Seasonal and Interannual Dynamics of Pelagic Rotifers in a Tropical, Saline, Deep Lake

Rocío Fernández,Sandra Guadarrama-Hernández,Javier Alcocer,Alfonso Lugo,Luis A Oseguera

doi:10.3390/d14020113

Rocío Fernández, Sandra Guadarrama-Hernández + Show 3 more

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https://doi.org/10.3390/d14020113

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Abstract

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: Brachionus sp. Mexico (related to B. plicatilis) and Hexarthra sp. (related to H. jenkinae). 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−2) and biomass (24 ± 63 mg DW m−2) were low; Brachionus sp. Mexico and Hexarthra 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, Brachionus sp. Mexico showed a higher abundance than Hexarthra sp. The dominant (≈80%) phytoplankton biomass in Lake Alchichica, the large (35–63 µm) diatom Cyclotella alchichicana, 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.

Highlights

Lake Alchichica, on the easternmost region of the Mexican Altiplano, shows a remarkable degree of microendemisms for a small (≈2.4 km2 ) and deep (62 m) lake [1].Ortega-Mayagoitia et al [2] reported eighteen endemic species up to date
The Brachionus species inhabiting Lake Alchichica belongs to the B. plicatilis (Müller, 1786) complex, while the Hexarthra species of Lake Alchichica is related to H. jenkinae (De Beauchamp, 1932)
The lack of genetic analyses hampered the exact species identification of Brachionus of Lake Alchichica, which may be a limitation of this study

Summary

Introduction

Lake Alchichica, on the easternmost region of the Mexican Altiplano, shows a remarkable degree of microendemisms for a small (≈2.4 km2 ) and deep (62 m) lake [1].Ortega-Mayagoitia et al [2] reported eighteen endemic species (from prokaryote to vertebrate) up to date. Lake Alchichica, on the easternmost region of the Mexican Altiplano, shows a remarkable degree of microendemisms for a small (≈2.4 km2 ) and deep (62 m) lake [1]. Lake Alchichica displays a remarkable low zooplankton species richness with just three species, one copepod—L. garciai—and two rotifers of two different families: Brachionidae and Hexarthridae. The lack of genetic analyses hampered the exact species identification of Brachionus of Lake Alchichica, which may be a limitation of this study. Recently it was confirmed that the Brachionus of Lake Alchichica is a single species by mean of COI sequences analysis, and applying three approaches (ABGD, PTP and GMYC) in DNA taxonomy on 30 sequences on adult

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