Seagrass population dynamics and biodiversity assemblages indicate negative effects of short-term nutrient enrichment in tropical island ecosystem
Year: 2024
Type: article
Abstract: Seagrass ecosystems of tropical islands are unique and are highly biodiverse and provide an array of ecosystem services that benefits the coastal communities. Despite these benefits, increasing coastal population and anthropogenic nutrient influx are severely damaging these ecosystems leading to severe loss and die-offs. Within this framework, this study assessed the influence of anthropogenic short-term nutrient enrichment (hereafter enriched) effects on seagrass population dynamics (recruitment, growth rate and mortality), morphometric traits, productivity, and leaf biodiversity assemblages in the islands of Andaman and Nicobar (ANI) of India and contrasted these findings with away from these enriched areas (hereafter pristine). Seagrass (Thalassia hemprichii and Cymodocea rotundata), sediment samples were collected in the dry season (October-May) of ANI. Reconstruction techniques, an indirect measurement of plant growth was used to derive leaf plastochrone interval (PI), i.e., number of days required to produce one leaf by the seagrass. Sediment, organic matter (OM) and carbon (C) were quantified using, loss on ignition and CHNS elemental analyzer.Under enriched conditions, the sediment grain size fractions were altered towards fine grain fraction (silt + clay) compared to sandy fractions under pristine conditions. This increased fine grain fractions helped in binding 1.4-fold and 1.5-fold and 3-fold higher sediment OM, C and N respectively, under enriched conditions for both seagrass species. The total N in leaves of T. hemprichii and C. rotundata increased 3.3-fold and 2.4-fold than pristine conditions and was positively related with sediment N under enriched conditions. Increased in N accumulation resulted in higher shoot densities, below ground biomass, leaf elongation rates, rhizome elongation and productivity for both T. hemprichii and C. rotundata than respective pristine conditions. Both T. hemprichii and C. rotundata took 26.07 (pristine-26.03) and 19.76 (pristine-29.6) days respectively to produce new seagrass leaf under enriched conditions. Despite higher horizontal elongation rates of both species, low apex densities resulted in lower meadow migration and increased meadow fragmentation under enriched conditions probably due to presence of other contaminants. Similarly, the above ground-biomass of T. hemprichii and C. rotundata decreased 1.4-fold and 1.5-fold, whereas the leaf length of T. hemprichii and C. rotundata was reduced by 1.3-fold and 1-fold, under enriched conditions probably due to algal proliferation. The leaf meiofauna abundance also decreased 1.3-fold and 1.5-fold in T. hemprichii and C. rotundata meadows under enriched conditions. The long-term average recruitment for both T. hemprichii and C. rotundata increased 1.3-fold and 1-fold under enriched conditions resulting in 3.5-fold and 11-fold higher current population growth rates. Increased current population growth rates resulted in 1.7-fold and 1.5-fold higher younger plants in both T. hemprichii and C. rotundata meadows respectively under enriched conditions. Contrastingly, these younger plants did not survive longer under enriched conditions, reducing the long-term seagrass population longevity to 4 years, whereas under pristine conditions both seagrasses survived to the age of 6 to 7 years. This study highlights that nutrient enrichment in tropical islands benefits seagrass in short-term but reduces seagrass meadow migration, population longevity and b
Language: English
Subfield: Oceanography
Field: Earth and Planetary Sciences
Domain: Physical Sciences
Open Access status: hybrid
Estimated APC paid: $3,850
OpenAlex ID: W4405689326