Effects of Artificial Lighting and Presence of Menidia Beryllina on Growth and Diet of Labidesthes Sicculus

Two atherinid species, Labidesthes sicculus (brook silverside) and Menidia beryllina (inland silverside), often co-occur in North American reservoirs. Menidia beryllina is a superior competitor for zooplankton and has displaced Labidesthes in a number of reservoir habitats. In Lake Texoma (Oklahoma-Texas), Labidesthes was thought extirpated from the reservoir after introduction of Menidia in the 1950s, but several recent populations were discovered in down-lake coves with established marinas. Artificial lighting from marinas might benefit Labidesthes by attracting terrestrial insects in these habitats. We conducted a field experiment to test effects of artificial lighting and abundance of Menidia on growth and diet of Labidesthes. Dry weight of Labidesthes at the end of our experiment was significantly higher in artificially lit treatments than in dark treatments, but there was no significant effect of Menidia abundance on weight of Labidesthes. We concluded this effect was attributed to greater availability of dipterans, which dominated the diet of Labidesthes, under artificial lights. Whereas Menidia is a more efficient planktivore than Labidesthes, increased abundance of dipterans near marinas likely promotes the coexistence of these 2 species. RESUMEN—Dos especies Aterı́nidos, Labidesthes sicculus y Menidia beryllina (charal de marea), suelen coocurrir en los embalses norteamericanos. Menidia beryllina es un competidor superior para zooplanctón y ha desplazado a Labidesthes en numerosos hábitats. En el lago Texoma (Oklahoma-Texas), se creı́a que Labidesthes habı́a sido extirpado del embalse después de la introducción de Menidia en los años cincuenta, pero se han descubierto recientemente poblaciones co-ocurrentes en ensenadas con marinas establecidas. La iluminación artificial de las marinas puede beneficiar a Labidesthes atrayendo insectos terrestres en estos hábitats. Llevamos a cabo un experimento para probar los efectos de la iluminación artificial y de la abundancia de Menidia en el crecimiento y la dieta de Labidesthes. El peso seco de Labidesthes al final del experimento fue significativamente mayor en los tratamientos de iluminación artificial que en los tratamientos no iluminados, pero no hubo un efecto significativo de la abundancia de Menidia en el peso de Labidesthes. Concluimos que este efecto fue atribuido a una disponibilidad más grande de dı́pteros, que dominaron la dieta de Labidesthes, bajo luz artificial. Ya sea que Menidia sea un planctı́voro más eficiente que Labidesthes, la mayor abundancia de dı́pteros cerca de las marinas probablemente promueve la coexistencia de las dos especies. Competitive interactions between 2 atherinid species, Labidesthes sicculus (brook silverside) and Menidia beryllina (inland silverside), have been well studied in North American reservoirs. In Lake Texoma (Oklahoma-Texas), L. sicculus, which was native to the region, was the second most abundant species from 1948 through 1952 (Riggs and Bonn, 1959). After the introduction of Menidia in 1953, Labidesthes numbers diminished and the species was thought extirpated from the reservoir by 1959. An experiment by McCommas and Drenner (1982) clearly demonstrated that, when in direct competition with Menidia, Labidesthes had a higher mortality rate than in the absence of competition. They suggested that the ‘‘tube-like’’ mouth morphology of Menidia allowed them to forage more efficiently on copepods than Labidesthes, which have a more ‘‘beak-like’’ mouth. Despite these reports of extirpation in Lake Texoma, populaTHE SOUTHWESTERN NATURALIST 51(4):510–513 DECEMBER 2006