“Jelly Bags” Seaweed at Port Eynon

A couple of things were especially interesting about the Spiral Wrack on Port Eynon beach late in June. The first was the abundance of it and the profusion of the yellow reproductive bodies (scientific name receptacle, common name jelly bags). The second was the variety of sizes, shapes, and different stages of development of these receptacles – and the presence of a number of unusual structures that can be classified as abnormal.

Spiral Wrack (Latin name Fucus spiralis Linnaeus; alternative common names Flat Wrack and Jelly Bags) is a common British seaweed. It lives in the mid-shore zone below the Pelvetia canaliculata zone (Channelled Wrack) of the upper shore, and above the Fucus vesiculosus (Bladder Wrack) and Acophyllum nodosum (Egg or Knotted Wrack) zones of the lower shore. It is exposed to the air for long periods of time between high and low tides. This alga is hermaphrodite with male and female reproductive structures on the same individual.

The receptacles of Spiral Wrack are developed as swollen tips, often bifurcate or forked, at the ends of the fronds. Cryptostomata, that elsewhere on the fronds remain as sterile pits containing only hairs, develop in this location as fertile conceptacles that produce both male and female gametes. Typically receptacles are broadly ellipsoidal to almost spherical and when full, ripe, and full of mucilage, are sometimes called jelly bags

On some fronds there are also smooth, elongated, swollen structures without the small protruberances and pores that are seen on receptacles. Examples of these can be seen well in Photograph 5. This unusual feature looks like a blister; and specimens of Fucus spiralis with blistered fronds are, apparently, not uncommon. These blisters are not to be confused with air bladders – like the ones found in Fucus vesiculosus. They are instead an irregularity or abnormality, with varying shape and size, thought to be due to some adverse conditions in the environment. They lack the regular, defined, shape of an air vesicle which is inherent in the structure of seaweeds such as Bladder Wrack and Egg Wrack. Perhaps recent encroachment by sand and partial burial in this part of the beach has stressed a seaweed that is normally free to float upwards in seawater while attached to rocks.

“Jelly Bags” seaweed might also be good for the feet. Walking barefoot through the squelching masses could have a certain therapeutic effect (if you don’t slip over first). However, for the most benefit, soaking the feet with a few handfuls of the jelly bags in a bucket of hot water and salt is traditionally thought to be an efficaceous treatment for corns!

Click her for more posts about Spiral Wrack on Jessica’a Nature Blog:

Flat or Spiral Wrack from Chapmans Pool

Three brown seaweeds: Furbelows, Sea Belt, and Spiral Wrack from Studland Bay in spring