Seasearch Pink sea fan survey

One of our specialist projects since 2001 has been to collect more data on sea fans in SW Britain. To date there have been a number of reports arising from this work all of which can be downloaded from this website. They are:

Pink Sea Fan Surveys 2001-2002

Devon sea fan surveys 2005

Cornwall sea fan surveys 2005

Pink Sea Fan Surveys 2004-2006

Lyme Bay Surveys June 2007

We now know that pink sea fans occur from Poole Bay in Dorset and around the whole of the south-west peninsular as far as Ilfracome as well as in the Channel Islands, Pembrokeshire and southern and western Ireland as far north as Donegal.

We know that the densest 'forests' of sea fans occur in deeper water, below 25m and generally on flattish rocks and wreckage.

We know that in most areas the populations are in generally good condition but in some there are significant levels of disease leading to mortality and overgrowth by other animals.

We know that white sea fans are healthy, but rare, that sea fan anemones are very rare indeed and that up to 20% of sea fans in some areas have sea fan nudibranchs resident on them.

So what else is there to discover?

In 2008 we have a number of targets for sea fan recording. These are:

Continue to look for sea fan forests, including those on deeper wrecks

We identified a new dense sea fan forest south of The Manacles in Cornwall in 2007 and want to continue to identify dense populations so they can be recorded and recommended for protection. Some of the densest sea fan forests can be found on wrecks - a new one was reported in Bigbury Bay in 2007.

Continue monitoring sea fan anemones on the Rosehill in Whitsand Bay

this is a continuing project photographing individual seafans on a regular basis and identifying changes to position and numbers of the rare sea fan anemones on them.

Continue to locate the extent of sea fan forests and sunset cup-corals on The Drop Off south of Plymouth

This is one of the densest areas for sea fans in the whole of the UK. We are gradually recording its extent and have recommended the area for protection.

Record the presence of sea fan nudibranchs throughout the range

Formerly found on about 20% of sea fans there was a dramatic drop in numbers n 2006 and we want to see if they increase in 2008.

So, whilst records from any site will be welcome, those from all the areas above will be particularly helpful.

How you can take part

In some cases we are arranging special sea fan recording dives but we hope that most of the information will come from divers who are diving these areas as a part of their dive plan for the year. All you need are copies of the forms and guidance notes, which can be downloaded below, a slate and means of measuring underwater (the Seasearch slates already have a scale printed on them so are ideal).

There are two recording forms, one for general use, and one for use on deep wrecks where bottom time is very limited. There are separate guidance notes for recorders for the general form and the, simpler wreck recording form has them printed on it. Follow the links below to download them

General recording form

Notes for Recorders

Wreck recording form

Anemones and Nudibranchs

One of the things we are looking out for in the general sea fan surveys is the presence of two animals that live on sea fans, the Sea fan anemone and the Sea fan nudibranch.

Sea fan anemone, Amphianthus dohrnii

Once thought to be quite common these little anemones now seem to be extremely rare. We have seen them at Lands End, The Manacles, off Plymouth and in Bigbury Bay, but nowhere else. Even here less than 1% of sea fans have them on them!

These two pictures show what you are looking for. The top one is a close up showing a single anemone. It is around 1cm across and, as you can see, is wrapped around one stem of the sea fan.

The bottom picture shows how you often get a number of anemones on a single sea fan. This is because of their reproductive strategy which uses basal laceration - basically tearing a new anemone from the base of the old one.

The presence of a number of anemones seems to encourage the settlement of other life, here a silty turf, in areas where the living skin of the sea fan has been damged by the base of the anemone.

Sea fan nudibranch, Tritonia nilsodneri

The sea fan nudibranch is much more common, at least in some areas. In the Manacles, Cornwall 26% of sea fans have sea fan nudibranchs or their eggs on them. On the other hand noe were seen in our previous survey at all in Pembrokeshire and they were rare in Lyme Bay and Purbeck.

The adult is an amazing mimic of the sea fan polyps both in colour and shape and very difficult to spot.

The egg sprials, though small, do stand out better since they are quite different shape to anything else on the sea fan. The picture shows a spiral of eggs around the tip of one of the sea fan branches.

For more information about these two species and sea fans as well visit the MarLIN website at www.marlin.ac.uk/ and follow the species links.