Projected future climate change and Baltic Sea ecosystem management

Abstract

Climate change is likely to have large effects on the Baltic Sea ecosystem. Simulations indicate 2-4 °C warming and 50-80 % decrease in ice cover by 2100. Precipitation may increase ~30 % in the north, causing increased land runoff of allochthonous organic matter (AOM) and organic pollutants and decreased salinity. Coupled physical-biogeochemical models indicate that, in the south, bottom-water anoxia may spread, reducing cod recruitment and increasing sediment phosphorus release, thus promoting cyanobacterial blooms. In the north, heterotrophic bacteria will be favored by AOM, while phytoplankton production may be reduced. Extra trophic levels in the food web may increase energy losses and consequently reduce fish production. Future management of the Baltic Sea must consider the effects of climate change on the ecosystem dynamics and functions, as well as the effects of anthropogenic nutrient and pollutant load. Monitoring should have a holistic approach, encompassing both autotrophic (phytoplankton) and heterotrophic (e.g., bacterial) processes.

Fig. 1

Projected seasonal (DJF = December to February, MAM = March to May, JJA = June to August, SON = September to November) and annual mean ensemble average sea surface salinity changes (in g kg⁻¹) from 1978–2007 to 2069–2098 (from Meier et al. 2012a)

Fig. 2

Log KDOC values for hexachlorobenzene (black), phenanthrene (squared), and tributyl phosphate (striped) at different locations in the Baltic Sea. Water samples were collected along a north–south gradient in August 2013, filtered to retrieve the dissolved fraction, and spiked with different organic pollutants. Error bars represent the standard deviation of data from four sampling points in each basin

Fig. 3

Conceptual model of climate-induced ecosystem changes in the Gulf of Bothnia by 2100. Illustration: Kristina Viklund and Mattias Pettersson

Fig. 4

Conceptual model of climate-induced ecosystem changes in the Baltic Proper by 2100. Illustration: Kristina Viklund and Mattias Pettersson

Fig. 5

Simplified schematic view of climate-altered food webs in the Bothnian Bay (upper), southern Bothnian Sea (mid), and Baltic proper (lower) in summer. Green arrows represent autochthonous and brown arrows allochthonous production. Organisms included in the food webs and their trophic position (in parenthesis); bacteria (1, 2), phytoplankton (1), flagellates (2, 3), ciliates (3, 4), zooplankton (2, 4, 5), and fish (3, 5, 6). Illustration by Mats Minnhagen