Hans De Blauwe images
Aurelia aurita
In Belgium, the media always correlates Aurelia-invasions to excellent weather conditions in summer. Instead, the occurrence or absence of Aurelia is correlated to winter conditions. Seawater temperatures are within the limits for strobulation (4 to 10°C) from December to April. Since 1987 until 2003 there were no records of medusa of Aurelia aurita in Belgium in the years 1994, 1995, 2000, and 2002. In these years seawater temperatures were higher than 6°C in February, so the polyps were not stimulated to strobulate. In normal years, the temperature of coastal seawater drops beneath 6°C in February. Polyps strobulate and the ephyra grow during he following three months until adolescent proportions. These medusae are beached in late spring and early summer, when tourists are common on our beaches.Abnormalities in the number of gonads are as frequent as in the beginning of the last century (Russell, 1970). Out of 1988 specimens, 39 specimen or 1.96% had five, six or seven gonads instead of four.
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