Detail of entangled branching rootlets of a detached kelp holdfast on a beach stone at Ringstead Bay, Dorset, UK, (1) 

This tentacle-like entanglement, which seems to exude blood as it clings to the pebble, is a kelp seaweed holdfast washed ashore at Ringstead Bay, Dorset. It is likely to be from a Tangleweed or Oarweed – Laminaria digitata (Hudson) Lamouroux. It has been separated from the stem and frond of the alga so it is difficult to name with certainty. It could also be from a Sea Belt or Poor Man’s Weather Glass, Laminaria saccharina (Linnaeus); both types of seaweed wash up on this beach.

The wrinkled leathery texture of the wavy-edged stem of some kelp drying out on the beach at Ringstead Bay, Dorset, UK (2)

The wrinkled, leathery, rufous brown subject for the second photograph is a detail of the strongly-waved, frilly edge of a flattened seaweed stem. This is part of the Furbelows kelp, Saccorhiza polyschides (Lightfoot) Batters. The stem is changing from its normal greenish brown to a darker reddy brown colour; and from a smooth thin structure to one with a thicker, rougher, rippled texture as it dies and dries out.

Translucent kelp frond with water droplets on the beach at Ringstead Bay, Dorset, UK (3) 

This third photograph shows one of many kelp fronds on the Ringstead shore that had completely lost their colour and opacity. The washed-up fronds were clear or tranlucent and seemed to both contain bubbles or capsules within the structure as well as to be covered on both upper and lower surfaces with droplets of rain water. The light was reflected by the shiny, smooth, wet surfaces. These fronds might be from either the Furbelows, or Tangleweed or Cuvie kelps – the isolated fronds or blades being indistinguishable to the casual observer.

The features that resemble bubbles in the blades are probably “unilocular sporangia” from which the spores for the new generation of kelp develop. 

The fourth and final photograph below shows a detail of the holdfast which is typical of the Furbelows kelp. It is a hollow, approximately ball-shaped structure by which the seaweed attaches to rocks. The surface is warty and there are short, stubby rootlets.

Knobbly texture of a drying globular kelp holdfast at Ringstead Bay, Dorset, UK (4)  

Revision of a post first published 29 September 2009


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