Temperature Requirements of Penilia avirostris Dana in the Hauraki Gulf, New Zealand

Abstract

IN a pilot survey, still in progress, of the plankton of the Hauraki Gulf, New Zealand, Penilia avirostris Dana was found from December 1948 until April 1949. In December, Penilia was found in small quantities at some stations only; except in one case, the numbers were less than 1 per c.m., and Penilia was only recorded from stations of surface temperature 17.8° C. or above. In January, when apparently extensive multiplication occurred, as many as 1,250 per c.m. were recorded, more usual records being 300–400 per c.m. The modal recorded surface temperature for January was 20° C. In February, with a modal recorded surface temperature of 20.4° C., the numbers of Penilia declined to 50–150 per c.m., and continued to decline until April, when a sample with less than 1 per c.m. was recorded at a temperature of 18.7° C. This decline in numbers was reflected in other species. In both January and February, Penilia was frequently the dominant member of the plankton, sometimes forming more than 50 per cent of the planktonic animal population of coastal waters of depth 10–20 fathoms.