This indicator is a HELCOM supplementary indicator and is applicable in assessment units shared by Finland and Sweden.
To decrease statistical uncertainty of the analysis, a high number of sampling stations per assessment unit is recommended. Since sample size (i.e., number of gravid females available for the analysis) may have high temporal (year-to-year) and spatial (stations within assessment unit) variability, bootstrapping can be applied to control for the sample size. For each station, a sample size of 50 gravid females and about 1,500 embryos is the recommended sample size within the Swedish National Marine Monitoring Program for evaluating the proportion of malformed embryos in the population. Depending on the area of the assessment unit, distribution of sustained populations of the species in question, and heterogeneity of hydrography, several survey regions should be included, with several stations per region (Assessment Protocol figure 1).
Assessment Protocol figure 1. Sampling design employed in SNMMP for biological effect monitoring of the amphipod Monoporeia affinis. Red dots denote sampling stations and ellipses are the survey regions (R1 to R10) along the Swedish coast. Basins are abbreviated as in Results figure 1. All stations are located in areas free from pollution point sources and, therefore, the indicators values are expected to be within BAC. For the assessment, a >50%-rule is applied.
Evaluating whether an area is in good status using amphipods is done by: