The Effects Of Reduced Salinity On Colonial Growth And Membership In A Hydroid

The effect of different salinity levels on colonial growth and gonozooid frequency of the hydroid Campanularia flexuosa Hincks has been studied. It is shown that the usual cumulative presentation of growth data tends to obscure evidence of acclimation and other features of importance to an interpretation of adaptations of the growth process to salinity changes. A method of analysis is described that not only demonstrates acclimation, but apparently shows how growth is controlled after disturbance by changes in salinity. One other response to reduced salinity and other unfavourable changes in water chemistry is an increase in gonozooid frequency due to the diversion of resources from the formation of new hydranths.

Plankton Of The Fladen Ground During Flex-76 .1. Spring Development Of The Plankton Community

Results from plankton sampling in the northern North Sea with the Continuous Plankton Recorder (CPR) and the Undulating Oceanographic Recorder (UOR) during the Fladen Ground Experiment in 1976 (FLEX 76) are summarised. The first evidence of the spring outbreak of phytoplankton was on 19 April, the day after the first signs of vertical stability of the water column were observed. This was followed by spawning of the euphausiid Thysanoessa inermis and rapid increase in the numbers of Calanus finmarchicus. C. finmarchicus was the most abundant species over the FLEX period (19 March to 3 June) and, together with T. inermis, accounted for over 80% of the dry weight of the zooplankton standing stock. By early June the standing crop of phytoplankton had been depleted and nutrients levels were reduced to very low concentrations in the upper 50 m.