Coldwater marine aquarium Blog 2008 March
4 March 2008

Nature and kelp

I have had a few hiking trips on the islands in the west lately. Here are som pictures.

As you can see, the sugar kelp in the tank (Laminaria saccharina) is still growing fast. I have 3 species of kelp now, in addition to the sugar kelp there is oarweed (Laminaria digitata) and one specimen of winged kelp (Alaria esculenta). The two latter are growing, but much slower. It could be that these species are adapted to areas with much stronger water flow. Take a look at the pictures here. The sides of the large rock is covered with oarweed. The oarweed's growth zone is where the waves break and the stiff stipes of the great kelp (Laminaria hyperborea) probably couldn't withstand the force.

Here is a shallow water kelp depository. When kelp is torn loose the flow will transport it to a depository. Usually a deep, calm place. But sometimes these depositories can be on land or in very shallow areas, like here. A real feast for detrivores. But kelp is hard to digest, toxic too, it contains phenoles I think. So the detrivores need help from bacteria to do some of the work. The kelp seen here was mostly still alive. But as the water warms up it gets covered with other algae the bacterial attacks will be too much.

I pruned out these two kelp specimens from the tank recently. They were now becoming too dominant. Time to replace them with some smaller ones. The largest had a lamina of 86 cm and a total length of 115 cm. They have grown to that size from practically nothing. The total wet weight of these two was 181 grams. I was surprised because the wet weight of a food cube is about 23 grams and I have been feeding less than two such a week this winter. So if the nutrient contents were the same those two specimens would contain over a month of feeding all by themselves. Now, I guess the nutrient contents are quite different. The algae may have much more water per volume, and more sugars/starchs than proteins. I must look into that. Still, it really is an eye opener in terms of algae as nutrient exporters.

I recently visited a very nice, shallow bay on some small western islands. The bay bottom consists of coarse sand with mud in. It receives some small runoff from land. The coolest thing about this bay is that the place where it connects to the ocean is shallow and relatively narrow. That place never dries out, there is always current and at low tide there is a little stream running. I could wade around there. It was a great place for coralline algae. I found particularly many nice pieces of Lithothamnion glaciale (most likely). They form round structures that lay loose on the bottom. I collected a few of those for the tank. Hope they will spread. There were many large spaghetti worms on the bottom in this location. I brought a few home. But they did not seem to do well in the tank. They did not rebury in the substrate. I tried to help them bury, but then they climbed out of the holes I made for them. I also colleced some new large sand bed briste worms, since I have such worm in the tank already and they seem to do well. These worms buried in a few minutes. I also collected a bunch of smaller worms from the bay by digging up a bucket of sand and sifting through it.

I got a number of new fish too. First I took some gobies, because only one of the sand gobies I collected in July last year is still alive. The rest died in the overflow or disappeared in other way. So I caught about 5 new gobies. Sand gobies, probably. Then I got one Shanny (Lipophrys pholis). This is a fish that gives the impression of not really liking water at all. It sort of tries getting out. You will often find it on dry land during low tide, hiding under rocks. They are very specialized at hunting in the shore zone. I have tried these a few times but they have invariably climbed into the overflow. The new guy got into the overflow once, but has stayed out after that. I have seen him under the rocks in the evening, So there should be hope for him. Then I got a new buttefish (Pholis gunnelus). These are also called "rock eels". The last one also climbed in the overflow. This one is abit bigger though. Hope it stays.


Dab (Limanda limanda), also called sand flounder. Really nice addition to the fauna.

The coolest new fish however, is a dab (Limanda limanda), also called sand flounder. I am not 100% sure it is this species, it could be one of two other species, but most likely it is. I will find out when I can get a really good view of the lateral line. The fish is only 6 cm. I was a bit sceptical to taking a flounder because I thought the sand bed was too small, with the sand shrimps aready there. But now I am really glad I did, even if I am still sceptical as to wether the bed can provide natural prey. But just seeing the flounder is incredible. I am very fascinated by weird, new solutions in nature. The flounder is different from anything I have ever seen. I have always wondered how these animals work. I mean, they look like they are made only to hide and not to hunt, completely flat with eyes on top. I could understand it if it was an ambush predator that was waiting for fish swimming over it. But that doesn't make all that much sense either. There are other specialized fish predators, and they have enormous mouths allowing them to suck in both water and large prey items. But the small mouths of flounders aren't convincing in this respect. They point towards smaller prey items. Now, after observing my specimen for some time, a picture of how these strange fish work is starting to form with me. First it's the way it moves over the sand. You can't really tell if it is swimming or crawling. It just slides gracefully over the bottom. Only the highly developed dorsal and anal fins are moving with a wavy motion, like some kind of worm or scolopender. It moves quite a lot. The eyes are huge. They're not placed inside the skull looking up, but on the far front of the skull and completely outside it. They are like a big steering house at the front of a vessel with view forward, to the sides and down. They are constantly scanning the surroundings for prey items. I have seen it snapping things many times, but never what these things are. Probably small worms, crustaceans or particles from my feeding.


This is (Palmaria sp.). This piece of a leaf has been lying there only attached by some mussel strings since summer. It has never shown any other sign of life than not decaying completely. Suddenly it starts coming to life again with lots of "leaves" springing out around the edge of the old one. Spring is in the air.. ehm water.

Other new additions are some bristle stars, including two specimens of black star (Ophiocomina nigra). I now have at least 3 species of bristle stars and about 20 specimens. Got about 7 new sea hares. Finally I have a population of these instead of just a few specimens. Got 3 small dog whelks. I have avoided dog whelks earlier because I knew that they were predators. But after having read about their feeding habits and speeds in a research article on the net I realize that a few dog whelks will never be a threat to the populations of mussels and post horn worms that I have. In fact there must be over a thousand post horn worms in the system now, and they multiply fast. They could use some predation. Large mussels (over 4cm) are immune to dog whelks. The dog whelks will probably be a fine addition to the fauna. No extra feeding will be needed to sustain them.

Worm spawning

Polychaete eggs

This is an egg capsule from a polychaete worm.

I increased the light levels in February to 6 - 7 hours of weak light. This has probably had an effect on some of the polychaete worms in the sand bed because suddenly these gelatinous balls of about 6mm diameter started showing up. They are anchored to the sand with an elastic line. After about two weeks there were close to 20 of them. They will dissolve and release planctonic larvae into the water. Nice to see that there is reproduction in the system. These balls started appearing before the last addition of worms so I know that it is not the newcomers that have spawned.

Chameleon prawn

Chameleon prawn (Hippolyte varians)

Urticina eques

Urticina eques

Urticina eques

This is one of Norways largest and most beautiful anemone species. I have been lucky enough to find a spot where some specimens are within reach for me while wading. So far I've got two red specimens. There are also orange and multicolored specimens out there. I will look for those this spring. The two I've got are really big, red and great looking. Really the most decorative things I have added to the tank in a long while. I point feed them with shrimp and fish. They seem to be very delicate creatures. The two I have were attached to rocks. A third one had to be scraped off the rock it was on and I tried to get it to reattach in the tank. But it got so stressed that I didn't want to keep it. Next time I may try to keep detached anemones in a bucket for a while and see if they will settle on a suitable rock there. The tentacles are very sticky, and they seem to get very stressed if touced by algae. So I had to remove some kelp to give them room.

Saw plenty of soft corals at the location. But none of them were attached to small rocks or could be reached without diving. I really hope it will be possible for me to get some soft corals at all. Currently it looks like getting into my brother in law's drysuit and strap on lead and stuff is the only option. Well, it's soon easter holiday, maybe I can drag some people out with me then.

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