The following references are intended to highlight the concept of thresholds, and the implications this may hold for Marine Systems: They delineate problems of the uncertainty of thresholds and the implications when there is interference in ecosystem integrity by Global Climate change and poorly managed fisheries and habitat conservation in marine areas.
1. This reference on “Thresholds in Ecological and Social–Ecological Systems: a Developing Database explains some research into this problem:
http://www.ecologyandsociety.org/vol9/iss2/art3/
“Increasing interest in regime shifts in ecological and linked social–ecological systems (SESs) has placed a strong focus on the thresholds of change. However, research into this topic has been hampered by a lack of empirical data. This paper describes a developing database established to address this need. The database is freely available and comprises a set of summarized published examples and a searchable bibliographic database of publications on the topic. Thresholds in the database are characterized in terms of a standardized set of 24 descriptors, including the variables along which they occur, the variables that change, and the factors that have driven the change. Readers are encouraged to contribute new examples. Examples range from conceptual models to empirical evidence. The former predominate in the literature and, although they make valuable contributions and will continue to be included, the intention is build up the number of examples based on data. Examples are presented in terms of whether the threshold occurs in the ecological system, the social system, or both, and the direction of interactions between systems. The paper concludes with some initial observations on thresholds based on the examples included so far, and poses some questions for future research. Research on a typology of thresholds is a priority topic in the emerging area of “sustainability science” and it requires a rich database of empirical data.”
2. Confronting he coral reef crisis:http://www.nature.com/nature/journal/v429/n6994/full/nature02691.html
The worldwide decline of coral reefs calls for an urgent reassessment of current management practices. Confronting large-scale crises requires a major scaling-up of management efforts based on an improved understanding of the ecological processes that underlie reef resilience. Managing for improved resilience, incorporating the role of human activity in shaping ecosystems, provides a basis for coping with uncertainty, future changes and ecological surprises. Here we review the ecological roles of critical functional groups (for both corals and reef fishes) that are fundamental to understanding resilience and avoiding phase shifts from coral dominance to less desirable, degraded ecosystems. We identify striking biogeographic differences in the species richness and composition of functional groups, which highlight the vulnerability of Caribbean reef ecosystems. These findings have profound implications for restoration of degraded reefs, management of fisheries, and the focus on marine protected areas and biodiversity hotspots as priorities for conservation.
3.Ecological Thresholds in Aquatic Ecosystems: The Role of Climate Change, Anthropogenic Disturbance, and Invasive Species Progress Review Workshop
http://archive.epa.gov/ncer/publications/web/html/06_07_07_ecological.html
4. A Balancing Act
A leading UMaine marine scientist says better management is needed to save the world’s oceans that are drastically out of sync http://umainetoday.umaine.edu/issues/v6i4/act.html
Pointing to a growing list of health threats to the world’s oceans, Steneck describes a common pattern of slow, incremental overload and sudden collapse, suggesting that the Blue Planet’s ability to absorb the insults of human misuse have clear limits. The notion of ecological thresholds is at the core of Steneck’s assessment of the seas. As pressure on the marine environment continues to grow, these thresholds are being met — and surpassed.
A classic example of the threshold phenomenon can be found in the sad tale of the green sea urchin. Prolific and plentiful across the Gulf of Maine, urchins spent decades quietly munching at the Atlantic’s undersea salad bar, unaware of the socioeconomic tsunami on the horizon.
As urchin populations in other parts of the world were rapidly depleted by overfishing through the 1970s and ’80s, a seemingly insatiable Asian market turned its hungry eyes toward Maine, creating a boom-and-bust fishery that crashed a multimillion urchin population in less than two decades.