Observations on Chaetognath Distributions in the Northeastern Gulf of Mexico During the Summer of 1974

Abstract

The chaetognath population was studied from zooplankton samples collected at twelve stations in the northeastern Gulf of Mexico in June 1974. Quantitative analysis of six stations revealed a large inshore population composed largely of juveniles and neritic species in the upper strata, and a progressively smaller and more evenly dispersed assemblage composed largely of oceanic, stenohaline species at stations further offshore. The high percentage of juveniles in surface samples evidenced an early-summer spawning peak for the population as a whole. Overlying low salinity water throughout the study area was characterized by the presence of two neritic species, Sagitta tenuis and S. friderici, in surface samples, while an underlying high salinity intrusion over the continental shelf was denoted by the submerged occurrence of stenohaline species. Fourteen species were grouped into three ecological categories denoting degrees of tolerance to environmental change: (1) neritic - Sagitta friderici, S. tenuis, S. helenae, S. hispida, (2) mixed water - S. enflata, S. minima, S. serratodentata, Pterosagitta draco, Krohnitta pacifica, and (3) oceanic - S. hexaptera, S. bipunctata, K. subtilis, S. decipiens, S. lyra.