Production of the Copepod Pseudodiaptomus forbesi Is Not Enhanced by Ingestion of the Diatom Aulacoseira granulata During a Bloom

Abstract

In 2016, a massive bloom of the chain-forming diatom Aulacoseira granulata occurred in the upper San Francisco Estuary, California, with chlorophyll concentrations up to 75 μg Chl L −1 . In this study, quantitative PCR was used to investigate consumption of the bloom organism by the numerically dominant zooplankter Pseudodiaptomus forbesi (Copepoda: Calanoida) and to estimate the contribution of the bloom to egg production. Copepods were collected on four transects during May and June 2016; egg production rates were somewhat elevated above previous rates measured in the estuary. Ingestion of A. granulata was highest on the first sampling day, just after the peak of the bloom, ranging from 175 to 945 cells copepod −1 day −1 . One month later ingestion rates dropped to 0-130 cells copepod −1 day −1 , despite continued dominance of A. granulata in the plankton. Ingestion of A. granulata provided from 0 to 21% (median 1%) of the estimated daily carbon required for growth and reproduction of P. forbesi. Although the copepods probably obtained nutrition from a microbial food web stimulated by the bloom, monitoring data showed little demographic response to this bloom. Thus, a massive diatom bloom in an unproductive estuary provided only a minor stimulus through an abundant consumer to the pelagic food web.

Hydrodynamics structure plankton communities and interactions in a freshwater tidal estuary

“…Low‐quality bacillariophytes such as the chain‐forming Aulacoseira granulata were occasionally dominant within the HE zone (Appendix S1: Figure S5); thus, grouping these with higher quality species may have obscured trophic relationships with zooplankton. Blooms of A. granulata were observed throughout the Delta during summer of 2016, including within our own dataset, yet these blooms were not associated with increases in the dominant calanoid copepod Pseudodiaptomus forbesi (Jungbluth et al, 2021). The lack of positive, bottom‐up interactions between chlorophytes and zooplankton is more understandable—chlorophytes were always a minor component of total biovolume and exhibited more extreme temporal variation (less mean reversion, diagonal elements of B close to 1), suggesting they are an ephemeral resource for grazers.…”

“…Cell biovolumes were quantified on a per milliliter basis (Hillebrand et al, 1999). In order to assess spatial and temporal variation in food quality for mesozooplankton, cyanobacteria or other taxa capable of producing toxins, for example, Microcystis , Anabaena , Planktothrix , Peridinium , and long‐filament‐forming taxa such as Melosira and Aulacoseira , were classified as “low” quality (Galloway & Winder, 2015; Jungbluth et al, 2021). All other phytoplankton taxa were classified as “high” quality.…”

Patterns and predictors of condition indices in a critically endangered fish

“…However, the relationship between Chl a and zooplankton is complex. While zooplankton generally increases with Chl a in other systems (McCauley & Kalff 1981;Yuan & Pollard, 2018), Chl a is a poor predictor of zooplankton biomass in the SFE (Montgomery et al, 2015;Kimmerer et al, 2018B), and a poor predictor of production for some of the major copepods that make up Delta Smelt diets (Kimmerer et al, 2014;Slater & Baxter 2014;Jungbluth et al, 2021). Moreover, Chl a was a stronger predictor of HSI and CF than zooplankton biomass (Table 4), suggesting that stimulation of secondary productivity is not the primary cause for the association between Chl a and condition indices.…”

The Anatomy of a Drought in the Upper San Francisco Estuary: Water Quality and Lower-Trophic Responses to Multi-Year Droughts Over a Long-Term Record (1975-2021)

“…For example, zooplankton abundance increased in the South-Central Delta region during droughts (Barros et al, this issue; Hartman et al, this issue), which mirrored the increase in chlorophyll concentrations in this region (Figure 7). Zooplankton could have taken advantage of the increased food supply made available by increased phytoplankton (Orsi and Mecum 1986;Owens et al 2019); however, there is not always a direct relationship between zooplankton growth rates and chlorophyll concentrations because the taxa of phytoplankton that contribute to chlorophyll concentrations are not all equally available or preferred food sources for zooplankton (Jungbluth et al 2021).…”