Reorganization of a large marine ecosystem due to atmospheric and anthropogenic pressure: a discontinuous regime shift in the Central Baltic Sea

Abstract

Marine ecosystems such as the Baltic Sea are currently under strong atmospheric and anthropogenic pressure. Besides natural and human-induced changes in climate, major anthropogenic drivers such as overfishing and anthropogenic eutrophication are significantly affecting ecosystem structure and function. Recently, studies demonstrated the existence of alternative stable states in various terrestrial and aquatic ecosystems. These so-called ecosystem regime shifts have been explained mainly as a result of multiple causes, e.g. climatic regime shifts, overexploitation or a combination of both. The occurrence of ecosystem regime shifts has important management implications, as they can cause significant losses of ecological and economic resources. Because of hysteresis in ecosystem responses, restoring regimes considered as favourable may require drastic and expensive management actions. Also the Baltic Sea, the largest brackish water body in the world ocean, and its ecosystems are strongly affected by atmospheric and anthropogenic drivers. Here, we present results of an analysis of the state and development of the Central Baltic Sea ecosystem integrating hydroclimatic, nutrient, phyto-and zooplankton as well as fisheries data. Our analyses of 52 biotic and abiotic variables using multivariate statistics demonstrated a major reorganization of the ecosystem and identified two stable states between 1974 and 2005, separated by a transition period in 1988-1993. We show the change in Baltic ecosystem structure to have the characteristics of a discontinuous regime shift, initiated by climate-induced changes in the abiotic environment and stabilized by fisheries-induced feedback loops in the food web. Our results indicate the importance of maintaining the resilience of an ecosystem to atmospherically induced environmental change by reducing the anthropogenic impact.

Synchronous marine pelagic regime shifts in the Northern Hemisphere

“…of appropriate length for our multi-decadal investigation. Even if the data used in this investigation represent mostly one trophic level, it has to be noted that other studies have identified ecosystemwide regime shifts in most of these areas [6,8,9,11,36,43,44,47]. Second, we identified temporal shifts in all these systems, individually and in aggregate, and examined their relationships to (i) large-scale climatic indices (Northern Hemisphere temperature (NHT) anomalies, Arctic Oscillation (AO), Atlantic Multi-decadal Oscillation (AMO) and Pacific Decadal Oscillation (PDO)), and (ii) spatial patterns of change in sea surface temperature (SST) and sea-level pressure (SLP) over the NH.…”

“…Important examples of regime shifts in large marine ecosystems have been reported for both the Northern Hemisphere (NH) [6][7][8][9][10][11] and the Southern Hemisphere [12,13]. As studies focusing on pelagic regime shifts around the world increased and became more global, researchers began to examine potential synchronicities in the variation of species and ecosystems that are often separated by great distances, and are even in different ocean basins [1,8,[14][15][16][17][18][19][20][21][22][23][24][25].…”

An empirical model of the Baltic Sea reveals the importance of social dynamics for ecological regime shifts

“…Many marine ecosystems, for example, have undergone abrupt changes known as regime shifts (3,4). In one prominent case, the Baltic cod fishery suddenly changed in the 1980s from historically high cod biomass and catches (henceforth the "cod boom") to a sprat-dominant ecosystem with low cod abundance (5)(6)(7)(8). This collapse, generally understood to have been precipitated by deteriorating environmental conditions and overfishing (7), had substantial negative socioeconomic impact on Baltic Sea fisheries, including among others the small-scale coastal fishery (9).…”

A Multivariate Baltic Sea Environmental Index

“…This might be perhaps the case in terrestrial ecosystems considered by Hallett et al (2004). But, our results indicated that this is surely not the case in marine areas such as the North Sea (Dippner et al 2010) and the Baltic Sea (Möllmann et al 2009). Our results indicate that the multivariate BSE index combined of large-and regional-scale indices has an excellent performance and a high versatility much better than each single large-scale index only.…”

“…macrobenthos communities in the southern North Sea fails after 2001/2002 (Dippner et al 2010) which might be addressed to a climate global regime shift (Swanson and Tsonis 2009). The same regime shift has been observed in the Baltic Sea (Möllmann et al 2009). …”