URCHIN RESEARCHIN’: SEA HEDGEHOGS OF THE REEF


Long-spined sea urchin Diadema antillarum (Melinda Rodgers / Dive Abaco)

URCHIN RESEARCHIN’: SEA HEDGEHOGS OF THE REEF

The long-spined sea urchin Diadema antillarum featured in this post is one of those creatures that handily offers its USP in its name, so you know what you are dealing with. Something prickly, for a start. These are creatures of the reef, and many places in the Caribbean and in the western Atlantic generally sustain healthy populations.

Long-spined sea urchin Diadema antillarum (Melinda Rodgers / Dive Abaco)

These animals are essentially herbivores, and their value to vulnerable coral reefs cannot be overstated. Where there is a healthy population of these urchins, the reef will be kept clean from smothering algae by their methodical grazing. They also eat sea grass.

Long-spined sea urchin Diadema antillarum (Melinda Rodgers / Dive Abaco)

HOW DO THE SPINES OF DIFFERENT KINDS OF URCHIN COMPARE?

Small sea urchins species have spines a few cms long at most. The long-spine variety exceed 10 cms, and the largest may have spines up to 30 cms (= 1 foot) long. The length, as shown here, means that when the creatures are safely lodged in crevices near their algae supply, their spines remain very visible.
Long-spined sea urchin Diadema antillarum (Melinda Riger / G B Scuba)
Anatomy of a long-spined sea urchin. You may possess a few of these organs yourself…

Long-spined sea urchin Diadema antillarum anatomy diagram (wiki)

Long-spined sea urchin Diadema antillarum (Melinda Rodgers / Dive Abaco)

CAN YOU GIVE US A TEST, PLEASE?

As with SAND DOLLARS and similar creatures, the skeleton of a sea urchin is known as a ‘test’. Urchin tests are remarkably beautiful, especially seen in sunlight. Here are 2 examples I photographed a while ago. You’ll immediately notice the delicate colours and the amazing complexity of the pattern and symmetry. The top one is (or is most like) a long-spined urchin test.
Long-spined sea urchin Test / Skeleton Diadema antillarum (Keith Salvesen / Rolling Harbour) Long-spined sea urchin Test / Skeleton Diadema antillarum (Keith Salvesen / Rolling Harbour)

A BIT ABOUT SYMMETRY

Sea urchins are born with bilateral symmetry – in effect, you could fold one in half. As they grow to adulthood, they retain symmetry but develop so-called ‘fivefold symmetry’, rather as if an orange contained 5 equal-sized segments. The graphic above gives a good idea of how the interior is arranged inside the segments.

Long-spined sea urchin Diadema antillarum (Melinda Rodgers / Dive Abaco)

A FEW FACTS TO HAND DOWN TO YOUR CHILDREN

  • Urchin fossil records date the species back to the Ordivician period, c 40m years ago
  • In the ’90s the population was decimated and still has not recovered fully
  • Urchins feel stress: a bad sign that the spines here are white rather than black
  • Urchins are not only warm water creatures: some kinds live in polar regions
  • Urchins are of particular use in scientific research, including genome studies
  • Some urchins end up in aquariums / aquaria, where I doubt the algae is so tasty
  • Kindest not to prod or tread on them
  • Their nearest relative (surprisingly) is said to be the Sea Cucumber 

Sea Cucumber (Melinda Riger / G B Scuba)

ARE THEY EDIBLE?

Apparently they are eaten in some parts of the world; their gonads and roe are considered a delicacy. As far as I know, they are not generally on the menu in the Bahamas. Correction invited. Personally, I could leave them or leave them.

CREDITS: Melinda Rodgers / Dive Abaco (1, 2, 3, 6, 9) taken Abaco; Melinda Riger / G B Scuba (4, 10, 11) taken Grand Bahama; Keith Salvesen / Rolling Harbour (7, 8) taken Abaco; Wiki graphic (5) taken from internet. RESEARCH Fred Riger for detailed  information; otherwise the usual magpie pickings…

Long-spined sea urchin Diadema antillarum (Melinda Riger / G B Scuba)

TUNICATES: SESSILE ASEXUAL SEA-SQUIRTS


Painted Tunicates Bahamas (Melinda Riger / GB Scuba)

TUNICATES: SESSILE ASEXUAL SEA-SQUIRTS

Painted Tunicates Clavina picta are one of several species of tunicate ‘sea-squirts’ found in Bahamas and Caribbean waters. These creatures with their translucent bodies are usually found clustered together, sometimes in very large groups. One reason for this is that they are ‘sessile’, unable to move from where they have taken root on the coral.

Painted Tunicates Bahamas (Melinda Riger / GB Scuba)

HOW DO THEY FEED?

Like most if not all sea squirts, tunicates are filter feeders. Their structure is simple, and enables them to draw water into their body cavity. In fact they have 2 openings, an ‘oral siphon’ to suck in water; and an exit called the ‘atrial siphon’. Tiny particles of food (e.g. plankton) are separated internally from the water by means of a tiny organ (‘branchial basket’) like a sieve. The water is then expelled. 

Diagram of adult solitary tunicate

Painted Tunicates Bahamas (Melinda Riger / GB Scuba)

WHAT DOES ‘TUNICATE’ MEAN?

The creatures have a flexible protective covering referred to as a ‘tunic’. ‘Coveringates’ didn’t really work as a name, so the tunic aspect became the name. 

Painted Tunicates Bahamas (Melinda Riger / GB Scuba)

IF THEY CAN’T MOVE, HOW DO THEY… (erm…) REPRODUCE?

Tunicates are broadly speaking asexual. Once a colony has become attached to corals or sponges, they are able to ‘bud’, ie to produce clones to join the colony. These are like tiny tadpoles and their first task is to settle and attach themselves to something suitable – for life – using a sticky secretion. Apparently they do this head first, then in effect turn themselves upside down as they develop the internal bits and pieces they need for adult life. The colony grows because (*speculation alert*) the most obvious place for the ‘tadpoles’ to take root is presumably in the immediate area they were formed.

 

Painted Tunicates Bahamas (Melinda Riger / GB Scuba)

APART FROM BEING STATIONARY & ASEXUAL, ANY OTHER ATTRIBUTES?

Some types of tunicate contain particular chemicals that are related to those used to combat some forms of cancer and a number of viruses. So they have a potential use in medical treatments, in particular in helping to repair tissue damage.

Painted Tunicates Bahamas (Melinda Riger / GB Scuba)

Credits: all fabulous close-up shots by Melinda Riger / Grand Bahama Scuba; diagram from depts.washington.edu; magpie pickings with a particular mention of an article by Sara MacSorley

Painted Tunicates Bahamas (Melinda Riger / GB Scuba)

 

LETTUCE SEA SLUGS: SOLAR POWERED ‘CRISPY BLISSFUL HEAVEN’


Lettuce Sea Slug, Bahamas (Melinda Riger / G B Scuba)

LETTUCE SEA SLUGS: SOLAR POWERED ‘CRISPY BLISSFUL HEAVEN’

The Lettuce Sea Slug Elysia crispata (transl. ‘Crispy Blissful Heaven’) was No.3 in the ‘WTF’ ‘What’s That Fish’ series (despite not actually being a fish at all). It is not by any means the weirdest creature featured so far but it is nonetheless an animal whose appearance excites curiosity. Unless you see one moving, it could easily be mistaken for a plant. Maybe even lettuce. It is in fact a SACOGLOSSAN.

Lettuce Sea Slug, Bahamas (Melinda Riger / G B Scuba)

The name ‘sacoglossan’ literally means ‘sap-sucker’. This group (or ‘clade’) comprises small gastropod mollusks that ingest the cellular content of algae (which isn’t really sap).

WHY WOULD THEY DO THAT?

Because they are… SOLAR POWERED slugs

Lettuce Sea Slug, Bahamas (Melinda Riger / G B Scuba)

WHAAAAA…..?

As I mentioned when I last visited these remarkable creatures, this isn’t a technical forum and too much science hurts my head. This species primarily lives off algae. May I give you the word KLEPTOPLASTY to drop lightly into your conversation? In a couple of sentences, algae / algal content is eaten but only partially digested. Certain elements are stored to produce photosynthesis by which light is converted to energy (cf plants) and the slug can in effect live and move around without food. You could entertain your neighbour at dinner (or maybe on public transport, why not?) by summarising the process as “chloroplast symbiosis”. Meanwhile, I’m fetching a beer. Two beers.

Lettuce Sea Slug, Bahamas (Melinda Riger / G B Scuba)

HOW DO THEY REPRODUCE?

This topic doesn’t seem to have excited much investigative interest, and there’s not much specific information about it. What there is sounds unnecessarily complicated, so I am just going to say authoritatively ‘they do it like many other slug species’ and hope that covers it. The pair shown below may be exploring the possibilities, or at least trying to work out which end is which. One is easy to tell, but the other? Time to make our excuses and leave…

Elysia_crispata_(Lettuce_Sea_Slug_pair) Nick Hobgood

HOW FAST, EXACTLY, DOES A LETTUCE SEA SLUG MOVE?

This rather beautiful video from ‘CORAL MORPHOLOGIC STUDIO’ will reveal all. You’ll soon see that progress is very slow. I recommend watching the first 30 seconds and you’ll get the idea. If you choose to persist, you will see the slug sort of turn and move off to the left.

DO SAY:        What an intriguing creature. It’s a true wonder of marine nature.

DON’T SAY:  Any good in a mixed salad?

Lettuce Sea Slug, Bahamas (Melinda Riger / G B Scuba)

Credits: Melinda @ Grand Bahama Scuba, Nick Hobgood, Coral Morphologic Studio, Laszlo Ilyes wiki

Lettuce Sea Slug (Laszlo Ilyes)

PREHENSILE TALES FROM THE REEF (3): SEAHORSING AROUND


Seahorse (Adam Rees / .Scuba Works)

PREHENSILE TALES FROM THE REEF (3): SEAHORSING AROUND

It’s Friday at last. It’s springtime. A spirit of benign goodwill is evident in the vicinity of Rolling Harbour. Seahorses are irresistible. Don’t even try to pretend they don’t make you smile. Hippocampophobia is an affliction that, as yet, has never been diagnosed in a human being – for whom fear of beards, clowns and the number 5 (quintaphobia) are known medical conditions. Immerse yourself with these little creatures – and then have a good weekend.

Seahorse (Adam Rees / Scuba Works)Seahorse (Adam Rees / Scuba Works)Seahorse (Adam Rees / Scuba Works)Seahorse (Adam Rees / Scuba Works)Seahorse (Adam Rees / Scuba Works)Seahorse (Adam Rees / Scuba Works)

All fantastic hippocampi photos: Adam Rees / Scuba Works

REMARKABLE REEF CREATURES TO ADMIRE


Octopus (Adam Rees : Scuba Works)

REMARKABLE REEF CREATURES TO ADMIRE

Here is a small collection of recent photographs from Adam Rees of Scuba Works. Three OCTOPUSES, an astounding FROGFISH,  a SEAHORSE, a MANTIS SHRIMP at close quarters, and a wonderful HAWKSBILL TURTLE. Clicking on a link will take you to a post with more photos and information about each creature. If these images don’t make you want to scuba then… what will?

Frogfish Hunting (Adam Rees : Scuba Works)Seahorse (Adam Rees : Scuba Works)Mantis Shrimp (Adam Rees : Scuba Works)Octopus 3 (Adam Rees : Scuba Works)Hawksbill Turtle (Adam Rees : Scuba Works)Octopus 2 (Adam Rees : Scuba Works)

All photos Adam Rees / Scuba Works, with thanks for use permission

‘WTF?’ IN BAHAMAS WATERS (3) : LETTUCE SEA SLUG


Lettuce Sea Slug ©Melinda Riger @ Grand Bahama Scuba copy

  ‘WTF?’ IN BAHAMAS WATERS (3): LETTUCE SEA SLUG

The ‘WTF’ series so far has covered Bahamas reef fish on the bizarre end of the unusual-to-completely-weird appearance spectrum. And it has stood, of course, for ‘What’s That Fish?’. Today, it doesn’t. The feature creature isn’t a fish at all; it looks like a plant; it is in fact a SACOGLOSSAN – specifically the Lettuce Sea Slug Elysia crispata

The head end is on the left…Lettuce Sea Slug ©Melinda Riger @ G B Scuba copy

The name ‘sacoglossan’ literally means ‘sap-sucker’ (the sapsucker bird has a different latin name, however). And the slug’s frilly edges supposedly resemble certain types of curly lettuce. I’ve no idea where the ‘crispata’ comes from, but I am sure it doesn’t relate to crisp lettuce. These are creatures of shallow, clear waters such as the sub-tropical reefs of the Bahamas.

Lettuce_Sea_Slug_LASZLO ILYES

 ‘SOLAR POWERED SLUGS’

This isn’t a technical forum and too much science hurts my head. This species primarily lives off algae. However I give you the word KLEPTOPLASTY to drop into your conversation. In a sentence, algae is eaten but only partially digested; certain elements are stored to produce photosynthesis by which light is converted to energy and the slug can live without food. But baffle your neighbour at dinner, why not, by summarising the process as “chloroplast symbiosis”. Meanwhile, I’m fetching a beer.

Lettuce Sea Slug ©Melinda Riger @ GB Scuba copy

My research suggests that very little is known about the mating behaviour of these slugs. The pair shown below may be exploring the possibilities, or at least trying to work out which end is which. One is easy to tell, but the other? Time to make our excuses and leave…

Elysia_crispata_(Lettuce_Sea_Slug_pair) Nick Hobgood

HOW FAST, EXACTLY, DOES A LETTUCE SEA SLUG MOVE?

This rather beautiful video from ‘CORAL MORPHOLOGIC’ will reveal all. You’ll soon see that progress is very slow. I recommend watching the first 30 seconds and you’ll get the idea. If you choose to persist, you will see the slug sort of turn a corner to the left.

Credits: Melinda @ Grand Bahama Scuba, Laszlo Ilyes, Nick Hobgood, Coral Morphologic, Wiki