Relationship between shoreline substrate type and sensitivity of seafloor habitats at risk to oil pollution

The aim of this paper is to study the relationship between the shoreline substrate type, the shoreline substrate sensitivity (in sensu the Environmental Sensitivity Index) and associated seafloor habitat's sensitivity (sensitivity of macrophytes and associated benthic invertebrates) to potential oil pollution in Tallinn Bay, the Baltic Sea. The sensitivity values of the seafloor habitats significantly differed among the studied shoreline substrate types, while the habitat sensitivity values did not match with the sensitivities of these substrate types. The average habitat sensitivity was high on shallow coastal sea adjoining cliffs (representing the shoreline substrate of lowest sensitivity), intermediate on till shores (the shoreline substrate of high sensitivity), low on sandy shores (the shoreline substrate of medium–low sensitivity) and artificial shores (the shoreline substrate of low sensitivity). This mismatch is explained by the fact that shoreline substrate sensitivity is a consequence of the shoreline natural persistence of oil and ease of cleanup, while the underwater habitat heterogeneity and community properties determine the sensitivity of the associated seafloor habitats to potential oil pollution. The layers of shoreline substrate types and seafloor habitat sensitivity are seen as elements of the Environmental Sensitivity Index (ESI) being developed for the Baltic Sea.