The paper I have chosen discusses benchmarks – references to natural undisturbed states. Although cited in 437 papers since published in 1997, the benchmark concept is originally by another marine biologist fisheries scientist Daniel Pauly, but was redefined and applied by Dayton.
The author argues that meaningful benchmarks are non-existent and that we cant measure change from a natural state, because we lack in understanding what natural is or was in first place.
I like this paper for two reasons: Firstly, it describes to fundamental issues understanding what drives changes and variation in communities, here on the example of Californian kelp forests. The piece teases apart physical (for example temperature, extreme weather events) and biological (predation, competition) processes, as well as anthropogenic impacts which affect ecological communities.
Secondly, the paper also but also has a sobering example for the knock on effects of exploitation, and the role of biodiversity mitigating the impacts, ideas which I am going to explore in more detail here. Sea urchins, which graze on kelp, can eliminate kelp forests, resulting in a habitat shift to deforested barren habitats. This is an alternative state that is stable and can persist for a very long time (a term coined, alternative stable state)
This doesn’t occur naturally because sea urchin numbers are kept low by their predators, notably sea otters, spiny lobsters and sheephead fish. These are referred to as keystone species – for their relatively large impact on other member of the community. Because otters are absent in many kelp forest habitats today and other species overfished, urchin numbers are uncontrolled. As numbers of urchins increase, so does their impact on kelp forests, often leaving desolate, barren areas behind.
The interesting point is that kelps still functioned in Southern California; even decades after sea otters became locally extinct due to the fur trade. This is in contrast to habitats in Alaska, where once sea otter populations became extinct, whole kelp forests were lost. In contrast to Alaska, California had much greater biodiversity with other species overtaking the role of the sea otters in controlling sea urchin populations. In the 1950’ other species, including spiny lobsters and sheephead fish were also exploited heavily in California, eventually resulting in a loss of kelp beds.
This example is meaningful to me for two reasons. Firstly, ecosystems can persist despite disturbances, because other species can take over the functional roles of extinct species. In this example other species are feeding on sea urchins, filling in the gap left by the local extinction of the otters. It emphasises the importance of species richness in buffering negative impacts on ecosystems.
The second, similarly important point is, that there is a limit to this buffering function. If human impacts continue to stress the system (here by exploiting the predators of sea urchins), eventually the system may switch to an alternative state. I guess the message is that biodiversity can stabilise degrading ecosystems from losing function, but only to some extend. Once a threshold is passed the ecosystems change.
As a biologist my day consists of reading papers about the state of the environment and the future of the planet and our role as humans in it. I find myself absolutely detached from these messages when reading. I know figures; predicted changes in pH and temperature, overexploitation rates of fish stocks, habitat fragmentation, species introductions, but I have lost the emotional relationship to the data.
Maybe that is a good thing, because realising the severity of the situation wouldn’t allow me to spend my time working on learning more about these ecosystems, to contribute to a better understanding, even if only in a small way. But I am not sure if this detachment it is right. It is really not a case that I don’t care, I do. But to emotionally understand I need time and sit down and think about it. Doing this can be overwhelming.
Do my co-workers feel the same way? Clearly to work in conservation they must care about the state of the world as I do, but I do wonder if they feel detached as well.