Lichens

A survey of the lichens of Sceilg Mhichíl took place in the summer of 2009. The survey showed that the island is an internationally important site for lichens.

The highly oceanic climate, isolated situation and geology all influence the lichen communities that have developed on this island. Sceilg Mhichíl supports a relatively rich diversity of 128 lichen species plus 2 lichenicolous fungi recorded during this survey including:

• 1 addition to the UK and Irish Flora: Lecania poeltii.
• 3 additions to the Irish Flora: Bacidia sipmanii, Caloplaca arcis and C. sorediella.
• 1 species for which Ireland has an International responsibility: Degelia ligulata.
• 2 RDB (Red Data Book) Vulnerable: Degelia ligulata & Ramalina chondrina.
• 4 RDB Near threatened: Anaptychia ciliaris subsp. mamillata, Opegrapha areniseda, Porina curnowii & Rinodina roboris var. armeriicola.
• 9 Nationally rare: Bacidia sipmanii, Caloplaca britannica, Degelia ligulata, Lecania poeltii, Opegrapha areniseda, Porina curnowii, Ramalina chondrina, Rinodina roboris var. armeriicola, Sphinctrina tubiformis (Lichenicolous fungi).
• 17 Nationally scarce.
• 28 Maritime indicator species.

Sceilg Mhichíl has been assessed in relation to other small Irish and Scottish Islands and based on this limited lichen data, has been classified as a Nationally important site for lichens.

The Conservation evaluation categories are based on Coppins and Woods 2003.

Surveyors

John Douglass (Scotland), and Paul Whelan (Ireland).

What is a lichen?

Lichens are the only known organisms that are composed of two or three different organisms. Typically they are composed of a fungus and an algae living together in such a close biological relationship that when separated the lichen as an organism ceases to exist. The algae uses sunlight to make food (photosynthesis), the fungus absorbs (saprophyte) nutrients from the environment. In some lichens these two organisms are joined by a bacterium that can photosynthesize (called a cyan bacterium). In other lichens cyan bacteria totally replace the algae. These latter lichens are jelly-like and live in damp strongly influenced by the Oceanic climate.
Sceilg Mhichíl is home to these three combinations of organisms that constitute lichens.

Sceilg Mhichíl and lichens

Its isolated location, geology and oceanic climate are key to its rich lichen biodiversity. 128 species were recorded there in 2009.

Skellig lichens and Geology

Sceilg Mhichíl is really the top of an Old Red Sandstone (ORS) mountain protruding above the Atlantic Ocean waves. ORS is about 400 million years old and is rich in the mineral silica.

Some lichens prefer calcareous substrates such as limestone or cement. Others prefer rocks rich in silica. The rocks of Sceilg Mhichíl are silica rich Old Red Sandstone with a little volcanic rock. There are no naturally occurring calcareous rocks, however due to the presence of Man on the island there are some cement and mortar substrates. Lichens have been recorded on both these substrate types on the island.

Skellig lichens and topography and other influences

The ground consists of loose boulders and smaller rocks. No trees or large shrubs are found that give shelter or substrate for lichens. Wind is persistent on the island.
Birds are found in abundance due to the rich source of seafood. Their droppings provide nutrients for lichens. The island’s invertebrates have a rich source of food in lichens.

Skellig lichens and the sea

The presence or absence of specific lichens in a locality is also determined by the influence of the sea. All parts of Sceilg Mhichíl are under the influence of the sea. Salt from the sea spray was recorded in all locations of the island, including the highest points.
Shoreline zonation of lichens on Sceilg Mhichíl is evident near the landing quay for the tourist boats. In 1913 the Irish lichenologist Matilda Knowles assigned species to coastal lichen zonation for the first time.

Lichens and Sceilg Mhichíl Food web

Lichens form a significant element in the food web on Sceilg Mhichíl, particularly the Ramalina species that constitute the bulk of the lichen biomass. Lichens are grazed by invertebrates, which in turn are eaten by non-seabirds of the island such as chough, rock pipit and raven. These in turn are prey to the islands top predator the peregrine falcon. This is just one example of a Sceilg Mhichíl food chain that contributes to the island’s food web.

Click for a photographic guide to selected lichens of Sceilg Mhichíl