Drivers affecting seagrass meadows: An approach for conservation and restoration in Mozambique

Abstract

Seagrasses and other shallow-water vegetation are important coastal habitat because they provide many ecosystem services, including food, shelter and nursery areas of shellfish and finfish as well as marine endangered species such as dugongs and sea turtles. However, following a worldwide trend, seagrass meadows in Mozambique are experiencing a reduction in area due to a combination of natural disturbances and anthropogenic impacts. The aim of this thesis was to assess two relevant drivers affecting seagrass ecosystem services, while contributing to developing innovative management tools for conservation, restoration and sustainable use of this ecosystem in Maputo Bay, Mozambique. The thesis focuses on the impacts from both global (ocean acidification, OA) and local (fishing) stressors on marine invertebrates and dugongs. The thesis also aims to develop innovative methods for shallow-water monitoring using drones and machine learning as well as developing appropriate seagrass restoration techniques. Paper I evaluates the biological response (growth rate and net calcification) of a marine calcifier (sea urchin), to different levels of variability of pCO2/pH imposed in the absence or presence of seagrass in the context of OA as a global stressor. The results showed that larvae growth rates significantly decreased with decreasing average pH in both absence and presence of seagrass. Moreover, larvae raised in presence of seagrass, maximized calcification during the day, and lowering their calcification during the night. These results have implications to better understand the mechanisms behind the sensitivity of organisms to OA in variable coastal ecosystems. Paper II shows the influence of gillnet fishing activities as a local stressor on dugong feeding grounds. A drone survey revealed overlap between dugong foraging areas and fishing grounds, increasing the risk of dugong entanglement when the gillnets are deployed at Inhaca Island, Mozambique. Thus, management initiatives to control gillnet fishing activity with involvement of the local community were highlighted to support future conservation efforts. A survey on local ecological knowledge was used in paper III to assess community perceptions at Inhaca Island on both global and local stressors in seagrass meadows, while evaluating how fishing communities are adapting to face potential future changes of seagrass habitats and associated services. Results showed that the fishing community at Inhaca Island depends on fishing activities for their basic livelihood, and they perceived sedimentation associated with floods as the leading cause of seagrass changes, followed by destructive fishing practices. A decrease in coastal protection and loss of habitats (and associated invertebrates and fish) are perceived as the main threats to their livelihood and wellbeing. Paper IV presents a field experiment to restore seagrass (Halodule uninervis), which is used as food by dugongs, with the aim to assess infauna biodiversity and colonization after planting. Two planting methods were tested, including a plug method and a single shoot method applied with two seagrass shoot densities. Results showed that the both methods influenced the transplants growth with consequences for the infauna abundance and composition. The results of this thesis are discussed in an integrated approach to understand both global and local drivers of changes in seagrass meadows in Maputo Bay, Mozambique, while proposing an effective conservation and management strategies, which include the use of innovative technologies such as drones, involvement of local communities and restoration approaches to enhance the role of seagrass as an important coastal ecosystem.