Temperate water reef at Wemeldinge

One of the pontoon's many inhabitants: the Japanese skeleton shrimp, Caprella mutica.

At the east side of the harbour of Wemeldinge (Oosterschelde, the Netherlands) a pontoon is placed to protect it against waves and as a temporal mooring place for visiting ships.

Mart Karremans, one of the regular participants joining the surveys of the 'Strandwerkgroep Waterweg Noord' lives at Wemeldinge. He told us a few years ago about the wonderful marine fauna and flora that inhabits the pontoon. So since 2006 we made it a tradition to take a snorkeling trip to Wemeldinge. To one of the most exuberant overgrown places of the Oosterschelde. Last saturday we took a plunge. All photo's are taken at this pontoon from 2006 to July 2010.

The pontoon is made of concrete. Near the waterline live several common limpets, Patella vulgata (Dutch: schaalhorenslak).

A layer of Sargassum muticum, wireweed (NL: Japans bessenwier) protects animals like sponges, sea squirts and sea-anemones from sunshine.

And forms a substrate for sea squirts and moss animals and a hiding place for skeleton shrimps.

The green seaweed Codium fragile, felty fingers (NL: viltwier) lives just below the water line.

Typical growth on the pontoon: sessile species like sea squirts, sponges, sea anemones, barnacles, molluscs and seaweeds are fighting for 'lebensraum'.

As colourful as a tropical reef.

Until 2009 the pontoon was also in use for suspended cultivation: ropes were hanging from the pontoon, where mussels (Mytilus edulis) could grow. It seemed to be uneconomical on such a small scale and unfortunately the ropes were removed.

Bryopsis hypnoides (NL: onregelmatig vederwier). This green weed is branched irregularly and to all sides contrary to its cousin Bryopsis plumosa (NL: vederwier). The red seaweed in front is probably banded weed, Ceramium rubrum (NL: roodhorentjeswier).

Agardhiella subulata. A red seaweed with a 'fleshy' feel. One of the more recently introduced species.

Like wire weed, Undaria pinnatifida, wakame (NL: wakame; the name of this weed in Japan) is an invasive species, that originates from Japan. Like gigantic Octopus' arms!

This brown seaweed can grow up to 2 m. In Japan it is cultivated for soups, salads, food supplement and medicinal purposes.

The typical wavy stipe of wakame reminds me of millstone ruffs (NL: molensteenkraag), a popular fashion item from the second half of the 16th till the first quarter of the 17th century. Think of paintings by Rembrandt and contemporary artists. Click here for more information.

The first time I found wakame in the Oosterschelde I thougt it was dabberlocks, Alaria esculenta. The frond of this weed has more or less the same appearance. It has incisions and looks ragged. However, the incisions of dabberlocks aren't the 'original' shape: they are caused by beating waves. Dabberlocks is cultivated in Ireland (called Atlantic wakame!) for the same purposes as wakame .

Fighting for space: when there is no place left to go, the frond of wakame is a welcome substrate for barnacles (Balanus spec.).

The last few years I have been trying to take photographs of this tiny creature. Finally I was successful. These crustaceans who do resemble walking stick insects, are belonging to the order of the Amphipoda and have names like skeleton shrimp and ghost shrimp. In Dutch: spookkreeftje, wandelend geraamte, hongerlijdertje and teringlijdertje (however I prefer it written the way it is spoken: teringlijertje; especially with a Rotterdam accent!).

This is Caprella mutica, the Japanese skeleton shrimp (NL: machospookkreeft). Its former Latin name was C. macho. Macho it is. It is quite big for this Amphipod: I have seen specimens up to 40 mm. Other Caprellids are up to 25 mm.

And it can fight: I saw these two Japanese skeleton shrimps having 'a rumble in the jungle'. I am not sure which one won. This is also an invasive species, quite probably replacing our native species.

You can find them by the millions. I observed banded weed, Ceramium rubrum (NL: roodhorentjeswier), a red seaweed, expanding and shrinking in a second. Quite strange because weeds don't expand and shrink in a second or at all. But it wasn't the seaweed, it were hundreds of Japanese skeleton shrimps pulling back because of my appearance (just because I am big, not ugly).

Remember the film Aliens or Star Trek species 8742? Just fantasize this creature 5 meter high!

They feed by making 'kowtow's', slashing their claws - which are very big in comparison to their bodylength - forth and back. That way they collect little worms and crustaceans carried by the currents. As is quite common with crustaceans, they also cannabalise on little brothers and sisters or other species of Caprellids.

View from above. They are very thin, hence their common name.

Close up. The milky coloured protrusions are its gills.

Japanese skeleton shrimp with breeding pouch: the protrusion with the red dots. Back at home selecting and editing photo's is a time consuming job. But a rewarding one! It is a kind of arm chair marine biology. Magnifying photo's to 100% reveals a lot of creatures I hadn't recorded at the time. Thanks to Canon's excellent 5D II and Sigma's 50 mm macro (still waiting for a new version of Canon's 50 mm macro).

Opossum shrimps (order Mysidacea) can be found in hundreds near the pontoon.

Female with breeding pouch.

Opossum shrimp swimming in its typical upright posture.

Paleamon serratus, common prawn (NL: gezaagde steurgarnaal), the biggest prawn in Dutch waters. The pontoon and seaweeds offer a perfect hiding place for prawns, little crabs and fish. In Dutch such a habitat is called 'kraamkamer': a delivery room.

Palaemon elegans, rockpool prawn (NL: sierlijke steurgarnaal): the more common species in Dutch waters.

BEHIND THE SCENE

The magnificent six (photo 2010: Mart Karremans).

Entering the water at low tide can be hazardous, especially carrying your costly gear (photo 2009: Mart Karremans)

Jumping of another pontoon: not the proper way when carrying your camera (photo 2009: Mart Karremans).

Me with an Ewa-marine underwater housing. Okay for snorkeling, but not for diving (photo 2008: Mart Karremans).

My weekly dive and snorkel-buddy Ruud Versijde (right) and me, both equiped with Ikelite underwater housing (photo 2010: Mart Karremans).

The pontoon (photo's 2010: top and 2009: below: Mart Karremans).

Me in need of a lot more lead (photo 2010: Mart Karremans).

In my next post: sessile animals on the pontoon like sea squirts, sponges, sea-anemones and a few passer-by's.

Literature:

• Een aanwinst voor de in Nederland voorkomende Caprellidae: Caprella acanthifera (Leach, 1814): nu autochtoon op onze kust. Marianne Lighthart. Het Zeepaard, no. 2, 2010.
• Handbook of the Marine Fauna of North-West Europe, P.J. Hayward and J.S. Ryland, 1995. ISBN 0198540558.
• The Hamlyn Guide to the Seashore and Shallow Seas of Britain and Europe. A.C. Campbell and J. Nicholls, 1976. ISBN 0600343960.

The web:

For the most recent scientific name of species: MarBEF Data System

Smooth flutemouth (Fistularia commersonii): long mouthed bigeye

This is Fistularia commersonii, the smooth flutemouth. It looks like an amalgam of the needlefish (family Belonidae), the trumpetfish (Aulostomidae) and pipefish (Syngnathidea). It seems a bit prehistoric with its elongated body, long mouth and very big eyes.

Last January my wife and I were on a diving and snorkeling holiday at Kandooma, the South Male atoll of the Maldives. The last day we went snorkeling we took off with a boat to the 'house reef'. Before we left the jetty I saw a few strange, big-eyed elongated creatures hiding under it. So after this trip I went snorkeling under the pier. The water was a bit murky, but I could see the flutemouths making their appearance.

When it was light they were quite shy. After dark they were not as shy as I expected. They didn't seem to be bothered by my appearance and the flashlight.

The smooth flutemouth has a few other names: the reef or bluespotted cornetfish, the coronet and the gladde fluitbek (in Afrikaans, which is a kind of my native language).

Its common length is 100 cm, like the specimens I saw and photographed, but it reaches 160 cm. Its tailfin has a long filament. This filament is lined with sensory pores, which may serve as a long range sensory system for detecting prey.

The flutemouth hunts fish and small invertebrates, like crustaceans, squid and cuttlefish. It is active day and night. Litlle Red Riding Hood: 'Why do you have those big eyes? To see better in the dark....'

Its beak looks big but has a small finish. I am sure the flutemouth sucks its prey with a gigantic force into its mouth, snapping its prey in two. Just like pipefish do. This snapping sound of a relative small pipefish is easily heard. I would love to hear the snapping sound of the flutemouth! Hence its name?

© www.aquamaps.org

Look at the map fot its distribution. Not to be seen in this map: the flutemouth has made its appearance in the Mediterranean. It is a so called Lessepsian species: a species that has made its entrance in the Mediteranean through the Suez canal.

A few websites with information about this species (click on it for a direct link):

• fishbase.sinica.edu.tw
• discoverlife.org
• mexfish.com

Horn-eyed ghost crabs (Ocypode ceratophthalmus) of Koh Yao Noi

When visiting Koh Yao Noi, an island near Phuket, Thailand, in 2007 I was so fortunate to encounter and observe Horn-eyed ghost crabs, Ocypode ceratophthalmus (Pallas, 1772)(NL: Gehoornde spookkrab), on the beach.


I saw something moving on the beach, like a leaf blown by the wind. Just a leaf. Some time later it was something ghostlike, a swift moving transparent thing: the first ghost crabs. Very agile and - especially the small specimens - very well camouflaged. I saw one, and then more and more of these crabs scavenging the beach.


More


and more.


This is where they are hiding and appearing: self made burrows.


A young specimen leaving its burrow.

Features
Adults are easily recognised because of the long horned eyes. It gives them a funny appearance. Younger specimens are less easy to recognize: they lack the horned eyes. Poore (2004; see literature): ‘The stridulating organ, a rough area on the inside of the large cheliped (claw) is a more reliable character to differentiate the species.’ With this stridulating organ they can make sound. I can’t remember hearing a particular sound or it should be like the noise cicadas and later on the day crickets are making. Its carapace width is 40 mm and rather rectangular.


Captured to have a closer look. The only way to capture the ghost crab is to let it ‘escape’ into water, where it’s less agile. Observe the typical rectangular carapace.


All alone in the big ocean. Horn-eyed ghost crabs are semi-aquatic. They need water for reproduction and respiration. Staying too long in water they will drown.


After his more or less involuntary swim he touched ground: a few seconds later he ran away with amazing speed.


Excellent 360º sight.


A young(er) ghost crab without the typical eye-extensions.

Biology
Generally scavengers, they also feed on bivalve molluscs and will attack and eat turtle hatchlings and cannibalise members of their own species (Richmond, 2002). I can not remember a lot of hostility or seeing crabs with amputated claws or legs as is quite usual with species like Grapsus. When one came too close, the other crab(s) ran away. Maybe it is just a matter of having enough ‘lebensraum’.


I saw a lot of crabs sifting sand for organic matter.

Ghost crabs make deep burrows above the high tide mark. It was a real treat to observe the ghost crabs making or improving their burrows.


Poore (2004): ‘They rarely leave the burrow during the day. At night however they run quickly over the beach where they scavenge and are known to forage almost a kilometre away from the sea.’ The Ko Yao Noi-ghost crabs were very active during the day. Maybe there aren’t many predators on the island, so they can be bolder. And there was enough organic matter to scavenge on the beach at ebb tide.


The first excavation. The sand is blocking a perfect (360º) view. Dangerous: predators like birds - coming from the right position and keeping low - could ambush.


So throw it a bit further away.


This crab, making or renovating a burrow, is clever. He doesn’t want the sand blocking his sight around the burrow. So he makes balls of sand and moves them out of sight.


After all this hard labour he was ‘dancing’ on the sand near the burrow. Not for joy: by trampling on the sand the surface will get even smoother. And maybe it gets more solid, so the entrance of the burrow will stay firm.


An entrance with typical smoothing patterns. The sand thrown out of the burrow is still moist.


Typical treading patterns near the entrance of a burrow.

These crabs are well adapted to living in burrows. Branch (1983): ‘Ghost crabs have a cavity on either side of te body between the bases of the third and fourth legs, which is fringed with hairs. These hairs serve to suck water from damp sand and pass it through the cavity to the gill chamber. They also serve to filter the water to exclude sand or mud.‘

Distribution
Its distribution is the Indo-Pacific, so for me as a Dutchman it is as exotic as it looks.

Searching the web
I found an interesting and extensive report of the off-road vehicle-impacts on beaches in Australia. With a frontphoto of a crushed horn-eyed. Click here.

Literature:

• Branch, M. & G., 1983. The living shores of Southern Africa. ISBN 0869771159.
• Edgar, G.J., 1997. Australian Marine Life, the plants and animals of temperate waters. ISBN 187633438X.
• Poore, G.C.B., 2004. Marine Decapod Crustacea of Southern Australia. ISBN 0643069062.
• Richmond, M.D., 2002. A field guide to the seashores of Eastern Africa and the Western Indian Ocean Islands. ISBN 9158687831.

Hiding in its burrow in the evening.

Click here for other photos of this crab.