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Functional-guild compositional structure and patchiness in subtidal Nanozostera macrobenthos across three contrasting
1Institute for Coastal and Marine Research, Nelson Mandela University, Gqeberha, Eastern Cape, 6031, Republic of South Africa; Department of Zoology and Entomology, Rhodes University, Makhanda, Eastern Cape, 6140, Republic of South Africa; Department of Zoology & Conservation Research Institute, University of Cambridge, Cambridge, UK.
Marine Environmental Research
|September 2, 2025
Summary
Seagrass beds in three South African estuaries show two distinct macrobenthic community structures. One is dominated by microgastropods, influencing overall patchiness and potentially masking regional biogeographic effects.
Area of Science:
- Marine Ecology
- Estuarine Ecology
- Benthic Ecology
Background:
- Seagrass ecosystems, particularly Nanozostera capensis, are crucial habitats supporting diverse macrobenthic communities.
- Estuarine systems exhibit varied environmental conditions (size, morphology, hydrography) that can influence ecological structure.
- Understanding functional guilds within seagrass macrobenthos is key to assessing ecosystem health and resilience.
Purpose of the Study:
- To investigate how differing environmental conditions in three adjacent warm-temperate estuaries affect the functional guild structure of seagrass-associated macrobenthos.
- To determine the relative abundance and patchiness of 28 identifiable subtidal macrobenthic functional guilds.
- To assess the influence of microgastropod abundance on overall macrobenthic assemblage patchiness and functional structure.
Main Methods:
- Comparative analysis of macrobenthic functional guilds across Knysna estuarine bay, Keurbooms Lagoon, and Swartvlei estuary.
- Quantification of relative abundance and spatial patchiness of 28 functional guilds within Nanozostera capensis beds.
- Examination of relationships between functional group structuring, environmental variables, and spatial patchiness.
Main Results:
- Two distinct functional-group structurings were identified: one dominated by epifaunal microgastropods feeding on periphyton, and another where this guild was insignificant.
- Spatial variation in microgastropod abundance was a major driver of patchiness in the entire macrobenthic assemblage.
- The dominance of microgastropods obscured potential relationships between functional composition and estuarine regions (mouth, lagoon, estuary).
Conclusions:
- Environmental conditions in adjacent estuaries can lead to divergent macrobenthic functional guild structures.
- Endemic microgastropods play a significant role in structuring seagrass-associated macrobenthic communities and their spatial patchiness.
- Further research is needed to understand the biogeographic drivers and ecological significance of microgastropod dominance in these seagrass ecosystems.
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