Some shallow-water invertebrates are capable of surviving deep sea conditions, enabling scientists to better understand how shallow-water organisms may have evolved to colonise the deep sea.
This conclusion was drawn from a study by Andrew Oliphant and coauthors published in a recent issue of the Journal of Experimental Biology.
Using the Atlantic ditch shrimp (Palaemonetes varians) as their model, the authors tested the ability of adult shrimps to withstand the effects of various pressure and temperature combinations, measuring both oxygen consumption and behaviour (the latter was observed by general activity and the loss of coordinated movements).
The shrimps were collected from the Lymington salt marshes (England) and from Bay of Mont Saint Michel (France).
The authors first tested the temperature tolerance of the shrimps and found that the shrimps were able to survive at a range of 0–31°C.
The authors then tested the pressure tolerance of the shrimps (using a pressurised incubator) and found that they were able to tolerate water pressures of up to 30 megapascals (MPa)—equivalent to the water pressure about 3000m deep—although many of the shrimps began to show signs of stress at about 15 MPa.
Even so, the shrimps were tolerating hydrostatic pressures far above what they normally experience in shallow water (which is only about 0.1 MPa—normal atmospheric pressure).
The authors hypothesise that the ability of the Atlantic ditch shrimp to withstand a broad range of temperatures and pressures is inherited from its ancestors.
This lends support to the hypothesis that many inhabitants of the deep sea are descended from ancestors living in shallow waters, as the various extinction events in the Earth’s geological history have caused periodic decimations of the deep-sea fauna, only to be repopulated by species descended from shallow-water species that have adapted to the low temperatures and high hydrostatic pressures of this habitat.
For more information, see the paper: Oliphant, A, S Thatje, A Brown, M Morini, J Ravaux and B Shillito (2011) Pressure tolerance of the shallow-water caridean shrimp Palaemonetes varians across its thermal tolerance window. Journal of Experimental Biology 214, pp. 1109–1117.