Diversity, biomass and distribution pattern of Sargassum beds in the South West lagoon of New Caledonia (South Pacific)

Abstract

Sargassum (Phaeophyceae, Fucales) is a genus of worldwide distribution recently recognised to proliferate in several regions of the South Pacific. In New Caledonia, species of this genus naturally structure one of the major lagoon habitats but their extent, composition and biomass remain largely unknown. To fill these gaps in our knowledge over large areas, we applied a combination of remote sensing and in situ methods applied to the Neo Caledonian South West Lagoon. Space borne high resolution Landsat (30-m resolution) and Quickbird (2.4-m resolution) images of the Neo Caledonian South West lagoon were used to estimate the spatial extent of the different beds of interest. Species composition was determined for 11 Sargassum beds and seasonal variations were investigated for four representative beds over an 18 month period using quadrats and transects. Relationships between surface cover and biomass were estimated from seasonal field data sets. Finally, four methods requiring variable levels of sampling effort were designed to estimate the total biomass at the scale of each bed, considering (or not) the specific composition, and spatial and temporal variations. Seven Sargassaceae species were identified. Mean surface cover (24.4-51.6%) and total biomass [3.4-1,461.9 t dry matter (DM)] varied widely between beds. Overall, biomass temporal variations were not significantly different, but species-level variations seemed to be bed-specific. The extent of the 11 beds was 9 km 2 ; their total biomass was estimated and compared using each of the four methods, and the most precise method provided an estimate of 2,900 t DM. This study demonstrates a way of characterising Sargassum beds, efficiently and on a large scale, using a combination of remotely sensed and in situ data. These methods should be useful for possible future biomonitoring of Sargassum beds in New Caledonia, and in other areas worldwide.

Seasonal changes in water quality and Sargassum biomass in southwest Australia

“…Sargassum species are brown macroalgae with a global distribution, and are especially dominant in shallow tropical and sub-tropical waters (Hanisak & Samuel 1987, Mattio et al 2008, Mattio & Payri 2011. Sargassum are commonly attached to rocks, but can also have floating life forms.…”

TAXONOMIC REVISION OF SARGASSUM SPECIES (FUCALES, PHAEOPHYCEAE) FROM NEW CALEDONIA BASED ON MORPHOLOGICAL AND MOLECULAR ANALYSES1

“…2008a) may represent currently untapped economic potential for pharmaceutical, cosmetic, and agro‐food industries (Prud’homme van Reine 2002). Despite their ecological importance and economic potential, New Caledonian Sargassum species are poorly known (Mattio et al. 2008a).…”

“…In New Caledonia, Sargassum species are among the most conspicuous algae inhabiting the lagoon and constitute a key habitat, sheltering significant biodiversity (Rossier and Kulbicki 2000). In addition, their significant biomass (Mattio et al 2008a) may represent currently untapped economic potential for pharmaceutical, cosmetic, and agro-food industries (Prud'homme van Reine 2002). Despite their ecological importance and economic potential, New Caledonian Sargassum species are poorly known (Mattio et al 2008a).…”

“…In addition, their significant biomass (Mattio et al 2008a) may represent currently untapped economic potential for pharmaceutical, cosmetic, and agro-food industries (Prud'homme van Reine 2002). Despite their ecological importance and economic potential, New Caledonian Sargassum species are poorly known (Mattio et al 2008a). In her catalog, Payri (2006) provided a revised phycological checklist, highlighting the need for a reassessment of Sargassum species' taxonomy.…”

Multi‐scale marine biodiversity patterns inferred efficiently from habitat image processing

“…The development of both in situ digital photography and remote sensing has increased the availability of habitat maps for species distribution modeling. In situ images are typically used to define a typology of habitats relevant for understanding species distributions at scales ,100 m (Dumas et al 2009), whereas remotely sensed images are used to map these habitats and associated species at scales .100 m (e.g., Mattio et al 2008). These habitat maps are increasingly used as spatially explicit layers in habitat suitability models, whereby biodiversity metrics (e.g., species richness, abundance, functional groups) can be mapped indirectly (Garza-Pe´rez et al 2004, Mellin et al 2007).…”