Last week I went for a little swim at the usual spot at Castle Beach. The viz was nowhere near as good as last month, but still OK. There are schools of sand eels and sand smelt and I even saw an eel. The contrast between growing brown seaweeds and withering red seaweeds has become even greater. Below you see some yellowed Harpoonweed and a ‘forest’ of Thong weed covered in epiphytes. As the light was a bit subdued, I focused on the most shallow area. The bare parts of the rock are covered with barnacles, dog whelks, sting winkles and limpets. The seaweeds are mainly Serrated wrack Fucus serratus, Sea lettuce Ulva, Grape pip weed Mastocarpus stellatus, some Ceramium and Laver Palmaria palmata, as well as Dumont’s tubular weed Dumontia contorta.
This snorkel session was also the first time I took a proper look underneath the kelp. Mowing through this forest is very interesting. Besides the gobies and starfish, there are a lot of sponges, bryozoans and hydroids to be seen. A picture from this ‘turf’ with many hydrozoans and a larger erect bryozoan (perhaps an Alcyonidium species?); these are groups I know very little about. A photo beneath that of some worms Bispira volutacornis, very beautiful:
The kelp is covered by a not so pretty, large, fluffy brown seaweed which might be Pylaiella littoralis (first picture). Large bushes of the slightly iridescent Dictyota dichotoma were also common, this is a species I have never seen in rock pools (second picture). The rocks underneath the kelp are also home to many red seaweeds, notably Sea Oak (I have to get back for some pictures).
In the deeper channels there were many Mermaid’s tresses Chorda filum, more than five meters in length. The shallow rocks were covered with Thongweed Himanthalia elongata and Grape pip weed Mastocarpus stellatus with assorted epiphytic tufts of fine red seaweeds.
As in Falmouth, the rock pools in Flushing are not looking that great at the moment. Lots of the Corallina has turned white/died (although the clumps in my tank are still their normal purple!). Of course, many species were still thriving, Grape pip weed Mastocarpus stellatus (top), Bunny ears Lomentaria articulata (bottom), new Thong weed Himanthalia elongata ‘buttons’ and a young blade of kelp along with some green Ulva:Among the seaweeds that were thriving was Slimy whip weed Chordaria flagelliformis (I am by no means a seaweed expert and I might be wrong about this, please comment if I am!) and also the beautiful Harpoon weed Asparagospis armata growing as an epiphyte on some darker coloured False eyelash weed. Harpoon weed is invasive and so a good candidate to do well int he aquarium (as most invasive species are quite opportunistic and not too finnicky). It died off in the tank before, but I decided to bring some home to try again now I have a chiller.
Another tangling invasive species: Bonnemaison’s hook weed Bonnemaisonia hamifera (a characteristic curved hook can be seen in the top-middle):Loads more seaweeds to be found but I will save those for another time. All kinds of tunicates pop up in spring, some of them pretty (see for instance here), some of them less so. For instance the invasive species, the Leathery sea squirt Styela clava and an out-of-focus photo of a second, large (>10 cm) species that did not get a lot of response on the NE Atlantic Tunicata FaceBook group. Aplidium nordmanni was offered, see here for a much smaller version of that species. Not a looker either in any case!
I brought my little aquarium net and found many juvenile (<1 cm) fish as well as Mysis shrimp. The fish look like gobies but it is hard to see. They were completely translucent and so you can see what this one just ate. I should take some bits of seaweed home to see what comes crawling and swimming out under a little USB microscope (quite easy to make little videos). It is hard to come up with decent images squatting and squinting on a slippery rock with a salt-encrusted mobile phone!
After some musing on animals that I had good- (here and here) or bad (here) experiences with during the past year-and-a-bit that I have my aquarium, I thought it would also be good to take stock of my experiences with seaweeds. Not many people have temperate marine aquariums, and only few of those who do seem to focus on seaweeds. That is understandable, because it is hard keeping seaweeds! I currently have almost no seaweeds in my tank, as I wanted a break from the problems I had with die backs and resulting detritus. Below a picture of my 130 liter aquarium at its prettiest (see this post); unfortunately it did not look that way for long (see this post):Although keeping seaweeds in the aquarium is difficult, they are so beautiful, diverse and abundant that it is definitely worthwhile to try. The range of shapes and colors is much greater than that of the vascular plants in freshwater tanks. Also, the fact that so few people seriously try to grow different seaweeds in their tank makes it an extra interesting challenge. My fellow aquarists reading this will agree that it is great to look at a ‘finished’ tank, but building it up and experimenting to ‘get it right’ is an integral part of the fun. Keeping a native tank means that you can collect yourself which is a great activity in itself (and free). being able to observe organisms in their own habitat also gives you some clues on how to best keep them in the aquarium. Anyway, below my personal- and somewhat disjointed thoughts on the topic of keeping seaweeds in the aquarium (with some links to previous posts). Quite a lot to write about so I’ll save some pondering for a part II.
1. Many Seaweeds are seasonal
Coming back to the same rock pools over the course of the year, it is very striking to see the composition of seaweed species change. Some species are annuals and always there (although sometimes somewhat overgrown and smaller), but many species are only abundant for a season or even less than that. For example, Dumont’s tubular weed Dumontia contorta was abundant only in early spring this year, whereas Codium tomentosum has just appeared now and will disappear come spring. This must be due to adaptation to annual variations in temperature and daylight (and competition with other species that are present in different months). Although light and temperature conditions can be kept constant in the aquarium, seaweeds are likely ‘programmed’ to thrive at specific times of the year. So in contrast to fresh water planted aquariums where plants just grow and need occasional trimming but otherwise stay the same, marine planted tanks never stay the same. A good example of how a tank can change over time is the series of monthly pictures taken by Jon Olav of his Norwegian native aquarium. I guess for some people, the unpredictability of seaweeds is a downside, not an upside.
2. ‘Planting’ Seaweeds is difficult
The above picture is of Grape pip weed Mastocarpus stellatus. Like many seaweeds, it is very firmly attached to the rocks. Ripping it off results in a handful of separate fronds which will just float around when transferred to the aquarium. Such species (see here for another example) can only be brought over to the aquarium attached to a rock. Some species readily grow on smaller rocks (Solier’s red string weed often is washed up attached to shells) but others don’t. It is possible with suitably shapedseaweeds to weigh them down using a piece of string and a pebble. (I am not sure about the lead weights used to weigh down plants in freshwater aquariums; on one hand lead is toxic, but on the other hand a layer of lead oxide will form around the weight which prevents leaching. Leaching should be less of a problem in salt water which is slightly alkaline anyway. I’ll stick with pebbles in any case!) Some seaweeds on Castle beach in Falmouth when pulled from the substrate take with it a shard of rock, which makes it easy to anchor them in the aquarium (check):
3. Seaweeds can get eaten
Herbivores, such as snails or prawns can start munching on some seaweeds, especially flat greens and reds seemed vulnerable. Perhaps if you provide enough food, they will leave the seaweeds alone (but you risk overfeeding and the disasters that come with that of course). If you are really into your seaweeds, you could also choose to ditch such critters.