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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.

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.  

Phytoplankton dominated by Rhizosolenia. diatom Neocalyptrella robusta

Phytoplankton dominated by Rhizosolenia. Note the single, large diatom Neocalyptrella robusta

Protopteridinium dinoflagellate x400

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).

Marine Flatworm

Flatworm 800 microns/0.8mm

Capitella polychaete larva

Capitella larva

Young Polydora larva with a copepod nauplius

Young Polydora larva with a copepod nauplius

Tintinnopsis radix tintinnid

Tintinnopsis radix with the active crown of cilia protruding through the end of the lorica

Diatoms Rhizosolenia and Striatella with Tintinnopsis 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 radix

Tintinnopsis retracted back into the lorica. Red arrow: ciliate cell, blue arrow: cilia

diatom bloom

Group of mixed diatoms in May

entomoneis diatom

Entomoneis x400

Licmophora colony

Licmophora x200

Phaeocystis, colonial flagellate embedded in mucilage. Old colony

Phaeocystis. Old and growing colony x5

Phaeocystis, colonial flagellate embedded in mucilage. magnified

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 marine water flea

Podon from 6th May sample

Porcelain Crab zoea larva

Zoea of porcelain crab photograph 6th May.

Trochophore larva of polychaete

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

Tintinnid Favella


Oikopleura tunicate

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.

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 diatom chain x200 with tubes_1.jpg

Lauderia x400


Skeletonema x400

Halosphaera prasinophyceae.jpg

Phycomata of the green alga Halosphaera 300 microns. Two different stages in the development

Pandorina green alga

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 x200.jpg

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. 

Ditylum brightwellii with Odonella mobilensis diatoms stack mar24-2.jpg
The common tintinnid which is abundant at present
Corethron diatom with Thalassiosira rotula

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.   

Oikopleura immature

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. 

Pandorina green alga

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! 

Marine Diatom Chaetoceros
Rhabdonema a marine diatom
Staurastrum a freshwater desmid found in seawater

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.

Edible periwinkle egg Littorina littorea

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.

Microsetella sp Harpacticoid  copepod female with egg sac

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

A Cumacea Crustacea from Milford Haven plankton

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.

Reproductive Stolon of Myrianida (Autolytus) carrying what appears to be eggs

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 ....

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