Preliminary investigation of light regime and the population dynamics of a deep sea scyphozoan, Periphylla periphylla, in a Northern Norwegian fjord
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Jellyfish blooms have been reported worldwide and have ecological and economical consequences. Causes of mass abundances have suggested and include eutrophication, climate change and overfishing. The deep-sea medusa Periphylla periphylla has colonized fjords of western Norway in mass numbers since the 1970s and more recently there have been reports of high population numbers in fjords of northern locations. The species experiences fatalities when exposed to light as the medusa pigment is photodegraded. The extended daylight hours of the summer months in northern Norway may be a factor limiting the northern distribution of the P. periphylla. Vefsnfjorden is the northemmost fjord with reported mass abundances. Samples were collected from the fjord over a four month period from Febmary to May of201O specimens were sorted by developmental stage. Here I present a decrease in both overall numbers of individuals and age classes in Vefsnfjorden, which was most likely caused byaflushing event in the fjord. The lack of early developmental stages collected in the later sampling trips sugge st the Vefsnfjorden population may have seasonal reproduction rather than year round as is the case with more southern populations.
Studentarbeid i biologi (bachelorgrad) - Høgskolen i Bodø, 2010