Density‐dependent nutritional value of the dinoflagellate Cochlodinium polykrikoides to the copepod Acartia tonsa

Abstract

The nutritional value of the dinoflagellate Cochlodinium polykrikoides to the copepod Acartia tonsa was evaluated over a range of ecologically relevant cell densities. Based on egg production rate, egg hatching success, and naupliar recruitment rate of A. tonsa, mixed-diet experiments indicated C. polykrikoides was nutritionally insufficient or had no nutritional value to A. tonsa at 600 mg C L 21 (330 cells mL 21 ), and was toxic at 1000 mg C L 21 (550 cells mL 21 ) when compared with the nontoxic flagellate Rhodomonas lens. However, the nutritional value of C. polykrikoides to A. tonsa at 100 and 200 mg C L 21 (55 and 110 cells mL 21 ) was greater than or equal to that of R. lens. The density-dependent nutritional value of C. polykrikoides to A. tonsa was also demonstrated in the long-term survival experiments. Survivorship of A. tonsa fed C. polykrikoides was lower than those fed R. lens at 900 and 1800 mg C L 21 . In contrast, C. polykrikoides supported higher survivorship of A. tonsa than R. lens at 180 and 540 mg C L 21 . The nutritional value of C. polykrikoides to A. tonsa decreased from beneficial to deleterious with increasing cell density. A putatively ''harmful'' alga is not always deleterious to grazers, and its ecological effects may be distinctly different during bloom and non-bloom periods.

Rapid gain and loss of evolutionary resistance to the harmful dinoflagellate Cochlodinium polykrikoides in the copepod Acartia tonsa

“…Common garden experiment-The dinoflagellate C. polykrikoides clone CP1 was isolated from Peconic Bay, Long Island, New York in 2006 and has remained actively toxic to copepods since that time (Jiang et al 2009(Jiang et al , 2010a. The flagellate Rhodomonas lens Pascher and Ruttner (CCMP 739) was obtained from the Provasoli-Guillard National Center for Culture of Marine Phytoplankton.…”

“…The latter design incorporated individual differences, but had the advantage of avoiding diet effects. Egg production rates of A. tonsa were measured under the standard rearing conditions at 400 mg C L 21 because C. polykrikoides at this concentration depressed egg production rates of A. tonsa but was not lethal to females (Jiang et al 2009). Adult copepods were acclimated in C. polykrikoides and R. lens suspension at 400 mg C L 21 for 24 h to ensure that egg production rates reflected the experimental diets (Tester and Turner 1990).…”

“…A 202-mm mesh was fixed above the dish bottom to avoid egg cannibalism. After a 24-h incubation at standard copepodrearing conditions (20uC, 14 : 10 L : D cycle, , 1 mmol photons m 22 s 21 ), all eggs and hatched nauplii were counted to calculate egg production rate (Jiang et al 2009). …”

“…The nutritional value of C. polykrikoides to copepods changes from beneficial to deleterious with increasing cell density (Jiang et al 2010a). At high cell densities, C. polykrikoides produces reactive oxygen species and other harmful compounds, negatively affecting copepod feeding, egg production, and survival (Jiang et al 2009;Tang and Gobler 2009). In addition to chemical defense, C. polykrikoides forms long chains in the presence of copepods, which lessens grazing mortality (Jiang et al 2010b).…”

“…At high cell densities, C. polykrikoides produces reactive oxygen species and other harmful compounds, negatively affecting copepod feeding, egg production, and survival (Jiang et al 2009;Tang and Gobler 2009). In addition to chemical defense, C. polykrikoides forms long chains in the presence of copepods, which lessens grazing mortality (Jiang et al 2010b). In this study, we tested the hypothesis that copepods can rapidly evolve resistance to harmful C. polykrikoides in two ways.…”