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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

An extract of the pink sea fan data is also available to use on the National Biodiveristy Network website. This includes all of the records of pinks sea fans, sea fan anemones, sea fan nudibranchs and sea fan false cowries, except for those from the Channel Islands which the NBN cannot yet display. It does not include the size, condition and fouling species data.

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 Ilfracombe 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 have been significant levels of disease leading to mortality and overgrowth by other animals.

We know that sea fans are easily damaged by trawling and gill netting.

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?

We continue to 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.

Continue to look at outlying populations

We are especially interested in sea fans at the present extent of their range to see if there is any spreading taking place in places like Dorset, North Pembrokeshire and Donegal. Look out for small sea fan 'sticks' as well as mature colonies. The range in North Pembrokeshire was extended slightly in 2008 with a sighting close to Strumble Head.

Continue monitoring the condition of sea fan populations around Lundy

Sea fans on Lundy suffered extensive damage from disease in the early 2000s and we are cntinuing to monitor their gradual recovery.

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 the site has now been included in a Special Area of Conservation.

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 in 2006 but by 2008 they seemed to be on the increase again.

Record the presence of sea fan anemones throughout the range

Numbers of sea fan anemones remain very small and have a more restricted distribution than pink sea fans as a whole.

Record the presence of false cowries, Simnia hiscocki, on sea fans. False cowries have been recoreded more often in recent years and we are interested in finding out more about their numbers and distribution.

Thus 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).

You can also enter your sightings on-line. Just follow the link below to register of on-line recording.

General sea fan recording form

Notes for Recorders

On-Line Sea Fan and Crawfish recording

 

 

Anemones, Nudibranchs and False Cowries

One of the things we are looking out for in the general sea fan surveys is the presence of these three animals that live on sea fans.

Sea fan anemone, Amphianthus dohrnii

Once thought to be quite common these little anemones now seem to be extremely rare. We have seen them in the Scilly Isles, near 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.

We have carried out a survey of sea fan anemones on the wreck of the Rosehill in Whitsand Bay over a six-year period and the results can be viewed here: Roeshill Sea Fan Anemones 2006-12.

 

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.

 

False Cowrie, Simina hiscocki

The False Cowrie that lives on sea fans has recently been shown to be a separate species to the one which lives on soft corals. Like the species, above it feeds on the sea fan polyps, but numbers are low and it does not seem to do any permanent damage.

We are interested in records of this species to establish its distribution and numbers.

Eagle eyes are required to spot it!

 

 

 

 

 

 

 

 

 

 


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