Abstract
Because of the high management relevance, commercial fish related aspects have often been central in marine ecosystem investigations. The iterative shiftogram method was applied to detect occurrence, type and timing of shifts in the single and multivariate time series linked to the spring spawning herring larvae in the Gulf of Riga (Baltic Sea). Altogether nineteen larval herring and related environmental variables were utilized during the period of 1957–2010. All the time series investigated, either single or multivariate, exhibited one or more shifts with variable type and timing. Multivariate shiftogram based on all time series identified two distinct states (1957–1983 and 1992–2010) in studied variables, separated by a smooth transition period lasting almost ten years. The observed shift was mainly related to hydroclimate and not to phenology or biota. Significantly increased variability was found in larval herring and recruitment abundances after the shift. While the shift in hydroclimate (1985–1991) was followed by the shift in phenology (1991–1997), the shift in biota occurred remarkably later (2003). It is likely that the dynamics in biota were affected by other drivers than those investigated in the current paper.
Highlights
Regime shifts are defined as abrupt changes between contrasting persistent equilibrium states of a system [1]
Regime shifts have been identified in several marine areas, the time-period covered in those studies rarely start prior to the 1950s [1,6]
In this paper we have studied nineteen time series describing the hydroclimate, phenology and biota [25] related to the early life history stages of the GoR spring-spawning herring, to explore the occurrence, timing and type of the shifts
Summary
Regime shifts are defined as abrupt changes between contrasting persistent equilibrium states of a system [1]. Regime shifts have been identified in several marine areas, the time-period covered in those studies rarely start prior to the 1950s [1,6]. The regime shift definition has been subsequently broadened to include biological systems, among others, describing changes in species abundance, community composition, trophic structure, ecosystem state and functioning, as a response to external drivers and forces affecting marine ecosystems. Such phenomena have been observed and explored in several major ocean basins [7] and at different trophic levels [8,9]
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