Genetics, morphology, and resource availability of two morphologies of eelgrass, in the Kromme Estuary, South Africa.

Abstract

Seagrasses are crucial coastal ecosystem engineers, providing habitats and nursery grounds for various marine species worldwide. However, seagrasses are declining globally due to natural and anthropogenic threats. In South Africa, the endemic and endangered Zostera capensis is the dominant seagrass species, it supports a wide diversity of invertebrates and algae and forms the base of estuarine food webs. In many estuaries, meadows of Zostera capensis have been lost or are declining, with major threats being eutrophication and climate change. As environmental conditions are changing, seagrasses have strategies such as adaptation and acclimation that allow populations to persist under shifting environmental conditions. In the Kromme Estuary, a predominantly open estuary on the Eastern Cape coast of South Africa, two distinct morphological forms of Zostera, characterised by short and long leaves, were observed. However, the factors underlying this morphological variation and its ecological significance remains unclear. It is not known whether differences between the forms are associated with environmental conditions and genetic variation, or whether morphological differences is associated with differences in abundance and diversity of associated fauna. This study 1) determined the morphological traits, genetic identity, and population traits of the two morphotypes of Z. capensis in the lower reaches of the Kromme Estuary and 2) estimated the abundance and diversity of invertebrate animals associated with the different forms of Z.