Sympatric seagrass shrimp show similar structure and selection along the seashore: a comparison of two cryptic Phycomenes zostericola lineages

Caridean shrimp are a diverse and abundant component of seagrass fauna (De Grave 1999). Seagrass shrimp enhance the nursery function of seagrass habitats and make a valuable indirect contribution to commercial fisheries, as they are an abundant and palatable food source for juvenile fisheries species (Heck et al. 2003). Although phylogeographic studies on caridean shrimp are not uncommon, most in Australia focus on freshwater species (Hughes et al. 1995; Hurwood & Hughes 2001). Broadscale connectivity studies on small marine shrimp were undertaken in South Africa (Teske et al. 2007). However, little other phylogeographic research has been done on shrimp in seagrass systems. Seagrass habitats are becoming increasingly fragmented and lost due to anthropogenic influences (Orth et al. 2006; Connolly 2009). As this vital habitat becomes lost, it becomes ever more urgent that we understand how seagrass fauna responds to change in general and specifically for individual species. These questions are further complicated by the presence of cryptic species and the similar or divergent responses that they may have to environmental change. Cryptic species are not rare in the sea; they are common among crustaceans and can be found at almost any depth and at all latitudes (Knowlton 1993) in the presence or