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Abstract In sunlit waters, significant predation is performed by unicellular, phagotrophic mixotrophs, that is, predators that also possess plastids. The success of a mixotrophic lifestyle will depend in part on how well mixotrophs acquire prey relative to specialized heterotrophs. Likewise, consequences of mixotrophy for productivity and element cycling will depend on the rate and efficiency at which mixotrophs consume prey biomass relative to heterotrophs. However, trait differences between mixotrophs and heterotrophs are not well characterized. In addition, cell size of mixotrophs varies widely, and constitutive mixotrophs include small flagellates deriving from diverse taxa, while larger species are primarily dinoflagellates. To determine whether similar constraints apply to phagotrophs across this broad range of size and taxa, we compiled 83 measurements of flagellate functional responses and compared maximum clearance rates (Cmax) and maximum ingestion rates (Imax) between trophic modes. We found that the average mixotroph has a 3.7‐fold lowerCmaxand 7.8‐fold lowerImaxthan the average heterotroph, after controlling for cell size. The smaller penalty forCmaxsuggests that relative fitness of mixotrophs will be enhanced under dilute prey concentrations that are common in pelagic ecosystems. We also find that growth efficiency is greater for mixotrophs and for flagellates with lowerCmax, indicating a spectrum of trophic strategies that may be driven by phototrophy vs. phagotrophy allocation as well as fast vs. slow metabolic variation. Allometric scaling shows thatImaxis constrained by a common relationship among dinoflagellates and other taxa, but dinoflagellates achieve a greater volume‐specificCmax. These results should aid in interpreting protistan communities and modeling mixotrophy.
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Widespread ciliate and dinoflagellate mixotrophy may contribute to ecosystem resilience in a subarctic sea: the northern Gulf of Alaska
Mixotrophy among ciliates and dinoflagellates in the northern Gulf of Alaska (NGA) was widespread during spring and summer, with mixotrophs contributing a median of 38 to 61% of total ciliate plus dinoflagellate biomass depending on season and year. The proportional contribution of mixotrophs was higher during a heatwave year (2019) than during a year of average temperatures (2018). The most common mixotrophic ciliates included Mesodinium spp. and several of 8 observed Strombidium species, while for dinoflagellates, the most common mixotrophs were Gymnodinium-like cells and Tripos (formerlyCeratium) spp. Onshore-offshore distribution gradients were seen mainly in summer when elevated freshwater inputs create a horizontal salinity gradient. A nearshore mixotroph assemblage consisted of nutritionally related Mesodinium spp. and dinoflagellate Dinophysis, as well as Tripos spp., while an offshore assemblage included Tontonia-like ciliates and dinoflagellates including Gymnodinium-like cells and Torodinium robustum. An 11 yr time series with lower taxonomic resolution revealed seasonality in some taxa and showed near-complete loss of Mesodinium spp. and Tontonia-like species during the longer 2014-2016 North Pacific marine heatwave. The constellation of nutritional strategies represented by NGA mixotrophs may be an important component of lower trophic level resilience to marine heatwaves, while high mixotroph contribution to ciliate plus dinoflagellate biomass may increase trophic transfer efficiency and contribute to high fisheries yields.
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- PAR ID:
- 10519483
- Publisher / Repository:
- Inter-Research
- Date Published:
- Journal Name:
- Aquatic Microbial Ecology
- Edition / Version:
- 1
- Volume:
- 90
- ISSN:
- 0948-3055
- Page Range / eLocation ID:
- 1 to 21
- Subject(s) / Keyword(s):
- mixotrophy, seasonality, heatwave, microzooplankton
- Format(s):
- Medium: X Other: pdf
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3354/ame02005
