Scorpion Spider Crabs
Category Archives: crustaceans
Crustacean Crevice Dwellers
I have done a fair bit of diving at Silver Steps this year and it is high time to publish some of the photos I took there, starting with the Crustaceans that inhabit the cracks in the rocks. Most pics were taken with the macro-wide angle lens, which is not only suited because of its perspective, but also because it is long and thin and so can be poked into the crevices where these creatures lurk. Above, two Velvet Crabs Necora puber, which are abundant and feisty – I only noticed the small female in the photo afterwards! Below a European Lobster Homarus gammarus, also quite common and some of them are quite big. They usually shuffle out of their den quite menacingly only then to retreat again. Although impressive animals, it is hard to get an aesthetically pleasing shot out of them I find.
Next, the Squat Lobster Galathea strigosa, also a common, but quite shy species which is just as happy upside down as right side up. Also common are Brown (or Edible) Crabs Cancer pagurus, the individual here not in a crevice but in a piece of steel wreckage.
The other big, common Crustacean here occasionally perches on rock walls but usually is found roaming the seabed: the European Spider Crab (rebranded by local fishmongers as ‘Cornish King Crab’ – sounds more appetizing than something spiderlike) Maja squinado brachydactyla. Like the lobster, the behaviour of these guys is a mixture of bravado and fear. The weird lens allows me to get close, but as it lets in very little light, I am forced to use a high ISO and slow shutterspeed, making these images not the crispiest.
The final photo is technically not great, but I like it because it shows how a range of species apparently gets on quite well at close quarters. On the left, a Common Prawn Palaemon serratus, which can grow quite large and is actually really beautiful with its blue and yellow stripes. Right behind it is a Squat Lobster, with two Edible Crabs lurking in the background and an upside down male Connemara Clingfish Lepadogaster candolii – the next post will be about the fish of Silver Steps!
A Late October Snorkel
Many other critters were found too and I took shots of a selection. First, a Sea Spider, all legs and crawling away. A tiny mat of colonial tunicate that looked like a persian rug on drugs. A quick shot of the ubiquitous (if you know where to look – on kelp fronds) blue-rayed Limpets and a stalked jellyfish. Finally, I spent a lot of time taking shallow-depth-of-field AND slow shutter-speed photos of a scorpion spider crab in a snakelocks anemone to get some sort of ‘artistic’ shot. It did not really work, but it was fun nonetheless and I will have a go at it again. After almost 2,5 hours in the water I stumbled back to the car to get changed – an afternoon well-spent!
Inachus
This seems like a familiar way to start a blog post but here I go again: ‘the weather has been terrible lately and I have not been in the water!’. March used to be my favourite time for snorkeling because the seaweeds look at their best, but the last three years it has been windy and wet, surely because of climate change…
To keep the blog going (a bit), I have dug out some images from a few dives last year featuring Inachus spider crabs. There are three species, I. phalangium, I. dorsettensis and I. leptochirus, which can be told apart by the arrangement of tubercules on their carapace, but these are often obscured by epiphyte growth, and so I am keeping it to Inachus sp. All species are associated with Snakelocks Anemone (Anemonia viridis) hosts. The photo above is taken using a weird ‘wide angle macro’ wetlens (INON UFL-M150 ZM80). This perspective always fascinated me but it is difficult to achieve. This lens does the job, although it is incredibly ‘soft’, especially around the edges. The close focusing also makes it difficult to direct the strobe light on the subject. So there is a tradeoff between getting the surroundings in view and sharpness. Below first some sharper shots using my 60mm macrolens, followed by some macro wide angle shots (they happen to be each of the different Anemonia colour morph):
I will leave you with the following interesting bit on the biology of these crabs by Diesel (Ethology, 1986):
I. phalangium females are site-constant, and live in the protection of one anemone or group. Males travel frequently between anemones harbouring females due to spawn; they copulate and guard the females until spawning, after which the male leaves again. A male operates in a patrol area containing 3-8 anemone groups and up to 8 females, visiting each female in turn repeatedly just before it is due to spawn. Patrol areas of different males may overlap, with resulting competition to fertilize a female’s next brood. Large males have higher reproductive success than small ones. Females live up to 8 months after the moult of puberty and hatch up to six broods, and males live up to 7 months as adults. A male could fertilize a calculated 26,000 eggs, whilst a female’s reproductive potential is ca. 4,200 eggs. Mortality risks are higher for males than for females, probably because of increased predation while leaving the protection of anemones in order to visit females. Males learn the positions of anemones harbouring females in their patrol areas, and when these are due to spawn. This allows a male to travel with a target and arrive punctually to fertilize the next brood due in his circuit. I. phalangium is the first marine invertebrate reported to use a “schedule” of localities and times for visiting prespawning females. In this way males minimize searching time and mortality risk, and maximize the number of broods fertilized.
Monster in a Barrel
Last Sunday we made the trek to Sennen Cove beach in the far west of Cornwall. I have not been in the water for weeks due to the windy weather (and it might be a few weeks before conditions improve), so the only way to get my fix is by going beach combing… With strong westerlies, this spot jutting out into the Atlantic seemed a safe bet, although when we arrived the strandline appeared quite sparse and I did not have hope of finding much. A single find by my eagle-eyed son however made the trip all worth it!
The photos above show the amphipod Phronima sedentaria inside its home, a hollowed-out salp. These small crustaceans use their claws to carve a home out of their barrel-shaped gelatinous host. This offers protection, and a space to rear their young. They occur worldwide in the open sea and are believed to vertically migrate from depths up to a kilometer to the surface each night. Although it was still actively wriggling about, it was essentially doomed after being washed up, so it was taken back in a margarine container filled with seawater and handed over to David Fenwick (www.aphotomarine.com) for further examination. He made some excellent photos of it, making clear why it provided inspiration for the ‘Alien’ movie! As I suspected from the size, this was a female, and brood was found in the salp tunic as well.
These things have been found before a few times in the UK (in Sennen and in the Scillies) but not commonly (4 records on the NBN Atlas and 0 on iNaturalist). I have recorded mine on the latter database (which means it can make its way to NBN as well). Let’s see what else the sea throws up this winter!
Dog Whelks at Kynance Cove
A trip to one of our favourite places today: Kynance Cove on the Lizard Peninsula. The weather was such that snorkeling was a big no, but after some wind and rain, luckily the sun came out for a bit (which it should, it is July!). I took some macro shots of the rocks at low tide using my new Cygnustech diffuser. This contraption makes the flash light much less harsh, and is pretty much essential when taking (non-natural light) macro shots. This is one of the best diffusers out there and I can highly recommended it (are plenty of reviews are available online). Some of the shots were taken with the Raynox DCR-250 macro attachment in front of the macro lens for a little bit of extra magnification.
Anyway, there is not a lot of animal diversity on this battered coast of green and red serpentine rock: barnacles, dog whelks, mussels and limpets mainly. Above a selection of photos highlighting some small Dog Whelks (Nucella lapillus). This predatory species can come in many more colour varieties than we found today (see here for example). The limpets are either the Common Limpet (Patella vulgata) or the Blackfooted Limpet (P. depressa); you need to be able to see the animal to be sure. The barnacles are Montagu’s Stellate Barnacles (Chthamalus montagui) (I might have this wrong; I must confess I never really gave barnacles the attention they deserve). Not too spectacular but you gotta try something when you cannot take photos underwater!
Tiny critters under rocks
When the viz is bad, I take my macrolens (sometimes with the Nauticam CMC-1 wetlens for a bit of extra magnification) out to the pools. Sometimes I stick to the surface of rocks and seaweeds (to look for stalked jellyfish for instance), but other times I turn over rocks under water to see what hides beneath. Quite a lot! There are larger animals, such as Topknots and different types of crabs (and Worm pipefish as pictured here) but mainly they are quite small (around a centimetre or even less). See the selection below (Tricolia, Bittium and Limacia were not from under rocks but I had to make the grid fit!).
Buoy Biodiversity
A while ago I played around with taking pics of the underside of a buoy, which was fun, and so i wanted to practice this some more. My mistake the first time (see here) was to use a fast shutterspeed (the buoy was bobbing about after all) which made the water look unnaturally dark. I tried again this weekend and it went a bit better, although I already know I can improve things. This time I thought it would be nice to put some names to the amazing fouling biodiversity (I did this before for some seaweed images, see here). Crustaceans (tube-dwelling Jassa), Sponges, Bryozoans, Seaweeds but especially a lot of Tunicates (seasquirts; both solitary and colonial species). David Fenwick (of AphotoMarine fame) had a quick look to help with some IDs; there is a more there but this was not meant to be exhaustive. I have underlined species that are invasive. Anyway, I am sure I will post more of these types of images: the buoys are always there and these organisms do not swim off when you try to take a photo!
Muddy Adventures
I went to the foreshore of our village with my son (9y) a week ago as he is always keen on some bare-handed eel catching. No pretty rock pools in this estuarine site, just mud, rubble, worms, oysters and sponges. Also Velvet Swimming Crabs (Necora puber) (named Devil Crabs locally as they are quite pinchy) and Rock Gobies (Gobius paganellus). I tried my hand at some TSCFWANF (Top Side Close Focus Wide Angle No Flash). This obviously resulted in a blown out sky. Next time I will try to use a home-made (milk container) softbox for a strobe to light up the foreground. Have not been in the water much, so long time no post. Hope to do some snorkelling or diving soon, weather permitting…
Rockpooling on St. Martins
Although St. Martins does not seem to have any rockpools, the beach that was nearest to us (called ‘Lawrences’) has a stretch of rocks lying on the sand that can be turned over at low tide, and so we did! A nice find was a small Sevenarmed Starfish Luidia ciliaris (these can grow up to half a meter across, although you will not find them that size in rockpools). We also found a Bootlace Worm Lineus longissimus, which is (probably) the longest animal on the planet. These nermertean worms secrete a powerful toxin in their mucus, but luckily for us it affects arthropods and not mammals. They are not very rare btw, I see them here in Flushing and Falmouth too. It was about 5 meters long (without stretching it), but they can grow ten times the size of this! In the second photo you can see it in its natural habitat, under a rock, with some photobombing crabs and worm pipefish. Another cool find was a juvenile Conger Eel Conger conger. Otherwise we found the usual suspects, lots of crabs and a bunch of fish, see for a small selection below.
Edible crab Cancer pagurus 
Furrowed crab Xantho hydrophilus 
juvenile Squat lobster Galathea squamifera 
Shore rockling Gaidropsarus mediterraneus 
an unusual reddish Cushion star Asterina gibbosa
