Mixoplankton interferences in dilution grazing experiments.

Area of Science:

• Marine Ecology
• Plankton Dynamics
• Aquatic Food Webs

Background:

• The dilution grazing technique is widely used to estimate grazing rates in aquatic ecosystems.
• Mixoplankton, organisms capable of both photosynthesis and phagocytosis, present challenges to traditional grazing estimation methods.
• The impact of mixoplankton on the accuracy of the dilution grazing technique remains poorly understood.

Purpose of the Study:

• To investigate how mixoplankton influence grazing rate estimations using the dilution grazing technique.
• To evaluate alternative methods for incorporating mixoplankton activity into grazing studies.
• To determine the role of light and community structure in mixoplankton feeding behavior.

Main Methods:

• Laboratory-controlled dilution experiments were conducted with defined mixtures of phytoplankton, protozoa, and mixoplankton.
• Experiments were performed under varying light conditions and species compositions.
• Chlorophyll concentrations and species-specific cell counts were used as proxies for biomass and grazing activity.

Main Results:

• Chlorophyll is an inadequate biomass proxy for phytoplankton in the presence of mixoplankton.
• Species-specific cell counts can partially account for mixoplankton activity and reveal grazing selectivity.
• Community-level experiments better reflect natural conditions than single-species studies; light enhances feeding activity, with diurnal grazing exceeding nocturnal rates.

Conclusions:

• Rethinking the dilution grazing technique is necessary to accurately incorporate mixoplankton.
• Routine examination of plankton communities and varied incubation timings (day/night) are recommended.
• In silico approaches may offer future solutions for quantifying mixoplankton contributions to grazing.