Temporal and spatial patterns of microbial community biomass and composition in the Southern California Current Ecosystem

Abstract

a b s t r a c tAs part of the California Current Ecosystem Long Term Ecological Research (CCE-LTER) Program, samples for epifluorescence microscopy and flow cytometry (FCM) were collected at ten 'cardinal' stations on the California Cooperative Oceanic Fisheries Investigations (CalCOFI) grid during 25 quarterly cruises from 2004 to 2010 to investigate the biomass, composition and size-structure of microbial communities within the southern CCE. Based on our results, we divided the region into offshore, and inshore northern and southern zones. Mixed-layer phytoplankton communities in the offshore had lower biomass (16 7 2 μg C L � 1 ; all errors represent the 95% confidence interval), smaller size-class cells and biomass was more stable over seasonal cycles. Offshore phytoplankton biomass peaked during the winter months. Mixed-layer phytoplankton communities in the northern and southern inshore zones had higher biomass (78722 and 32 79 μg C L � 1 , respectively), larger size-class cells and stronger seasonal biomass patterns. Inshore communities were often dominated by micro-size (20-200 μm) diatoms; however, autotrophic dinoflagellates dominated during late 2005 to early 2006, corresponding to a year of delayed upwelling in the northern CCE. Biomass trends in mid and deep euphotic zone samples were similar to those seen in the mixed-layer, but with declining biomass with depth, especially for larger size classes in the inshore regions. Mixed-layer ratios of autotrophic carbon to chlorophyll a (AC:Chl a) had a mean value of 51.57 5.3. Variability of nitracline depth, bin-averaged AC:Chl a in the mixed-layer ranged from 40 to 80 and from 22 to 35 for the deep euphotic zone, both with significant positive relationships to nitracline depth. Total living microbial carbon, including auto-and heterotrophs, consistently comprised about half of particulate organic carbon (POC).

Subsurface Chlorophyll Maximum Layers: Enduring Enigma or Mystery Solved?

“…These postulates are generally consistent with data and interpretations presented in a recent study by Taylor et al (2014) (Figure 7). Appropriate assessment of postulates 7 and 8 in the context of TSWS would require a comprehensive review of models, measurements, and optical estimates (e.g., Behrenfeld & Boss 2003, Cetinić et al 2012, Mignot et al 2014) of C p :Chl (or Chl:C p ) in the context of recent studies employing newer methods for determining the carbon content of phytoplankton (e.g., Graff et al 2012, Li et al 2010, Taylor et al 2014).…”

“…Stations are binned along a trophic gradient according to nitracline depth (mesotrophic to oligotrophic); C p :Chl is calculated for the mixed layer (ML) and deep euphotic zone (deep EZ), which corresponds to the SCML. The trend in mixed-layer C p :Chl is consistent with acclimation to reduced nutrient supply (Babin et al 1996) and an increased relative abundance of cyanobacteria (Taylor et al 2014) in progressively more oligotrophic surface waters. Assuming that the subsurface chlorophyll maximum layer (SCML) (deep EZ sample) is near the nitracline and thatĒ ncline decreases with its depth, the increase in C p :Chl in the SCML with z ncline is consistent with postulate 8-a floristic shift from diatoms and larger eukaryotes in more eutrophic waters toward cyanobacteria in oligotrophic waters (C p :Chl increases) having a greater influence than the acclimation of nutrient-replete phytoplankton to lower irradiance in the oligotrophic SCML (C p :Chl decreases).…”

“…In the same region, measured C p :Chl in SCMLs dominated by dinoflagellates near a shallow nitracline were much higher than this trend (Cullen & Horrigan 1981, as expected (Chan 1978). Figure adapted from Taylor et al (2014), which includes a discussion of these influences.…”

“…Appropriate assessment of postulates 7 and 8 in the context of TSWS would require a comprehensive review of models, measurements, and optical estimates (e.g., Behrenfeld & Boss 2003, Cetinić et al 2012, Mignot et al 2014) of C p :Chl (or Chl:C p ) in the context of recent studies employing newer methods for determining the carbon content of phytoplankton (e.g., Graff et al 2012, Li et al 2010, Taylor et al 2014). None of this is possible here, although the study by Fennel & Boss (2003) is an excellent point of reference; the foundational literature is considered Patterns in the ratio of phytoplankton biomass to chlorophyll a concentration (C p :Chl) measured over six years in the California Current Ecosystem (Taylor et al 2014) illustrate trends that are generally consistent with model results and with less comprehensive (and sometimes less certain) sets of observations over the past 50 years, including estimates from the same region , Li et al 2010. Generally, C p :Chl increases nonlinearly with growth irradiance in nutrient-replete phytoplankton, increases with nutrient limitation of growth at a given light level, and is consistently higher for cyanobacteria compared with eukaryotes (Geider 1992).…”

Introduction to CCE-LTER: Responses of the California Current Ecosystem to climate forcing

“…The authors show that the inclusion of glider data in the PP models substantially improves estimates of PP and suggest that this be done on a routine basis. Taylor et al (2015) study microbial community patterns in the CCE-LTER region using a set of samples collected between 2004 and 2010 on 25 CalCOFI cruises as part of the CCE augmented sampling. They use flow cytometry and digital epifluorescence microscopy to understand the spatial and seasonal variations of different components of the autotrophic and heterotrophic plankton o200 mm.…”