Growth and photosynthesis of the 'brown tide' microalga Aureococcus anophagefferens in subsaturating constant and fluctuating irradiance

Abstract

ABSTRACT. Durlng the summer of 1985, a small (2 to 3 pm) chrysophyte, Aureococcus anophagefferens, bloomed and dominated the phytoplankton assemblage, and recurred each summer for the followlng 12 yr in bays of Long Island, New York, USA. Macronutrlents remained at h~g h levels throughout the years but Secchi d~s c depths were as low as 30 cm in somc arcds, corresponding to a 1 ",, light depth of about 80 cm. In batch culture, A. anophagefferens malnta~ned hlgh growth rates at low irrad i a n c e~. The ln~tial slope of the growth versus irradiance curve, a,, was 0.021 + 0.003 divisions d-' (pm01 quanta m-2 S-')-' which is similar to that for bloom formers such as Skeletonema costaturn. In continuous culture, constant and fluctuating irradiance regimes resulted in equivalent steady state growth rates at 0.46 divisions d.'. Short-term carbon fixation per unit chlorophyll a was about twice as high in the fluctuating irradiance regime compared with constant irradiance. Differences between short-term carbon fixation and cell growth could not be accounted for by dark fixation or exudation and are assumed to be due to photorespiration. The photosynthesis versus irradiance parameter, P,,,,, (light saturated photosynthetic rdte), was similar in both irradiance regimes; however, g, (initial slope) was consistently higher in the fluctuating regime, indicating that photosynthetic efficiency is higher in fluctuating irradiance.

Effects of organic carbon, organic nitrogen, inorganic nutrients, and iron additions on the growth of phytoplankton and bacteria during a brown tide bloom

“…During experiments in which DOC enhanced brown tide growth, the 1% light depth at WNB was 3-fold shallower than spring conditions (> 6 m in mid-May to < 2 m in June; Gobler 1999). Furthermore, the light used in our experiments was equal to levels found at 1.4 m in WNB (see 'Methods'), and below irradiances yielding maximal photosynthesis in A. anophagefferens (Milligan & Cosper 1997). Hence, heterotrophic C uptake during the experiments could have enhanced A. anophagefferens net C acquisition by A. anophagefferens, and probably yielded a competitive advantage over strictly autotrophic species.…”

“…While multiple factors have been implicated as potential bloom initiators (reviewed by Bricelj & Lonsdale 1997), nutrients have been most frequently cited (Cosper et al 1987, 1989, 1993, Dzurica et al 1989, Keller & Rice 1989, Smayda & Villareal 1989, Milligan 1992, Nixon et al 1994, Gobler & Cosper 1996, Berg et al 1997, LaRoche et al 1997, Breuer et al 1999. To date, a consensus as to which nutrient(s) control A. anophagefferens growth in the field does not exist, as inorganic nitrogen (Nixon et al 1994, LaRoche et al 1997, dissolved organic carbon (DOC) (Dzurica et al 1989, Milligan & Cosper 1997, Breuer et al 1999, dissolved organic nitrogen (DON) (Dzurica et al 1989, Berg et al 1997, LaRoche et al 1997, urea (Dzurica et al 1989, Berg et al 1997) and iron (Milligan 1992, Cosper et al 1993, Gobler & Cosper 1996 have all been hypothesized to influence initiation of brown tides.…”

“…Iron may also be an important nutritional factor for the growth of A. anophagefferens based on (1) multiple laboratory investigations which have indicated that A. anophagefferens cultures grow maximally with high Fe levels (Cosper et al 1993, Benmayor 1996, Gobler & Cosper 1996, and (2) natural and manipulated Fe additions which have stimulated growth of A. anophagefferens field populations (Milligan 1992, Cosper et al 1993, Gobler & Cosper 1996. Additionally, other laboratory research also suggests that A. anophagefferens may utilize DOC to supplement its cellular carbon requirements (Dzurica et al 1989), particularly during the lower light conditions that can persist during blooms (Milligan & Cosper 1997).…”

A comparison between glass fiber and membrane filters for the estimation of phytoplankton POC and DOC production

“…Filters of the above-mentioned types have been used for the purpose of separating particulate from dissolved (i.e. extracellular release of photosynthate) production, for instance GF/F in Witek et al (1997), CE 0.45 pm in Milligan & Cosper (1997) and PC 0.2 pm in Maurin et al (1997). According to the surveyed literature, -0.2 pm seems to be the most widely accepted pore size as operational cut-off for the dissolved fraction.…”

Microbial food web interactions in two Long Island embayments

“…The C:chl ratio during the dinoflagellate bloom (11 May) was determined from the chlorophyll concentration and from phytoplankton biovolume converted to carbon using a conversion factor of 140 fg C µm -3 (Lessard 1991). The C:chl ratio also was determined during the bloom of A. anophagefferens (30 June) by assuming that this alga dominated the chlorophyll biomass at the time, using a conversion factor of approximately 2.1 pg C cell -1 to estimate phytoplankton carbon biomass (Milligan & Cosper 1997). C:chl ratios on both dates were ~60.…”