Introduction | 10419926

Apart from being one of the best surfing beaches in Cornwall Fistral beach has an interesting rocky shore environment ready for investigation. We all know that barnacles are those small grey scratchy protrusions but do we know why they are where they are on the rocky shore and what function they serve?

The rocky shore is the interface between the land and the sea. It can act as a flood defence barrier, it provides habitat for breeding, nurseries and refuge for fish and crustaceans of which are important for harvest or as part of the trophic regime supporting human resources.

The rocky shore environment is varied and dynamic and the organisms that spend all or part of their life cycle there are numerous in number and varied in their adaptions to cope. All organisms that spend time in this environment are affected by abiotic and biotic factors. Biotic factors include larval dispersal, predation and grazing and competition for resources. Abiotic factors include substrate, wave action and tide. The rise and fall of tides mean that organisms are subject to environmental gradients including exposure, light, temperature, salinity and desiccation. Depending on height on shore these conditions will vary. (Field Studies Council, No date

The rocky shore is divided into zones and these are influenced by the reaches of the tides (Figure 1).

Figure 1 Intertidal or littoral zones (Fenwick, D., No date)

Barnacles are one of many organisms found on the rocky shore in the UK. The three main species are Semibalanus balanoides, Chthamalus stellatus and Chthamalus montagui (Connel, 1961) (Crisp, et al., 1981). Barnacles are members of the phylum Arthropoda, subphylum Crustacea, class maxillopoda, subclass Theocostracea and infraclass Cirripedia. (Fish & Fish, 2011). Barnacles are solely marine and were not classified as crustaceans until the 1830,s by J.V Thompson (Winsor, 1969) as they were previously thought to be molluscs.The adult barnacle is sessile and it sits in a hard calcareous shell of which the former barnacles have six. When the tide is out the barnacle seals itself inside to prevent desiccation allowing it to survive the low tide and when the tide goes out it pushes out its six cirri or thoracic appendages (Figure 2) which filter food particles that are suspended in the water pulling them in for consumption.

Figure 2 Anatomy of a barnacle (Washington.edu, 2007).

The barnacle is hermaphroditic and capable of cross fertilisation generally with neighbours. Barnacles have two larval stages. They release the first stage naupilii to the sea to feed, grow and moult and develop into the second larval stage the cyprid. The cyprid selects a site usually of barnacles of the same species and attaches itself to the substrate using two modified antennae. These antennae pour out a kind of cement and the cyprid metamorphoses to a juvenile barnacle. (Fish & Fish, 2011).

This investigation examines barnacles found on Fistral and explores their distribution and abundance in relation to height. It also explores other aspects such as barnacle function and trophic role in the community.