Dataset: Mesocosm study: sea star behavior

This dataset is part of a larger experiment to investigate how pH influences trophic links between intertidal sea stars (Leptasterias hexactis), snails (Tegula funebralis), and macroalgae (Mazzaella flaccida). Organisms were placed for 7 days in mesocosms containing seawater at either ambient (~7.9) or low pH (~7.0). The pH was modified using equimolar additions of sodium bicarbonate (NaHCO3) and hydrochloric acid (HCl). The water in each container was changed daily. The mesocosm array consisted of 40, 13-liter (L) circular plastic containers with a mesh barrier down the center to separate predator, prey, and/or basal resource but allowing for passage of waterborne cue. Mesocosms were filled halfway with seawater, allowing 10 centimeters (cm) of refuge space for snails above the waterline. Mesocosms were held within a seawater table under constant flow to maintain consistent temperatures.

Each mesocosm was assigned to one of four trophic treatments and one of two pH levels, resulting in five replicates per treatment and pH (4 trophic × 2 pH × 5 replicates = 40 mesocosms). The first trophic treatment was a “no-predator” configuration, composed of four snails and four 3-cm-diameter circular pieces of Mazzaella macroalgae cut out of blades (four pieces = 0.33 g ± 0.03 in total, with each piece standardized to have similar initial mass), both placed on one side of the central barrier of the mesocosm. The second trophic treatment was a “cue only” treatment in which one sea star was housed on one side of the barrier with four snails and macroalgae on the other side. The third was a “complete interaction” treatment in which one sea star, four snails, and macroalgae were all located on the same side of the barrier. The final trophic treatment was a “no prey/no grazing” configuration, for which one sea star was placed on one side of the barrier with the macroalgae on the other.

Consequences of pH for the predatory behavior of sea stars was quantified using image analysis (ImageJ) of photographs of animal position recorded every 2 min for 16 min daily starting immediately after the organisms were placed into the mesocosms. The behaviors were also stable through time and were, therefore, quantified only over the first 4 days of the experiment, following each water change. Sea star foraging behavior was evaluated through their tendency to move and the distance that they traveled (cm) during the assessment period.

See Jellison, B.M. & Gaylord, B. Oecologia (2019).