On a survey looking for introduced (non-native) species carried out in 2000 they found this beautiful sea anemone (Sagartia elegans). It was only found in one marina: Hawthorne Cove Marina in Salem Harbor, MA (along with quite a few other neat introduced animals and plants). In late summer it would appear in the fouling community (community living attached to man-made structures) underneath the docks in great numbers, but by winter it disappeared. It was apparent that temperature during the winter was stressing this animal, but no one had looked at the animal with any sort of scrutiny. I decided that I would do just that.
Another possibility is that their predator, the nudibranch Aeolidia papillosa , ate the whole population. Aeolidia is a specialist predator on sea anemones and does especially well in the winter. While it is possible that Aeolidia could have consumed every last individual of Sagartia , I find it unlikely. I cannot for say sure.
Originally my research, starting in 2010, was going to be on the anemone's range expansion as it took hold in the Gulf of Maine, but after the winter of 2010-2011 the anemone completely disappeared and never returned. My topic changed from where are they going to why did they disappear?
The most plausible of reasons is that temperature was just too low that winter. After looking at the historical sea water temperatures, the winter of 2010-2011 wasn't any colder than the previous few winters. To further confuse the situation I found that
Sagartia's minimum temperature tolerance is around 6 °C (43 °F). This is warmer than at least a portion of every winter for the past ten years! They should have disappeared a long time ago! In order for them to survive the winter they must have some sort of warm-water refuge to get through the winter. Turns out they may...
One potential temperature refuge within Salem harbor is a coal and oil-fired power plant. The power plant is less than 100 meters from Hawthorne Cove Marina (the only place we've found Sagartia). Power plants use sea water as a coolant and then pump the warmed water back into the system. This power plant is allowed to draw up to 420,000 gallons of sea water per minute and sea water exiting this can be raised up to 9.6 °C (17.3 °F) (Anderson et al. , 1975)! An increase of only several degrees during the winter would be enough to keep the sea anemones alive throughout the winter months. If Sagartia took refuge in the discharge channel of the power plant, it is possible that they could ride the currents out during the summer and find their way to Hawthorne Cove Marina. If the power plant turned its power down, stopped for a short while, or ran an anti-fouling compound through their coolant lines during the winter, that could have spelled the end to Sagartia.
We still don't know why Sagartia actually disappeared; we probably never will. It is likely a case of temperature as multiple laboratory and field studies I've performed have found that 6 °C (43 °F) is just too cold for these animals. If something happened to their refuge during the winter then they would have disappeared. As I get more information I will update you guys.
Thank you for reading!
Anderson, C.O., Jr., Brown, D.J., Ketschke, B.A., Elliott, E.M., and Rule, P.L. 1975. The effects of the addition of a fourth generating unit at the Salem Harbor Electric Generation Station on the marine ecosystem of Salem Harbor. Massachusetts Division of Marine Fisheries, Boston.
NOAA. 2013. National Weather Service Forecast Office. National Oceanic and Atmospheric Administration, Washington.