The density of individuals and the total biomass decreases with depth, the level of oligotrophy
of the surface layers, and distance from the coast.
The freshwater zooplankton assemblages of southern Chile are characterised by their low species richness and high predominance of calanoids copepods, due mainly to oligotrophy.
Also, another important factor is the effects of trophic webs in pelagic environments of lakes, in oligotrophy it predominate calanoids copepods and daphnids low abundance or absence and there is low species number in lakes with fishes (Soto and Zuniga, 1991; De los Rios and Soto, 2007).
We state that narrow tidal amplitude in the Cuban shelf (less than 20 cm after Rodriguez and Rodriguez 1983) and oligotrophy of water and sediments (Lluis-Riera 1972) would be the causes, at least partially, of the low density of meiofauna in comparison with other tropical sites.
We suggest that low estimates of meiofauna in comparison with other tropical sites would be caused by narrow tidal amplitude and oligotrophy of waters in the SW Cuban shelf.
Suspensivores are uncommon in subterranean waters, hardly surprising considering their general oligotrophy
The literature on Chilean North Patagonian lakes and ponds revealed the marked role of oligotrophy
in species richness and calanoid dominance (De los Rios-Escalante, 2010; De los Rios-Escalante et al.
Values of this index equal to or less than 20 indicate ultra-oligotrophy
, values between 21 and 40 indicate oligotrophy
, values between 41 and 50 evidence mesotrophy, values between 51 and 60 evidence eutrophy, and values equal or greater than 61 indicate hyper-eutrophy.
Nevertheless, an oligotrophy
to mesotrophy transition has been observed in some lakes located mainly between 38 to 41[degrees]S, due to the replacing of the native forest of their basin by agricultural zones, towns and industries (Soto, 2002).
Matsumura-Tundisi (1997) considered dominance of Calanoid copepods over Cyclopoida and low densities of rotifers and cladocerans as indicators of oligotrophy
, previously demonstrated by Gannon and Stemberger (1978).
Calanoid copepods are dominant in the zooplankton assemblages of Chilean inland waters due mainly to the oligotrophy
of their habitats (Soto & Zuniga, 1991; De los Rios & Soto, 2006) but also to their high conductivity (Soto & De los Rios, 2006).
tenerum and Pyrocystis noctiluca, characterised by the area's oligotrophy
, and on the left side, the neritic influence can be observed, where nutrients and Trichodesmium erythraeum, Oscillatoria spp.