9 July 2010

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.


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.

  • 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