Seagrass is an early responder to nitrogen enrichment in oligotrophic oceanic coral atoll environments

• Published in: Marine pollution bulletin Vol. 209; no. Pt B; p. 117224
• Main Authors: Arnull, Jessica, Hashim, Aminath Shaha, Ganeshram, Raja S., Moosa, Hassan, Wilson, A. Meriwether W., Tudhope, Alexander W.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.12.2024
• Subjects: Enrichment experiment; Indian Ocean; Maldives; Nitrogen pollution; Seagrass; Thalassia hemprichii; Thalassia hemprichii; Maldives; Seagrass; Nitrogen pollution; Indian Ocean; Enrichment experiment
• ISSN: 0025-326X; 1879-3363; 1879-3363
• DOI: 10.1016/j.marpolbul.2024.117224

Seagrass meadows in oceanic coral atoll settings play key roles in sediment stabilisation and biodiversity enhancement. However, seagrass is susceptible to anthropogenic disturbance including nutrient input. Here, we experimentally enriched Thalassia hemprichii meadows with N-based fertiliser in two similar reef-top settings with different recent histories of disturbance, in Laamu atoll, Maldives. Enrichment resulted in enhanced overall leaf production, but in different ways at the two sites. At the ‘more impacted’, and slightly deeper site, the dominant effect of high-nutrient treatment was growth of new leaves, but this also coincided with cyanobacteria and filamentous green-algal blooms. In contrast, the ‘less impacted’ site, leaf extension rates (tagged and new) significantly increased. Isotopic analysis confirmed fertiliser uptake into biomass. Our findings highlight that the response of seagrass to nutrient enrichment is context dependent. This study, the first of its kind in the Indian Ocean, highlights the need and opportunity for nutrient and seagrass monitoring and associated policy development. Overview of key significant results (α = 0.05). Black upward and downward arrows indicate significant results in the same direction. Horizontal arrows indicate no significant change. The outbreak in cyanobacteria at Site 1 is represented by the red markings. [Display omitted] •Experimental nitrogen enrichment of Thalassia hemprichii meadows in the Maldives•Enrichment resulted in enhanced overall leaf production.•δ15N signatures confirmed fertiliser uptake into biomass.•Enrichment at the site with more recent disturbance coincided with an algal bloom.•First experimental study of this kind in the Indian Ocean