Copyright © 2005 by the author(s). Published here under license by the Resilience Alliance. Troell, M., L. Pihl, P. Rönnbäck, H. Wennhage, T. Söderqvist, and N. Kautsky. 2005. Regime shifts and ecosystem service generation in Swedish coastal soft bottom habitats: when resilience is undesirable. Ecology and Society 10(1): 30. [online] URL: http://www.ecologyandsociety.org/vol10/iss1/art30/ Synthesis Regime shifts and ecosystem services in Swedish coastal soft bottom habitats: when resilience is undesirable Max Troell 1 , Leif Pihl, Patrik Rönnbäck, Håkan Wennhage, Tore Söderqvist, and Nils Kautsky ABSTRACT. Ecosystems can undergo regime shifts where they suddenly change from one state into another. This can have important implications for formulation of management strategies, if system characteristics develop that are undesirable from a human perspective, and that have a high resistance to restoration efforts. This paper identifies some of the ecological and economic consequences of increased abundance of filamentous algae on shallow soft bottoms along the Swedish west coast. It is suggested that a successive increase in the sediment nutrient pool has undermined the resilience of these shallow systems. After the regime shift has occurred, self-generation properties evolve keeping the system locked in a high- density algae state. The structural and functional characteristics of the new system state differ significantly from the original one, resulting in less valuable ecosystem goods and services generated for society. In Sweden, loss of value results from the reduced capacity for mitigating further coastal eutrophication, reduced habitat quality for commercial fishery species, and the loss of aesthetic and recreational values. Key Words: alternate stable states; shallow soft bottoms; eutrophication; filamentous algal mats; resilience; ecosystem function; ecosystem goods and services. INTRODUCTION Many coastal marine ecosystems worldwide are subject to increased supply of nutrients from direct point discharges (sewage, industries, etc.), terrestrial run-off, and atmospheric deposition. Nitrogen loading in the Skagerrak and Kattegat regions on the Swedish west coast has increased about four-fold since 1930 (Rosenberg et al. 1990, Aure et al. 1996, Rosenberg et al. 1996). A small tidal amplitude, generally less than 20 cm, makes the coastal zone and, especially the inner archipelago, sensitive to increased nutrient loading. Phytoplankton production has doubled, from around 100 g-C-m -2 -y -1 in the 1950s and 1960s, to 200 g-C-m -2 -y -1 during the period of 1980 to 2000 (Richardsson and Heilman 1995, Lindahl 2003). Over the same time period, coastal sedimentation has increased about five-fold, from 30 to 140 g-C- m -2 -y -1 (Lindahl 2003). Observed indications of eutrophication include increased frequencies of phytoplankton blooms and reductions of oxygen in bottom waters (Baden et al. 1990), as well as an increased occurrence of filamentous algae on shallow soft bottoms along the Swedish west coast (Afzelius 1978, Wennberg 1987, Österling and Pihl 2001). The average cover of green algal mats in 10 shallow (0-1 m) bays on the Swedish Skagerrak Coast, increased significantly from <3% during the period of 1976 to 1978, to 40% in 1992 to 1994 (Pihl et al. 1995). From 1994 to 1996, the distribution of algal mats was monitored by aerial photography in shallow (0-1 m) soft bottom areas along 200 km of the Swedish Skagerrak Coast, and the average cover of green algal mats ranged from 30 to 50% of the total shallow soft bottom habitat in the archipelago (Pihl et al. 1999). Resilience is the ability of a social-ecological system to undergo, absorb, and respond to change and disturbance, while maintaining its functions and controls (Carpenter et al. 2001). The definition of resilience includes three equally important aspects: (1) the ability of the system to resist a disturbance so that it is not overwhelmed, but instead retains its functions, (2) the capability of the system for self- 1 Beijer Institute