Anthopleura elegantissima: a thermoregulating anemone?

Ileana Freytes
University of Puerto Rico, Río Piedras
ileana.freytes(at)hotmail.com

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ABSTRACT: Anthopleura elegantissima, a common intertidal anemone, can be exposed to air for long periods during low tide. High temperature stress during these periods can lead to the expulsion of two types of symbiotic algae harbored in the anemones' tissues (bleaching). To prevent this, the anemones must maintain low body temperatures. We placed single anemones of different sizes in a temperature controlled wind tunnel and measured their internal body temperature over a 9-hour exposure period. Anemone size was a determining factor in the anemone's ability to thermoregulate, smaller anemones warmed much faster than bigger anemones. We also tested groups of similarly sized anemones to determine how aggregation affected individual thermoregulation. The thermoregulating capacity of anemones as a group was more efficient than that of individuals. When their ability to thermoregulate by evaporative cooling was suppressed, all sized anemones warmed up much faster. Our results suggest that A. elegantissima can thermoregulate, but its capacity to do so is dependent on size and aggregation. Evaporative cooling through the release of water is the mechanism used by A. elegantissima to resist temperature changes.

Why?

The temperate anemone Anthopleura elegantissima is an important part of the intertidal environment of the northwestern coast of the United States. A. elegantissima can have symbiotic relationships with two microscopic algae, which makes it a unique species. During low tide periods, A. elegantissima could be exposed to wind from 2 to 15 hours a day.; high temperatures during exposure could lead to symbiont expelling (bleaching) (Muller-Parker et al., 2007). A. elegantissima can survive without the algae; however, their loss affects their hosts negatively (Sebens, 1983). Since symbiont loss should, therefore, be avoided, A. elegantissima should have adaptations to resist temperature change and keep their symbionts safely housed in their tissues.

It can be asked, then: Can Anthopleura elegantissima thermoregulate? If so, what are some factors that affect its ability to do so?

• Is internal temperature of A. elegantissima homogeneous?
• Does anemone size affect thermoregulation?
• Does aggregation affect thermoregulation?
• Is evaporative cooling the method of thermoregulation for A. elegantissima?

How?

We used a temperature and wind speed controlled wind tunnel. The wind tunnel was set at a flow speed of 0.5 m/s, similar to the wind speed experienced on intertidal rocks. Temperature was set at 22°C (room temperature), since temperatures in the intertidal can be this warm in the summer season. The relative humidity in the wind tunnel averaged 34.8% (SD = 2.72) (measured by a U12 HOBO data logger). The test area was illuminated by overhead fluorescent light bulbs.

To mimic the thermal inertia of the intertidal to which A. elegantissima is normally attached, we placed anemones on individual pieces of slate tile. Anemone sizes were measured as the anemone’s wet weight.

To start the experiment, the tiles with their attached anemones, were placed on a platform suspended in the working section of the wind tunnel. The platform consisted of a square Plexiglas plate covered with cloth and attached to the top of the wind tunnel by long screws. The anemones were haphazardly arranged on the platform approximately 6 cm apart. Type K 24 gage Teflon-coated Omega thermocouples were inserted into the anemones’ mouths. We placed another Omega thermocouple on the platform approximately 6 cm behind the anemones to track wind temperature. The thermocouples were connected to an Omega multiprobe switchbox, which, in turn, was connected to an Omega single input thermometer. The anemones were initially submerged in 11°C seawater. After 10 minutes and an initial temperature measurement, we removed the water from the platform to mimic a falling tide, and then kept the anemones exposed to the wind flow and air temperature for the duration of the run.

REFERENCES:
Muller-Parker, G., Pierce-Cravens, J., Bingham, B.L., 2007. Broad thermal tolerance of the symbiotic dinoflagellate Symbiodinium muscatinei (Dinophyta) in the sea anemone Anthopleura elegantissima (Cnidaria) from northern latitudes. Journal of Phycology, 43(1), 25-31

Sebens, K.P., 1983. Population dynamic and habitat suitability of the intertidal sea anemones Anthopleura elegantissima and A. xanthogrammica. Ecological Monographs, 53(4), 405-433

Home     Temperature profiles    Size effect    Aggregation effect     Evaporative cooling

This research project was done in the facilities of the Shannon Point Marine Center as part of the MIMSUP program.