Characterising southern ocean phytoplankton community variability and environmental coupling: zonal, sectoral, and seasonal perspectives
Date
2024-03
Authors
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Stellenbosch : Stellenbosch University
Abstract
ENGLISH ABSTRACT: Marine phytoplankton communities vary in functional groups prevalence across the Southern
Ocean. The variability of phytoplankton groups, some drivers of important biogeochemical processes,
is intricately linked to their adaptation to specific environmental conditions. Community group
composition will thus vary as the surface water environment does. In the southern Ocean, different
latitudes (ocean zones), longitudes (ocean sectors), and times of year (seasons) support distinct
community profiles. In characterising the relationships that exist between specific phytoplankton
groups and major environmental drivers, we can contribute to the baseline understanding of the
Southern Ocean ecosystem, with implications for the biogeochemical processes its phytoplankton
support and the trophic food web these primary producers underpin.
Phytoplankton community structure was determined by chemotaxonomic pigment reconstruction
(CHEMTAX) for historically under-surveyed austral spring and winter voyages to the Indian and
Atlantic Ocean sectors of the Southern Ocean. Complimented by ship-board environmental monitoring
of the physical sea surface environment (temperature, salinity, and light) and macronutrient
parameters (nitrate, phosphate, silicate), the relationships between phytoplankton groups and major
environmental drivers were explored using Canonical Correlation Analysis (CCA). From this analysis
we determined group-environment associations that promote similar community structures three broad
zonal regions: northernmost temperate, transitional sub-Antarctic, and southernmost polar.
Phytoplankton communities across these regions appear to become increasingly dominated by fewer
groups placing greater importance on key functional groups further south.
Some group-environments associations appear independent of ocean zone, sector, or season,
emphasizing the coupling between major groups components of Southern Ocean phytoplankton
communities and their environment. The consistency of positive coupling relationships falls within
two classifications: physical environment associated groups (phaeocystis cryptophytes,
chlorophytes, coccolithophores, cyanobacteria, and pelagophytes) and nutrient associated groups
(diatoms, dinoflagellates, and prasinophytes). These relationships suggest that changes to the
Southern Ocean physical environment and nutrient regimes will drive group-specific community
restructuring to either favor or hinder some groups over others, with knock-on consequences for the
biogeochemical processes
those groups drive and the trophic chains they support.
AFRIKAANSE OPSOMMING: Geen opsomming beskikbaar.
AFRIKAANSE OPSOMMING: Geen opsomming beskikbaar.
Description
Thesis (MSc)--Stellenbosch University, 2024.