Seaweed farming pressure affects seagrass and benthic macroalgae dynamics in Chwaka Bay (Zanzibar, Tanzania)

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.

Sungkyunkwania multivorans gen. nov., sp. nov., a member of the family Flavobacteriaceae isolated from seawater from a seaweed farm

A Gram-staining-negative, non-flagellated, non-gliding and rod-shaped bacterial strain, designated PDB-16T, was isolated from seawater from a seaweed farm on the South Sea in Korea, and its taxonomic position was investigated using a polyphasic approach. Strain PDB-16T grew optimally at 30 °C, at pH 7.0–7.5 and in the presence of 2 % (w/v) NaCl. A neighbour-joining phylogenetic tree based on 16S rRNA gene sequences revealed that strain PDB-16T formed an independent lineage within the evolutionary radiation encompassed by the family Flavobacteriaceae . Strain PDB-16T contained MK-6 as the predominant menaquinone and iso-C15 : 0, iso-C15 : 1 G and iso-C17 : 0 3-OH as the major fatty acids. The major polar lipids detected in strain PDB-16T were phosphatidylethanolamine and two unidentified lipids. The DNA G+C content of strain PDB-16T was 42.1 mol%. Strain PDB-16T exhibited very low 16S rRNA gene sequence similarities of less than 89.7 % to the type strains of any bacterial species with validly published names and less than 90.1 % to uncultured bacteria clones. The 16S rRNA gene sequence similarity values and the differences in phenotypic properties between strain PDB-16T and some phylogenetically related genera were sufficient to support the proposal that strain PDB-16T should be distinguished from previously known genera of the family Flavobacteriaceae . On the basis of the data presented, strain PDB-16T is considered to represent a new genus and novel species, for which the name Sungkyunkwania multivorans gen. nov., sp. nov. is proposed. The type strain of Sungkyunkwania multivorans is PDB-16T ( = KCTC 32138T = CCUG 62952T).