Quantification of long-term changes in the German Bight using an ecological development index

Radach, G. 1998. Quantication of long-term changes in the German Bight using anecological development index. – ICES Journal of Marine Science, 55: 587–599.During recent decades, remarkable long-term changes have taken place in manycoastal ecosystems of north-west European shelf seas. These changes have beendescribed in many papers, but an overall quantication is lacking. An ecologicaldevelopment index (EDI) is proposed here, consisting of two parts – a statisticaldescription of the state of the ecosystem and a metric in a multi-dimensional space ofstatistical descriptors of states for quantitatively characterizing the change of anynumber of state variables by only one characteristic number. The concept of the EDIis generally applicable by yielding a measure of the distance between system states.Indices are comparable between diVerent ecosystems and within diVerent subspaces ofthe ecosystem’s state space, provided the same characterization is used. The concept isapplied to the 32-year time series (1962–1993) of measurements of nine physical(sea-surface temperature, salinity), chemical (phosphate, nitrate, nitrite, ammonia,silicate), and biological (biomass of diatoms and agellates) state variables atHelgoland. The analysis of consecutive 5-year quantiles of monthly mean values,which are used as statistical descriptors, elucidates the long-term perturbations of thecoastal marine system in the German Bight. It is shown that the states of the ecosystemin the 1970s and 1980s have abandoned the region of the 1960s, but are possiblyreturning in the 1990s to the situation of the 1970s.