Using historical data to detect temporal changes in the abundances of intertidal species on Irish shores
Simkanin, C and Power, A and Myers, A and McGrath, D and Southward, A and Mieszkowska, N and Leaper, R and O'Riordan, R, Using historical data to detect temporal changes in the abundances of intertidal species on Irish shores, Marine Biological Association of The United Kingdom. Journal, 85, (2005) pp. 1329-1340. ISSN 0025-3154 (2005) [Refereed Article]
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 eĦects, such as climate change and commercial exploitation, but also of operator error.
The error or diĦerences 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 eĦect 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 eĦect of operator on our results, which can increase the occurrence of a false positive (Type 1) or of a false negative (Type 2) outcome.