Marine microbiology — Ultramicrobacteria: Which statement about ultramicrobacteria (nanobacteria) in marine systems is correct?

Introduction / Context:
Open-ocean microbial communities are dominated by very small cells with high surface-area-to-volume ratios. These ultramicrobacteria drive biogeochemical cycles and sustain higher trophic levels via the microbial loop.

Given Data / Assumptions:

• Ultramicrobacteria are abundant in oligotrophic marine waters.
• Heterotrophic nanoflagellates graze on bacteria as a key carbon pathway.
• We assess dominance and trophic role.

Concept / Approach:
Small cell size enhances nutrient uptake at low concentrations, favoring ultramicrobacteria in oligotrophic oceans. Their high abundances make them primary prey for heterotrophic flagellates, transferring dissolved organic carbon into higher trophic levels through predation.

Step-by-Step Solution:
Recognize ultramicrobacteria dominance in nutrient-poor marine systems. Acknowledge grazing by nanoflagellates as a major carbon flux. Therefore, both dominance and food-source roles are correct.

Verification / Alternative check:
Flow cytometry and epifluorescence counts show vast numbers of small bacteria in surface waters; grazing experiments quantify significant consumption by nanoflagellates.

Why Other Options Are Wrong:

• Only (a) or only (b): incomplete; both statements are supported.
• None: contradicts well-established marine microbial ecology.

Common Pitfalls:
Confusing “dominant in biomass” with “dominant in numbers.” Although tiny, they dominate numerically and in process rates.

Final Answer:
Both (a) and (b)