Date of Award

Winter 1983

Project Type

Dissertation

Program or Major

Zoology

Degree Name

Doctor of Philosophy

Abstract

While much is known concerning the structure of the amphipod-dominated marine sandy-beach communities along the Atlantic coast of the United States, little is known about the functional relationships within them. The goal of this study was to determine the seasonal trophic dynamics and life history of the sandy-beach amphipod Haustorius canadensis in order to gain a better understanding of the functioning of northern New England sandy-beach communities. Haustorius canadensis is one of the three dominant amphipods on these beaches and remains strictly intertidal throughout the year making it an ideal organism for this study. The site chosen for this study was Long Sands Beach in the town of York, Maine, where H. canadensis maintains an average abundance of approximately 35000 m('-1) of beach front. The population was sampled monthly from November, 1978 through June, 1982 using a modified stratified random design. During the first two summers of the study the sampling frequency was increased to biweekly to gain a more complete picture of the reproductive dynamics of the amphipod. In addition, 24 months of data on the relationship of length and weight, and 14 months of data on caloric content were obtained. Haustorius canadensis exhibits a mixed annual/biannual life history in northern New England as compared to an annual life history south of Cape Cod, Massachusetts. The difference in temperature regimes is suggested as the cause of this change in life history pattern. The caloric content of male H. canadensis shows a seasonal cycle, peaking in late summer, while the females do not exhibit a cycle. It is hypothesized that the male cycle is due to the increased productivity of epibenthic diatoms during the summer months. In the females, this somatic cycle is masked by the reproductive cycle. Production was calculated using four methods, which are compared in terms of their assumptions and results. Annual production, using the instantaneous growth model, averages 100.1 gm(ash-free) m('-1) yr('-1). The production to mean biomass ratio averaged 1.48 over the study period. Production is highly seasonal; summer production is about 4.5 times the winter production. Production by a cohort exhibits 2 to 3 peaks over the cohort's life span, the major peak due to the one-year-old individuals.

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