| 1. |
- Holeton, Claire, et al.
(författare)
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Decreased astaxanthin at high feeding rates in the calanoid copepod Acartia bifilosa
- 2009
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Ingår i: Journal of Plankton Research. - : Oxford University Press. - 0142-7873 .- 1464-3774. ; 31:6, s. 661-668
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Tidskriftsartikel (refereegranskat)abstract
- In marine food webs, copepods are the major producers of a carotenoid pigment astaxanthin, which is an important antioxidant. The availability of astaxanthin for higher trophic levels can be affected by changes in phytoplankton stocks and copepod feeding; however, the functional relationship between food availability and astaxanthin production is poorly understood. We hypothesized that with a given food type and quality, astaxanthin content in copepods is positively related to feeding and egg production rates. The hypothesis was tested by measuring astaxanthin accumulation in concert with ingestion and egg production rates in the copepod Acartia bifilosa exposed to different algal concentrations (Tetraselmis suecica; 0 to 1200 mu g C L(-1)). Egg production and ingestion rates increased with increasing food availability and reached a plateau at >= 400-600 mu g C L(-1). In contrast, increasing accumulation of astaxanthin with increasing food availability was observed only at concentrations <= 150 mu g C L(-1). Contrary to our hypothesis, at 600-1200 mu g C L(-1) copepods had maximal ingestion and egg production rates, but low astaxanthin contents. It is suggested that this low accumulation of astaxanthin at high food concentrations results from a food-dependant decrease in assimilation efficiency. These findings are important for the understanding of astaxanthin dynamics within marine food webs, where increases in phytoplankton biomass may translate to a trade-off between zooplankton quantity and its nutritional quality for zooplanktivores.
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| 2. |
- Holmborn, Towe, 1979-, et al.
(författare)
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Biochemical proxies for growth and metabolism in Acartia bifilosa (Copepoda, Calanoida)
- 2009
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Ingår i: Limnology and Oceanography. - Waco : American society of limnology and oceanography. - 1541-5856. ; 7:11, s. 785-794
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Biochemical proxies are becoming increasingly common for growth assessment in zooplankton. Their suitability is often unknown, however, and proper calibration is lacking. We investigated correlations between physiological variables (ingestion, egg production, and respiration rates) and biochemical indices related to protein synthesis (RNA content, RNA: DNA ratio, RNA: protein ratio, and protein specific aminoacyl-tRNA synthetases [spAARS] activity) in copepods Acartia bifilosa exposed to different algal concentrations (0-1200 mu g C L-1). All variables assayed increased with increasing food concentration either linearly (spAARS) or nonlinearly (all other variables). Egg production and ingestion rates were significantly and positively correlated with RNA content and RNA: protein ratio, whereas correlations with spAARS and RNA: DNA ratio were weaker or nonsignificant. However, when RNA: DNA ratio and spAARS activity were used as predictors of ingestion, together they had higher explanatory value than did either variable separately. As there were substantial differences in saturating food concentrations among the assayed variables, applicability of biomarkers as proxies of physiological rates will be more reliable if restricted to the nonsaturated phase of the functional response of either variable, unless both variables saturate simultaneously. These findings contribute to methodology of zooplankton growth assessment and to our understanding of biochemical processes underlying growth and metabolism in copepods.
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