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Free Content Plankton of the Florida Current.

Part VI. the Chaetognatha

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Plankton collections from 0-350 meters at a station located 10 miles east of Miami, taken during the period from June 19, 1950, to February 4, 1952, provided material for studies of relative abundance of species, seasonal variation in abundance and vertical distribution, and breeding periods. Data on diurnal migration was obtained during a 24-hour period by sampling 0-731 meters at a station 40 miles east of Miami.

In order of relative abundance, species at the 10-mile station were: Sagitta enflata, S. serratodentata, S. minima, Pterosagitta draco, S. bipunctata, Krohnitta pacifica, S. decipiens, S. hispida, S. hexaptera, S. lyra and K. subtilis, S. helenae, and, each forming less than 0.1 per cent of the total, S. planctonis, S. macrocephala and Eukrohnia hamata. With the exception of S. helenae and E. hamata and the addition of E. fowleri, these species also were collected at the 40-mile station.

Species collected in adequate numbers showed seasonal maxima in abundance which usually occurred in summer and sometimes also in another season. The maxima of some coincided generally with their major breeding periods.

Differences in relative abundance suggest the presence at the 10-mile station of neritic influence which is lacking at the 40-mile station.

No correlation was found between periods of abundance of any species and percentage of either the Gulf of Mexico or Yucatan components of the Florida Current at the 10-mile station. However, it is suggested that S. hispida may be an indicator of Gulf water under certain conditions.

Vertical distribution was highly variable seasonally. The depths at which the major concentrations of each species live were much greater at the 40-mile than at the 10-mile station. It is believed that this results principally from reaction to temperature.

Sagitta enflata, S. hexaptera, S. lyra, S. serratodentata and Pterosagitta draco were found to migrate diurnally. There is also evidence of diurnal migration by S. decipiens, K. subtilis and K. pacifica.

From a study of length and maturity stages, it is concluded that length is not a generally useful index of stage of maturity and that several species may spawn more than once in a lifespan. Data on length at each stage of maturity of species collected in both the Florida Current off Miami and in colder waters indicate that the animals may mature at a smaller size in tropical oceanic waters. Evidence is given that six Florida Current species breed more or less continually throughout the year in addition to their major breeding periods and that two breed only at certain seasons. There were insufficient data to determine the spawning periods of remaining species.

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Document Type: Research Article

Publication date: 1960-01-01

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