Last weekend I was out on a seaweed gathering trip to a shoreline location that was not very protected. While I was there I took this photo of a cluster of ochre sea stars (Pisaster ochraceus) in a somewhat protected cranny of the bedrock shoreline. It’s not unusual to find such clusters of these sea stars, and this time it occurred to me that they can’t all be getting food to eat there, so they must forage elsewhere. I am now curious about the foraging patterns and clustering behavior of these sea stars.
Some questions that come to mind:
- Why are they gathering together in the first place? Is it because they like being together or perhaps they tolerate togetherness in order to be in a better (more protected?) location. I have seen (usually smaller) clusters on beaches in protected areas, so perhaps this suggests there is some advantage to hanging together (or they just like company).
- Do they regularly show up in this particular spot, and if so, does the gathering consist of the same individuals.
- How much/often do these sea stars need to eat?
- How often do they move out to forage, and how long does it take them to get back (assuming they do at all)?
- Do individuals have a limited home range that they are limited to (beyond just that imposed by suitable habitat and speed of motion), or do they wander along in search of food (or whatever else motivates them) without particular concern for where they’ve been?
- Would it be difficult to mark individuals (especially in a cluster) and track them over time?