Condition, reproductive activity, and gross biochemical composition of the Manila clam, Tapes philippinarum in natural and newly created sandy habitats of the southern coast of Korea

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From: Journal of Shellfish Research(Vol. 26, Issue 2)
Publisher: National Shellfisheries Association, Inc.
Document Type: Article
Length: 7,745 words
Lexile Measure: 1520L

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ABSTRACT Sand was added to the mudflat in a small bay on the southern coast of Korea in an attempt to create a new habitat for the Manila clam (Tapes philippinarum) in the muddy intertidal zone. To evaluate whether the newly created sandy habitat was functionally similar to natural ones, seasonal variations in condition, reproductive activity, and biochemical composition of clams in created and natural conditions were compared from May 2000 to October 2001. Clams reared in the newly created and natural habitats had similar patterns and levels with respect to condition and tissue dry weight. Standardized animal condition and tissue dry weight of clams peaked in spring, when protein and carbohydrate reserves were at maximum levels, and declined progressively throughout the summer-autumn period to October, as a result of continuous spawning. Condition and tissue weight were quickly restored during the winter-spring period, concurrently with accumulation of protein and carbohydrate reserves. Similar biochemical compositions and reproductive cycles for the clam stocks in the two habitats are likely to be related to their similar environmental conditions, in particular food availability. Comparison of the isotopic signatures of T. philippinarum tissues and potential food resources suggested that food availability in the study area was mostly dependent on resuspension of microphytobenthos, along with seasonal dynamics of phytoplankton. These observations clearly show that newly created sandy habitats may provide habitat functions that enable Manila clams to have similar biological cycles to those in natural habitats.

KEY WORDS: Clam culture, Tapes philippinarum, condition, reproductive cycle, biochemical composition, created habitat

INTRODUCTION

The Manila clam, Tapes philippinarum (Adams & Reeve 1850), is a mollusc species that lives in sand, sandy-silt, or muddy-gravel sediments from the intertidal to subtidal zones a few meters in depth. It is also one of the most widely exploited bivalve resources for human consumption. Because of its high productivity and commercial importance, it is now cultivated worldwide. Numerous studies, particularly for commercial production, have enhanced understanding of the growth, reproduction, and physiological ecology of the clam under different environmental conditions, and thereby enabled rearing outside its normal habitat (Bourne 1982, Beninger & Lucas 1984, Xie & Burnell 1994).

In contrast to a progressive increase in T. philippinarum production in coastal areas where the clam was introduced, a steady trend of decreasing annual production has been observed in indigenous habitats on the Korean coast, from approximately 74,000 tonnes in 1990 to around 38,000 tonnes in 2000 (Ministry of Maritime Affairs and Fisheries Republic of Korea 2005, National Fisheries Research and Development Institute 2004). The major causes of this decline have long been recognized and include habitat loss through reclamation of tidal flats, habitat disturbance by marine pollution, overexploitation of the species, mass mortality (main causes are unknown yet), and predation of mud shrimp on young clams (Chung et al. 1994, Chung et al. 2001). Of these, the loss of clam habitat caused by large-scale reclamation for intertidal flats in Korea has been extensive during the past few decades (Koh 2001). About 40% of a total...

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Gale Document Number: GALE|A168820715