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The Seashore

Catenella caespitosa (small red alga)

Catenella caespitosa

Catenella below a frond of Pelvetia in the upper shore

Now here's a peculiar thing. Red algae are not commonly found high up on seashores their photosynthetic pigments (phycoerythrins and phycobilins) are denatured by the strong sunlight that they get there. Catenella caespitosa is an exception. It looks more like black moss than red seaweed due to its protective black pigmentation and it's only found on sheltered shores. These tend to face north in our part of Pembrokeshire and therefore get less sunshine. It also confines itself to dim, moist cracks and crevices or finds similar conditions by living under other species like Pelvetia canaliculata and Fucus spiralis. It has no known use for humans and so does not have a common name. The Latin name comes from catena = a chain and caespes = turf.

Catenella caespitosa

It is a perennial alga and like other algae at this height above chart datum is a hermaphrodite. Tiny spermatia (male gametes) are released but unlike many algae the red spermatia do not have a flagellum and so drift with the currents to fertilise the oogonium (female gamete). The latter is in a flask shaped bag at the edge of the frond. As well as this sexual method of reproducing they also release spores, asexually, into the water.

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