Diversity of Tanaidacea (Crustacea: Peracarida) in the World's Oceans – How Far Have We Come?

Tanaidaceans are small peracarid crustaceans which occur in all marine habitats, over the full range of depths, and rarely into fresh waters. Yet they have no obligate dispersive phase in their life-cycle. Populations are thus inevitably isolated, and allopatric speciation and high regional diversity are inevitable; cosmopolitan distributions are considered to be unlikely or non-existent. Options for passive dispersion are discussed. Tanaidaceans appear to have first evolved in shallow waters, the region of greatest diversification of the Apseudomorpha and some tanaidomorph families, while in deeper waters the apseudomorphs have subsequently evolved two or three distinct phyletic lines. The Neotanaidomorpha has evolved separately and diversified globally in deep waters, and the Tanaidomorpha has undergone the greatest evolution, diversification and adaptation, to the point where some of the deep-water taxa are recolonizing shallow waters. Analysis of their geographic distribution shows some level of regional isolation, but suffers from inclusion of polyphyletic taxa and a general lack of data, particularly for deep waters. It is concluded that the diversity of the tanaidomorphs in deeper waters and in certain ocean regions remains to be discovered; that the smaller taxa are largely understudied; and that numerous cryptic species remain to be distinguished. Thus the number of species currently recognized is likely to be an order of magnitude too low, and globally the Tanaidacea potentially rival the Amphipoda and Isopoda in diversity

Groundwater estuaries of salt lakes: buried pools of endemic biodiversity on the western plateau, Australia

Subterranean or groundwater estuaries occur in porous and cavernous substrates where groundwater abuts the ocean. Like surface estuaries, they are strongly stratified, temporally and hydrochemically heterogeneous environments that support complex hydrogeochemical and biological processes and ecological communities. Here, we contend that groundwater estuaries also occur where groundwater flow approaches salt lakes and provide evidence in the context of groundwater (valley or phreatic) calcretes in palaeovalleys of the arid western plateau of Australia. The calcrete groundwater estuaries display marked and complex physico-chemical gradients along, across and through the groundwater flow path. From the first principles and the density differences between water bodies, we may expect the form and dynamics of the saltwater front to mimic that of marine estuaries but with the dynamic and temporal response to changing hydrology heavily dampened, and driven by the episodic groundwater recharge and lake filling typical of arid regions. The calcrete aquifers support diverse biological communities of obligate groundwater animals, largely endemic to a given calcrete body. These communities comprise both macro and microinvertebrates, predominantly a suite of crustacean higher taxa, and a great diversity of diving beetles (Dytiscidae) isolated in the calcrete aquifers between ca. 5 and 8 million years ago. © 2009 Springer Science+Business Media B.V.W. F. Humphreys, C. H. S. Watts, S. J. B. Cooper, R. Leij

Deep-Sea Benthic Faunal Impacts and Community Evolution Before, During, and After the Deepwater Horizon Event

Oil from the Deepwater Horizon blowout reached the seafloor through deep-sea plumes and sedimentation of oil and oiled marine snow. This oil caused extensive damage over wide areas to both hard-bottom and soft-bottom communities. The most sensitive bioindicators were deep-sea planar octocorals for hard-bottoms and macrofauna and meiofauna diversity and taxa richness for soft-bottoms. Both hard-bottom and soft-bottom communities are very vulnerable to deep-sea oil spills. Deep-sea corals grow slowly and thus have extremely slow recovery rates. Four years after the spill, there was no recovery of the lost biodiversity of the macrofauna and meiofauna. Future research should be focused toward recovery and restoration. For hard-bottoms this could take the form of restoration projects. For soft-bottoms the restoration strategy could be “restoration in place” because fresh sediments, which fall to the seafloor continuously, can cap the contaminated sediments over time. Both strategies require monitoring to ensure desired outcomes are achieved