Spawning Site Utilization in a Delaware Population of Fundulus heteroclitus (Pisces: Cyprinodontidae)

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Abstract
Populations of F. heteroclitus in mid-Atlantic salt marshes deposit eggs on the marsh surface in empty shells of the Atlantic ribbed mussel (Geukensia demissa). Experimental placement of eggs in this location was associated with normal development and hatching; placement of eggs in tidal ditches resulted in developmental arrest or death of the eggs. Eggs placed in the ditches were subject to siltation and extended periods of immersion in water of < 2.0 ml/l dissolved O2. The distributions of both eggs and G. demissa shells were quantified in seven 10 m deep plots along ditches in a Delaware marsh. Empty shells were unevenly distributed but were found over the entire 10 m at densities as great as 10/m2, with the greater numbers usually occurring beyond 2 m from the ditch. Shells located 1-10 m from ditches were used as spawning sites with a maximum mean of 2.7 .+-. 1.1 spawns/m2 occurring in the 5th meter of a heavily used plot. The distribution of spawning in shells is probably influenced by height of the mussel shell in relation to tidal inundation, as well as size and condition of the shell, and possibly by plant distribution.