Moreira-Saporiti, Agustín ORCID:, Hoeijmakers, Dieuwke, Msuya, Flower E., Reuter, Hauke ORCID: and Teichberg, Mirta ORCID: (2021) Seaweed farming pressure affects seagrass and benthic macroalgae dynamics in Chwaka Bay (Zanzibar, Tanzania). Regional Environmental Change, 21 (1). pp. 1-12. DOI

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Farming of Eucheuma denticulatum is a major activity in Zanzibar affecting seagrass ecosystems primarily through shading and
trampling. The aim of this study was to test the impacts of shading and trampling during seaweed farming on seagrass meadows
composed by Halophila stipulacea and Thalassia hemprichii and their associated benthic macroalgae. Areas covered by these
species were selected for the building of seaweed farms in three treatments: seaweed farm plots (with shading and trampling
effects), trampling plots (with trampling effects only), and control plots (with no shading or trampling effects). Reduction of light
within the plots was recorded over 9 weeks. Percentage cover of seagrasses and macroalgae and shoot density of seagrasses were
measured over 12 weeks to assess the impact of shading and trampling by seaweed farming activities. Light was significantly
reduced in the seaweed farm plots by 75 to 90%by the end of a seaweed growth cycle. H. stipulacea, despite its capacity for rapid
growth, was significantly affected by the combination of shading and trampling under the seaweed farm treatment, while the
climax seagrass species T. hemprichii was unaffected. Due to the decline in H. stipulacea, benthic macroalgae cover increased in
the seaweed farm treatment, suggesting a change in seagrass community dynamics. In contrast, trampling had a negative effect on
the benthic macroalgae as an isolated disturbance, which suggests that seagrasses are more resistant to trampling than macroalgae
and would likely dominate the benthic macrophyte community under these conditions.

Document Type: Article
Programme Area: PA3
Research affiliation: Integrated Modelling > Spatial Ecology and Interactions
Ecology > Algae and Seagrass Ecology
Refereed: Yes
Open Access Journal?: No
ISSN: 1436-3798
Date Deposited: 14 Jan 2021 17:13
Last Modified: 26 Mar 2024 13:30

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