| Popis: |
Five species of Chaetognatha occurring within the lower Chesapeake Bay during a 2-year, monthly survey were, in order of relative abundance: Sagitta tenuis, S. elegans, S. enflata, S. hispida and S. tasmanica . Two seasonal groups were evident; S. elegans and S. tasmanica were winter-spring inhabitants, while S. tenuis, S. enflata and S. hispida occurred during summer-fall. Principal peaks of abundance were caused by S. tenuis in September of each year and S. elegans in February or May. An annual incursion of S. enflata was observed each fall, with peak abundance in November. Only a single generation of S. elegans was produced during its abbreviated tenure in the Bay, whereas S. tenuis was observed to breed continuously through the summer and early fall. Stage III S. tenuis disappeared from collections in November, when lower temperatures terminated maturation. Further temperature decreases through December eliminated S. tenuis from the Bay. S. elegans appeared first in January or February as Stages I–III. Stages II and III were replaced in April by their Stage I progeny. More developed stages occurred again in May, but were reduced in size. This winter-spring species was eliminated as water temperatures approached and exceeded 20 °C in June. Seasonal abundance, species composition and distribution of the Chaetognatha within Chesapeake Bay most likely depend on availability of shelf chaetognaths, hydrographic conditions both on the shelf and in the Bay, and on tolerance of individual species to reduced salinity. |
