Vulnerability, resilience and adaptation: the future for the seagrass, Zostera capensis
Date
2018-12
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Stellenbosch : Stellenbosch University
Abstract
ENGLISH ABSTRACT: The seagrass Zostera capensis forms a vital component of southern African estuarine
systems as it provides critical ecosystem services which support biodiversity, estuary
functioning and economically important fishery industries. This intertidal seagrass is
restricted to estuaries and sheltered bays, and appears to rely chiefly on vegetative
reproduction, limiting its dispersal capacity along the often-harsh coastlines of southern
Africa. As such, these isolated and highly clonal populations are likely to be more
vulnerable to the impacts of global change, the effects of which are likely to cascade
through the ecosystem. South African estuaries are both highly threatened and poorly
protected, and little is known about the standing of the southern-east African coastline
in this regard, increasing the urgency of assessing the status of this keystone estuarine
species. A genomic approach can provide a cost-effective, comprehensive
characterisation of evolutionary history and potential, and can be applied to evaluate
vulnerability, resilience and adaptive potential. As such, the ezRAD method was
employed to obtain SNP data and examine both the neutral and putatively adaptive
genomic variation and differentiation of 12 Z. capensis populations across its range.
Anthropogenic drivers of genomic variation were investigated, and a spatial planning approach was utilised to evaluate regions that protect genomic diversity and
evolutionary resilience. Results showed that every meadow had a high degree of
clonality and low genomic diversity; this in combination with the lack of effective
protection and negative feedback between environmental pressures and genomic
diversity, increase the vulnerability of this species to further declines and even local
extinctions. However, variation at putatively adaptive loci indicate local adaptation to
temperature and precipitation regimes, which could confer some level of resilience to
future environmental change. Although loci under selection are shared across sites,
differences in their observed frequencies differentiate sites into a west coast and an east coast cluster. The formation of these clusters may have occurred as far back as the last
glacial maximum where ensemble models project a loss of habitat between the two
clusters, as well as a stable area of suitable habitat on the western-south coast, in terms
of sea surface temperature, which may have served as a refugial area. In order to
increase the representativeness of marine protected areas and the persistence of
species therein, it is critical that conservation planning take measures of genomic
variability into account. In this regard current and proposed MPAs based solely on habitat are far from sufficient, and their shortcomings are compounded by discordance
with the distribution and intensity of environmental pressures. However, by including
any one measure of genomic diversity, distinctness or adaptive potential, conservation
managers may sufficiently represent the evolutionary processes behind the patterns of
variation, while simplifying the conservation prioritisation procedure.
AFRIKAANSE OPSOMMING: Geen opsomming
AFRIKAANSE OPSOMMING: Geen opsomming
Description
Thesis (PhD)--Stellenbosch University, 2018.
Keywords
Zostera capensis -- Protection, Coastal biodiversity -- South Africa, Zostera capensis -- Conservation, Seagrasses -- Adaptation, UCTD, Resiliance (Ecology), Global environmental change