Monthly Archives: February 2016


Nudibranch (pronounced noodabrank) means “naked gill”.  This refers to the gill-like appendages sticking out of the backs of most nudibranchs and is the organ that allows them to breath.  Most nudibranchs also have appendages called rhinophores, usually located at the head.  These have scent receptors and are used to taste, smell, and navigate.  Most nudibranchs can retract these tentacle-like organs into a pocket in their skin so they are protected from hungry predators.

Nudibranchs are Gastropods in the phylum Mollusca. They are related to snails, slugs, limpets, and sea hares.  Unlike other mollusks nudibranchs do not have shells as adults.  The shell is only found in the larvae stage and disappears when it becomes an adult.

There are over 3,000 species of nudibranchs and new species are being added to the list all the time.  Nudibranchs come in all sizes from just a few millimeters to over 12 inches and weighing up to 3 pounds like the beautiful Spanish dancer.   They can be a myriad of colors, spotted, striped or solid with trim. They are found in cold temperatures and warm temperatures.

There are two main types of nudibranchs dorids and eolids.  The dorids breathe through gills that are located on their backs in a cluster.  Eolids have appendages called cerata that can cover their entire backs and can be threadlike, club-like, branched or clustered in several groups.  The cerata have multiple functions including breathing, digestion, and defense.

Nudibranchs see only light and dark.  Information about their environment is gathered by the rhinophores or sense of smell and some by sense of taste through tentacles surrounding the mouth.  Nudibranchs and all other mollusks, have a radula, an organ with many tiny teeth, which they use to scrape up food.  All nudibranchs are carnivorous.  They feast on a variety of foods including sponges, hydroids, anemones, fish eggs, barnacles and even other nudibranchs.  Some species dine exclusively on one type of food and one species of that food.

The colors of nudibranchs come from the colors of the foods they ingest.  Color can camouflage them or, when bright and flamboyant, signal to predators that they are poisonous.  Some nudibranchs eat corals that contain algae. They absorb the algae’s chloroplasts and store them in their cerata where the chloroplasts will continue to photosynthesize and supply the nudibranch with nutrients.

What they eat can also supply a means of defense.  Eolid nudibranchs that eat organisms that have nematocysts, or stinging cells, can store them in their cerata and use them to sting predators if they are attacked.  Some dorid nudibranchs, like the fried egg nudibranch, have a unique defense system.  They secrete toxic slime that stinks and mucks up the water, warding off would-be predators.  True to their classification as slugs they do very little work to prepare these defenses. They simply absorb toxins manufactured by the foods they eat.  Not to stereotype the character of all nudibranchs, there are some industrious species of nudibranchs that manufacture their own toxins.

The majority of nudibranchs cannot harm humans.  Two exceptions are Glaucus atlanticus and a close relative Glaucus marginata.  They eat Portuguese man-o-war, absorb the nematocysts, and can use them to cause a pretty nasty sting even to humans.

All nudibranchs are hermaphrodites which means one individual is both male and female.  The lucky little guys can mate with any individual that happens by.  This is a plus because during the majority of a nudibranchs life they live alone and searching for a mate is inhibited by the fact that they never move very far and they can’t move very fast.  When two adults meet they each extend a tubular organ that they connect together and through this they fertilize each other’s eggs. The eggs are deposited in a spiral pattern, all rings evenly spaced from one another.  They are suspended in a gelatinous substance that holds them in place and gives the egg mass a ribbon-like appearance.  The larger “ribbons” of the Spanish dancer eggs can even look like an underwater rose.

Sadly nudibranchs don’t live very long.  Some live up to a year but most live only a matter of weeks.

Facts about some common Hawaiian nudibranchs:

Phyllidiidae varcosa, more commonly known as the Scrambled Egg Nudibranch or the Fried Egg Nudibranch.  The latter name seems more fitting to me because the white ridges on the body with the yellow spots resemble an egg white and yolk.  These are very commonly seen in the waters off Kona.  An individual can reach up to 3.5 inches (14cm) in length. They are common throughout the Philippines and the Indo-Pacific too.  The fried egg nudibranch, like all other Phyllidiidae species, will secrete a toxic mucous when disturbed.  This excretion is deadly to other marine animals.  The toxin comes from sponges they eat.  They eat the toxic sponges than store the toxin in their bodies to use as a defense mechanism.

Fried Egg Nudi (1)

Glossodoris rufomarginata also known as the White Margin Nudibranch is another species seen in Kona.  It is also found in other areas of the Indo-Pacific and the Red Sea. These are small nudibranchs ranging from 1-2 inches (2.5 to 5cm).  They will be found in depths of 15 to 100ft (5 to 30m) but I usually see them in the 25 to 35 foot (8-12m) range hanging on the ceilings of arch formations.

White Margin Nudi

Halgerda terramtuentis, the gold lace nudibranch, is endemic to Hawaii which means it is only found in Hawaiian waters.  They are abundant in Hawaii and can be found in shallow waters usually no deeper than 30ft (10m).  They grow to a maximum of about 2in (5cm).

Gold Lace Nudi

Pteraeolididae ianthina, or blue dragon nudibranch is an example of a nudibranch that gets its color from the food that it eats.  They eat hydroids that have zooxanthellae living in them.  The zooxanthellae photosynthesize to produce nutrients and this also produces the color that is transferred to the nudibranch when it eats the hydroid.  Curiously, just like plants, the zooxanthellae can produce different colors so the “blue” dragon nudibranch can be colors other than blue.  In Hawaii I have only seen blue colored blue dragon nudibranchs but they are found throughout the Indo-Pacific in various colors.  No matter the color of the body, they all have purple band markings on their oral tentacles. These nudibranchs also ingest the nematocysts of the hydroids, store them in their cerata and use them for self-defense.

Blue Dragon Nudi

Hiatodoris fellowsi is another endemic nudibranch.  Its common name, Fellow’s Nudibranch.  They are named after biologist David Fellows who was the first to collect a specimen.  These are strikingly beautiful nudibranchs with their snowy white bodies and contrasting jet black gills and rhinophores.

White Margin Nudi

~Stacey Herman

Black Water: Marlin

Anyone who has spent any time around Honokohau Harbor has seen a few of these strung up at the fuel pier. Marlin get huge, so it is excusable if you gawked in awe at the 400 pound dead sea monster on display, but the lifeless form is missing what makes them really special.  By nearly every measure, living marlin are probably the most impressive fish swimming in our oceans today.  For starters, they are world travelers.  One animal was tagged off the coast of Delaware and later recovered near Mauritius- a journey of over 9000 miles!  At 50 miles per hour, marlin are not only faster than anything most divers have seen underwater, they are faster than most speed boats.  And while that 400 pound animal may be more than twice your bodyweight, at 1400 pounds, the largest animal on record was more than 3 times a big as that.  Thus, I’d like to use this blackwater blog to celebrate the marlin for the oceanic apex predator that it is.  And I’d like to start with a little known species of odontocete called the dwarf sperm whale (Kogia sima).
Dwarf sperm whales have never been photographed underwater.  They are notoriously difficult to approach and are known for slipping under the water and descending just out of sight of humans.  So imagine my excitement as I found myself in the water with my camera as a pod slowly swam toward me!  The boat crew watched in near silence as their fins dipped below the surface, and the animals descended.  I may have seen a shadow in the distance, but that was probably my imagination.  I just floated hoping the animals would get curious and come back to play.  A minute or so later, the boat crew saw me nearly jump out of the water, muffling some sort of alarm through my snorkel.  Angry reef fish are quickly calmed by simply swimming away.  Even aggressive sharks can be stiff-armed.  But what can you do when a 12-foot long marlin charges you in blue water?
Marlin series (1)
Three photos taken in sequence during the encounter.
We have never seen an adult marlin on a blackwater dive, but we have seen quite a few of their young.  Marlin breed in the late summer and into the early fall and are capable of spawning as many as 7 million eggs at one go.  The resulting young (pictured below) will take 2 years to reach sexual maturity but grow at a rate of more than half an inch per day.  Out of that 7 million eggs, maybe one or two will reach sexual maturity and far fewer will reach the legendary benchmark of “grander” (over 1000 pounds).
Istiophoridae larva best 2 watermarked
Istiophoridae larva head on watermarked
Post flexion marlin photographed on a blackwater dive in May of this year (2015)
Fortunately for me, the apex predator granted me life as it decided to turn at the last minute (as seen in the sequence of photos above), but I’m afraid we have not been so sympathetic to the fish.  Blue marlin have declined by more than 30% of their population in just the last 14 years alone and fishing pressure for this species is increasing.  No blue marlin fisheries are considered to be sustainably managed. Thus, like other banner-species of ocean conservation such as oceanic sharks and even bluefin tuna, marlin are in a lot of trouble.  Sure, they provide a lot of meat, but because they are apex predators, pollutants such as mercury bioaccumulate in their tissues, so they have some of the highest levels of mercury (>.5 parts per trillion) of any marine fish!
-Jeffrey Milisen

Black Water: Sea Moth

When we speak of Gasterosteiformes in Hawaii, we are generally referring to the order of pipefishes and seahorses.  Offshore, that usually refers solely to the pelagic seahorse, Hippocampus fisheri.  We see seahorses infrequently in the late summer and fall, usually at a rate of one seahorse for every ten dives or so.  Imagine Bryce and my surprise, one night, when we came across a member of this family that we didn’t even realize was possible in Hawaii.

Meet the Hawaiian seamoth (Eurypegasus papilio).  Sea moths are related to seahorses, pipefish, sea dragons, and sticklebacks in that they all possess bony external plates.  Seamoths shed their plates, and in some cases they will go through a set of plates every 5 days.  As an adult, this strange little fish will settle in water between 80 and 115 meters deep from the Big Island to Kure.  The underslung mouth implies that the Hawaiian sea moth feeds on benthic animals, and the snout is probably used to help extricate small crustaceans from their holes in the sea floor.  For now, the young is limited to the epipelagic zone, attracted to our lights just like, well, a moth.

-Jeffrey Milisen

Black Water: Clown Squid

Young animals stay near the surface until maturity, but large ones like the squid pictured above, stay down deep and only come to the surface at night.  Adult animals are so rare, it is likely that none have been seen alive and only a few exist in museum collections.  A quiet hush fell over the blackwater divers when I picked up the large specimen for shipment to a cephalopod expert as we all realized that at our feet lay one of the rare night beasties that could show up on our favorite dive.  Once again, we are reminded of just how many animals we have yet to see down there.

-Jeffrey Milisen

Black Water: Beroe

Meet the Beroe

This week we celebrate the genus of ctenophores known as Beroe.  Ctenophores as a group all move by coordinating rows of beating cilia.  They occupy all marine ecosystems, can be quite large and their beauty will entrance even seasoned blackwater divers.  They have limited few rudimentary senses and no central nervous system.  Instead, they have a nerve net around the mouth. Ctenophores are hermaphrodites, thus they do not have male and female sexes and selfing-or self fertilization- has been observed in some species.  Unlike typical jellies in the phylum cnidaria, ctenophores do not produce nematocysts but can recycle nematocysts from cnidarian prey.  Instead, some species have cells called colloblasts that shoot an adhesive substance at prey. Most of the ctenophores that we observe on blackwater dives are clear and lack bioluminescence.  The brilliant colors that we see are simply our own lights refracting off the body of the animal.

While most other ctenophores play an important role in preventing over-abundances of copepods and small fishes in pelagic environments, the 24 species of Beroe keep their close cousins in check by eating other ctenophores.  They have evolved a sac-like body form that is capable of expanding to envelop and pinch off other gelatinous animals.  Beroid 5 watermarkedCtenophore Beroid watermarked
-Jeffrey Milisen

Black Water: Salp

A single salp oozoid that will never get laid.
Salps are the most common organism in the epipelagic environment and thus, far and away the most common animals we see on a blackwater.  Unlike most of the blackwater inhabitants, salps, aka tunicates or sea squirts, share our Phylum chordata.  That means that at some point in their lives they have a notochord.
I will be the first to admit that all of this taxonomy isn’t very interesting, so lets change the subject to sea squirt sex.  The individual oozoid stage is asexual and reproduces by selfing or making a whole bunch of genetic copies of itself in the form of a chain that can either be circular (cyclosalpa) or in a long string (salpa).  These chains are composed of a bunch of individuals known as blastozooids which are all attached by a complex network of “plaques” or information sharing connections that allow the salps to swim in a coordinated, synchronized fashion.  The blastozooid, or colonial, phase of a salp is the sexual one.  To simplify this, if you lived life like a salp, your kids, the result of sex with your spouse (or the mailman-we don’t judge at KHD!), would spawn a bunch of identical twins (reproduction through parthenogenesis) that would then go off to find someone else to reproduce with.
Are you creeped out yet?  No?  Because it gets weirder.  The blastozooid, or sexual form of a salp, undergoes sequential hermaphroditism. So they are females that produce female gametes (eggs) when they first mature, but eventually change sex into males as they get older.  While this process seems very complicated, it is also very efficient.  Salps can reproduce almost as fast as some bacteria!  That means that when conditions are just right (lots of phytoplankton food) they can bloom and inflict severe repercussions on the local plankton productivity.

Cyclosalpa blastozooid 2 small watermarked

Argonauta watermarked

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Cyclosalpa blastozooid colonies-These are many salp zooids in their sexual phase.

Phronima and eggs small watermarked

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The empty cavities of salp zooids are habitat for a whole host of organisms.  Look for crustaceans like this phronima, argonauta octopodes and even fish inhabiting the interior of salps.Salp oozoid 2 watermarked

Amphipods on pyrosome watermarked (1)

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Pyrosomes: A different kind of salp

-Jeffrey Milisen