Marine Ecology Progress Series
MEPS is a leading hybrid research journal on all aspects of marine, coastal and estuarine ecology. Priority is given to outstanding research that advances our ecological understanding.
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DOI: https://doi.org/10.3354/meps15293
copiedFunctional surrogacy of the seagrass Ruppia cirrhosa for endangered Zostera capensis in supporting estuarine macrofaunal diversity
- Cloverley Lawrence
- Richard S. K. Barnes
- Martin Kyle Smith
- Clement Arendse
- Ntando Majola
- Noxolo Njapha
- Kezia Dreyer
- Lucienne Human
- Aldwin Ndhlovu
Seagrass loss is accelerating globally, yet the extent to which co-occurring macrophytes can compensate for associated biodiversity declines remains poorly understood. The endangered eelgrass Zostera capensis co-occurs with the disturbance-tolerant Ruppia cirrhosa in many South African estuaries. We assess whether R. cirrhosa can maintain macrofaunal diversity and ecosystem functions in the context of Z. capensis declines in the Swartvlei Estuary. Species abundance, richness, diversity and evenness did not differ significantly between vegetation types, however, significant differences in community composition between vegetation types at mixed sites were revealed, with R. cirrhosa assemblages exhibiting greater multivariate dispersion and turnover along the estuarine gradient. Seagrass structural characteristics (leaf width, canopy height, biomass) and water-column variables (salinity, turbidity, dissolved oxygen) were associated with variation in assemblage structure, suggesting that both habitat architecture and water-column conditions can influence macrofaunal communities. A common species pool occurred across all sites, with shifts in relative dominance driving among-site turnover rather than gains or losses of unique taxa. R. cirrhosa supports diverse macrofaunal communities but does not fully replicate those in Z. capensis beds, providing only partial functional replacement where eelgrass has declined and failing to meet like-for-like surrogacy because its assemblages remain consistently different and more variable. These differences in predictability and functional representation mean that R. cirrhosa should be viewed as a complementary, rather than fully equivalent, habitat for macrofaunal biodiversity. These results have important implications for restoration prioritisation, biodiversity offsetting and reliability of ecosystem services in estuarine systems.
KEYWORDS
Cloverley Lawrence (Corresponding Author)
- South African National Parks, Rondevlei Scientific Services, Sedgefield, 6573, South Africa
- Institute for Coastal and Marine Research, Nelson Mandela University, Gqeberha 6031, South Africa
Richard S. K. Barnes (Co-author)
- Institute for Coastal and Marine Research, Nelson Mandela University, Gqeberha 6031, South Africa
- Department of Zoology and Entomology, Rhodes University, Makhanda, 6140, South Africa
- Department of Zoology and Conservation Research Institute, University of Cambridge, Cambridge, United Kingdom
Martin Kyle Smith (Co-author)
- South African National Parks, Rondevlei Scientific Services, Sedgefield, 6573, South Africa
- Department of Ichthyology and Fisheries Science, Rhodes University, Makhanda 6140, South Africa
Clement Arendse (Co-author)
- South African National Parks, Rondevlei Scientific Services, Sedgefield, 6573, South Africa
Ntando Majola (Co-author)
- Centre for Trace Metal and Experimental Biogeochemistry (TracEx), Department of Earth Sciences, Stellenbosch University, Stellenbosch 7600, South Africa
Noxolo Njapha (Co-author)
- South African National Parks, Rondevlei Scientific Services, Sedgefield, 6573, South Africa
Kezia Dreyer (Co-author)
- South African National Parks, Rondevlei Scientific Services, Sedgefield, 6573, South Africa
Lucienne Human (Co-author)
- Institute for Coastal and Marine Research, Nelson Mandela University, Gqeberha 6031, South Africa
- South African Environmental Observation Network (SAEON), Elwandle Node, Nelson Mandela University, Gqeberha 6031, South Africa
- Institute for Coastal and Marine Research, Nelson Mandela University, Gqeberha 6031, South Africa
- Biogeochemistry Research Infrastructure Platform, University of Cape Town, Cape Town 7701, South Africa
Handling Editor:
Christian Wild, Bremen, Germany
Reviewers:
C. Griffiths and 2 anonymous referees