August 2024
Biodiversity Doubles in Weeks
As we turned into August the biodiversity was down to the lowest of the year and very few diatoms; rotifers dominated. A sample from Neyland on the 10th showed a huge boom in young copepods and the appearance of prawn Palaemon larvae. There were also large numbers of veliger larvae of the Edible Periwinkle Littorina littorea.
The Dale samples 19th August were dramatically different to just 2 weeks before. Rotifers had almost completely disappeared having been dominant for 2 months. A small bloom in diatoms had begun, primarily four species. Leptocylindricus danicus and Pseudo-nitzschia pungens are currently common as chains. The latter have overlapping cells with thick silica walls (see photo below). Both species are small, each cell typically 40 microns long. By contrast the diatom Neocalyptrella robusta is almost visible to the naked eye and in significant numbers. The other diatom species is one of the very hairy types, Chaetoceros curvisetus. The long hairs help stability in the water, reducing the chances of sinking, and puts off being eaten by copepods. The photo below shows it next to a super little ciliate protozoan called Didinium (photo of the month on the homepage). This is my favourite protist and I always get excited seeing one. There were several examples present. The one below has the typical 2 bands of cilia while the one on the homepage has 4 as it is about to divide.
Zoea larva of a prawn Palaemon sp
Harpacticoid Copepod with eggsac
Periwinkle veliger larva
Two tiny diatom species dominating the phytoplankton: Leptocylindricus danicus (left) and Pseudo-nitzschia pungens (below)
As a carnivore Didinium can consume other ciliates (and there were many present), in fact, any creature up to its own size.
Didinium with the diatom Chaetoceros curvisetus
Neocalyptrella robusta, a large diatom
Two different larvae that I rarely see were in the latest sample. I was excited to get my first decent shot of a pilidium larva, an early phase in the development of a Ribbon Worm. A bit like a beanie hat with ear flaps it is transparent so the gut inside can be seen. The flaps are ciliated and a large tuft on the top is a sensory structure. Height was about 250 microns. This is a dispersal stage for a limited number of Ribbon Worms (phylum Nemertinea) and is likely to be a species called Cerebratulus, a species found low down on sandy shores. The larva does not grow into being an adult Ribbon Worm but one develops inside the clear space above the gut of the pilidium.
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As if that was not exciting enough, a second larva that I have only ever seen once before was active in the sample: a Muller larva, approximately 300 microns when extended. They are just found in the early stages of Polyclad flatworms and exist in the plankton for just a day or two, making them tricky to find. Under the microscope the larva never stopped moving around, probing and extending. It has eight lobes, all covered in cilia. In fact the entire animal shimmered with rapidly moving cilia. The photo shows just one eye but there are two, just difficult to get both together. The dark central mass is the gut with a mouth on the side, here on the left. ​​
Yet another larval form of interest was a nauplius. Probably the most abundant creature in the 19th August sample were the enormous numbers of copepod nauplii. Few adults just eggs and larvae, making looking at material under the microscope a little frustrating as they would come hurtling through disrupting the specimen you were looking at. While most were copepod larvae there were also some barnacle nauplii which you can tell due to projections, like ears, on the side of the head. However, one drew my attention and a few photos later realised that it is almost certainly the nauplius of a parasitic barnacle called Sacculina carcini. A larva I rarely see. The distinct "ears" can be seen in the photo. As the second part of the name suggests this parasitises the Common Shore Crab Carcinus maenas. Like other barnacle nauplii as it settles it changes into a cypris larva except in this species the female settles on a crab. It then further metamorphoses into a kentrogon form which penetrates and worms its way into the host. Extending through the entire body the ovary protrudes outside the host (see photo) to attract a male cypris to enter and and setup inside the ovary.
Pilidium larva of a Ribbon Worm
Muller larva of a Polyclad flatworm
Nauplius of Sacculina
Sacculina on a Shore Crab
Acanthometra
Other notable creatures in the plankton this month were the ongoing bloom of tintinnids with more than six species abundant. Favella is always a favourite but one image was strange and I think it is a Favella being eaten by another protozoan ("amoeba-like"). It was very active inside the lorica and appeared to be consuming the ciliate. Another protist was the beautiful "radiolarian" Acanthometra - first sighting this year.
What an exciting month this has been.
A protozoan invading the lorica of Favella to consume it
Two tintinnid ciliates Favella
July 2024
The Diatom Bloom has gone with Rotifers the dominant organism
Over several samples this month I saw the collapse of the phytoplankton. The needle-like Rhizosolenia diatoms were still fairly abundant at Neyland, in the eastern Haven, on the 7th July but near the waterway entrance at Dale all phytoplankton had reached the lowest density this year by 19th July. There is always a dip at this time between the spring and autumn although the dinoflagellate component usually remains strong. Not so this year as I was surprised to see only 2 specimens of dinoflagellate. However, general ciliates (protist) like Euplotes have exploded in numbers. These are consumers and not part of the phytoplankton. The sudden collapse of the diatoms has created a great deal of organic particulate matter; an ideal food source for these and most other zooplankton that have increased this month. ​
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Almost certainly this has also fuelled an explosion of marine rotifers, all being the genus Synchaeta. Despite being largely microscopic they are complex organisms with a head, trunk and foot region. At the top of the head are cilia making up the corona, a pair of structures appearing like a wheel that moves them rapidly around in the water. Currents created by the cilia bring particulate matter to the mouth and currently there is plenty of this in the Haven. As well as adults there are huge numbers of eggs, both attached to the female or free floating. Rotifers are most common in freshwater often without males when reproduction is by parthenogenesis. The males of Synchaeta are much smaller than the female. It is tricky photographing rotifers as they rarely slow down. Fortunately, the one here stopped long enough for a few seconds of video that could be used to produce a stacked image.
A female Synchaeta rotifer carrying an egg x200
Favella, a tintinnid x200
The almost exclusively marine group tintinnid is another type of ciliate. Small thimble-like forms have been abundant so far this year but as seen in previous months (see photos below) they have been slowly declining in numbers. However, during July while the small ones disappear the larger species, Favella, has had a sudden increase throughout the Haven. In fact, at Dale I have never collected so many live ones as these samples. Unlike the species recorded earlier this year, which have the lorica (a shell or test they secrete) studded with minerals, Favella's lorica is transparent and the single-celled protist can be seen inside attached by a stalk to the base. In the photo above taken on 20th July, it has withdrawn inside the lorica that looks like a wineglass and the cilia can be seen clearly. Again, this is a particulate feeder using the cilia to bring minute particles into the lorica. This is a stacked image created from a video clip.
A pair of different ciliate species (this photo and top right) approximately 20 microns long. Most are difficult to identify
July has been a month of "worms". Early on there was a sudden appearance of fluke larvae (Trematodes) or cercaria. Typically, the adult lives as a parasite in a host like seabirds. Various stages of cercaria live in the plankton and pass through molluscs and other secondary hosts. Even under low magnification (x10) the violently wriggling larvae of Fellodistomids are visible. The stiff hairs over the body increase surface area and help to reduce sinking in the water column. By the end of the month polychaete larvae of all stages in the development of Polydora were very common.
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In addition a very strange worm-like creature turned up. I have photographed the odd one before but this time there were quite a few and in different stages of development. They were active Moving slowly about the larger ones seemed quite rigid but could fold back on itself. There were no signs of chaete/bristles (suggesting polychaete) but the body was covered in cilia. Larger specimens had a light brown "head" and a body as long as 450 microns. A photo of the largest example is given here; small ones were like the back/left half of the image here as if the head grew to extend the body. Very odd! Any ideas would be gratefully received.
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Until next month, when I hope there will be an increase in diversity as we begin the autumnal rise.
June 2024
The Diatom Bloom declines along with reduced Biodiversity
Phytoplankton species and density has declined to the levels seen back in early March. This is quite usual, a slump between the spring and autumnal peaks. Within an enclosed area like Milford Haven nutrients can remain relatively high encouraging diatom growth. Gales (it was very rough on 13th June) can disturb and raise nutrients from the bottom and along with agricultural runoff keep diatoms multiplying. Although the variety has declined there is a prolific bloom in the needle-like Rhizosolenia setiger and is currently the most dominant diatom. If the nutrients have increased after the gale we may see an increase in others species soon. Bacillaria and Odontella, which bloomed throughout the winter and early spring, have now all but disappeared. The large diatom Neocalyptrella robusta is typical of warm water and has been slowly increasing in the last few years in the late summer samples. The appearance in June is earlier than usual. The Phaeocystis bloom, mentioned last month, never came to much and has declined.
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Phytoplankton also includes many dinoflagellate species and this protist group is dominated at the moment by Protoperidinium a genus that is armour-plated which helps protect them from being eaten. This theca is made from cellulose "plates" on the inside of the cell membrane. They are very small, about 60 microns across, and whirl about driven by two flagella, one at the top and another at the side where a girdle goes around the cell. This can be just seen in the photo here. The carotene/red pigment is typical of many dinos and when present in huge blooms results in what is called a red tide.
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Phytoplankton dominated by Rhizosolenia. Note the single, large diatom Neocalyptrella robusta
The dinoflagellate, Protoperidinium x400
The June photo of the month shows a young trochophore larva. Polychaete larvae of all developmental stages were generally abundant for species like Capitella and the spionid worm Polydora. The former species is quite barrel shaped and distinct. Both of these species are common in the plankton during the spring and summer and the adults can be found in the sediment throughout the Haven. Polychaetes are true worms but other worm-like organisms appeared this month. The odd flatworm (Platyhelminthe) turns up on occasion but every June sample had several with what seemed to be a single eyespot and reddish body. They were tricky to photograph as they were very active gliding around the slide.
The number of copepods were low but numerous larval forms were present. There were so many nauplii larvae of different stages of development I was able to see them shedding the exoskeleton (quite rapidly as it happens).
Flatworm 800 microns/0.8mm
Capitella larva
Young Polydora larva with a copepod nauplius
Tintinnopsis radix with the active crown of cilia protruding through the end of the lorica
Diatoms Rhizosolenia and Striatella with Tintinnopsis lorica
Another protist group of single-celled organisms is the Tintinnid. This month these ciliates were the most prolific of all the active creatures. Over the winter a small, thimble shaped species reached its peak but June samples were over-run with Tintinnopsis radix. Over the years I have seen a few specimens but not like this. Tintinnids make a case (lorica) within which the cell lives. Like a wineglass it tapers at one end and is open at the other, through which the cilia project to propel the organism rapidly through the water. If you scroll down to last month there is a photo of a Favella lorica that is transparent. Tintinnopsis is much smaller and studs the outside with minerals. The ciliate inside attaches to the lorica base and can quickly retract.
Tintinnopsis retracted back into the lorica. Red arrow: ciliate cell, blue arrow: cilia
Group of mixed diatoms in May
Entomoneis x400
Licmophora x200
Phaeocystis. Old and growing colony x5
Phaeocystis. Enlarged section of the colony
May 2024
Diatom Bloom Peaks along with new Crustacean appearances
The phytoplankton has been stunning over the last 3-4 weeks with Thalassiosera rotula and Lauderia the most dominant with Ditylum and Rhizosolenia maintaining high densities too. Thankfully the very motile Bacillaria has diminished to low numbers except in estuary samples above Neyland. With less rain the microscopic freshwater algae, so common in the winter samples, has now almost disappeared. What has been common in the Dale samples, despite the recent calm conditions, are benthic diatoms. These are diatoms associated with living in sediment or attached to seaweed and rock. Entomoneis along with Navicula are common on the saltmarsh and yet many are turning up in the plankton this month. Perhaps the most notable benthic diatom this last week is the colonial species Licmophora that grows especially well on seaweed, hydroids and other creatures of the shore. The fan of grouped diatoms can form beautiful patterns. The photo below was taken this month when hundreds were present, very unusual as only the odd one or two occur normally. Flagellates and dinoflagellates can be an important part of the phytoplankton and these are on the rise. Phaeocystis is a colonial form and occasionally turn up embedded in small blobs of gelatinous mucilage. However, at the moment these colonies are not dispersing as they usually do and are growing large. A decade or so ago this happened in May to produce huge amounts of mucilage that filled nets and covered the beaches. Hopefully that will not occur this year.
Crustacean larvae were on the increase last month and this continued with many barnacle nauplii metamorphosing into the non-feeding cyprid stage for settling on rock. As you may have seen the Photo of the Month is Evadne, a marine water flea species which occurred for the first time in my Dale samples. Podon appeared for the first time this year after a bloom of them last September. Only two were found in the last week and both were recently dead, probably in the net. I think this is why the eye is red in the photo rather than black. Wherever I have collected in the last few weeks there have been crab zoea larvae. At both Dale and Neyland there were a dozen or more Common Shore Crab zoea. The most exciting for me is when I see the zoea of a porcelain crab. It was only a few years ago I found my first one and they are always spectacular. The species most likely to occur in Dale is that of the Broad-clawed Porcelain Crab Porcellana platychelles. They have very long spines to stabilise them in the water column.
Podon from 6th May sample
Zoea of porcelain crab photograph 6th May.
Trochophore polychaete larva x400 (6th May)
The porcelain crab zoea is tricky to photograph but I always like to have a go.
Likewise, the "ciliary ring" I showed last month. You will see if you visit previous photos of the month that it has now been Identified (thanks to Prof Otto Larink) as an early trochophore larva of Polygordius.
Trochophores are the main early larval stage of polychaete worms found on the shore and this month they were in great abundance, both as very simple balls of ciliated cells to well developed larvae. Example below. Tintinnids have been the most common zooplankton member over winter but now on decline. These were the small species with mineral studded loricas (see March below) but this month the larger species with a clear, wine-glass lorica began to appear, Favella.
Favella
Oikopleura. Appearing in some numbers
April 2024
Diatom blooms continue as general diversity increases. Also a correction!
During the first few weeks of April I have managed plankton collections from the Dale Fort Jetty, the Gann and from pontoons in both Dale and Neyland. Diatoms have increased substantially in both quantity and diversity since last month. 34 species now up from 22 towards the end of March. The most significant blooms are with Lauderia and Skeletonema. The former is always abundant coming into spring/summer but the latter is only occasionally seen. Most common in Dale it also occurred in Neyland and Gann samples.
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During the last month every sample taken has had at least a few of a spherical green alga called Halosphaera. The first example appeared amongst what I believed was the freshwater Pandorina (see March blog below). The most recent collections have had significant numbers of the Halosphaera, a member of the Prasinophyceans that are regarded as modern reps of the earliest green algae. The group is comprised of marine flagellates although they are so diverse some lack the flagella. They all have chloroplasts and a few, including Halosphaera, can engulf food (phagotrophy) as well as photosynthesise. An individual Halosphaera is unicellular with a pit from which come four flagella from a complex base within the cell. What I am finding are not individuals but a planktonic stage within the life cycle and this is where I need to correct what I said last month. What I thought was Pandorina was actually part of the stage in the development of the planktonic phycoma-cyst phase of Halosphaera. The outer wall of the ball is a tough, resistant material within which lipid provides nutrient and buoyancy. The cytoplasm divides to form many unicellular flagellates before eventually a slit in the wall allows them to escape. (From Algae by Graham & Wilcox, Prentice Hall 2000)
Lauderia x400
Skeletonema x400
Phycomata of the green alga Halosphaera 300 microns. Two different stages in the development
Nauplii larvae of both barnacles and copepods is booming and at the Neyland end of the Haven quite a few cypris larval stages were present. This is the final phase that searches out a suitable spot on the shore for the barnacle to settle.
The ophiopluteus larval stage of a brittlestar was interesting to see (note the calacite rods standing out in the photo). Only one but the earliest record of seeing an ophiopluteus. Previous record was late June.
A barnacle cypris larva before settling on a hard substrate. Note the bivalve veliger above
Ophiopluteus, larva of brittlestar x200
This amazing ciliary ringed organism is the Photo of the Month and its ID still baffles me. Almost a millimetre across it was a single specimen caught off the DF Jetty. The central body is similar to a starfish bipinnaria and is quite complex. It is the complexity that leads me to think it is some type of echinoderm related creature. The two dots look like statocysts that help determine which way up it is. Near the bottom of the photo there appears to be an opening (mouth?) and the dark spot higher up seemed to be the end of a gut(?) with plenty of movement between the two. If anyone has any ideas please let me know, thank you..
March 2024
Ditylum and Tintinnids are blooming
The plankton year has progressed slowly after an initial flurry of activity back in January and February. However the diatoms are changing. In the middle of winter Odontella sinesis and the sliding diatom, Bacillaria paxillifer, completely dominated the phytoplankton. The sample taken 25th March had both of these in decline especially the latter. Instead the total species number had doubled with the small and delicate Ditylum brightwelli blooming in huge numbers. The photo left shows several dividing. There is also an Odontella mobiliensis (top right), a species on the increase.
One of the freshly occurring diatoms is Corethron criophilum, one of my favourites, quite a hairy/spikey species. These reduce the rate of sinking and so help to keep it in the water column. Around 100 microns in length the photo below is a photo stacked image (25 photos) with two cells of a Thalassiosira rotula underneath. The latter has made a sudden reappearance and is beginning to bloom.
The common tintinnid which is abundant at present
Since last September tintinnids had been fairly stable in numbers; commonly occurring but not really abundant. That has changed with a massive increase to become the most dominant animal in the samples. When the net was slowly pulled from the water the bottom looked a red-brown colour, almost like a sediment. Once in a dish there were large numbers swimming about randomly and plenty of the dead/empty loricas lying on the bottom. This species has the outside of the lorica covered in tiny minerals. The photo shows a few cilia protruding.
This was one of the first tunicate Appendicularians of the year. Oikopleura appears typically in the spring and disappears with the onset of winter. A dozen or so were found in the late March samples, all very young, probably less than a day or two old.
For a graph and a brief discussion of their abundance see here.
Over the previous few days the wind has been strong, almost certainly disturbing sediments from the Gann and Dale beach bringing both foraminiferans and dead diatom frustules up into the water column and plankton. There were plenty of estuarine and saltmarsh diatoms (dead and alive) commonly found on the surface of the mud. The are rapid "movers" unlike the usual phytoplankton species. A feature of the last few months has been the appearance of freshwater algae, possibly due to the flooding of rivers. The ball of green cells 300 microns across is, I think, Pandorina, a colony of cells glued together by mucilage. (please see correction in April, above). They stand out because they are bright green against the marine diatoms that are a duller brownish due to fucoxanthin.
Crustaceans were largely absent with just a few copepods and a small number of nauplii. The latter were made up of both barnacle and copepod larvae.
February 2024
Spring is coming, lots of eggs
With several samples in the last 4 weeks, the first of these was rather disappointing with a sudden drop in diversity. The diatoms have remained fairly stable in quantity with Odontella and the sliding diatom, Bacillaria paxillifer, abundant. Several species of Chaetoceros are also common. These have long spine-like hairs that provide a degree of stability in the water, reducing the tendency to sink. A new diatom that I have not recorded before occurred: Rhabdonema sp. (probably R. adriaticum). Apparently they have thickened lines of silica (called costae). The photo here is of a small chain, quite typical of the species. Quite small, this one was just 60 microns across.
Even smaller is a strange alga, 50 microns approximately, that is angular with three arms and various small teeth emerging from the cell walls. It is intriguing for several reasons and took me a while to track down an ID. A desmid, or at least half a desmid, because it is constructed from two semi-cells attached at an isthmus where a nucleus is located. Desmids are only found in freshwater and this is Staurastrum, a plankton species from a large water body, possibly St. pingue or St. planctonicum. Almost certainly they arrive in the Haven from the Cleddau rivers, down from the Preseli Hills and probably Llys-y-fran. Marien van Westen from the Dutch Desmid Society has been helpful, can't be sure of the species as my photos of a semi-cell are not the best angle. The cellulose cell wall is tough and they can persist for decades in the environment. Either way, in the last month instead of finding the odd one they have become abundant in every drop of water I place on a microscope slide. As I say, intriguing!
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Eggs: the copepods have been laying many eggs over the last month with increasing numbers of their nauplii larvae hatching. Amongst the debris you always get there is plenty of empty egg shells. There are also many eggs appearing that are very difficult to identify as they tend to look similar to each other. This especially applies to polychaete worms. Tiny balls of cells spinning around with cilia beating manically could mean hatching trochophore larvae, found in both marine worms and molluscs but it is too soon to tell. One egg very easy to identify are those belonging to periwinkles. Small ones will be those of the small periwinkle Melaraphe neritoides that have been common for a few months now but many large ones appeared this month, the Edible Periwinkle Littorina littorea. Usually they have two or more embryos developing inside. The one pictured here was over 300 microns in diameter, three times bigger than Melaraphe. The outside has considerable debris stuck to it.
Harpacticoid copepods are a group that tend to live in sediments or wet soil (I have found them in Sphagnum moss from the top of the Preseli Hills), few live in the plankton. Euterpina acutifrons is an exception and occurred in samples last year (see copepods). The photo here is another species, Microsetella sp. that turned up and was carrying egg sacs. Not recorded by me before and lives permanently in the plankton. Almost a millimetre long it moved fast and was tricky to capture with a pipette.
A bit of a surprise for me this early in the year were several zoea crab larvae. They can live for a number of months and in the autumn were common off Skomer Island until December, so they may have come in from the open sea. But to find more than one in a sample suggests they are quite common at the moment. I liked one of the photos so have it as photo of the month.
January 2024
New Year's Eve Surprise
Happy New Year! Before 2023 was out I did a sample on 30th December from the Dale Fort Jetty. The water had been fairly calm off Dale for some days as it is sheltered from the strong south-westerlies that was bringing heavy weather into the Haven. Initially, looking into the pot there was little sign of life but once home and under a low magnification it was an amazing surprise. A dozen or more tiny crustaceans, about 2-3 mm long were wriggling madly. These were Cumaceans, a strange order of Crustacea that spend most of their time in sediment. On occasions they swim up into the water column before eventually dropping back down to the benthos once more. This can be deliberate or just the effects of storm disturbance. Creatures spending time like this are referred to as tychoplankton.
As well as Cumaceans a Syllid polychaete was present which I see off and on through the year, but never in the middle of winter. This is an epitokous stage called a stolon. It is non-feeding and produced at the end of the body of an adult living on the shore. This is the reproductive phase in the life cycle, producing male and female stolons that find a mate in the plankton. The male dies and the female looks after the eggs. This one doesn't look quite right as they are usually in a clump rather than along the back. More plankton samples were made on 14th January, again very calm.
Copepods have been increasing in numbers with developing eggs still present (see last month). Most copepods are young stages (both nauplii and the copepodites present). There were a number of huge copepod adults around 4mm long (top and side view above). The Skomer team passed me a plankton sample 16th January and it was very low in diversity but plenty of these large Calanoid copepods, too. The photo above right is a tiny Bopyrid isopod, approximately 200 microns long. I see a few during the year but my last two samples have had them in some abundance. They are external parasites on copepods so this could be coinciding with the increasing Calanoid numbers?
There has been a sudden abundance of planulae. A planula is the larval stage of sea anemones and the middle of this month saw the biggest density of them I have ever seen. Some were quite small (young?) forms around 100 microns in length (bottom left) and others more advanced looking and about 250 microns (older?), bottom right. I love watching planulae moving slowly across the screen, covered in beating cilia and several longer ones sensing what is in front of them. Absolutely beautiful.
Diatom density and diversity has been stable with no particular bloom over the last month although dinoflagellates are increasing. Until next month ....