Ruth M. O'Riordan

Using historical data to detect temporal changes in the abundances of intertidal species on Irish shores

An historical data set, collected in 1958 by Southward and Crisp, was used as a baseline for detecting change in the abundances of species in the rocky intertidal of Ireland. In 2003, the abundances of each of 27 species was assessed using the same methodologies (ACFOR [which stands for the categories: abundant, common, frequent, occasional and rare] abundance scales) at 63 shores examined in the historical study. Comparison of the ACFOR data over a 45-year period, between the historical survey and re-survey,showed statistically signi¢cant changes in the abundances of 12 of the 27 species examined. Two species(one classed as northern and one introduced) increased signi¢cantly in abundance while ten species (¢ve classed as northern, one classed as southern and four broadly distributed) decreased in abundance. The possible reasons for the changes in species abundances were assessed not only in the context of anthropogenic eiects, such as climate change and commercial exploitation, but also of operator error. The error or diierences recorded among operators (i.e. research scientists) when assessing species abundance using ACFOR categories was quanti¢ed on four shores. Signi¢cant change detected in three of the 12 species fell within the margin of operator error. This eiect of operator may have also contributed to the results of no change in the other 15 species between the two census periods. It was not possible to determine the eiect of operator on our results, which can increase the occurrence of a false positive (Type 1) or of a false negative (Type 2) outcome.

Brooding in the intertidal barnacles Chthamalus stellatus (Poli) and Chthalamus montagui Southward in south-western Ireland

At Lough Hyne Marine Nature Reserve, western Cork, Ireland, the intertidal barnacles Chthamalus stellatus (Poli) and Chthamalus montagui Southward were shown to be capable of breeding in their first year after settlement. In C. montagui, zero, one or two broods and in C. stellatus, zero, one, two or in a single case three broods were produced in the first summer. Whether or not barnacles brood in their first year is probably due to a combination of the time since settlement and size attained. In their second year after settlement, both species are multiple brooders, producing two broods during the summer season.

Variation in the reproductive cycle of Elminius modestus in southern Ireland

The reproductive cycle of the Australasian barnacle Elminius modestus (Crustacea: Cirripedia) was studied at three sites within Whitegate Bay, Cork, Ireland over 15 months. At all three sites, there were seasonal trends in development of the male and female reproductive organs with, for example, the ovaries regenerating whilst eggs were being brooded. Throughout the year, significantly lower percentages of animals were brooding embryos at the site of a warm-water outfall than at another site nearby. The factors which may affect the reproductive cycle of E. modestus are discussed.

The reproductive cycles of Chthamalus stellatus (Poli) and C. montagui Southward in south-western Ireland

Abstract The reproductive cycles of two intertidal barnacles, Chthamalus stellatus (Poli) and C. montagui Southward, were studied at Lough Hyne Marine Reserve, Cork, Ireland, over 28 months. In both species there were seasonal trends in development of the male and female reproductive organs with, for example, the ovaries regenerating while eggs were being brooded. Breeding occurred mainly during June–August but also at other times. The sizes of the ova and eggs of the two species were compared and the timing of the cycles relative to other areas considered.

Seasonality and vertical zonation of zooplankton in a semi-enclosed sea lough

Zooplankton was collected by a diver-towed net close to the substratum at four depths (0, 6, 12 and 18 m) over a 17 month period in three locations in Lough Hyne, Co. Cork, Ireland. Zooplankton was identified to phylum or class levels and mean numbers were calculated for each taxon, site and depth. Seasonality was observed in several meroplanktonic groups (Echinodermata, Nemertea, Mollusca and fish postlarvae), and in gelatinous zooplankton. Depth preference was found to be statistically significant in the polychaetes (larvae and pelagic species), molluscan and ascidian larvae. However, the influence of depth on overall zooplankton community composition was found to be negligible. Sampling location, adjacent substrata and flow conditions were found to influence zooplankton in that area.

The current distribution and abundance of the Australasian barnacle Elminius modestus in Portugal

The current distribution and abundance of Elminius modestus (Crustacea: Cirripedia) were examined at 15 sites along the Portuguese coast in March/April 1998. Elminius modestus was found at two sites only but was absent from a site where it had previously been recorded. The site at Faro is the most southerly location on continental Europe where Elminius has yet been recorded and it is nearly 300 km south of where it was previously found.

Prolonged settlement and prediction of recruitment in two sympatric intertidal Chthamalus species from south-west Ireland

Attached cypris larvae and less than one month old metamorphs of Chthamalus stellatus and C. montagui (Crustacea: Cirripedia) were sampled from random quadrats on two shores in County Cork, Ireland, from July 1996 to June 1997. Cyprids of C. stellatus were much more abundant than those of C. montagui , but the relative abundance of metamorphs of the two species did not differ significantly. Cyprid abundance predicted metamorph recruitment intensity during peak settlement in C. stellatus but not in C. montagui .

Influence of disseminated neoplasia, trematode infections and gametogenesis on surfacing and mortality in the cockle Cerastoderma edule

Cerastoderma edule is a widely distributed bivalve mollusc, commercially exploited throughout Europe and is also an important food source for birds and crustaceans. Recently, mass surfacing and mortalities of cockles have been observed and reported at sites in Ireland and elsewhere, particularly in the summer months. One such site is Flaxfort Strand, Courtmacsherry Bay, County Cork, Ireland, an important feeding area used by many seabirds during the summer months. For the past few years large numbers of surfaced cockles have been observed at the site in a moribund condition. Samples of cockles from this area were collected over the summer months and their health status assessed. Cockles that had surfaced (moribund) and those still buried in the sediment were quantified and screened: sex, gonadal maturity and size class of cockles were also determined. Disseminated neoplasia and trematodes were observed in screened cockles. The most significant finding during the study was that mortalities and surfacing of cockles was related to a greater incidence of disseminated neoplasia. No neoplasia was observed in the smallest and largest size classes. There was a significantly higher prevalence of neoplasia in moribund cockles than in buried cockles, whereas in both groups a similar concentration of trematode metacercariae was observed in the screened tissues. Also, most of the cockles that had surfaced were either in the process of spawning or were spent. Overall a much larger percentage of moribund cockles exhibited both trematode infections plus neoplasia compared with buried cockles. A combination of the presence of neoplasia and trematodes, along with stress related to spawning, may immunocompromise the cockless, causing the animals to surface and become moribund.

The sizes at settlement in natural populations of the cyprids of Chthamalus montagui and C. stellatus

The lengths of chthamalid cyprids collected during August 1996 on six rocky shores in County Cork, Ireland are reported. The lengths showed a bimodal distribution. The smaller length mode corresponded well with the length range of laboratory-reared cyprids of Chthamalus montagui (Crustacea: Cirripedia), whilst the larger length mode was greater than the length range reported for laboratory-reared C. stellatus . Size may be a useful means to identify Chthamalus cyprids in field investigations.

Increases in the abundance of the invasive barnacle Austrominius modestus on the Isle of Cumbrae, Scotland

The distribution and abundance of the Australasian barnacle Austrominius modestus around the Isle of Cumbrae, Scotland, were examined in October 2007. The species was found at all of the nineteen sites examined, which included highly exposed to highly sheltered sites. Its abundance varied from common to occasional. Over fifty years after its initial appearance as a single specimen (1954), Austrominius now appears to be well established on the island. Factors that may have influenced its spread and establishment are described, however, at this stage the relative importance of these cannot be determined. Consequently, further research is planned here, to collect quantitative data on the abundance of Austrominius and the other barnacle species that occur intertidally and how their relative abundances vary both within and between shores.