A note on the barnacle larvae of the Clyde Sea Area as sampled by the Hardy Continuous Plankton Recorder

H. Barnes
1950 Journal of the Marine Biological Association of the United Kingdom  
The Marine Station, Millport In the course of an extensive series of tests on the Hardy Continuous Plankton . Recorder (Hardy, '1939) carried out in the Clyde Sea Area during March and April 1949, a number of runs were made both during the time of the spring dia~om outburst and over the period when barnacle larvae were a dominant feature of the zooplankton. It should be emphasized that the work was originally planned not as a plankton study but only as an investigation of the comparative
more » ... comparative performance of a number of recorders. Nevertheless, the limited data on cirripede larvae do give some quantitative information regarding the distribution and the total population of barnacle larvae over a. moderately large area, and the quantitative relations of the stages, as well as providing some evidence bearing upon the hypothesis that the diatom outburst is a controlling factor in the development of the later stage larvae. Since the results of these tests have not yet been published the following points regarding the performance of these recorders may be mentioned: (I) The excellent depth-keeping properties of the machines have been fully confirmed; a constant depth of 10:t 0"5 m. was maintained over long distances by both machines under test. (2) The amount of water filtered is probably the theoretical volume, since great increase in filtering surface (obtained by fitting large nets inside the machines) gave no significant increase in catch. This was true even with clogging which became apparent during the diatom outburst. It should, however, be remembered that the diatom was largely Skeletonema costatum; quantities of larger phytoplankton species could lead to incomplete filtration. . Thanks are due to Mr W. W. Brown who took part in the recorder investigations, to Mr M. W. H. Bishop for confirming the identity of the larval stages counted, and to Captain Stewart and the crew of the Calanus for their willing help in all the boat work. THE COLLECTION AND COUNTING OF THE MATERIAL The plankton recorders were towed together in pairs under varying experimental conditions, and a statistical examinationof the results has shown that in none of the tows here quoted was there any significant difference in the performance of the two machines. In Table I , therefore, only the mean catch
doi:10.1017/s0025315400056198 fatcat:l5xu3sixavhyvobkor4cmuozii