14 October 2009

Grey seals, gannet and other discoveries

A week ago I made a wonderful trip with Mart Karremans and Herman Nijhuis, two 'strandwerk'-friends, to the Westerschelde. We took kayaks to go to the Hooge Platen, a sandbank.

There is a small dune on the sandbank. It even has a name: De Bol.

Herman and Mart searching and studying molluscs. I went looking for patterns, shapes and colours.

The oysters had wonderful colours. The red-brown colour is due to iron in the ground.

A bivalve heavily pierced by the boring sponge Cliona celata.

Even rubbish is a photo opportunity.

When we approached it from behind, we first thought it was a great northern loon, Gavia immer (NL: ijsduiker). When we saw its head it was obvious: a juvenile gannet (Morus bassanus). I adore adult gannets with their beautiful yellow head fading into white, just as juvenile gannets, with their patterned feathers. We couldn't establish its cause of death.

It was perfect weather and a calm sea, so Mart and I decided to kayak to another sandbank near Breskens. En route we encountered around 15 grey seals (Halichoerus grypus).

It looks just like a submarine. Grey seals, especially the males, are impressive animals. The bridge of their nose is higher and make them look less cute than the harbour seal, Phoca vitulina (NL: gewone zeehond). Males can reach 2,3 meter and weigh to 310 kilo. Two times I saw a seal jumping out of the water like a dolphin.

They were very curious and 5 seals followed us to the other sandbank. As soon as we landed, they lost their interest. When we paddled back, they followed us in minutes.

Photo: Mart Karremans

One of the beautiful patterns. More of this natural art I will soon reveal on my weblog: mick otten's nieuws van het fotografenfront
Wipe that stupid grin of your face! Sorry: kayaking with friends, perfect weather, curious grey seals and beautiful sand patterns. Why should I stop grinning?
Photo: Mart Karremans

1 October 2009

Botrylloides and other tunicates I could not remember...

Colonies of Botrylloides diegensis or violaceus with hundreds of skeleton shrimps (Caprella spec.)

Having a blog and my last post was 3 march 2009... It's about bloody time for an update!

This post is about tunicates, also called sea squirts or ascidians. As strange as it may seem, these animals are chordates: in their short larval state they have a dorsal nerve cord that disappears when they settle on substrate. For more information about their anatomy, ecology etc. see the book and website reference at the end of this post.

At the age of 16, I bought 'The Hamlyn Guide to the Seashore and Shallow Seas of Britain and Europe' (Campbell and Nicholls, 1976). By then it was the first good illustrated and comprehensive fieldguide. I still recognise a lot of animals and seaweeds just from the illustrations of this book; they are etched in my brain. But now at the age of 49 I have problems remembering new species, because they are not in the Hamlyn Guide. And there are a lot of new species invading our Dutch waters.

As you can imagine, my copy is dirty, stained and swollen of all the times I browsed it.

So I forced myself to give a lecture about tunicates for our local 'Strandwerkgroep Waterweg Noord'. Now I do recognize a lot of the ascidians! And I hope Marco Faasse (a very enthusiastic friend who devotes - I think - all his leisure time to marine biology) will no longer be annoyed by my ignorance...

On my blog follows a summary of the more common Dutch ascidians. I start with a few colonial species: Botryllus and Botrylloides.

Botryllus schlosseri - Golden star tunicate (NL: Gesterde geleikorst)

All kinds of colour and form of Botryllus growing on a turned stone at Neeltje Jans, North Sea. The golden star tunicate is a species I recognize easily, because... it is described and depicted in the Hamlyn Guide!

This ascidian is one of my favourites because of its colour and the star like arrangement of the zooids (the individual embedded animals).

Botryllus growing on sea-lettuce (Ulva spec.).

Botrylloides diegensis or violaceus - Chain sea squirt or Orange sheath tunicate (NL: Gewone slingerzakpijp)

This colonial ascidian is a more recent invader. There are two species in Dutch waters. You can not identify the two species by its looks. That is why I use a kind of 'double' name: Botrylloides diegensis or violaceus.

Botrylloides diegensis or violaceus growing on another tunicate: Styela clava (NL: Japanse knotszakpijp).

The pink and orange ascidians are Botrylloides diegensis or violaceus, the skin coloured one is Didemnum vexillum (NL: Druipzakpijp).

Like lava form an erupting volcano.

Some invaders I really love!

Photographs taken at Wemeldinge (Oosterschelde), Neeltje Jans (North Sea) and 't Koepeltje (Lake Grevelingen).

Book reference:
R.H. Millar, 1970
P.J. Hayward and J.S. Ryland, 1995
A.C. Campbell and J. Nicholls, 1976

Website: ANEMOON: photographs and descriptions of Dutch marine flora and fauna