Revealing Hidden Diversity in a Unique Island Ecosystem: The Evolution, Ecology and Conservation of Anchialine Shrimp in the Pacific Basin

Abstract

Due to varying anthropogenic pressures, there is an urgency to accelerate research into unique island environments and their biota before they are lost forever. For many islands, one of the most threatened ecosystems may be the anchialine ecosystem. Anchialine habitats are land-locked bodies of water which have no surface connection to the ocean yet contain salt or brackish water that fluctuate with the tides due to subterranean connections to the sea. Unfortunately, these unique habitats have received little attention while experiencing significant negative impacts from anthropogenic activities such as urbanization, groundwater extraction/contamination, and the introduction of invasive species. Given these threats, we risk losing these ecosystems without knowing the nature and extent of the biodiversity contained within them. In this regard, understanding the genetic structure and relationships of taxa endemic to these habitats may help illuminate the processes driving the evolution of anchialine organisms. Such knowledge has important implications in developing sound conservation strategies for these organisms and their imperiled ecosystem. In this context, the research presented here examined the genetic variation, population structure and phylogeographic patterns within and between five species of anchialine Carideans (Halocaridina rubra, Caridina rubella, Antecaridina lauensis, Metabetaeus minutus and Halocaridinides trigonophthalma) endemic to the rapidly vanishing anchialine ecosystems of the Pacific Basin. Overall, analysis of intraspecific mitochondrial sequence data (i.e., cytochrome oxidase subunit I [COI] and large subunit ribosomal [16S-rDNA] genes) revealed two main patterns. First, the contrasting patterns of population structure and connectivity exhibited by each ‘species’ appear to result from complex interactions between intrinsic (i.e., life history traits) and extrinsic (i.e., historical geologic and oceanographic) processes. Second, the diversity of taxa inhabiting the anchialine habitats of the Pacific may be vastly underestimated with many of the species previously described representing cryptic species complexes. This research not only provides additional understanding into the ecology and evolution of anchialine organisms in general, but has application in areas of conservation management; such as identifying source populations of invertebrate species in the wildlife trade as well as populations/habitats warranting conservation management and demonstrating that levels of diversity in subterranean crustaceans are in many cases vastly underestimated.