SUSSEX MARINE SITES OF NATURE CONSERVATION IMPORTANCE

Site: Whirlpool Hole						Ref. No. 14
Location: Just east of the Boulder Buoy, 3 km south of Selsey Bill					Other conservation designation?: No
Lat./Long. position of centre of site: 50° 41' 40" N  0° 48' 85" W			OS grid ref. of centre of site: SZ 837 885			Author: Robert Irving
Sea bed type: Steeply sloping seabed of gravel, with a few large boulders at the base.			Depth range (below chart datum): 10-20 m			Date identified: June 2001

Summary

Whirlpool Hole is an uncharted seabed feature which lies approximately 3 km south of Selsey Bill. Whilst no specific topographical survey has been carried out as part of the Sussex SEASEARCH Project, its overall shape appears to be funnel or cone-like. Interest in the feature is largely geomorphological. The diameter of the opening of the hole is in the region of 100-150 m, at the depth of the surrounding seabed (~ 10 m BCD). Its base is 10-15 m across at a depth of about 20 m BCD. The sides of the hole are at a slope of about 45° and are lined with gravel and pebbles and occasional cobbles. There are a few large limestone(?) boulders (~ 1 m in diameter) which have collected at the base of the hole. It is presumed that the hole has come to be in its present form by strong tidal action preventing it becoming filled with surrounding sediments.

Biological Description

The sides of the hole are lined with silty gravel and pebbles with occasional flat cobbles. Attached life is largely confined to the larger flat cobbles (being less mobile than the gravel and pebbles), with the exception of tubeworms Pomatoceros triqueter and occasional white anemones Actinothoe sphyrodeta. The cobbles are covered with various sea squirts (including Molgula sp., Didemnum maculosum and Botrylloides leachi) and occasional bryozoans (Cellepora pumicosa and Flustra foliacea in particular).

The large rounded boulders at the base of the slope (20 m BCD) are festooned with encrusting sponges, sea squirts and bryozoans, their tops adorned with dense clusters of hornwrack Flustra foliacea. The communities here are quite different (and certainly more diverse) than those on the surrounding pebbles and gravel.

Interestingly, McDonald (1985) describes Whirlpool Hole as being very similar to the Mixon Hole, with a sheer cliff of the same geological formation as the Mixon (i.e. a limestone cap over stiff blue clay, with a rubble strewn slope with boulders at the bottom). The descriptions from the two Sussex SEASEARCH dives undertaken at the site did not mention any likeness to the Mixon Hole, but it may be that that particular side of the hole to which McDonald was referring, was not surveyed. Clearly the strong tidal currents, which are a definite feature of this area, have had, and continue to have, a considerable influence on the existence of this hole.

Justification

Whirlpool Hole appears to be a unique geomorphological natural feature off the Sussex coast, the only other physical feature of any similarity being the Mixon Hole (mSNCI ref. no. 2).

References: Irving, R. A. 1998. Sussex Marine Life - an identification guide for divers East Sussex Council, Lewes Irving, R. A. 1999. Report of the Sussex Seasearch Project, 1992-1998 Sussex SEASEARCH Project, English Nature, Lewes, and Brighton & Hove Council, Brighton McDonald, K. 1985. Dive Sussex - A Diver Guide Underwater World Publications, London

Sussex SEASEARCH dive nos.: 716/50 & 58

Site Location

Diagrammatic representation of site: Whirlpool Hole