Reproductive strategy of the jellyfish Aurelia aurita (Cnidaria Scyphomedusae) in the Suez Canal and its migration between the Red Sea and Mediterranean
Keywords:
gelatinous plankton, life span, medusae, ephyraeAbstract
The life history of the common jellyfish A. aurita (Linnaeus) in the Suez Canal was investigated by monthly sampling over a 28 month period from September 2006 to December 2008. Young medusae of 2–3 cm diameter appeared during February/March. Growth was rapid. Some specimens of this cohort reached 16 cm and spawned by March/May and then decreased in size or died. Others reached a maximal size of 10 cm by September, after which spawning took place. A few mature individuals remained after spawning in the next year but decreased in size. Release of ephyrae seems to be induced by a lowering of ambient environmental temperature to below 16°C, with peak of release occurring in December–February. A drop in temperature may be the primary cue for strobilation in the Suez Canal. A. aurita seems to be an immigrant plankter to the Suez Canal, and much interest was focused on determining from which end of the canal these organisms were invading the opposite sea. However, the canal itself, along with its lakes, should also be considered as a substantial permanent habitat in its own right. The canal cannot be considered only as a funnel or corridor through which animals pass like ships from one sea to the other.
A. aurita appears to enter the Suez Canal from the south via water currents; to do so it needs to be carried over a distance of 20 km along the canal from the Gulf of Suez into the Bitter Lakes, then pass across the Bitter Lakes before being carried a further 12 km along the canal into Lake Timsah. Transport of A. aurita southward along the canal from the Mediterranean is unlikely to take place during most seasons of the year because it would require transport against the dominant-water flow; it is possible only during a brief period (July–September) of reversed flow. Because the main part of the 80 km from the Red Sea is canalized, passive transport of A. aurita by water currents from the north could occur within a week during the brief period of reversed flow even at the low speed of 0.5 km hour−1. Moreover, conditions (barriers, obstacles and/or links) along the migratory route of the Suez Canal, in either direction, are likely to determine the success of passive transport of A. aurita.
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