Hold that pose, little crab!

Yellowline Arrow Crab (Stenorhynchus seticornis), Caribbean
Yellowline Arrow Crab, getting situated on a sponge

Yellowline Arrow Crab (Stenorhynchus seticornis), Caribbean
A Yellowline Arrow Crab strikes a pose
by B. N. Sullivan

This series of photos depicts a Yellowline Arrow Crab (Stenorhyncus seticornis), a common Caribbean species.  With its distinctive pointy-headed spidery shape, bulging eyes, yellow knees and tiny purple claws, it is an interesting photo subject.  As we approached this individual, it skittered onto a bright orange sponge -- also quite photogenic.

But crabs are not always the best photo models.

In this instance, the crab first struggled to get situated on the sponge, as if it wasn't quite sure how to arrange all of those gangly legs.  A few moments later it was settled in place, and I snapped its portrait.

I began to move around a bit, hoping to catch it from a slightly different angle, but my crabby friend would have none of it.  Without a by-your-leave, the crab simply left the scene.

It was time to look around for another subject.

Yellowline Arrow Crab (Stenorhynchus seticornis), Caribbean
"I'm outa here...!" - Yellowline Arrow Crab

I took these photos of the Yellowline Arrow Crab during a night dive at Little Cayman Island.

Bearded Scorpionfish: A Name That Suits

Bearded Scorpionfish (Scorpaenopsis, barbatus), Red Sea
Bearded Scorpionfish (Scorpaenopsis, barbatus), Red Sea
by B. N. Sullivan

Meet the Bearded Scorpionfish (Scorpaenopsis barbatus).  Both the common and scientific names of this fish refer to the frilly, fleshy flaps of skin protruding from its chin.  (The Latin name "barbatus" translates to "bearded.")

Like others in its family, Scorpaenidae, the Bearded Scorpionfish is an ambush predator.  Its strategy is to lie in wait for its prey to come swimming past at close range, and then to spring forth with its mouth wide open to engulf its meal in one big gulp.  In order to do this successfully, it helps to be as inconspicuous as possible.  It helps to be camouflaged.

The scorpionfish usually rests on algae-covered rocks, or among corals and marine plants.  The frills on this guy's chinny-chin-chin are a part of its disguise, helping it to blend in with its usual surroundings.

Despite its elaborate camouflage, the individual in these photos was easy to spot since it was out in the open, resting on a patch of sand.  Hoping I could get a close-up photo of its head, I lay down on the sand, too, and inched toward the fish.  To my delight, my subject did not flinch or flee after the first shot, so -- still on my belly --  I was able to move around carefully and face him to take a head-on shot of his impressive 'beard' at close range.

Bearded Scorpionfish (Scorpaenopsis, barbatus), Red Sea
Bearded Scorpionfish (Scorpaenopsis, barbatus), Red Sea

A Beautful, Fragile Bryozoan Colony

Lace Bryozoan (Reteporelina denticulata)
Macro photo of a Lace Bryozoan (Reteporelina denticulata)
by B. N. Sullivan

This beautiful marine organism is a colony of Lace Bryozoa (Reteporelina denticulata).  Despite their appearance, Bryozoans are neither a coral nor a plant.  Taxonomically, the Bryozoa form a phylum all their own.  Most of the more than 4,000 species of Bryozoans live in the sea.

The name Bryozoa translates to "moss animal."  The individual animals that make up the colony are microscopic.  This species builds lacy calcareous structures of interconnected branches, made from the mineralized exoskeletons of thousands of tiny individuals.  The macro photo at the top of this page gives a good idea of how intricate and intertwined the branches can be.  It takes the colony of organisms a very long time to build these lovely structures.

The colonies are pretty, yet they are quite brittle and therefore very fragile.  If you come across a Bryozoan colony while diving, be careful not to touch it or bump it. The delicate structures will almost surely break if handled.

Almost all Bryozoans are sessile -- that is, the colonies are attached to some hard substrate like rock or hard coral.  The photo below shows a colony of Reteporelina denticulata growing on a hard coral (Porites lobata).  Once in awhile, a diver may come across a small Bryozoan colony that appears to be growing out of packed sand or mud, but closer inspection will almost certainly reveal that it is in fact attached to a rock or lump of coral rubble that is buried.

The Bryozoan species pictured here is rarely seen at depths of less than about 10 meters, but we have seen them on rocks below 40 meters.  In our experience, larger colonies are found at deeper depths -- perhaps because they are less likely to be disturbed and damaged by surge.

I photographed the Lace Bryozoan colonies shown here off the coast of Puako, Hawaii at depths between 20 and 30 meters.  The colonies pictured here are quite large for the species -- approximately four inches (10 cm) across.

Lace Bryozoan (Reteporelina denticulata)
Lace Bryozoan colony growing on coral in Hawaii

Basking Sea Turtles in Hawaii

Green Sea Turtle (Chelonia mydas), basking at Puako, Hawaii
Green Sea Turtle (Chelonia mydas), basking at Puako, Hawaii
by B. N. Sullivan

Imagine that you are in Hawaii, walking along near the edge of the ocean.  You come upon a sight like that in the photo at the top of this page -- a sea turtle lying on the sand or on the rocks.  You may notice that its carapace is dry, indicating that it has been out of the water for awhile. You may feel alarmed, wondering if it is stranded.  You think: Maybe a wave washed it ashore and it doesn't know how to get back into the ocean. Or perhaps it crawled out of the water intending to nest, but got stuck.

If it is a Green Sea Turtle (Chelonia mydas),  chances are very high that it has come ashore intentionally, it is not distressed or stranded, and it is not about to lay its eggs.  It is engaging in a behavior called "basking" -- another term for sun-bathing.

So far as anyone knows, only green sea turtles engage in this behavior, although no one is certain why they do it, or why they are the only sea turtle species who like to bask.  One proposed explanation for basking has to do with temperature regulation, since other kinds of reptiles are known to do this.  Another hypothesis is that basking ashore allows the turtles to rest for relatively long periods of time (hours) without risking predation, e.g., by sharks.

Regardless of the reason, Green Sea Turtles do come ashore regularly in many locations in the main, human-populated, Hawaiian islands, none of which are known to be nesting areas for this species.  They come ashore to bask in the sun.

So, if you come upon a turtle on the beach or rocks near a shoreline in Hawaii, what should you do?  You can watch them for awhile if you like -- just don't get close enough to disturb them.  You can photograph them, but please don't use a flash.  Don't try to move them or "help" them back into the ocean.  They need no assistance: when they are ready to go back to sea, they will do so unaided.  So don't block their path to the water, either!

Here are a couple more photos of basking turtles.  The first shows one turtle already basking while a second is preparing to "haul out."  The final photo shows a turtle who apparently has decided she has worked on her tan enough for the day, and is returning to the water.

Green Sea Turtles in Hawaii
Green Sea Turtles near the water's edge in Hawaii

Green Sea Turtle returns to the ocean after basking
A Green Sea Turtle returning to the ocean after basking
All of the basking sea turtles on this page were photographed at Puako, on the west coast of the Big Island of Hawaii.

For more information about this behavior of sea turtles in Hawaii, see:

Whittow, G.C., & Balazs, G.H. (1982). Basking behavior of the Hawaiian green turtle. Pacific Science, 36(2), 129-139 -  (11-page PDF)