Chaetognaths of the Arabian Sea
317
below 450 m. According to ALVARINO (1965), it is abundant at depths below 800 m.
SILAS and SRINIVASAN (1969) noted its occurrence at 600 m and down to 1300 m.
These meso- and bathyplanktonic species are known to be cosmopolitan. The earlier
relevant records, summarized with the present data in Table 4, show that the temperature
range varies little, while the difference in the salinity pattern may indicate a certain
tolerance to salinity changes associated with habits of vertical migration.
All hauls except for "Varuna" station 2009 (Table 3) were made at night or in the early
morning and all specimens arc either juvenile or stage I. Diurnal migration is well known
in chaetognaths (MICHEL, 1911; MOORE, 1949; HAMON, 1956 and others), and it is
likely that at dawn the young follow the adults in this downward migration. The
specimens may be late migrants caught in the top layer of the population range, or those
brought up to a shallower depth by the upwelling of deep water.
317
below 450 m. According to ALVARINO (1965), it is abundant at depths below 800 m.
SILAS and SRINIVASAN (1969) noted its occurrence at 600 m and down to 1300 m.
These meso- and bathyplanktonic species are known to be cosmopolitan. The earlier
relevant records, summarized with the present data in Table 4, show that the temperature
range varies little, while the difference in the salinity pattern may indicate a certain
tolerance to salinity changes associated with habits of vertical migration.
All hauls except for "Varuna" station 2009 (Table 3) were made at night or in the early
morning and all specimens arc either juvenile or stage I. Diurnal migration is well known
in chaetognaths (MICHEL, 1911; MOORE, 1949; HAMON, 1956 and others), and it is
likely that at dawn the young follow the adults in this downward migration. The
specimens may be late migrants caught in the top layer of the population range, or those
brought up to a shallower depth by the upwelling of deep water.