| Summary: | This is the first long-term study (monthly samples at two 4-year intervals: 1998 to 2001 and 2013 to 2016) on rotifers in a saline, deep lake. The pelagic rotifer assemblage of Lake Alchichica is simple and comprised by two species, both new and most likely endemic: <i>Brachionus</i> sp. Mexico (related to <i>B. plicatilis</i>) and <i>Hexarthra</i> sp. (related to <i>H. jenkinae</i>). Similar low species richness and composition are found in other saline lakes associated with salinity. Rotifers in Lake Alchichica were an irregular component of the zooplankton community. Rotifers’ overall abundance (471 ± 1211 ind m<sup>−2</sup>) and biomass (24 ± 63 mg DW m<sup>−2</sup>) were low; <i>Brachionus</i> sp. Mexico and <i>Hexarthra</i> sp. contributed similarly to the annual mean abundance (54% and 46%, respectively) and biomass (53% and 47%, respectively). Abundance and biomass were tightly coupled, but there was no regular pattern in their seasonal dynamics. When co-existing, <i>Brachionus</i> sp. Mexico showed a higher abundance than <i>Hexarthra</i> sp. The dominant (≈80%) phytoplankton biomass in Lake Alchichica, the large (35–63 µm) diatom <i>Cyclotella alchichicana</i>, is inedible for rotifers, thus rotifers most probably relied only on nanophytoplankton (≤20 µm). Seasonal and interannual differences in rotifers seem related to food availability (oligotrophy) and probably to biotic interactions (e.g., competition). Rotifer abundance and biomass values in 1998–2001 went down to 12.5% in 2013–2016. Climate change and stochastics events leading to pulses of the rotifers’ food, and biotic interactions seem to be the most plausible explanation.
|
|---|