Marine regime shifts
What do the Baltic Sea, Hawaiian coral reefs, and kelp forests have in common? All are marine systems that are susceptible to so-called regime shifts. These shifts are large and persistent (and often abrupt) changes in ecosystem structure and function. Often, they are associated with impacts on economies and well-being, due to for example fisheries declines, loss of tourism revenue, or the loss of resilience to climate change. Better understanding of regime shifts is important as they tend to be difficult to anticipate and costly to reverse.
"Understanding the social-ecological interactions behind regime shifts, and how to avoid them, will be key to maintaining healthy oceans and the ecosystems services they provide," says Carl Folke, Science director at the Centre and one of several researchers from the Centre who contribute to the November 24 special issue of the Philosophical Transactions of the Royal Society—Biological Sciences.
Professor Folke is also one of the issue's editors together with Alessandra Conversi, Christian Möllmann, and Martin Edwards.
Small impact, big change
The complete special issue, entitled "Marine regime shifts around the globe: theory, drivers, and impacts", features more than 80 authors from different disciplines, across 6 continents. Altogether, the issue includes nearly 20 studies that explore the science behind regime shifts in ocean ecosystems worldwide, and how they can be managed.
Regime shifts are addressed from the different perspectives of theory, ecosystem observations, modelling and management. The articles featured in the special issue clearly tells us that there are regime shifts for many marine ecosystems, and that even small increases in human stressors can lead to abrupt major changes in their status.
One of the articles "Marine regime shifts: drivers and impacts on ecosystem services" is written by Juan Rocha, Johana Yletyinen, Oonsie Biggs, Thorsten Blenckner, and Garry Peterson, and reviewed the scientific literature for 13 types of marine regime shifts. More specifically, the group of authors used network analysis to look into the co-occurrence of different drivers and ecosystem service impacts.
"Our systematic analysis demonstrates that all types of marine regime shifts have multiple drivers, with climate forcing, fishing, agriculture, demand for food and fibre, deforestation, urbanization, and nutrient input being the most prominent cluster," the group of authors write.
They also conclude that all analysed regime shifts impact a variety of ecosystem services, with biodiversity, fishing productivity, and aesthetic values clustering amongst the most commonly impacted.
Reefs in Hawaii
In another of the special issue's articles "Identifying multiple coral reef regimes and their drivers across the Hawaiian archipelago", Jean-Baptiste Jouffray, Magnus Nyström and Albert Norström write together with researchers from the Center for Ocean Solutions at Stanford University, University of Hawaii, NOAA, and the Scripps Institute of Oceanography.
Based on one of the most comprehensive coral reef datasets available in the world the group of authors identify what different reef regimes there are in the Hawaiian Archipelago, and what explains reefs being in a particular state. Besides the unexpected discovery, that over half of the reefs in Hawaii are dominated by algae, they found – confirming the findings in the article by Rocha and colleagues – that although some drivers seem particularly important, both anthropogenic and natural drivers factors are involved explaining why certain reefs are found in a particular regime.
"Higher numbers of herbivorous fish, which are important consumers of algae, proved to be the strongest indicator of reef state throughout the study region. Areas with low herbivore numbers, on the other hand, tended to be overtaken by algae", Jean-Baptiste Jouffray explains.
Social and political aspects
Centre researcher Saskia Otto is part of a group of scientists contributing with an article entitled "Synchronous marine pelagic regime shifts in the Northern Hemisphere". It suggests that the main factor of marine regime shifts on large scales is temperature together with atmospheric circulation. The group of scientists examined whether regime shifts observed in eleven marine systems from two oceans and three regional seas in the northern hemisphere are synchronous, applying the same methodology to all.
Understanding the biophysical factors triggering marine regime shifts is of course key, but as Juan Rocha and colleagues emphasize in the article mentioned above, "avoiding regime shifts is likely to fail if management is limited to single, well-understood variables or local scales, and ignores factors such as trade or stochastic events".
Along this line, Henrik Österblom and Carl Folke contribute with a paper entitled "Globalization, marine regime shifts and the Soviet Union". In it they analyse fishing activities of the Soviet Union in relation to all large marine ecosystems of the world from 1950 until the collapse of the Soviet Union in 1991. This indicated that one single actor could have a disproportionately large effect on global fisheries, pushing exploitation to new levels. Soviet fishing activities were coordinated through a system of central planning. Global synchronicity can thus also result from human activities, and not just global patterns of climate. Interestingly, Soviet fishing also contributed to triggering regional and global governance responses for improved management.
"The Soviet Union has been one of the largest actors ever in global seafood exploitation and pioneered the global expansion of fishing activities at an unprecedented scale. They were the fore-runners of the globalization of fishing activities that we are observing today," Henrik Österblom explains.
From a governance perspective, understanding political and economical aspects of marine regime shifts are central to protect healthy oceans, recover ecosystems that are in decline, and increase the benefits that marine systems provide to communities around the world.
Conversi, A., Möllman, C. Folke, C., Edwards, M., (editors). 2014. Marine regime shifts around the globe: theory, drivers and impacts. Philosophical transactions of the Royal Society - Biological Sciences 370(1659). Forthcoming 2015 January.