Budding modes.

<p>Budding modes of <i>Aurelia coerulea</i> and <i>A</i>. <i>relicta</i> polyps. (A) Polyp producing a Directly Budded Polyp (DBP) from the stalk; (B) polyp producing Stolonal Budded Polyps (SBP) from the pedal stolon. Scale bars: 1 mm.</p

Ephyrae production.

<p>Cumulative number of ephyrae produced by <i>A</i>. <i>coerulea</i> polyps at 14°C under different combination of salinities and food regimes (F1, F2, F3 = food regimes of 9.3, 18.6, 27.9 μg C ind⁻¹ week⁻¹, respectively; Salinity 24 or 37 ppt). No ephyrae were produced by <i>A</i>. <i>relicta</i> polyps.</p

Calyx diameter increase.

<p>Comparison of means of calyx diameter increase of the <i>Aurelia coerulea</i> and <i>A</i>. <i>relicta</i> polyps incubated under different combinations of experimental conditions over 85 days. F1, F2, F3 = Feeding regimes of 9.3, 18.6, 27.9 μg C ind⁻¹ week⁻¹, respectively; Salinity 24 or 37 ppt; Temperature 14°C or 21°C. Vertical lines: SD.</p

Regression-regeneration cycle.

<p>Regression-regeneration cycle of <i>Aurelia relicta</i> polyp. (A) fully active polyp, (B) polyp in transition, (C) unattached, drifting non-feeding stage. (o), oral side. Arabic numbers indicate the progression of the process. Scale bars: 1 mm.</p

Statistical results.

<p>Statistical results.</p

Experimental conditions.

<p>Experimental conditions.</p

Respiratory response to temperature of three populations of <i>Aurelia aurita</i> polyps in northern Europe

<div><p>The benthic life stage (polyp or scyphistoma) of the bloom-forming jellyfish, <i>Aurelia aurita</i> (Linnaeus, 1759), also known as the moon jellyfish, contributes to the seasonal occurrence and abundance of medusa blooms via asexual reproduction. <i>A</i>. <i>aurita</i> is widely distributed in coastal areas in northern Europe, and one of the most studied jellyfish species. While the physiology of the visible medusa is largely understood, understanding of the physiology of the perennial benthic life-stage is scarce. To measure the physiological tolerance of <i>A</i>. <i>aurita</i>, the scyphistoma’s temperature sensitivity across its distributional range was investigated. Respiration rates of polyps from three northern European locations exposed to 11 temperatures between 2 and 22°C were measured. There was a significant difference in respiration rate among the three polyp populations, which may reflect on differences in their thermal tolerance window. A critical temperature was reached at 14°C with the metabolic rate decreasing below and above that temperature. This pattern was less pronounced in the Norwegian population but polyps were able to survive, at least temporarily, those temperatures exceeding their natural range. While polyps collected from northern Norway, with a narrow environmental thermal window, displayed a low baseline metabolism with a Q₁₀ value of 1.2, polyps from southern England and Scotland had Q₁₀ values of 1.6 and 2.5, respectively. Differences in polyps’ respiration rates across their distributional range suggest that populations have evolved adaptations to local environmental thermal conditions.</p></div

Podocyst production.

<p>Mean production rates of podocysts (PC) obtained from polyps of <i>Aurelia coerulea</i> and <i>A</i>. <i>relicta</i> under different combinations of experimental conditions over 85 days. F1, F2, F3 = Feeding regimes of 9.3, 18.6, 27.9 μg C ind⁻¹ week⁻¹, respectively; Salinity 24 or 37 ppt; Temperature 14°C or 21°C.</p

Budding rates.

<p>Mean budding rates and upper standard deviation from polyps of <i>Aurelia coerulea</i> and <i>A</i>. <i>relicta</i> under different combinations of experimental conditions over 85 days. F1, F2, F3 = Feeding regimes of 9.3, 18.6, 27.9 μg C ind⁻¹ week⁻¹, respectively; Salinity 24 or 37 ppt; Temperature 14°C or 21°C. DBP = Directly Budded Polyp, SBP = Stolonal Budded Polyp.</p

Mean monthly water temperatures at Eggum (Norway), Dunstaffnage (Scotland) and Horsea Lake (southern England) where <i>Aurelia aurita</i> were collected.

<p>Horsea Lake temperature data were taken from [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0177913#pone.0177913.ref020" target="_blank">20</a>]. Norwegian temperature data were received from the Institute of Marine Research—Norwegian Marine Data Centre (NMD) and temperature data from Scotland were received from the Scottish Association for Marine Sciences (SAMS).</p