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VOL. 75 (4), 883-899, 2009 A FASCINATING EXAMPLE OF MICROALGAL ADAPTATION...

changing our pre-conceived ideas on the adaptation of microalgae to
crude oil in this fascinating example of the extremely contaminated
freshwater ecosystem.

First of all, a surprisingly high biomass of microalgae proliferates
even in the more contaminated areas of Arroyo Minero. Microalgae
have been able to grow in contact with recalcitrant contamination
by fuel patches. These algae are the base for a few species of
zooplankton and micro-invertebrates.

The coexistence of more than 30 species of microalgae in the
same water body is a usual characteristic of all inland freshwater
and marine ecosystems that has been called «the Paradox of the
Plankton» (30). After thousand studies on the most diverse aquatic
ecosystems, the Paradox of the Plankton is a well-established fact
(31, 32). Even in red tide events there several species coexist (33).
In contrast, only four species were detected in the crude oil spill
area of Arroyo Minero. However, many phytoplankton species
inhabits Arroyo Minero River previously to the crude oil spill area
(we identify 39 microalgal species of Cyanobacteria, Bacillariophyta,
Chlorophyta, Dinophyta and others). Apparently, adaptation to crude
oil contamination is not easy and most of microalgal species are
unable to adaptation at toxic effect of petroleum.

Extreme environments (characterized by extreme values of pH,
toxic minerals, temperature, and other factors) frequently support
unusual communities of phytoplankters (34). It is frequently assumed
that extremophile species more than mesophile species inhabit the
extreme environments. However, the 4 species living in the crude
oil spill area of Arroyo Minero are mesophile species. Only species
of Chlorophyta and Cyanobacteria Division were able to proliferate
in the crude oil spill area.

Recent works suggest only a few mesophile species (mainly
Chlorophyta) are able to proliferate in extreme environments. This
pattern was observed by first time in the Guadiamar River (S, Spain)
after the toxic heavy metal spill of Aznalcollar mine (35) and
confirmed in the heavy metal contaminated environments of Aguas
Agrias, Spain (36), Mynydd Parys, Wales, UK (37), and Rio Tinto,
Spain (38). In la Hedionda, Spain, an example of extreme sulphureus
waters, also proliferate a few mesophile Chlorophyta species (39).

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