weird crustacean parasites in it. A few days ago Leslie examined a purple
sponge we had hand collected and found a species of alpheid shrimp (snapping
shrimp) inside it. Snapping shrimp are the ones that make all that crackly racket
that you hear while snorkeling on the reef.
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Purple
sponge |
Alpheid shrimp are commonly found in association with sponges, but what is unique
about Leslie’s find is that she appears to have found two forms of the same shrimp
species inside the sponge. About 10 years ago Emmit Duffy documented two species
of alpheid shrimp that live in association with big vase sponges in the Caribbean,
and these shrimp were found to be eusocial, that is, they have a caste system,
like ants and bees in which the same species has different body forms divided
by task and ability to reproduce. Ants have a queen that can reproduce, and workers
and soldiers that cannot, and they care for the young. Duffy found the same thing
in these alpheid shrimp in the Caribbean, a eusocial crustacean. No eusocial
alpheids have ever been described in the Pacific. If the alpheid shrimp Leslie
found in association with the purple sponge are found to be eusocial then it
could be a notable discovery. We may not be able to determine if these shrimp
are indeed eusocial crustaceans on this trip, but it is certainly a subject that
will need further investigation.
When we came up from our second dive
at La Perouse the wind was up, and the sky was grey, and lightning could be seen
off in the distance. We decided to run for the safety of the ship, while the
other small boat remained. In addition to having an amazing day of collecting
and surveying the folks in the other boat got to see an unusual site, the great
guano waterfall of La Perouse, as the skies opened up and unloaded enough rain
to nearly fill one of their 5 gallon collecting buckets in only an hour and a
half. Luckily for us, during that time, we were happily drinking hot chocolate
and eating chicken soup in the galley, sharing tales of blue dragons and stranger
things.
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Sabra’s garden – limu kohu at La Perouse Pinnacle. Photo: Andy Collins |
*All images and information from French Frigate Shoals are provided
courtesy of the Northwestern Hawaiian Islands Marine National Monument,
Hawaiian Islands National Wildlife Refuge, the Northwestern Hawaiian
Islands State Marine Refuge, and NOAA's Pacific Islands Fisheries
Science Center in accordance with permit numbers NWHIMNM-2006-015,
2006-01, 2006-017, and DLNR.NWHI06R021 and associated amendments.
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