Changes in phytoplankton as indicated by spectrophotometric chlorophyll estimations 1952-53 67 



Stages of the cultures, the comparison being between the same species, so different 

 growth rates are not involved. 



Table II shows the Bacillariphyceae, identified as named and classified in Hendey's 

 list (1954). Fifty-four species were found, as compared with twenty species found in 

 1951-52, but the autumn growths cannot be compared with 1951-52 since the samples 

 were not enriched and exposed until February 1952. 



Skeletonema costatum, Navicu/a sp., and Nitzschia closterium were again the most 

 regular in occurrence. Species absent from our lists before 1953 were Thalassiosira 

 condensata found in February, Eucampia zoodiacus in January, Rhizosolenia setigera 

 in June, November and December, R. styliformis in July, also Fragilaria striatula in 

 April. 



The Algae listed in Table III are as named and classified in Parke's list (1953). 

 The most regular occurrence of the Chlorophyceae were the Chlorella sp. and 

 Chlamydomonas sp. The three others listed grew well in the spring, Ulothrix sub- 

 flaccida which was found once in February, 1952, was present from February to early 

 April in 1953. 



Of the Chrysophyceae, the CoccoUthophora sp. were always in the cultures. Phaeo- 

 cystis globosa, which was absent from the 1952 cultures, grew in 1953, increasing to a 

 great mass in May. This caused the blocking of the sea water filtration. 



One member of the Cyanophyceae was present in January and late April in 1953, 

 an Oscillatoria sp. The growth of such sessile forms as this and the Ectochaete sp., 

 Ulothrix subflaccida, and Stichococcus sp., though not truly planktonic showed that 

 some must have been present in the water at the time of sampling. 



Hemiselmis mfescens, a species of the Cryptophyceae, which grew in January 1952, 

 was very plentiful in November and December 1952, also in April and the early 

 autumn of 1953. 



I would like to express my thanks to Dr. M. V. Lebour, Dr. M. Parke, Dr. T. J. 

 Hart and Mr. T. R. Tozer for much help in the identifications, also Mr. F. A. J. 

 Armstrong for the temperature observations. Finally for the collection of the sea 

 water I have pleasure in thanking the captains and the crews of the R.V. Sula and the 

 R.V. Sarsia. 



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