Photosynthesis/irradiance relationships in the Ross Sea, Antarctica, and their control by phytoplankton assemblage composition and environmental factors

Abstract

The photosynthetic parameters of natural phytoplankton assemblages from the Ross Sea, Antarctica, as well as unialgal cultures of the diatom Pseudonitzschia sp. and the colonial haptophyte Phaeocystis antarctica were investigated to determine if differential responses to irradiance could explain the distribution of phytoplankton in the Ross Sea. Field assemblages had photosynthetic responses that suggested acclimation to low irradiance levels, and the initial rate of photosynthesis per unit chlorophyll (α) and the theoretical maximum rate of production (P , respectively. An increase in both α and P B max were noted as the season progressed. However, no differences existed between the photosynthetic responses of phytoplankton assemblages dominated by diatoms and those dominated by P. antarctica. A significant influence of irradiance (reflected in changes in α and the photoadaption index E k ) was observed in the field observations, and this effect was corroborated by laboratory experiments. The carotenoid accessory pigment 19'-hexanoyloxyfucoxanthin in P. antarctica also varied with irradiance, but fucoxanthin did not. These results suggest that the spatially distinct distribution of P. antarctica and diatoms that is often observed in the Ross Sea probably does not result simply from different photosynthetic responses, but from a complex series of controls, potentially including trace metal effects, vertical mixing, and other factors. KEY WORDS: Photosynthesis · Diatoms · Phaeocystis · Accessory pigments Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 226: [1][2][3][4][5][6][7][8][9][10][11][12] 2002 phyte, is found primarily in the south central polynya in spring, and diatoms generally become dominant during summer in the western coastal region. While some locations are clearly dominated by a single form both in terms of numbers and biomass, many locations also represent mixtures of the 2 major groups (and others: Smith & Asper 2001). P. antarctica remains as an important constituent of the phytoplankton throughout the growing season in the south central Ross Sea, although by mid-summer its biomass has decreased and its physiological state is approaching senescence (Smith & Asper 2001). On the other hand, diatoms continue to grow at low rates over much of the entire region (Smith et al. , 1999.The causes for these spatially distinct distributions remain controversial. Past studies have not demonstrated differences in the 2 chemical and physical environments, although mixed layers may be slightly shallower in the west due to greater in situ ice melt and stratification (Arrigo et al. 1999). In contrast, Smith & Asper (2001) compared mixed layer depths of stations dominated by diatoms and Phaeocystis antarctica and found no difference between the 2 taxa in either spring or summer. Mixed layers of ca 30 m are formed in the south central region (along with ice-free conditions) and persist longer (from November through early March: Smith et al. 2000) than t...

Photosynthesis–irradiance responses in the Ross Sea, Antarctica: a meta-analysis

“…This is consistent with the previous results of van Hilst and Smith Jr. (2002) and Robinson et al (2003) using less extensive data sets, but in contrast to the extensive laboratory results of Arrigo et al (2010), who found that α B and P B m values of P. antarctica grown at constant irradiances (from 5 to 125 µmol quanta m −2 s −1 ) and saturating nutrients were always greater than those of the diatom Fragilariopsis cylindrus. The diatom had low P B m (from 0.46 to 0.54 µg C (µg Chl) −1 h −1 ) and α B values (0.014 to 0.043 (µg C (µg Chl) −1 h −1 (µmol quanta m −2 s −1 ) −1 )) when compared to those of the haptophyte (from 1.4 to 6.4, and 0.038 to 0.11, respectively).…”

Influence of irradiance and iron on the growth of colonial Phaeocystis antarctica: implications for seasonal bloom dynamics in the Ross Sea, Antarctica

“…This hypothesis can explain the observed spatial and temporal separation of P. antarctica and diatom blooms in the Ross Sea, if it is assumed that diatoms are better adapted to the stable higher irradiance of more stratified waters (Arrigo et al 1998b, 1999, 2003, Sedwick et al 2000. However, this idea is challenged by the results of field and laboratory studies that indicate little difference between the photosynthesisirradiance characteristics of P. antarctica and diatoms in the southern Ross Sea (van Hilst & Smith 2002, Smith & van Hilst 2004.…”

“…This hypothesis can explain the observed spatial and temporal separation of P. antarctica and diatom blooms in the Ross Sea, if it is assumed that diatoms are better adapted to the stable higher irradiance of more stratified waters (Arrigo et al 1998b, 1999, 2003, Sedwick et al 2000. However, this idea is challenged by the results of field and laboratory studies that indicate little difference between the photosynthesisirradiance characteristics of P. antarctica and diatoms in the southern Ross Sea (van Hilst & Smith 2002, Smith & van Hilst 2004.Availability of iron is also likely to influence the timing and location of Phaeocystis antarctica and diatom blooms in the Ross Sea. Certainly there is good evidence for the role of iron availability in limiting phytoplankton growth rates in this region, as shown in the results of shipboard bioassay experiments (Martin et al 1990, Sedwick & DiTullio 1997, Sedwick et al 2000, Coale et al 2003.…”

Temperature effects on growth, colony development and carbon partitioning in three Phaeocystis species

“…Our data suggest that the geographical ranges of P. antarctica and P. pouchetii are broadly restricted by temperature, whereas the ability of P. globosa to bloom in disparate environments may depend more on other factors, such as nutrients, grazing, and irradiance. The highest growth rate for P. antarctica was observed at 4°C in our experiments, which is higher than the in situ water temperature from -1.86 to 0°C at which P. antarctica blooms develop in the Ross Sea (Arrigo et al 1999, van Hilst & Smith 2002, suggesting that P. antarctica growth is more strongly regulated in situ by light and nutrients than by temperature. However, growth of P. antarctica during spring may also be a function of its ability to maximize its growth and photosynthesis during periods of low irradiance induced by high solar angles, relatively deep vertical mixing, and the presence of ice (Moisan & Mitchell 1999, Kropuenske et al 2009).…”