Water column dynamics of <i>Vibrio</i> in relation to phytoplankton community composition and environmental conditions in a tropical coastal area

TLDR

Vibrio abundance typically follows seasonal patterns driven by temperature and salinity in temperate coasts, but this relationship is unclear in tropical waters where the study’s two sampling periods were oligotrophic with stable temperatures and salinity. The study aimed to assess Vibrio dynamics off Mangalore, India, across two temporally separated sampling periods. Vibrio abundance was quantified using culture‑independent methods and related to phytoplankton composition and environmental variables. Vibrio density was 10–100 times higher in December 2007 than in February–March 2008, coinciding with a diatom‑dominated phytoplankton community; PLS regression identified diatom biomass as the main predictor, and low nutrient levels and predator abundance suggest that primary producer‑derived organic matter and high water‑column turnover, rather than top‑down control, drive Vibrio abundance.

Abstract

Summary Vibrio abundance generally displays seasonal patterns. In temperate coastal areas, temperature and salinity influence Vibrio growth, whereas in tropical areas this pattern is not obvious. The present study assessed the dynamics of Vibrio in the Arabian Sea, 1–2 km off Mangalore on the south‐west coast of India, during temporally separated periods. The two sampling periods were signified by oligotrophic conditions, and stable temperatures and salinity. Vibrio abundance was estimated by culture‐independent techniques in relation to phytoplankton community composition and environmental variables. The results showed that the Vibrio density during December 2007 was 10‐ to 100‐fold higher compared with the February–March 2008 period. High Vibrio abundance in December coincided with a diatom‐dominated phytoplankton assemblage. A partial least squares (PLS) regression model indicated that diatom biomass was the primary predictor variable. Low nutrient levels suggested high water column turnover rate, which bacteria compensated for by using organic molecules leaking from phytoplankton. The abundance of potential Vibrio predators was low during both sampling periods; therefore it is suggested that resource supply from primary producers is more important than top‐down control by predators.