49. Effect of Ocean Acidification on the Nutritional Quality of Phytoplankton for Copepod Reproduction

Morgan T Meyers (1), Edward J Carpenter (1), William P Cochlan (1), Wim J Kimmerer (1)

1 Romberg Tiburon Center for Environmental Studies, Tiburon, CA, 94920, USA

Background
Phytoplankton are the oceans’ primary producers of polyunsaturated fatty acids (PUFA), which support the health and reproduction of heterotrophic marine organisms at higher trophic levels. It is hypothesized that future ocean acidification (OA) conditions could change the availability of phytoplankton PUFAs for ecologically significant consumers such as copepods, affecting their reproductive success in an increasingly acidified environment.

Methods
Three species of phytoplankton (Rhodomonas salina, Skeletonema marinoi, Prorocentrum micans) were grown under present-day (400ppm CO2, pH~8.1) and predicted future (1000ppm CO2, pH~7.8) oceanic conditions using nitrate-limited semi-continuous batch cultures. For four days, female Acartia tonsa copepods were fed a phytoplankton mixture from either the present-day or predicted-future treatment cultures. To assess changes in phytoplankton PUFA content, fatty acid profiles were analysed via capillary gas chromatography. Copepod egg production (EP), hatching success (HS), and egg viability (EV) were analysed to assess changes in copepod reproductive success.

Findings
CO2 concentration changed the composition of fatty acids in the phytoplankton used for the copepod diet. Under high pCO2 conditions, the relative proportion of PUFAs to total fatty acids was smaller (R. salina 21.5%; S. marinoi 14.1%; P. micans 14.4%) compared to that found in phytoplankton cultured under present-day pCO2 conditions (R. salina 28.8%, S. marinoi 32.7%, P. micans 39.3%). Copepod reproduction analyses show that females fed the high pCO2 phytoplankton had lower EP (median=13 eggs female-1), HS (median=12%), and EV (median=0%) compared to reproductive success of females fed the present-day pCO2 phytoplankton (EP median=25 eggs female-1; HS median=91.5%; EV median=98%).

Conclusions
This laboratory study demonstrates that OA can change the nutritional quality of primary producers, which affects the potential reproductive success of fundamental primary consumers.