Category Archives: Marine Invertebrates

Stick swimming crab

A stick swimming crab in the waters off the Big Island, Hawaii

This month, Becky’s April Squares challenge theme is ‘Bright.’ (See more responses here.) First up I thought I’d share something very unusual, which I consider myself lucky to have seen.

You’ve probably heard of stick insects, but the stick swimming crab is a far less often encountered creature. Most crabs scuttle about on the sea floor, but swimming crabs have flattened segments on their legs, which they use to propel them through the water. But even with this different method of propulsion, swimming crabs tend to stay close to the bottom.

The stick swimming crab (Charybdis baculum) has a different approach. It heads for the bright light at the surface where it paddles along, maneuvering with its spindly legs. It will sometimes snag bits of floating debris and attach them to its body to enhance its appearance. Its goal is to look like a small, drifting haven for juvenile fishes and other marine organisms that often gather under such floating islands, which offer them some protection from predators. With the stick swimming crab, that safety is an illusion. Instead, they’re part of the crab’s lunch box, to be picked off at its leisure.

Stick swimming crabs spend most of their time at the surface, but return to the sea floor for periodic molts. This one looks like it has recently molted.

Oh wait, it’s just a stick.

Also posted in response to this week’s Friendly Friday challenge theme of “Something Learned.” See more responses here.

Helmet urchins on the coast

This scene drew my attention because of the smooth, round rock nestled into a matching recess in the shore (bottom left in the top photo). It was when I zoomed in (bottom photo) that I noticed the large number of helmet urchins stuck to the shoreline. These cheerful-looking purple blobs live in the harsh tidal zone, and area of crashing waves and surging water. They feed on algae that grows there.

In the middle photo, an a’ama crab skirts a colony of urchins. When the tide comes in, the crab will move to higher ground, but the urchins will stay put, tenaciously defying everything the ocean throws at them.

Uplifting moments from 2020

This week’s Sunday Stills challenge theme is ‘Your 2020 Retrospective.’ See more responses here. Also posted in response to Becky’s January Squares challenge theme of ‘Up.’ See more responses here.

In this retrospective I’ve focused on events and photos that were uplifting for me during the difficult year that was. Most of these photos haven’t run before, but were taken at the same time as those in posts that ran in 2020. Links to the original posts are at the end of the captions.

Varicose phyllidia

This varicose phyllidia is a small nudibranch, which I saw several times over the course of a week or so. Apart from being a lot smaller than the clumpy nudibranchs I saw a couple of months back, the varicose phyllidia has gills under the mantle skirt rather than in an exposed, wavy clump.

This one was two to three inches long. In the middle photo, the tiny white-spotted toby and small brown surgeonfish give a sense of scale.

Day octopus squabble

A couple of days ago, I saw an octopus while snorkeling. It was on a vertical face of rock and when I showed up it slipped around the corner out of sight. I followed and could see it had gone into a recess there. I saw a tentacle moving and then, moments later, a round white thing appeared, a tentacle clasped around it.

I was mystified. I thought it might be the remains of an urchin or something. The white globe disappeared back into the depths. Moments later it appeared out of the side of the recess and it quickly became clear that the round white balloon was the head of another, completely white octopus. This white coloration is adopted when an octopus is feeling aggressive or threatened.

After a brief flurry of tentacles the white octopus disengaged, shot away a short distance, and changed color again as it landed on a rock. The octopus I’d first seen appeared again at the entrance of the recess. There was a little more to and fro before the evicted octopus gave up and moved away and the first octopus slipped back into the depths of the recess. My take on this was that the octopus I saw first wasn’t happy to find the other octopus in its lair and turfed it out.

The top photo shows the evicted octopus gathering itself after being run off. The second photo shows it on the move, still with the white coloration. The third photo shows the victor in the dispute, looking a little smug if I may say so.