Early studies of Mediterranean-Atlantic species

Following on from the descriptive lists of species recorded from the voluntary marine nature reserve during the 1970s, the next step was to start to investigate the dynamics of communities of high nature conservation importance, concentrating on just a few individual species. In 1984, the Nature Conservancy Council initiated a monitoring programme looking at the growth rates and longevity of certain species and communities. In the intertidal, these included rockpool communities and cup corals (notably the common Devonshire cup coral Caryophyllia smithii and the far less common scarlet and gold star coral Balanophyllia regia). In the subtidal, species of interest included the pink sea fan Eunicella verrucosa, the sunset cup coral Leptopsammia pruvoti and the yellow staghorn sponge such as Axinella dissimilis (formerly recorded as A. polypoides).

Both of these NCC-funded intertidal and subtidal studies were designed and established by Dr Keith Hiscock. The intertidal rockpool and cup coral studies continue to this day on an annual basis, now undertaken by on-island Wardens. The subtidal studies were largely wound-up after six years (once it was considered most questions regarding growth rates and longevity had been answered), although studies of sunset cup corals at the Knoll Pins have continued, albeit intermittently, using contracted staff.

The main results from these studies have shown:

• Pink sea fans grow at a very slow rate, with individual branches (not all at once) growing approximately 1 cm/yr. An individual fan, 50 cm broad either in height or width, is likely to be at least 50 years old (see also separate section below).
• Since the start of monitoring photographs being taken (in the early 1980s), the number of individual sunset cup corals at the Knoll Pins has been gradually declining. More fully grown ‘adults’ are being lost than new recruits are growing from larvae. The reason for this is unclear. The latest monitoring event (in 2022) showed there to be more settlement of larvae in recent years, which is encouraging (see separate section below).
• The yellow staghorn sponge was found to extend the length of some branches in some years, yet contract their length in other years. This species is also likely to be long-lived (possibly to 50 years or more) when environmental conditions are favourable.

Full details of these early studies are given in Fowler & Pilley (1992a) Report on the Lundy and Isles of Scilly marine monitoring programmes, 1984-1991. Vol.1: Report

Intertidal Devonshire cup corals and scarlet and gold star corals

Two species of cup coral occur on the lower part of the Devil’s Kitchen shore in Lundy’s south-east corner, only exposed during periods of good spring tides: the Devonshire cup coral Caryophyliia smithii and the scarlet and gold star coral Balanophyllia regia. Individuals of both species are found together attached to the undersides of bedrock and large boulder overhangs. Two sites are monitored here, one since 1984, although it is only in recent years that visits have been on a regular annual basis.

Prior to this study taking place, it was not known how stable these populations might be. Was there a settlement of new recruits each year? Was there a continuous turnover of individuals? Did numbers vary widely from year to year?

The results of this on-going study have shown numbers of both species being monitored (though of Devonshore cup corals in particular) to be highly variable from year to year. The latest information from these studies is listed in the Bibliography.

The condition of pink sea fans at Lundy

A study of pink sea fans was initiated in 1984 by the Nature Conservancy Council in order to monitor their growth rates. Photographs were taken of individual sea fans which could be re-identified each year, with a marked grid held behind each sea fan. The study found that the growth rate of these gorgonian corals was slow (at about 1 cm/yr) and that in any one year, growth might occur at the extremity of one branch but not at others.

Some years later, a separate study, between 1995 and 2001, aimed to assess the overall condition of individual pink sea fans at Lundy as one of a number of surveys undertaken by volunteer divers as part of a range of citizen science projects (Irving & Northen, 2004). The size (height and width) of each sea fan was noted together with a measure of the degree of fouling by other organisms such as drift algae, hydroids, barnacles (Solidobalanus fallax) and bryozoan colonies (Cellaria sp).

Fortunately, this study began before any obvious signs of anything being wrong became apparent. It was in 2000 and 2001 when the condition of the pink sea fans (particularly off the east coast) was noted to have declined considerably. The first sign was that the amount of drift seaweed fragments becoming entangled on the fans had increased. These fragments led to the feeding polyps becoming smothered and the fleshy tissue covering the branches decaying. The exposed black skeleton of the branch then became colonised by fouling organisms.

A follow-up study of pink sea fans throughout the south-west in 2001 and 2002 led by Chris Wood utilising volunteer divers belonging to the Marine Conservation Society found that, of all the sites surveyed, the sea fans at Lundy fared the worst (see diagrams below).

The mean condition scores (where 5 is pristine and 1 is >80% of fan Is damaged or overgrown) of sea fans at Lundy from 1998 to 2010. Note the decline in condition in the years 2000 and 2001. Data obtained by volunteers in most years but by professional biologists in 2003 and 2010 (after Irving, 2011).

The mean condition scores of sea fans from various locations off SW England and the Channel Islands in 2000 and 2001. Data obtained from Marine Conservation Society volunteer divers and published in an MCS report authored by Chris Wood in 2003.

A follow-up study into the demise of pink sea fans at Lundy was undertaken by Dr Jason Hall-Spencer and colleagues at the University of Plymouth, leading to a paper being published in 2007 in the journal Diseases in Aquatic Organisms. They identified the problem was being caused by an infection of Vibrio bacteria. This was the first recorded incidence of a disease being found in a coral species growing in cold, temperate waters rather than in warm-water corals associated with tropical reefs (Hall-Spencer et al., 2007).

The population of pink sea fans at Lundy has still to fully recover from the bacterial infection around the turn of the 21st century and may never reach the numbers present during the 1970s. However, some new sea fans have appeared and continue to appear, so we live in hope.

All reports concerning studies of pink sea fans at Lundy can be found in the Bibliography.

The story of the sunset cup coral at Lundy

The sunset cup coral Leptopsammia pruvoti is unreservedly the jewel in Lundy’s underwater crown with its stunning bright yellow colour making each individual coral stand out against an often drab and dull background of silted hydroid-bryozoan turf. It was discovered at Lundy by a young Keith Hiscock in August 1969 who then spent a year trying to find out what it was! It turned out to be a Mediterranean cup coral and this was the first time it had been seen in British waters. Besides being the largest of the solitary cup corals found in British waters (the width of the stony base reaching 17 mm and a height of 60 mm), it is also the rarest. Whilst most individuals are bright yellow all over, some have orange colouring around the mouth – hence the common name of ‘sunset’ cup coral.

Lundy is at the furthest north of its geographical range, with just a handful of other sites in SW England where it is found (Isles of Scilly, Plymouth drop-off and some of the reef outcrops in Lyme Bay). The coral is also found at Sark in the Channel Islands, off Brittany, at scattered sites off the coasts of Spain and Portugal, and along the northern shores of the western Mediterranean.

Lundy’s small (and sadly diminishing) population of these corals is to be found on vertical and overhanging bedrock at the Knoll Pins, as well as individuals being scattered at a few other locations off the north-east coast of the island. Their depth range at Lundy is from 15 m to 30 m (below chart datum).

A long-term photographic monitoring study of these corals has been on-going since 1984, at two sites on the Knoll Pins where their numbers are concentrated. Sadly since this time, their numbers have been diminishing, with fewer than 30% of the number originally recorded now being present. Since 2007, individual corals have been identified (by allocating unique numbers to individuals), which has allowed their plight to be evaluated in greater detail.

The possible cause or causes of this demise have also been investigated though, as yet, with no one prime suspect identified. Possibilities include:

On the edge - the range of the sunset cup coral extends from the warmth of western Mediterranean waters to the chilly waters of the Outer Bristol Channel. It has been proposed that the species once had a much more extensive coverage in SW Britain (and quite possibly beyond) about 700+ years ago when seas were generally warmer and that the few scattered populations in SW Britain are all that’s left in ‘ideal’ locations only.

Lifespan and water temperatures – studies have determined the maximum  lifespan of individual specimens in the NW Mediterranean to be 13 years. The age of an individual can be measured by counting growth rings in the corallum (the stony structure of the coral). Some of the older individuals at Lundy have been shown to be at least 15 years old, having been re-identified in photographs in 2007 and 2022. Across the species geographical range, mean sea surface temperatures range from 12°C at Lundy to 19°C in the Ligurian Sea (NW Mediterranean). One wonders if the longer lifespan here is a direct consequence of a slower metabolic rate linked to cooler sea temperatures.

The impact of other associated organisms – various organisms may be having an adverse impact on individual sunset cup corals. These include: the acorn barnacle Adna anglica, which grows on the corallum and calyx of the cup coral and probably competes for planktonic food; the horseshoe worm Phoronis hippocrepia, which was observed growing close to the base of corals in 1997 and 1998 and is suspected of boring into the coral’s base thereby weakening its attachment to the rock surface; the ‘grab-a-mouthful’ feeding behaviour of ballan wrasse Labrus bergylta, which have been observed to peck at the hydroid-bryozoan turf in the hope of consuming amphipods or isopods, thereby dislodging weakened corals which might be regarded as ‘collateral damage’.

One bit of good news in this rather sorry saga is that newly settled corals are now being regularly found in amongst the older, larger individuals. First seen in August 2001 (see photo to right), these ‘new recruits’ to the population are difficult to see, being only 2-3 mm in diameter and often obscured by the surrounding hydroid-bryozoan turf.

As part of the latest assessment of the sunset cup corals at the Knoll Pins East site, a comparison was made of the total population counts and the proportion of adult individuals (i.e. those with a calyx diameter greater than 5 mm) to ‘new recruit’ individuals (i.e. those with a calyx diameter less than 5 mm) – see diagram below.

Pie diagrams indicating the varying proportion of ‘adults’ to ‘new recruits’ within the sunset cup coral population at the Knoll Pins East site. The overall size of each ‘pie’ indicates the size of the population at the time of that year’s monitoring event. Whilst the population has reduced in size over the 15 years, one encouraging sign is that the proportion of ‘new recruits’ apparent in 2022 has increased.

The process of identifying individual sunset cup corals from year to year

All reports concerning studies of sunset cup corals at Lundy can be found in the Bibliography.

The MarClim programme

MarClim stands for Marine Biodiversity and Climate Change. The programme is led by the Marine Biological Association based in Plymouth and was initiated in 2002.

MarClim has the most spatio-temporally extensive time-series of rocky intertidal systems globally. Eighty seven species of invertebrate and macroalgae of boreal (cold water), Lusitanian (warm water), and invasive origins are surveyed at one hundred sites around the coastlines of the UK and northern France and surveyed every year. Lundy is proud to have been chosen as one of these sites. MarClim has shown some of the fastest biogeographic range shifts in response to climate change in any natural system. More information about the MarClim programme can be found here.