Investigating transplantation as a mechanism for seagrass restoration in South Africa

Abstract

The extent of seagrasses has declined globally, with restoration through transplantation seen as an important tool for reversing population loss, yet restoration studies for African seagrass species are scarce. This study investigated the use of different planting patterns (straight‐line, compact, and star) and core sizes (11, 18, and 25 cm Ø) in transplanting ecotypes (intertidal and subtidal) in the predominantly open Knysna and temporarily closed Klein Brak estuaries in South Africa. Cores of the endangered seagrass, Zostera capensis, were transplanted in two experimental repeats per ecotype and core size along transects to investigate survival of plants post‐transplant. No significant differences were observed among core sizes, patterns, or ecotypes in the Knysna Estuary, but cores with the compact pattern had better survival rates in the Klein Brak Estuary. Holes left by the smallest cores in donor sites recovered faster through sediment deposition compared to larger holes. Our study demonstrated that seagrass restoration in South Africa is challenging due to limited suitable habitats and strong environmental variability in estuarine ecosystems. It is important that careful consideration, including of genomic diversity and population structure, as well as ecological similarity between donor and recipient populations must be made for each restoration site when assessing its restoration potential. Effective “no‐take bait zones” and upstream catchment management will be important for protecting potential donor meadows.

Using transplantation to restore seagrass meadows in a protected South African lagoon

“…The principal challenge to upscaling Z. capensis restoration is the with vastly different environmental conditions found within estuaries across its range, therefore restoration efforts will need to be population and site specific ( Adams, 2016 ). For example, attempts in two estuarine systems in South Africa, Klein Brak and the Knysna Estuary, both showed a 100% loss of Z. capensis transplants within 3-months ( Mokumo, Adams & von der Heyden, 2023 ), despite following a similar approach to the work presented here. Both estuaries have strong freshwater inflows and fluctuations in physicochemical conditions, water levels and turbidity ( Mokumo, Adams & von der Heyden, 2023 ), making their environments more variable than the conditions found in Langebaan, with changes in salinity a likely variable in the loss of transplanted cores in Klein Brak.…”

“…For example, attempts in two estuarine systems in South Africa, Klein Brak and the Knysna Estuary, both showed a 100% loss of Z. capensis transplants within 3-months ( Mokumo, Adams & von der Heyden, 2023 ), despite following a similar approach to the work presented here. Both estuaries have strong freshwater inflows and fluctuations in physicochemical conditions, water levels and turbidity ( Mokumo, Adams & von der Heyden, 2023 ), making their environments more variable than the conditions found in Langebaan, with changes in salinity a likely variable in the loss of transplanted cores in Klein Brak. Conversely, a restoration project in a relatively protected site characterised by sandy and muddy flats in Maputo Bay, Mozambique, also without significant freshwater flow, recorded survival rates of 75% after 12 months for transplanted Z. capensis cores ( Amone-Mabuto et al, 2022 ).…”

“…This has also negatively impacted genomic diversity of some Z. capensis populations, further threatening the long-term resilience of seagrasses in South Africa ( Phair et al, 2020 ). Although fast-growing, Z. capensis does not colonise quickly, so management intervention through restoration of anthropogenically-impacted meadows is needed in the region ( Adams, 2016 ; Mokumo, Adams & von der Heyden, 2023 ; Watson et al, 2023 ). Presently there is lack of knowledge on how best to implement Z. capensis restoration, with one restoration trial in Maputo Bay, Mozambique ( Amone-Mabuto et al, 2022 ) and attempts in Klein Brak and Knysna Estuary, South Africa, presenting variable success ( Mokumo, Adams & von der Heyden, 2023 ).…”

“…Although fast-growing, Z. capensis does not colonise quickly, so management intervention through restoration of anthropogenically-impacted meadows is needed in the region ( Adams, 2016 ; Mokumo, Adams & von der Heyden, 2023 ; Watson et al, 2023 ). Presently there is lack of knowledge on how best to implement Z. capensis restoration, with one restoration trial in Maputo Bay, Mozambique ( Amone-Mabuto et al, 2022 ) and attempts in Klein Brak and Knysna Estuary, South Africa, presenting variable success ( Mokumo, Adams & von der Heyden, 2023 ). For example, Mokumo, Adams & von der Heyden (2023) reported 100% loss of transplants within three months following a restoration trial, suggesting that environmental variability, as well as local site and seagrass population dynamics are important considerations for regional restoration attempts.…”

“…A key challenge for restoration efforts remains selection of the transplant site and donor meadow, and refining transplantation methods to maximise transplant survival ( Fonseca, 2011 ; Cunha et al, 2012 ; Park et al, 2013 ; van Katwijk et al, 2016 ). Although Fonseca, Kenworthy & Thayer (1998) outlined key selection criteria, applicability of this framework is limited in some cases due to local-scale contextual processes ( Calumpong & Fonseca, 2001 ; Lange et al, 2022 ; Mokumo, Adams & von der Heyden, 2023 ). Site-specific factors such as water flow, wave action and tidal gradients together with seagrass traits, can have varying impacts on restoration outcomes ( Calumpong & Fonseca, 2001 ).…”