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Albert D.J.,Roscoe Bay Marine Biology Laboratory | Walsh M.L.,Roscoe Bay Marine Biology Laboratory
Journal of Sea Research | Year: 2014

The bell diameter of adult Aurelia labiata in Roscoe Bay increased from spring (April) to early summer (May/June) and decreased over the rest of the year (2009/2010). The increase in bell diameter in the spring would have been supported by the increase in zooplankton that occurs in the northeast Pacific at this time. Over the summer, bell diameter may have decreased because the food available/medusa would have been decreased by the arrival of a large number of juveniles and may have decreased further over the fall and winter when zooplankton levels are known to be low. Adults and juveniles were intermingled during 2010, 2011, and 2012. Correlations between the number of adults and number of juveniles obtained in individual net lifts across the entire bay and in different parts of the bay were all positive and most were statistically significant. In 2012, salinity in the entire water column of the west side of the bay dropped below 20. ppt in July and most medusae migrated to higher salinity in the east side of the bay, a distance of about 0.5. km. The mingling of adults and juveniles supports other evidence that adult Aurelia sp. medusae do not prey upon juveniles. The ability to withstand months with insufficient food and to inhibit preying on juveniles would contribute greatly to the survival of Aurelia sp. jellyfish. © 2013 Elsevier B.V.

Jellyfish live in complex environments and must continually make behavioural choices. In field observations, adult Aurelia labiata were confronted with a conflict between swimming up elicited by touch of the manubrium and swimming down elicited by low salinity. Following a touch, downward-swimming medusae (1.5-2.0 m deep) turned and swam to within 0.5 m of the surface when the salinity in the top 1.5 m of the water column was greater than 20 ppt but medusae uniformly refused to swim up into the top 1.25 m when the salinity was less than 20 ppt even after being touched three times. The central nervous system of A. labiata appears to have neural circuitry that specifies their response when medusae encounter stimuli that elicit incompatible behaviours. Upward-swimming adult medusae had animal, vegetable or cellulose (paper) material dispersed ahead of them. Medusae captured each material on the bell margin and transported it to a gastric pouch. Medusae displayed only minor behavioural differences in the process. Having sensory, neural and muscular systems organized to capture and pass to the stomach, a huge variety of materials allows medusae to survive in different seasons and environments. © 2014 Springer International Publishing Switzerland.

Controlled observations in Roscoe Bay examined whether Aurelia labiata medusae would respond to three environmentally significant stimuli: low salinity, seawater movement and seawater depth. Significantly more upward-swimming medusae turned and swam down or sideways when they encountered an experimentally created low-salinity plume than did upward-swimming medusae that encountered a seawater plume or a seawater plume containing milk powder. Downward-swimming medusae that encountered a plume containing freshwater continued swimming down. Significantly more upward-swimming medusae exposed to an experimentally created stream of seawater that gently pushed them horizontally turned and swam down than did upward-swimming medusae not exposed to the seawater stream. Downward-swimming medusae continued to swim down when pushed horizontally. A stronger seawater stream that tumbled as well as pushed medusae horizontally was less effective. In a shallow area near the time of a low tide, most medusae were in the top metre of a 2 m water column whilst in an adjacent area where the water was 4-6 m deep, almost all medusae were below 1. 5 m. These observations add to a growing body of evidence that the ecological distribution of A. labiata is influenced by their ability to respond adaptively to significant environmental stimuli. © 2011 Springer Science+Business Media B.V.

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