March 2026
Larval Increases Dominated by a Sudden Barnacle Blizzard
Summary
At the turn of the month there was a proliferation of various larval stages dominated by the trochophores of marine worms. These tiny, pale ciliated balls of cells moved rapidly around the samples (see 3rd March photo of pale dots. Also the red arrows indicate crab zoea and the red ring is around the Phyllodoce trochophore shown in the Photo of the Month). There were many crab zoea larvae and some barnacle nauplii. At the end of the month the nauplii numbers had exploded, possibly due to the fine weather warming the barnacles on the shore. The density was so high that it was difficult to see anything else through the blizzard. (see 20th March photo. Circled is a single periwinkle veliger). No diatom bloom has started.
Phytoplankton
The numbers of winter diatoms, like Odontella sinensis and O. mobiliensis, are reducing; the sliding diatom Bacillaria paxillifer is still present in reasonable numbers along with some Helicotheca tamesis, Corethron and Paralia sulcata. The lovely spring diatom Ditylum is now increasing and my first Delphineis for five months has appeared. They are very small diatoms that adhere to sand grains to form tiny colonies. The freshwater desmid Staurastrum that was common over the winter after being flushed by the rivers down to the Haven have largely died so that while still in the plankton they are now dead. Their tough cell wall can remain for years. Green alga are rare in the plankton but the marine species, Halosphaera, is still present in very small numbers. Dinoflagellates are beginning to appear, a few Protoperidinium and a single Tripos furca. Rather unexpected at the end of the month after calm conditions there were a number of the resting stages of P. oblongum. (see last month below). These are normally present after rough weather in autumn not the beginning of spring.
3rd March:
20th March
Staurastrum sp x600
(above) and resting spore of Protoperidinium
O.sinensis. Possible development of spermatogonium
Two views of Shore Crab zoea larva
(3rd March)
Zooplankton
There was a continued presence of the species seen last month like the planula larvae of sea anemones, cyphonautes larvae (bryozoa) and even more actinotrochas of Phoronis (a close relative of the sea mats or bryozoans). As I said in February I have never seen so many before and they are still appearing in the samples.
As well as the actinotrocha another favourite turned up: a Muller's larva that live in plankton for just a day or two. This is a super little creature and I managed to film its antics as it swum slowly around, changing shape and probing the material it encountered. The photo shown here was quite red whereas most I have seen are bluey-grey. It was also quite large, 250 microns. Muller's larvae are a unique stage in the development of polycladid flatworms, an example of which is the gorgeous Candy-stripe Flatworm Prostheceraeus vittatus that lives on rocky shores. The photo of the adult flatworm was taken at Musselwick, a shore near Dale.
Without doubt the most abundant zooplankton members were crustacean larvae. At the start of the month it was decapod (crabs and prawns) zoea larvae with a few barnacle nauplii. Last month I was amazed at the number of Common Hermit Crab zoea (see the Photo of the Month) and two occurred this month but there were twenty or more zoea of the Common Shore Crab Carcinus maenas. I might find the odd one or two but this was probably the record! However, by the end of the month finding anything through the intense blizzard of barnacle nauplii was very difficult. Possibly the warm weather - it reached 20 degrees C in parts of Wales - warmed the rocky shore to synchronise the barnacle Semibalanus balanoides to breed. A few eggs occurred and plenty of shed egg cases but it was noticeable that all the nauplii larvae were of a similar age. With so many nauplii it was especially tricky to see other, smaller plankters although the slightly larger mollusc veligers, both bivalve and gastropods, did stand out
Actinotrocha larva of Phoronis
Candy-stripe Flatworm Prostheceraeus vittatus
Gastropod veliger larva
Muller's Larva
Barnacle nauplii 20th March
So, what were all those pale balls swimming in their thousands on 3rd March, shown at the top of this piece? They are trochophores, first stage larvae of marine worms (polychaetes). Last month there were many eggs of the marine worm Malacoceros and these must have hatched now. The adults live in mucus-lined tubes on the middle shore of sand and mud - plenty around Dale. The photo of a Malacoceros trochophore here does not show the two developing eyes but the ring of cilia around the middle is distinct as well as the sensory tuft at the top. A high proportion of the trochophores were this species although there were high numbers of a second worm, Sabellaria. The ball of cilia covered cells have long bristles (chaetae) flowing from the posterior end. Adults live in sandy tubes they adhere to rocks.
Trochophore of a Sabellaria worm
Trochophore of Malacoceros a polychaete
A harpacticoid copepod species
Last month I ended on an interesting harpacticoid copepod species and likewise here. A different species and certainly not a true planktonic one. It is very "worm-like" as rather than swimming it is adapted to crawl through sediment. Harpcticoids are typical of sand and mud and this one must have been brought into the water column by wave action and turbulence.
All photos shown were taken this month except the Candy Stipe Flatworm
February 2026
A Sudden Boost after a Poor Start
Summary
Bad weather has made sampling tricky this year and at the start of February it was no different. Rough weather produced samples high in detritus and material lifted from the sea bed, both dead and alive. In fact, continuing on from January, the dominant plankton community was of benthic (bottom dwelling) and estuarine species. A window of calm conditions occurred near the end of the month and a sample taken 17th February recorded a spectacular biodiversity, especially of zooplankton, with some unexpected results.
Phytoplankton
Although Odontella sinensis and O. mobiliensis were, again, fairly common, the most dominant (and annoying diatom because of its movement) was the sliding diatom Bacillaria paxillifer. What I call the sweet wrapper diatom, Helicotheca tamesis, is increasing in numbers with no Corethron found at all (common last month). A species that has made a huge increase is Paralia sulcata, reported last month. Next to Bacillaria this was probably the most common species found and in longer chains than a few weeks ago. High in silica and very compact they live on sediment surfaces but are easily taken into the plankton and often common at this time. The lovely spring diatom Ditylum has made an appearance with a small number present. Estuarine diatoms like Navicula were common along with plenty of the freshwater desmid Staurastrum. Dead cells can be common in turbulent conditions as the cell wall is remarkably resistant to decay and are easily lifted from the bottom. However, this month there were plenty with green chloroplasts inside suggesting that they are alive and washed down in the flooded rivers. Another green alga present was the marine species, Halosphaera. These green algal forms stand out in the plankton because, by contrast, diatoms are golden brown and part of the brown algae such as bladderwrack and kelp.
With the bad weather dinoflagellate numbers continue to be low with only resting forms present like those of Polykrikos and Protopteridinium. Of the latter the spores of P. oblongum are particularly striking with their red organelles of stored lipid, looking to me like a rich chocolate with raspberry filling. One very odd occurrence was a single Noctiluca cell (the only living dinoflagellate found) more often associated with autumn.
Chains of Paralia sulcata x400. An abundant benthic diatom species this month
Bacillaria paxiflifer - the dominant diatom
Staurastrum sp x600
(freshwater desmid)
Helicotheca tamesis
Ditylum brightwellii x400
Noctiluca x100
Resting spore Polykrikos x600
Resting spore P. oblongum
Zooplankton
Four examples of foraminifera this month
Less than 24 hour old actinotrocha larva of Phoronis
The samples taken early in the month had few zooplanktonic organisms and those present were benthic species like a diversity of foraminifera. These amoeba-like creatures secret a shell or test in which they live. Few are true plankton but in turbulent weather will be abundant. Some examples from 4th February are shown here. Planula larvae of sea anemones were still present but the most spectacular larval form was the actinotrocha of Phoronis (a close relative of the sea mats or bryozoans). I always like finding them, with every part of the body covered in beating cilia to drift the organism through the water. The most surprising aspect was that if I ever find them it will just be the odd one but here it was at least five. The number of tentacles increase with age and are visible in the photo here hanging down below the central region with the gut. Above this is the pre-oral lobe with the mouth at it's base. As the actinotrocha swims so this collapses forward over the mouth. These ones are the oldest I have found in shore samples. Last August was the previous best examples found. As they grow the larvae tend to move away from the shore developing many tentacles and one mature actinotrocha was found in plankton from off Skomer and was my photo of the month August 2025.
Other planktonic larvae consisted of veligers, both of bivalves and gastropods. With still large numbers of periwinkle eggs, especially the small periwinkle Melaraphe neritoides, it is not surprising. There were also plenty of young trochophores, the larvae of marine worms. They are near impossible to identify to species when they are so young. Malacoceros is a common polychaete worm found living in mucus-lined tubes on sediment seashores, in the middle shore. Here it feeds on organic matter. They have a distinctive egg which is currently becoming abundant in the plankton. I found one young larva but they are not the trochophores I mentioned earlier.
Melaraphe eggs
Malacoceros, a polychaete, developing egg
Periwinkle veliger larva
Arrow Worm Parasagitta elegans
Tomopteris helgolandica lives permanently in the plankton
T. helgolandica closeup of the head
A radiolarian (x600) becoming abundant
Probable harpacticoid species, Peltidium interruptum
There were several permanent planktonic organisms (called holoplankton) that did not require high magnification. The unexpected arrow worm Parasagitta elegans was 15 mm long. It was a surprise as I have never found one this close to the seashore in the winter, more likely to see them in summer coming in with the tide from the Atlantic. They are fast predators of copepods, which are not abundant at the moment. Arrow worms are transparent and quite difficult to see in samples although the master of this gelatinous invisibility is the beautiful polychaete worm Tomopteris helgolandica. The occasional one of these can appear at any time but are so difficult to see, even though they are several centimetres long. Staring at the sample in a dish under low magnification I could make out a disturbance at the bottom of the dish with material being moved around by an invisible culprit. I never fail to become excited by them. This species is the most common Tomopteris and has a tail at the end of the body. The gut is one of the few organs that can be seen inside the body and the pharynx behind the eyes is constantly moving, contracting and expanding.
Although copepods were few, especially the large calanoid types there were a reasonably large number of the small harpacticoid copepod Peltidium interruptum (ID has not been verified as yet). Again I have not seen these at this time before. It is a species that curls up in a ball, dark brown in colour and is widely distributed around the UK but not normally associated with the shore. Harpacticoids are typically benthic, associated more with sediment. Peltidium is found in off-shore sediment and possibly the turbulent water this year has brought them to the shore. Another crustacean that was common was a 3mm cumacean that lives in mud but at this time of year enters the plankton. Check out photo of the month a year ago.
Another species worth mentioning this month was the steady increase in a tiny radiolarian, a single-celled protist, probably Acanthostaurus. Requiring a high magnification, I have see the odd one or two this winter but now they have become commonplace in all samples. The cell is supported by a solid skeleton of spicules. They feed on bacteria and diatoms but also have symbiotic organisms that can photosynthesise.
All photos shown were taken this month
January 2026
Very Low Numbers So Far This Year
Summary
After a high diversity of zooplankton on 23rd December I expected great things for the New Year. A sample in the first week of January had a few different larval forms and diatoms but nothing like December. Then came the bad weather, snow, heavy rain and wind, one week after another. The only window to sample was 21st January. The conditions were still bad and was the worst I have ever known while sampling, with waves crashing over the top of the jetty. Samples were thick with organic debris, the count on diatoms low and zooplankton exceptionally low
Phytoplankton
The two species of Odontella, O. sinensis and O. mobiliensis, along with the sliding diatom Bacillaria paxillifer, remain common through the winter but are rapidly being joined by ever increasing numbers of the lovely species Corethron. The two frustule valves are slightly different and there are numerous spines. Paralia sulcata was also quite common and occurs in short chains. They have high concentrations of silica present in the frustule and the chains are very tightly compact. They live on the surface of sediment and easily lifted into the plankton during turbulent periods. This also applies to Pleurosigma and Gyrosigma diatoms which occurred in singles as they are non-chain diatoms.
Amongst the debris tiny star-like clusters of Thalassionema nitzschiodes occurred. The long needles of Rhizosolenia were quite common but I was a little surprised to find the very large species R. robusta. Until recently known as Neocalyptrella robusta, it is banana shaped and considered a warm water species.
The second component of phytoplankton is dinoflagellates, very diverse in December, but are not good survivors in rough weather. However, one genus, did occur in some numbers at the start of the month, Dinophysis.
I was surprised on 21st January to see several silicoflagellates (I saw none last year) and one was a rare species. There were Dictyocha speculum and D. fibula, respectively. They are very small (about 25 microns across) and easy to miss. They get their name from the skeleton of silica on which the cell then adheres to.
Dinophysis, probably D. caudata x600
Corethron dividing
.jpg)
A chain of Paralia sulcata x400
Thalassionema nitzschiodes
Rhizosolenia (Neocalyptrella) robusta
Zooplankton
Biodiversity was low although early January a few interesting larvae were present: a pilidium and many planulae. The latter are the larvae of cnidarians, like sea anemones and they are delightful to watch cruising around. Common at the beginning of the month. The pilidium is the larva of a nemertean, a phylum group known as the ribbon worms, that are found on the shore. The most famous species is the bootlace worm that when unravelled (as it commonly is found in a slimy ball) can be many metres long. The pilidium is not that common to find. This one was probably a 4-day old larva and they can develop for weeks during which time they will disperse along the coast or off-shore.
What is particularly fascinating about the pilidium development is that after it is well formed it does not metamorphose into the adult but creates the juvenile inside the body of the pilidium. It can eat its way out or just break-out depending on the species.
One huge surprise was a single, mature Oikopleura, that occured at the start of the month. This is a tunicate (sea squirts) that lives permanently in the plankton but is a summer species, normally appearing at the end of April. Also unusual at this time was the group of rotifers, Synchaeta, that forms the Photo of the Month on the home page. If they occur in Dale the population develops in the late spring.
Barnacles laying eggs can occur at almost any time and it was interesting to see many developing eggs at the start of the new year in the plankton.
Planula larva of a sea anemone
.jpg)
Silica skeleton of Dictyocha fibula
.jpg)
Dictyocha speculum
4 day old pilidium larva (ribbon worm Nemertea)
Oikopleura
Barnacle egg with nauplius inside
Egg of the small periwinkle, Melaraphe neritoides, common in the 21st Jan sample
Egg capsule of Edible or Common Periwinkle