Patella vulgata were excluded from barnacle dominated areas at Port St Mary, Isle of Man by wire fences attached to the rock in September 1977, December 1977, April 1978 and July 1978. The sequences of algal colonization of these exclusion areas differed markedly with season: in autumn diatoms were followed directly by Fucus, in winter and spring diatoms were followed by green algae and then Fucus, and in late summer Fucus sporelings arose directly on the barnacles. There was no evidence that the initial stages were necessary for the subsequent recruitment of Fucus.

The breakwater in Plymouth Sound offers a simple case of two adjacent populations ofintertidal organisms subjected to quite different degrees of exposure to wave-action. The other environmental factors, with a few exceptions, are approximately the same each side, and the effects of the wave-action should be clearly demonstrable.

Some preliminary observations in North Cornwall (Orton, 1946) showed that the periods of breeding of the three British species of limpets were different. In order to determine these differences more accurately, and to study the breeding cycle, samples of limpets from six localities in Britain were examined at regular intervals for 5 years. This paper gives the results obtained for the common limpet Patella vulgata, which was present at all the localities sampled and was the most intensively studied of the three species. Later papers will deal with the remaining species and with other aspects of the investigations.

The English Channel may conveniently be divided into a western basin and an eastern basin separated by a line drawn approximately between the Cherbourg peninsula and the Isle of Wight. In these basins, the environmental factors are very different. Thus the water of the western basin is on average warmer and slightly more saline than that of the eastern basin and its temperature variation is less extreme. The French side of the Channel is warmer than the English coast only in the western basin. The tidal oscillations in the two basins are out of phase with each other and the strongest tidal currents occur where the two basins join. The main residual flow is up-Channel with minor coastal eddies.

The shores at the western end of the Channel are generally rocky, they are close to deep water, and so are exposed to frequent heavy swells. The shores of the eastern basin are generally erodible, and accumulations of sand and shingle tend to reduce the force of the waves. The water of the eastern basin generally contains more suspended matter and the shores are usually scoured by sand and shingle.

The distribution of the following animals is given in some detail and compared with earlier records: Ammonia sulcata, Actinia equina, Chthamalus stellatus, Balanus balanoides, B. perforatus, B. crenatus, B. improvisus, Elminius modestus, Verruca stroemia, Hemioniscus balani, Patella vulgata, P. depressa, P. aspera, Monodonta lineata, Gibbula umbilicalis, G. pennanti, G. cineraria, Littorina saxatilis, L. littoralis, L. littorea, L. neritoides, Paracentrotus lividus. The distribution of certain other species is also discussed: Balanus balanus, Haliotis tuberculata, Gibbula magus and Calliostoma zizyphinum.

It is well known that towards the limits of an animal's geographical range both its abundance and exact boundaries may fluctuate from time to time. These fluctuations can sometimes be correlated with environmental changes, and thus may help to assess the relative importance of the factors that control distribution. For example the distribution of the common intertidal barnacles Chthamalus stellatus (Poli) and Balanus balanoides (Linnaeus) underwent changes which were attributed to a general rise in temperature over several years (Southward & Crisp, 1954a). The abundance of these barnacles has fluctuated further since 1951–52, and we are now able to analyse more closely the relation between the population changes and environmental variations.

1. Vertical traverses down the shore were worked at four localities in the Isle of Man, with varying degrees of wave-exposure, for which factor a coefficient is given.

2. The upper limit of distribution is high water neaps in a sheltered place, and up to high water of extreme spring tides at greater waveexposure. The lower limit similarly drops with increasing exposure.

3. Barnacles are largest and most abundant in a wave-exposed locality. The effect of wave-exposure may be reproduced by a current.

4. In sheltered localities the optimum level for growth, mean size, etc., is at low water for newly settled barnacles, but moves progressively up to high water as they grow older. In a very exposed situation, however, the optimum is always at low water.

5. In an exposed situation the gonads mature in their first year below about half-tide level, and in their second year above this level. With decreased wave-exposure the age of maturation rises, especially at high water until in a very sheltered place few barnacles mature at all.

The long term effects of macroalgal canopy removal on community composition were investigated over a 12 year period. Experimental removal of the dominant Ascophyllum nodosum canopy led to short term changes in community composition, the major features of which were still apparent 12 years later. Ascophyllum was slow to recover despite high recruitment, and experimental plots were dominated by Fucus species. After 12 years a mixed assemblage of Fucus serratus, Fucus vesiculosus and Ascophyllum had developed. Canopy removal resulted in a change in the balance between grazing limpets and the cover of red algal turf in the understorey community. The cover of turfing algae declined significantly allowing the area grazed by limpets to extend. This led to a 3–6 fold increase in the limpet population 12 years after canopy removal.

The distribution and abundance of Ascophyllum nodosum, Fucus serratus and F. vesiculosus were described at four sheltered, rocky shores in the south of the Isle of Man. Canopy removal experiments were performed at mid tide level of one sheltered, canopy dominated shore to investigate the interactions between the dominant canopy alga, Ascophyllum nodosum and the competitively inferior canopy species of Fucus serratus and F. vesiculosus. Ascophyllum was removed from replicated plots, 2×2 m in size, in both winter and summer; the early growth and survival of fucoids in the presence and absence of the Ascophyllum canopy were monitored and the eventual development of a new canopy described. Juveniles of F. serratus originally present beneath the undisturbed canopy of Ascophyllum died following canopy removal but new recruitment resulted in some canopy development, principally in the winter experiment. Fucus vesiculosus, despite being completely excluded from the Ascophyllum zone of all four shores described, dominated the canopy removal plots of both winter and summer experiments. The Ascophyllum canopy did not recover over a five year period of observation, although a considerable increase in the abundance of Ascophyllum juveniles occurred.

1. Church Reef, in Wembury Bay, near Plymouth, was selected for a survey of common intertidal plants and animals.

2. Four traverses were accurately levelled relative to Ordnance Datum, and their floras and faunas examined.

3. The relation between predicted tide levels and probable actual levels is discussed, and the importance of the “splash zone” is stressed.

4. As an outcome of 2 and 3, it appears that on Church Reef the most critical levels on the shore, for the species examined, are: (a) between Mean and Extreme Low Water Springs; (b) between Mean Low Water Neaps and Springs; (c) at Extreme (Lowest) High Water Neaps. The least critical level is Mean Low Water Neaps.

5. Two special problems are presented by the upper limits of Littorina saxatilis and L. neritoides, and by the frontiers between Ascophyllum and Fucus spiralis and between F. spiralis and Pelvetia, where the algæ do not overlap.

6. The work of previous authors is discussed for comparison with the present paper.

7. An important difference is suggested between the nature of the zonation of sedentary animals and plants on the one hand, and that of animals capable of locomotion on the other hand.

The abundance of the common intertidal barnacles, Chthamalus montagui, Chthamalus stellatus, Semibalanus balanoides and Elminius modestus has been monitored since 1951 at a site near Cellar Beach, River Yealm, south Devon. Counts are made at 12 levels on a transect between high tide and low tide. The two chthamalids are of warm-water distribution while S. balanoides is a boreo-arctic species; changes in the abundance of these species are linked to environmental temperature. Maximum fluctuations occur in the lowermost third of the intertidal zone. The proportion of Chthamalus adults is correlated with annual mean inshore sea temperature two years earlier, while the proportion of S. balanoides adults is negatively so correlated. This relationship accounts for over 40% of the variance. A smaller part of the variance (<20%) is explained by intensity of larval settlement, also related to climate. The fourth barnacle, E. modestus, is an Australasian immigrant that arrived in England during World War II and reached south Devon in 1948. It increased during the 1950s on the transect but has since stabilized at a low level of abundance that shows large interannual variations not directly related to temperature. Between 1951 and 1975, coinciding with a secular decline in sea temperature, there was a long-term trend towards reduction of Chthamalus and increase in S. balanoides; this trend has reversed since. Removal of the long-term trend reveals a short-term fluctuation of approximately 10-y frequency that correlates with a cycle in sea temperature two years earlier. These cycles are close to the 10–11 y solar (sunspot) cycle between 1951 and 1975.

Since the rate of global climate change began to accelerate in the 1980s, the coastal seas of Britain have warmed by up to 1°C. Locations close to the northern range edges of a southern trochid gastropod Osilinus lineatus in Britain previously surveyed in the 1950s and 1980s were resurveyed during 2002–2004 to determine whether changes in the success of near-limit populations had occurred during the period of climate warming. Between the 1980s and the 2000s, the range limits had extended by up to 55 km. Populations sampled over a latitudinal extent of 4 degrees from northern limits towards the centre of the range showed synchronous increases in abundance throughout the years sampled, suggesting a large-scale factor such as climate was driving the observed changes. These increases in abundance and changes in range limits are likely to have occurred via increased recruitment success in recent years.

An energy budget has been assembled for a population of the limpet Patella vulgata inhabiting the mid-tide level of a moderately sheltered shore in the Isle of Man. The average biomass during the two year study was 346 kJ m−2, and the energy budget in kJ m−2 year−1:

We describe an experiment where Ascophyllym nodosum was removed from two 1 x 1 m plots in south-western Iceland in August 1985. The plots were studied regularly until 2005. Recovery of the Ascophyllum canopy took 7–8 years. The understorey algae in one of the plots consisted mostly of extensive growth of Cladophora rupestris, which died within a year of Ascophyllum clearance. No Cladophora had reappeared by 2005, although it was healthy and abundant in control plots throughout the study period. Thus even after 20 years the community had not recovered from disturbance.

In an attempt to identify the causes of the natural population fluctuations on British rocky coasts, an exploratory programme on the recruitment fluctuations of certain ‘key species’ has been operating for several years. The choice of species and the emphasis upon their recruitment have been discussed elsewhere (Lewis, 1976) and were justified as the most economical means of gaining the ability to (a) ‘explain’ major changes in the general character of rocky shore communities, and (b) make predictions about natural events against which to detect regional or temporal consequences of man-made changes in water quality. Mussels, barnacles and limpets are being studied but it is the last with which most interpretative progress appears to have been made, and this paper is concerned solely with Patella vulgata L. It is, however, essentially a preliminary report in a continuing study and it illustrates the practical and interpretative problems inherent in formulating and substantiating hypotheses in this type of work.

Limpets and barnacles are important components of intertidal assemblages worldwide. This study examines the effects of barnacles on the foraging behaviour of the limpet Patella vulgata, which is the main algal grazer in the North-west Atlantic. The behaviour of limpets on a vertical seawall on the Isle of Man (UK) was investigated using autonomous radio-telemetry, comparing their activity patterns on plots characterized by dense barnacle cover and plots from which the barnacles had been removed. Limpet behaviour was investigated at mid-shore level, but two different elevations were considered. This experiment revealed a significant effect of barnacle cover on the activity of P. vulgata. Limpets on smooth surfaces spent a greater proportion of total time active than did limpets on barnacles. Movement activity was also greater in areas that were lower down in the tidal range. In general, limpets were either predominantly active during diurnal high or nocturnal low tides and always avoided nocturnal high tides. Individuals on barnacles at the higher elevation concentrated their activity during nocturnal low water. All the other groups of limpets (smooth surfaces on the upper level and all individuals on the lower shore) had more excursions centred around daylight hours with an equal distribution of activity between periods of low and high water. Inter-individual variability was, however, pronounced.