Correlations of planktonic bioluminescence with other oceanographic parameters from a Norwegian fjord

Abstract

In August 1985 and 1986, a senes of bathyphotometric measurements were made In icefree waters of Vestfjord, Norway, to quantify stimulable in situ bioluminescence. In 1986, we tested and identified the causative bioluminescent plankton. In all profiles, peak or maximum bioluminescence intensity was always within a zone of 15 to 30m below sea surface, with marked decreases below 50m. Maximum biolurninescence intensity from all profiles for both years ranged from 3 X 10' to 2 X 10' photons S-' cc-' of turbulently-flowing seawater. Testing some of the plankton on board ship revealed that the brightest flashes were produced by the copepods Metridia longa and M lucens and the ostracod Conchoecia sp. Dinoflagellates of the genus Protopendnium emitted light at an intermediate level. The total number of dinoflagellates ranged from 1300 to 3700 cells I-' at water depths of 10 to 30m, and sharply decreased at 80 to lOOm (2 to 11 cells I-'). It was estimated that dinoflagellates accounted for 96 % of the measured light from the surface to a depth of loon?. Several species of the luminous d~noflagellate Ceratium were found. However, their contribution to the overall light budget never exceeded 25 %. P. curtipescontributed at least 50 % of the measured light field at 30m and above. In general, luminous zooplankton (larval copepods and euphausiids) contributed less than 4 % of the light produced above 100 m. The number of bioluminescent dinoflagellates correlated with bioluminescent intensity at the 0.05 significance level. Correlation analysis of beam attenuation coefficient w t h biolun7inescent intensity yielded high r values resulting in an overall level of significance of less than 0.01, and, therefore, may be a useful indicator for bioluminescence.