Egg Deposition by Atlantic Silverside, Menidia menidia: Substrate Utilization and Comparison of Natural and Altered Shoreline Type Richard G. Balouskus & Timothy E. Targett Received: 22 July 2011 / Revised: 26 February 2012 / Accepted: 27 February 2012 / Published online: 28 March 2012 # Coastal and Estuarine Research Federation 2012 Abstract Egg deposition by the intertidal spawning fish Atlantic silverside (Menidia menidia) was compared among six shoreline types (Spartina alterniflora, Phragmites aus- tralis, sandy beach, riprap, riprap-sill, and bulkhead) and various substrates. In spring 2010, M. menidia egg density was measured daily near Roosevelt Inlet, Delaware Bay, USA. Over 3,000,000 eggs were collected during 50 sam- pling days. Eggs were deposited at all six shoreline types, with >93 % of eggs collected from S. alterniflora shorelines. Choice of substrate for egg attachment was similar across shoreline types with >91% of eggs collected from filaments of the green alga Enteromorpha spp., a disproportionately high utilization rate in comparison with Enteromorpha spp.'s relative coverage. This study demonstrates that S. alterniflora shoreline, in association with Enteromorpha spp., is the preferred spawning habitat for M. menidia and that hardened shorelines and shorelines inhabited by P. australis support substantially reduced egg densities. During the past few decades, the area of intertidal fringing salt marsh, comprised of Spartina alterniflora (smooth cordgrass), has decreased in US Mid-Atlantic estuaries, while invasive Phragmites australis (common reed) (King et al. 2007) and several types of shoreline hardening including bulkhead, rip- rap, and riprap-sills have become more common (USGS 2011). Shoreline hardening has greatest effects on the zone of transition, including the intertidal and shallow subtidal zones, the most ecologically productive regions in estuaries (Toft et al. 2007; Bilkovic and Roggero 2008). Riprap and bulkhead structures have been shown to negatively impact, through reduced diversity, growth and abundance, a range of populations of fauna (primarily fishes and benthic inverte- brates) living adjacent to them (Able et al. 1998; Seitz et al. 2006; Bilkovic and Roggero 2008; Pister 2009). Bulkhead and riprap structures alter the natural shape of the shoreline, remove undercut crevice habitat, change shore-zone wave dynamics, reduce shallow water habitat, and reduce or elim- inate intertidal plant communities. Disturbance of natural shorelines by shoreline hardening is one of the primary contributors to the expansion of a non- native genotype of P. australis along the Mid-Atlantic coast of the US (King et al. 2007). P. australis has led to a displacement of native macrophyte communities (such as S. alterniflora), degradation of wildlife habitat and alteration of ecosystem processes (Weinstein and Balletto 1999; Minchinton et al. 2006). P. australis-dominated marshes are utilized by estuary resident fishes for feeding and spawning (Able and Hagan 2003). However, due to increased elevation of established P. australis marshes, the length of time the intertidal marsh interior is submerged is reduced, resulting in a decrease in usage by estuarine fishes (Weinstein and Balletto 1999; Able and Hagan 2003; Able et al. 2003). Reduced access to intertidal area reduces viable locations for intertidal spawning. Estuaries and Coasts (2012) 35:1100–1109 DOI 10.1007/s12237-012-9495-x Keywords Intertidal . Spawning . Eggs . Menidia . Spartina . Enteromorpha Introduction The intertidal zone of estuaries serves as important spawning habitat for many species of fish (see review by DeMartini 1999). The physical structure of estuarine habitats, particular- ly the shore-zone, continues to be modified by human activity. R. G. Balouskus (*) : T. E. Targett College of Earth, Ocean, and Environment, School of Marine Science and Policy, University of Delaware, Lewes, DE 19958, USA e-mail: rbalousk@udel.edu