Sandy beach monitoring to detect impacts against a background of long-term trends and variability in intertidal macroinvertebrate communities : an Orkney case-study

Abstract

Orkney Islands Council Harbour Authority’s (OICHA) long-term intertidal macroinvertebrate monitoring data from Scapa Flow, Orkney sandy beaches were reviewed, processed and analysed. Monitoring data for 13 sandy beaches were considered, and these are all characterised as Dissipative or Ultra-dissipative reflecting the sheltered nature of the sandy beaches. The impacts of variability and inconsistencies in macroinvertebrate sample identification and enumeration on data analysis were evaluated. In validation of recent data, it is found that abundance is reliably characterised, but with some inconsistencies in assignment of specimens to taxa are observed. The time series (1974-1990 and 2002-2016) of macroinvertebrate data were analysed for temporal (between year) and spatial (between site) variability; no Scapa Flow-wide temporal patterns are detected. At three sites temporal and spatial variability were investigated in detail and revealed shifts in macroinvertebrate time series in 2010/2011 due to extreme cold winters. Baseline macroinvertebrate data and Ecological Quality for the 13 Scapa Flow sites were described; the mean number of taxa (family level) is high (48) and in agreement with the expected number of taxa for sheltered sandy beaches. All sites are classed as having at least slightly disturbed ecological condition with one being classed as moderately disturbed in both recent (since 2002) and historical (1974-1990) time periods. Recommendations to OICHA regarding the future of the monitoring programme are given and include but are not limited to: continue the monitoring of ten sites in case of oil pollution; continue to monitoring of three sites for the effects of organic effluent discharge from Stromness waste water treatment facility; consider including the sandy beach monitoring as part of the OICHA non-native species monitoring programme; and reduce the sampling frequency at Dead Sand which is a moderately disturbed site.