Global distribution patterns of non-halacarid marine intertidal mites: implications for their origins in marine habitats
We investigated the taxonomic, ecological and global biogeographical trends of non-halacarid marine mites with a view to understanding their origins in the marine environment. While halacarid mites are typically marine, numerous other mite taxa occupy littoral habitats, including rocky-shores, boulder beaches, salt marshes and mangrove forest floors, and occur in most geographical regions. Location
This study concerns the extant taxa of non-halacarid marine mite from intertidal zones, worldwide. Methods
A literature survey was undertaken to compile the records for localities and habitats of all the known species of non-halacarid intertidal mite. Simple analyses were used to determine their taxonomic and geographical trends. A multivariate analysis was used to compare how closely the biogeography of selected faunas conformed with the generally accepted marine biogeographical zones. Results
Although the species records are incomplete because of variable sampling intensities among regions, there is clear indication that these marine mite faunas are species-poor (only 162 species were recorded in the literature). The records for some groups (ameronothroid and hyadesiid mites), some habitats (rocky-shores) and some world regions (Eastern Atlantic-Boreal, Sub-Antarctic and Southern New Zealand) are apparently representative of actual faunas, whereas those for the mesostigmatid and non-halacarid prostigmatid mites, and mangrove and salt marsh habitats, are clearly incomplete. The faunas comprise mites from four suborders, the Mesostigmata, Prostigmata, Oribatida and Astigmata. Structuring of the lower taxonomic levels differs markedly among the suborders; mesostigmatid and prostigmatid mites comprise low species to genus and species to family ratios, relative to oribatid and astigmatid mites. These mite groups also differ with respect to ecological and geographical attributes; ameronothroid (oribatid) and hyadesiid (astigmatid) mites exhibit wider generic geographical distributions and stronger marine trophic links. Conclusions
The emerging trends suggest different geological time-scales for the evolutionary incursions into the marine environment by the mesostigmatid and prostigmatid mite group and the oribatid and astigmatid mite group. They suggest that members of the latter have had longer associations with marine intertidal systems. The origins of both groups are also likely to differ from those of the typically marine halacarid mites.