Date of Award

12-2006

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Marine Biology

Advisor

James McCleave

Second Committee Member

Sara Lindsay

Third Committee Member

Les Watling

Abstract

Crangon septemspinosa Say, the sand shrimp, is an ecologically important and common inhabitant of coastal and estuarine waters of the western Atlantic, ranging from the Gulf of St. Lawrence to eastern Florida. Although sand shrimp are widely distributed, abundant, and considered to play an important role in the energetics of estuarine ecosystems, gaps in knowledge exist. To help fill this void, the present investigation was undertaken to describe the intertidal distribution and relative abundance of sand shrimp in relation to environmental variables in three adjacent estuarine systems, the Sheepscot, Kennebec, and Damariscotta Rivers, located along the mid-coast of Maine. Additionally, diet composition and feeding intensity of sand shrimp were determined by identifying prey items and examining the relative degree of gut fullness. Monthly sampling (June - October) using an epibenthic sled resulted in the collection of over 14,000 shrimp from wide ranges of temperature (9.4 - 25.9°C), salinity (3 - 34), and dissolved oxygen concentration (6.52 - 13.15 mg l-1). However, most large catches of sand shrimp were confined to narrower ranges of these environmental conditions. Maximum concentration and distribution of sand shrimp occurred when surface temperatures were between 10 and 18° C and salinities were ≥22 in the three estuaries. High shrimp abundance and widespread distribution in the estuaries occurred late in the sampling season as freshwater discharge declined and temperatures dropped below 20° C. Sand shrimp were differentially distributed according to sex and reproductive status. Ovigerous females and males were more abundant in the lower estuary where low temperatures and high salinities predominated. Penetration up the estuary by female and juvenile shrimp did not appear to be as limited. Overall, juvenile shrimp were a substantial portion of the total catch in each estuary despite their limited abundance and patchy distribution during the early part of the sampling season. Visual analysis of foregut contents revealed that sand shrimp consume a variety of primarily benthic organisms, including polychaetes, molluscs, and crustaceans. Aside from organic debris, no single food category dominated, suggesting an unspecialized feeding strategy. There were slight differences in diet composition between size classes, in that smaller shrimp appeared to predominantly consume smaller prey items. Foregut fullness was significantly associated with tidal cycles suggesting that sand shrimp enter the intertidal zone to feed.

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