The MIB lab seeks to understand how projected physical and chemical changes to the world’s oceans will impact the behavior of their inhabitants.
Predator-Prey Research
The spiny lobster Panulirus interruptus is a surprisingly flexible predator. In a laboratory setting, it normally eschews chemically protected sea hares, unless deprived of food (36). Prior to our research, no one had reported lobsters attacking sea hares in the field, and we confirmed that along most of the California coast, lobsters ignored sea hares that we placed in front of them in the subtidal kelp beds where they forage. Our breakthrough came with the hypothesis (whispered to us by a treasured colleague) that lobsters might be hungrier in no-take reserve kelp forests on the channel islands, where competition is fierce, and food might be scarce. Based on the behavior of food-deprived lobsters in the laboratory, this hunger hypothesis predicted that lobsters in these reserves might actually consume the otherwise eschewed sea hare. This is exactly what we observed, resulting in our only publication from data collected entirely underwater using SCUBA (37)!
Lobster prey have their own defense mechanisms. For example, hermit crabs become more vigilant in water taken from lobster tanks. The following bar graph from MIB-lab member, Ali Sidun, shows that hermit crab feeding rate (normally around 12 mg per half hour, dark blue bar) is strongly reduced (orange bar) when the scent of lobster or crab predator is included in their water. We assume, and cursory observations of feeding animals confirm, that this reduced feeding is due to their increased vigilance (interest in feeding lags as they attempt to escape, etc.).
However, if one adds some carbon dioxide (CO2) to the predator water, reducing the pH from 8.1 to 7.6, the hermit crabs immediately eat much more enthusiastically than in predator water maintained at natural (8.1) pH. The “fear” of the predator seems to have disappeared (rightmost light orange bar, above figure). Similar results have been reported in other species in response to chronic decreases in pH, meant to mimic global climate change. Our observations of a clear reversal of anti-predator behavior by much more rapid pH drop is somewhat unique and implies very strongly that the impacts of CO2-induced acidification are already felt in tidepools during night-time low tides.
Recently we have increased our analytical power by using image analysis and machine learning to measure the diverse behavioral responses of hermit crabs to the chemical combinations of olfactory signals of predators and carbon-dioxide enriched water.
The MIB lab has also begun to study a puzzling behavior of sea hares that are placed in lobster water:
Although there are many details to iron out about this distinctive parapodial opening, such as why in the world do they do it, the opportunity to study the phenomenon in a neural model species like Aplysia makes understanding the effect of acidification on anti-predator behavior at the neural/ionic level a real possibility.
Marine Invertebrates as Model Species
More generally, in the face of global climate change, accessible intertidal organisms like hermit crabs, sea hares, and limpets may be useful model species to establish first principles. For example, the near-future weather in Southern California is projected to include extreme heat spells. What are the sub-lethal effects of such heat spells on behavior? We are discovering that overheated intertidal habitats can inhibit feeding in hermit crabs.
Overheating can also inhibit movement in the eco-system engineer, Lottia gigantea (the owl limpet, as studied by MIB-labbies, Alex Guerrero, Nelson Gould, and Sarah Otto)
