Fine-scale layer of hydromedusae is revealed by video plankton recorder (VPR) in a semi-enclosed bay in northern Norway
| Autor: | M. F. Norrbin, H. P. Jacobsen |
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| Rok vydání: | 2009 |
| Předmět: | |
| Zdroj: | Marine Ecology Progress Series. 380:129-135 |
| ISSN: | 1616-1599 0171-8630 |
| Popis: | High resolution images of zooplankton organisms were recorded in situ using a digital autonomous video plankton recorder (VPR) in a semi-enclosed bay in northern Norway. Data from vertical VPR profiles was used to estimate the depth distribution and abundance of zooplankton along a bay-wide grid. Images were recorded simultaneously with hydrographical data, and the spa- tial distribution of different organisms was related to several water column characteristics, such as chlorophyll a, density, and buoyancy frequencies. In June, unusually high abundances of hydrome- dusae (Rathkea octopunctata and Obelia sp.) were located in a fine-scale layer of a few metres thick- ness. This layer could be associated with relatively high buoyancy frequencies, reflecting a density gradient present throughout the entire sampling area. Aggregation of hydromedusae around density discontinuities may have enabled retention of medusae in the bay. Ctenophores and appendiculari- ans were distributed above the medusae layer, while peaks of copepod abundance were found out- side the layer boundaries. We suggest that the bloom of R. octopunctata was initially caused by liber- ation of new medusae from successful benthic hydroid colonies, and that proliferation of this species was sustained by asexual, manubrial budding in the medusae stage. |
| Databáze: | OpenAIRE |
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