Resilience can be defined as the capacity of a system to withstand stress. In seagrass ecology, the focus centres on the capacity for the seagrass ecosystem to remain within the same ‘regime’; essentially, a seagrass meadows capacity to maintain its own ‘structure and function’ i.e. it still looks and behaves like, a seagrass ecosystem!
Central to resilience thinking is the understanding that people are part of the natural world too, and therefore we humans, some remotely, and some intimately, interact with seagrass ecosystems for our survival. Some of our interactions can be positive, others negative, but it is the sum effects of these interactions that can transform one ecosystem (e.g. a seagrass ecosystem) into another (e.g. mud) causing an ecosystem ‘regime’ shift. What once was a seagrass meadow no longer looks or behaves like a seagrass meadow!
When we wipe out the most sensitive species in a seagrass meadow, humans reduce the resilience of the seagrass ecosystem to change. However, in contrast, when resilience is enhanced, the seagrass ecosystem is more likely to tolerate disturbance events without collapsing into a different state (e.g. mud) that is controlled by a different set of relationships. This new state of the system may also be less desirable if the productivity of the ecosystem i.e. the characteristics that benefit humans (called ‘ecosystem services’) are diminished. This is the case of when seagrass meadows become degraded and are depleted of their biodiversity. High biodiversity (including high genetic diversity) acts as an ‘insurance policy’ for seagrass ecosystems because it increases the chance that at least some species will be survive and sustain important ecological functions such as water purification and carbon fixation in a changing environment.
Johan’s keynote described three key considerations for ecosystems in the coastal zone.
- Trophic interactions
- Feedback mechanisms
Critically, he discussed that there has been an assumption that “we can afford to lose the most sensitive species” because there will be other species (that fulfill similar ecological roles available), but this is predicated on the assumption that species will go extinct randomly, which of course, they don’t!
Johan explores how in the past 10 years’ research has shown that seagrass meadows respond in different ways in different places depending upon local extinction events. In particular, he discusses the effect of the absence of top predators (top-down control) and how it interacts with ‘bottom-up’ effects such as the eutrophication of coastal seagrass meadows. He finally links these patterns to the positive and negative feedbacks witnessed in seagrass ecosystems and explores how seagrasses are ‘ecosystem engineers’ and therefore alter the abiotic and biotic environments in which they are found.
Johan’s take home messages:
- High-diversity within and of trophic levels ‘insures’ seagrass ecosystems against environmental change
- Strong feedbacks and mutualism within and across coastal systems make them more resistant to change.
He argues that to effectively manage our (humans) relationship with seagrass ecosystems we need to reduce pressures that push seagrass towards undesirable ‘regime shifts’ (e.g. seagrass to mud!) to strengthen response diversity, and to weaken undesirable feedback mechanisms whilst strengthening those deemed as desirable ones.