Cyclopoid copepods as indicators of trophic level in South American reservoirs: A new perspective at species level based on a wide spatial-temporal scale

Abstract

Aiming to identify efficient indicators for reservoir water quality, the abundance of cyclopoid copepods, 11 limnological variables, and a modified trophic state index (TSI) for tropical/subtropical reservoir systems were studied in 30 different reservoirs in South America. A total of 331 fieldwork campaigns, originated from six different studies on a wide spatial-temporal scale were analyzed. Samplings included small to large reservoirs (varying between 6 and 2250 km(2) area) with oligo, meso and eutrophic conditions, and places with punctual eutrophication from fish cage farms. Spatial scale ordination was relevant for variables and reservoirs, but the temporal scale was also important in all analyses, positioning the same reservoir sampled in different years contrasting correlations in terms of species and variables. Principal component analysis consistently indicated the importance of chlorophyll, nutrients (phosphorus and nitrogen), turbidity, transparency, and depth for proper ordination of reservoirs according to their trophy. Of all the 13 cyclopoid species identified, ten were planktonic and at the end, after conclusive statistical correlation analysis, five species were selected as efficient water quality indicators. Redundancy analysis related different species with different trophic aspects: Acanthocyclops robustus, Microcyclops anceps and Tropocyclops prasinus were positively associated with chlorophyll and inversely associated with water transparency, Thermocyclops decipiens and T. inversus with electrical conductivity, and slightly associated with chlorophyll and total nutrients (phosphorus and nitrogen), and finally Thermocyclops minutus was positively correlated with transparency. Spearman correlations indicated that only T. inversus abundance was correlated with water temperature, but T. decipiens was not correlated with TSI, which is intriguing because this species has been commonly associated with eutrophic waters. Despite tolerate a wide range of trophic conditions, as pointed in RDA, T. decipiens seems to be replaced by other more resistant species when trophic conditions become too high - hypereutrophic environments. Four other selected species were correlated with TSI, and T. minutus was negatively correlated, confirming its association with oligotrophic waters. From all species found, we conclude that A. robustus, M. anceps, T. prasinus, T. decipiens and T. minutus are good indicators of trophic state level in South American reservoirs.