Here today, gone tomorrow - the Peacock worm Sabella pavonina

As you walk along the water's edge on a very low tide admiring the sparkling scene, cast your eyes down to the sandy mud where you may see a scattering of mysterious rubbery tubes, slimmer than a pencil, standing half-buried but erect and open.

Peacock worm
Sabella pavonina

If they are still covered by water you may be lucky enough to see a delicate circular fan emerge and sway gently in the current. The appearance of this beige coloured feathery crown with maroon rings shows that the Peacock worm is actively seeking suspended particles for food or building material from the safety of its tube.

The body of the worm is similar to that of the familiar garden earthworm but pairs of stiff bristles on each segment enable the worm to move quickly within the tube where it spends its entire life. Only the crown or 'feather duster' emerges into the water.

Divers can enjoy the sight of 'fanning' Peacock worms scattered mainly on muddy sand or amongst eelgrass or maerl but it is between the tides that the highest density is reached. Under favourable conditions our shores can bristle with vast numbers of healthy tubes, often in clumps of 70+. However this can change quite quickly as I found during a prolonged study in the Fal and Helford estuary complex.

Between 1970 and 1986, populations of these worms declined dramatically but they then staged a gradual comeback from about 1992 which became apparent during the course of my marine recording. A diligent search through the literature and meteorological records linked the 1980s loss to periods of prolonged low winter temperatures, plankton blooms in hot summers and the use of organo-tin anti-fouling paint on boats. These toxic paints had severely damaged many shellfish and were banned for use on small boats in 1987.

Data collected during the course of monitoring the return of the species showed that worms were most successful living between narrow limits of exposure between tides corresponding to an upper limit of 0.75m above Chart Datum (lowest astronomical tide) with an optimum of 0.5m above CD. Calculations showed that this meant that they were exposed only on about 17% of all the tides when frost, drying or overheating could be stressful.

Small sediment particles trapped on the tentacles of the fan were quickly mixed with mucus to extend or repair the tube and the surrounding muddy sand ensured an abundant supply. Below the surface of the sand the tube was thickened to resist crushing and the tail end of mature worms reached some 15cm down amongst a sandy-mud-small stones mixture. Shores with deep mud and few stones offered less stability and could clog the delicate fan. Detailed work indicated that the main period of reproduction was in the late spring.

The Fal estuary sediments are well-known for their content of various metals and related elements, a reminder of the rich industrial mining heritage of the area. The Helford River has been far less affected and it has been interesting to compare the Peacock worms from both places. The worms are in close contact with the particles which are sorted by size for tube-building but healthy Peacock worm populations are found in sediments with either high or low heavy metal content suggesting a degree of tolerance.

The limited periods of tidal exposure and hence limited access to the worm beds prolonged the study which ran from 1995-2001+ during which time the numbers continued to escalate. However a brief but severe algal bloom along the south Cornish coast in the late summer of 2002 killed a wide range of marine animals with which it was in contact - this included the main Helford Peacock worm beds and also some in the Fal. Once again the many thousands were reduced to a mere scattered handful. No doubt these survivors will re-establish the species again in due course - a challenge to someone else to develop another PhD thesis?

Dr Pamela E Tompsett

Extract from HVMCA newsletter No.28 Spring 2004