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Second to the diatoms, dinoflagellates are the second most important primary producer in the sea and yet are quite animal like. These single-celled creatures are always present in Dale plankton samples and are extremely varied from forms barely 25 microns to Noctiluca often visible to the naked eye at several millimetres across.

Two different flagella are present. Some like Noctiluca are naked others are covered in armour plates or thecae.

dinoflagellate Akashiwo

The tiny dino, Akashiwo, approx 50 microns across

Noctiluca dinoflagellate

Noctiluca among barnacle larvae

dinoflagellate Noctiluca extended tentacle

Noctiluca extended tentacle used to catch food.

The Dinoflagellates

dinoflagellate Noctiluca scintillans

Noctiluca scintillans, approx 1mm across

Bouyancy is achieved by accumulating lighter ions in the cytoplasm. Noctiluca is the best example of a bioluminescent plankter and people use social media to track the best shores where waves break in a blue glow of light. While common in the open sea samples within the Haven usually only have this species in autumn.

Armoured or thecate Dinoflagellates

Ceratium dinoflagellate
The dinoflagellate Ceratium flagellum
The dinoflagellate Ceratium fusus

Ceratium spp, approx 200 microns

Ceratium furca with flagellum visible
Dinophysis dinoflagellate
dinoflagellate protoperidinium
Protoperidinium dinoflagellate

Dinophysis sp, approx 60 microns

Protoperidinium spp, approx 80 microns

Haptophyta and Climate Change

As stated before, classification is difficult as there is so much biodiversity and variation within the single-celled organisms. This group contains an array of species that are mainly marine and probably the most important with regard to carbon cycles and climate change. This importance has existed for the last 150 million years. Some of these haptophytes have outer scales of calcium carbonate called coccoliths and a blizzard of these drop to the bottom of the oceans taking 25% of all sea carbon to create a limestone sea floor. 

The haptophyte most abundant around Milford Haven is Phaeocystis and does not have a coccolith. Its significance, however, is also profound as it can cause huge blooms. These produce dimethylsulphide (DMS) which can stimulate/enhance cloud formation over the ocean and cooling.  

Phaeocystis globosa colony
Phaeocystis globosa colony with diatoms

These photos are of non-motile Phaeocystis when it comes together in colonies encased in mucilage. When blooms cocur in the Haven these coalesce into huge clumps of mucus often completely filling the plankton net. When cells are mobile they have two flagella between which is another extension called the haptonema from which the group get their name. 

Photo below is of a Phaeocystis colony with a polychaete larva stuck to the mucus

Phaeocystis globosa colony with polychaete larva stuck to mucus
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