Net-plankton diatoms of Puerto Rican water reservoirs as potential bioindicators of trophic status

Abstract

Diatoms are a group of unicellular algae enclosed in a siliceous exoskeleton called the frustule. This ornamented structure allows for taxonomic identification. Diatoms are frequently used as indicators to monitor the integrity of aquatic ecosystems in Europe, Africa and the United States. This study aims to expand the knowledge of these microalgae for the future inclusion of diatom monitoring as part of trophic status monitoring in Puerto Rican Reservoirs. Net-size plankton was sampled from six reservoirs, (Cerrillos, Cidra, Guajataca, La Plata, Patillas and Toa Vaca) which were selected to encompass a wide range of trophic status. A total of six samples were collected from each reservoir between March 2012 and April 2014. Samples were analyzed with light and SEM-microscopies and identified to the lowest taxonomic rank possible. Shannon-Weaver’s diversity index, H’, ranged between 0.015 and 2.313, Margalef’s richness index, R, ranged between 1.071 and 4.969, similarity between samplings measured with Jaccard’s index ranged between 25% and 100% index ranged between and Pollution Tolerance Index values were between 2.04 and 3.00. A total of 32 taxa were registered. Dominant taxa in these reservoirs were species of Achnanthidium sp., centric diatoms, Navicula sp.and Ulnaria sp. Mesotrophic reservoirs (Guajataca and Toa Vaca) had the most diverse communities and the highest richness. Some organisms present in the phytoplankton communities, such as Achnanthidium minuttisimum and Ulnaria ulna, could aid in the differentiation of low nutrient states from high nutrient states. The study showed that net-phytoplankton taxa seem to be useful in the bioindication of the trophic conditions in subtropical reservoirs.

Las diatomeas son un grupo de algas unicelulares que poseen un exoesqueleto de sílice conocido como la frústula. Esta estructura ornamentada permite la identificación taxonómica de estos microorganismos. Las diatomeas son utilizadas frecuentemente como indicadoras para monitorear la integridad de sistemas acuáticos en Europa, África y Estados Unidos. Se colectaron muestras de net-plancton en seis embalses seleccionados para representar un amplio espectro de estado trófico. Estos embalses fueron Cerrillos, Cidra, Guajataca, La Plata, Patillas y Toa Vaca. Un total de seis muestras fueron colectadas para cada embalse entre marzo del 2012 y abril del 2014. Los valores para el índice de diversidad Shannon-Weaver, H’, estuvieron entre 0.015 y 2.313, el índice de riqueza de especies, Margalef, R, entre 1.071 y 4.696, la similitud entre muestreos estuvo entre 25% y 100%, expresado en el índice de Jaccard y el índice de Tolerancia de Contaminación estuvo entre 2.04 y 3.00. Un total de 32 taxones fueron registrados. Los taxones dominantes fueron Achnanthidium sp., diatomeas céntricas, Navicula sp.y Ulnaria sp.. Embalses mesotróficos (Guajataca y Toa Vaca) presentaron las comunidades más diversas y la mayor riqueza de especies. Algunos organismos presentes en las comunidades de fitoplancton, tales como Achnanthidium minuttisimum y Ulnaria ulna, pudieran asistir en la diferenciación de estados pobres en nutrientes y estados ricos en nutrientes. Nuestro estudio muestra que las diatomeas del net-plancton pueden ser útiles en la bioindicación de las condiciones tróficas en embalses subtropicales.