Ulva prolifera O.F.Müller   
   (= Enteromorpha prolifera (O.F.Müller) J.Agardh)   

Kingdom: Plantae
Phylum: Chlorophyta – green algae
Class: Ulvophyceae
Order: Ulvales

British distribution: Round the whole coast, commonly in estuaries.
World distribution: Evidently widespread.

Ulva prolifera on estuarine sand and mud

A common green alga near the top of the shore, on rocks or other algae, on open coasts or in estuaries and harbours, where it may grow mixed with U. intestinalis or other species of the genus. It is better known as Enteromorpha prolifera, but Enteromorpha is now considered to be part of the genus Ulva (Maggs et al., in Brodie et al, 2007).

The fronds are tubular, though often more or less flattened, little to much-branched. The arrangement of the cells, in longitudinal and transverse rows in the central part of the frond, is characteristic of this species, as are the cylindrical chloroplasts seeming to fill the cell and the usually single, central pyrenoids. Critical identification details are provided by Burrows (1991) (as Enteromorpha prolifera) and updated and clarified by Maggs et al., in Brodie et al (2007).

Ulva prolifera: showing longitudinal and less distinctly transverse rows of more or less quadrate or rectangular cells, often paired, with mostly single, central pyrenoids.

The life history is an isomorphic alternation of generations. Gametes (biflagellate) and zoospores (quadriflagellate) are released from the tips of the fronds, which have a slightly darker appearance when fertile.

Release of biflagellate gametes from cells at tip of frond.

Predictably, the fronds are colonised by epiphytic diatoms, particularly, it seems, on some of the smaller, more rigidly tubular branches:

Ulva prolifera, showing colonisation by diatoms
Ulva prolifera, showing colonisation by diatoms

Photographs: estuarine shore at Longniddry, East Lothian (Firth of Forth), April 2001. Initially these were identified as the closely similar U. flexuosa, though with some concern about pyrenoid numbers, but reassessment following the publication of Brodie et al. (2007) indicates that the species illustrated here is U. prolifera, which is now known to be much the more frequent species (Hardy & Guiry, 2006).

•   Brodie, J., Maggs, C.A., & John, D.M., eds. (2007). Green seaweeds of Britain and Ireland, British Phycological Society [London].
•   Burrows, E.M., (1991). Seaweeds of the British Isles: 2 Chlorophyta. Natural History Museum, London.
•   Hardy, G., & Guiry, M.D., (2006). A checklist and atlas of the seaweeds of Britain and Ireland, revised edition, British Phycological Society, London.

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