There is a bevy of research on resilience of ecosystems. One of the topics within the resilience work is alternative stable states. When a system shifts, or one system collapses, another system comes about. Now in the world of ecosystems, that new system may may alter things for the worse. That is one of the concerns in shifting systems. Typically a “good” functioning system processes a lot of energy. If the system shifts, and the biodiversity drops, for example, the new system (usually referred to as a regime) will not process as much energy, or as much energy as quickly. We humans are not an anomaly, we rely on these systems to life.
Until fairly recently most of the work on system shifts was theoretical, and a lot still is, but some systems have been observed that have shifted states. Not that is has not happened before, but observing this kind of thing, especially before there was as much attention on this kind of thing (and a new terminology to boot), was challenging.
So a little story:
Back in 1983, an up to then unknown shifting of states, and shifting of ecosystem roles was observed. Amos Barkai a graduate student working on islands off South Africa noticed odd species compositions. Another graduate student, C McQuaid, helped with the study. They were graduate student’s of G M Branch
The main players:
West Coast Rock Lobsters (Jasus lalandii).
A marine whelk, Burnupena papyracea. Typical adult size is 4 cm (1.5 inches), but it gets a bit larger.
Barkai observed the waters around one island (Malgas) were filled with lobsters, while the waters around another island (Marcus) had higher biodiversity, with few or no lobsters.
Ooooooo, a mystery, questions, questions, questions:
In performing the study the two researchers determined that usually the Whelks are eaten by lobsters, but on the island Marcus the lobster were eaten by whelks.
Not quite that simple:
A bryozoan growing on the Whelks helped them avoid predation by lobsters.
McQuaid and Barkai ran these experiments.
The authors of the eventual paper (1988 in Science) Branch, and McQuaid write:
“It was a much more complicated story than we initially thought,” explained Branch. “Yes it was true that whelks were excluding lobsters. But it is probably also true that they could only secure that ascendancy because they were protected by this bryozoan.”
I’m not sure why the supervising professor, Branch, wasn’t on the paper.
Marcus Island was overfished for lobsters: This perturbation apparently allowed the whelk populations to become vast. Now when the lobsters come into this area they are decimated.
The second Island (Malgas), 2 km away and offshore, never had the lobster fishing pressure.
Alternative stable states:
30 years later the conditions still stand, lots of lobsters on Lakes and few on Whelk-overrun Marcus.
Part of a past problem, lobster move in and decimate the areas. When too many lobsters are present many animals suffer, including things like abalone which are harvested. The presence of Urchins aid hiding of young abalone. Studied by Branch and another of his grad students; LK Blamey.
So the initial regime shift was the invasion of the lobsters, which altered the number of urchins, which in-turn, altered the presence and abundance of several other organisms?
A question still remains, how did the Whelks manage to combat the lobsters after the invading lobsters were reduced and not initially, before the lobsters were present at all.
Notes:
Branch (now an emeritus professor at the University of Cape Town), and his colleagues, conducted surveys in 2016, and little has changed. “Malgas Island is still dominated by lobsters,” Branch said.
Sources and Reading:
Barkai A, and MCQuaid C. 1988. Predator-Prey Role Reversal in a Marine Benthic Ecosystem. Science 242 (4875): 62-64.
Blamey LK, and Branch GM. 2012. Regime shift of a kelp-forest benthic community induced by an ‘invasion’ of the rock lobster Jasus lalandii. Journal of Experimental Marine biology and Ecology 1-2: 33-47.