Marine algae in Devon

In 1981 I went to Wembury in Devon for my A level biology field trip. We did all the usual sorts of things, quadrat surveys, and plotting the transition of species down the shore. It was a particularly interesting and enjoyable day out, and one which kindled a long-standing interest in ecological interactions and natural history more generally. So, as soon as I realised that the annual British Phycological Society seaweeds course visited Wembury, and was based at the Marine Biological Association in Plymouth, I signed up immediately.

Picture of Wembury

The Mew Stone from the rocky shore at Wembury Point

Led by the rather wonderful Christine Maggs and Francis Bunker, the three day course was a perfect combination of field trips, lectures and lab work. I’d already done a little bit of microscopic seaweed identification, so knew what I was letting myself in for, though as the macroalgae are a group which I’ve not looked at much, there was quite a bit of new stuff, and names, to take in.

Anyway, this blog piece can’t really do justice to the amazing range of material covered, or include pictures of all the species we found, but here’s a selection of interesting nuggets, with the seaweeds in vaguely taxonomic order.

The coast at Plymouth

Looking up towards the MBA

It was a bit damp and cold on the first morning, but we only had to walk a hundred yards onto the rocky shore below the MBA to start collecting. Right at the top of the shore in nutrient-enriched stone on the Victorian bathing areas was some green Blidingia minima, as well as the red Porphyra linearis. The latter is a delicate purplish membrane in the family Bangiaceae, and is a winter and early spring annual.

Picture of Porphyra linearis

Porphyra linearis

Heading down the shore there was a nice range of habitats, and species, and sometimes we even got distracted by animals…

Picture of Painted Top Shell (Calliostoma zizyphinum)

Painted Top Shell (Calliostoma zizyphinum)

In one of the lectures, Christine noted that the red algae have been around a very long time; the first single celled organisms containing the photosynthetic pigment phycoerythrin appeared over 2 billion years ago. Of all the algae (which is not a natural group, taxonomically), the reds are the most numerous, and among the reds, the class Florideophyceae contained most of the species we saw.

Within that group, the order Ceramiales contained some of the most beautiful seaweeds, as well as some of the most difficult to identify. Though some can be identified on macroscopic features, many of the ones we looked at needed microscopic examination, so you certainly need the relevant volume of Seaweeds of the British Isles (and we had some useful supplementary handouts as well).

The type genus of the order is Ceramium, and I’d previously managed to key out a couple of this often rather tricky and variable group. However, to save time so I could get on with groups that I didn’t know at all, this time I simply identified these to genus and left it at that.

Picture of Ceramium

One of the Ceramiums under a microscope

The family Callithamniaceae proved a bit tricky too. The fine filamentous alga Aglaothamnion byssoides took me a little while to determine, though I got there in the end, and others on the course also found a couple of Callithamnion species.

Picture of Aglaothamnion byssoides

Aglaothamnion byssoides

Quite a few species in the family Rhodomelaceae turned up too. The rocks at Plymouth and Wembury were covered in lots of the short flat Osmundea pinnatifida (Pepper Dulse). Smaller quantities of O. osmunda were also there; it is redder and bigger than the former species, and it was good to be able to compare them. The trip to Wembury also turned up O. oederi, which is brittle and had a distinctive odour, plus O. truncata, which Christine described for the first time in 1994.

Picture of Osmundea pinnatifida

Osmundea pinnatifida

Within the same family, though morphologically quite different, is the genus Polysiphonia. Like Ceramium, these can be tricky to separate, but as a group are very distinctive under the microscope. Luckily for us Pilar Diaz Tapia is currently working at the Marine Biological Association, and she has done a huge amount of work on Polysiphonia. One of the species highlights on the last day was to be shown the rare Polysiphonia ceramiaeformis, which Pilar had collected at Wembury; it is also easy to identify it under the microscope since it Ceramium-like pincers at its apices.

Picture of Polysiphonia

A Polysiphonia species

Polysiphonia is also a good example of the triphasic life cycle of many red algae. One of Christine’s lectures covered this extremely fascinating topic, and this was a complexity unique to the red algae of which I was previously unaware.

Picture showing triphasic life cycle

Picture source: Mark W Denny and Steven D Gaines (2007), Encyclopedia of Tidepools and Rocky Shores. University of California Press.

Moving through the families, in Delesseriaceae we found about four species: Polyneura bonnemaisonii; Cryptopleura ramosa; Apoglossum ruscifolium; and Hypoglossum hypoglossoides.

Picture of Apoglossum ruscifolium

Apoglossum ruscifolium

Picture of Hypoglossum hypoglossoides

Hypoglossum hypoglossoides

The species in the class Corallinales are completely different, and contain the familiar coralline algae that you see on most rocky shores. Corallina officinalis is the common one, but it is another tricky group, and includes the recently separated C. caespitosa, and C. elongata. Mercifully, another of the relatives, Mesophyllum lichenoides, is easily recognisable in the field.

Picture of Mesophyllum lichenoides

Mesophyllum lichenoides

As the course progressed, the collection of identified species on the table grew:

At Plymouth Hoe there was also lots of the rather variable sponge Halichondria panicea, this one also sporting some interesting-looking strings of triangles:

Picture of Halichondria panicea

Halichondria panicea

Thinking seaweeds, I tried keying this out, but got nowhere, which wasn’t surprising since Francis informed me that it is a hydroid, Dynamena pumila, ie an animal….

Picture of Dynamena pumila

Dynamena pumila

Still, the Gigartinales are red seaweeds, and is another seemingly diverse collection of species. A common one is Mastocarpus stellatus, which has a triphasic heteromorphic life history. To illustrate this, Christine brought back a rock bearing the two phases that look very different. Indeed, for many years it was thought that the crust and the weed were separate species, with the crust having the name Petrocelis.

Picture of Mastocarpus stellatus

Mastocarpus stellatus on the rock, showing the thallus and the crust stages of its life cycle

At first sight it can be hard to tell species apart, even between families. These two are a case in point: Furcellaria lumbricalis has a relatively long holdfast, with a rhizoid-like structure pointing down, and is a darker brown (despite being a red alga!) than Polyides rotunda. The latter has a round holdfast.

Picture of Furcellaria lumbricalis

Furcellaria lumbricalis

Picture of Polyides rotunda

Polyides rotunda

Unsurprisingly, we saw a few non-native species as well. Caulacanthus okamurae is a Japanese species, discovered in the Mediterranean in 2004 and more recently in south-west England.

Picture of Caulacanthus okamurae

Caulacanthus okamurae

In addition, we saw a couple of nice Gelidium species (Gelidiales), as well as the rather cute Champia parvula (Rhodymeniales), which is pretty much limited to the south west coast.

Picture of Champia parvula

Champia parvula

In the same class is the very distinctive Lomentaria articulata (Bunny Ears), though there are closely-related similar species too, so it’s important not to get too complacent identifying them.

Picture of Lomentaria articulata

Lomentaria articulata

Picture of Lomentaria clavellosa

Lomentaria clavellosa

Picture of Queen Anne's Battery

Queen Anne’s Battery marina

A visit to the marina at Queen Anne’s Battery was a good source for other non-native species, not least Grateloupia turuturu in the class Halymeniales.

Picture of Grateloupia turuturu

Grateloupia turuturu

Finally, for the reds, we found Plocamium lyngbyanum, for which there are still relatively few records since the Plocamium genus is one of many that has been the subject of some detailed genetic work over the last decade, and new species have been separated from Plocamium cartilagineum. Mercifully, it turns out that there are morphological characters that can help to separate them in the field as well.

Picture of Plocamium lyngbyanum

Plocamium lyngbyanum

If the field trips, lab work and lectures weren’t enough, we also had the chance to see the MBA herbarium, and were delighted to be shown it by the legendary Gerald Boalch, who has been at the MBA since 1958, and is an extremely eminent phycologist.

The brown algae are the ones that tend to be the most noticeable on most rocky shores, since this group includes all the big, easily visible species, especially the Fucus species. Interestingly, they are taxonomically very different from the reds and the greens, and are placed in the Chromista, which may even be a separate kingdom, depending on your point of view. In any event, these contain chlorophylls a and c, as well as the photosynthetic pigment fucoxanthin. The chloroplasts have four membranes, and are believed to have been acquired from red algae at some very distant point in the past.

Simple enough to recognise is the membranous Petalonia fascia, though others are rather more tricky, such as the fine filaments of Ectocarpus.

Picture of Petalonia fascia

Petalonia fascia

Picture of Ectocarpus


The Fucales that we saw included the non-native Sargassum muticum, as well as the rather beautiful Cystoseira tamariscifolia (Rainbow Wrack), which has a fantastic blue iridescence underwater. It is largely southern in distribution and not overly common.

Rather more common is the dichotomously-branched Himanthalia elongata (Thongweed):

Picture of Himanthalia elongata

Himanthalia elongata

Various kelps were present in Plymouth and Wembury, and it was useful to have the differences between the Laminaria species clearly explained:

  1. Rough stipe: hyperborea (stipe round, snaps easily, and fairly stiff as well, and often covered in epiphytes)

    Smooth stipe: 2

  1. Droopy, flexible stipe: digitata (oval stipe, which does not snap easily, usually no epiphytes)

    Stiffer stipe, lighter colour: L. ochroleuca (no epiphytes)

The first two species are generally common and are north Atlantic cold temperate species, though the third is a warm temperate Lusitanian species, first found in south west in 1940.

Picture of Laminaria digitata

Laminaria digitata

Finally, the green algae, the Chlorophyta. At the top of the beach at Plymouth in a nitrogen-rich location one of the species was Prasiola stipitata. Mostly visible in the winter, macroscopically it wasn’t especially obvious, being a small green thallus like so many others, but under the microscope it has a really distinctive pattern of lighter and darker square patches; the dark areas producing female gametes and the lighter ones male.

Picture of Prasiola stipitata

Prasiola stipitata

The branched filaments of various Cladophora species were present in various habitats too. C. rupestris was the most common, being quite dark on the upper shore at Wembury, though C. lehmanniana and C. pellucida were also found.

Picture of Cladophora pellucida

Cladophora pellucida

Lastly, there were some Codium species. These big green finger-like weeds are a single cell, and the only way you can tell them apart is to slice off the top and make a squash under a slide so you can see the shape of the utricles. We had two species: Codium tomentosum, which is one of the native species, plus C. fragile ssp fragile, which is non-native and has long points on the utricles.

Picture of Codium tomentosum

Rounded utricles of Codium tomentosum

Picture of C. fragile ssp fragile

Pointed utricles of C. fragile ssp fragile

And finally, it ended. It was a brilliant overview of marine algae, and perfect for relative beginners such as me, as well as much more experienced people. Indeed, some attendees were doing the course for a second time, and I can well imagine you get more out of it the more you know. Now I just need to get to the coast again.


2 thoughts on “Marine algae in Devon

  1. Very much enjoyed reading this blog, sums up the course so well! Hope you get to the shore again soon, and with the newly found knowledge I’m sure you will find some interesting species to blog about which we may not have here!

    Liked by 1 person

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