Abstract
BackgroundMacroalgae play a structuring role in benthic ecosystems, which makes it very important to monitor their cover rates and study their community structures and changes in time. Such studies are usually led by autonomous divers and often do not generate sufficient data to provide enough material for strategically-sound conservation plans. This paper describes the dataset generated in the framework of the evaluation of the potential of a complementary data acquisition method: annotating videos transects obtained using an underwater Remotely Operated Vehicle (ROV).The focus was on Cystoseirabrachycarpa, together with the abundance of several other macroalgae species, which could be identified using the ROV images after validation through specimen identification. Furthermore, in order to allow future uses, such as monitoring the status of colonisation of the invasive algae Caulerpacylindracea, the ROV was sent to some deeper transects on sedimentary habitats (40 m) below the Posidonia meadows lower limits.New informationThe project, while providing some interesting insights on using a ROV as a tool to study marine biodiversity, generated a dataset for the distribution of 19 macroalgae on both standardised and new transects in the Bay of Calvi (Katz et al. 2021). The observed species of macroalgae included: Acetabulariaacetabulum, Amphiroarigida, Caulerpaprolifera, Caulerpacylindracea, Codiumbursa, Colpomeniasinuosa, Corallinales (order), Cystoseirabrachycarpa, Cystoseiracrinita, Cystoseiraspinosa, Cystoseirazosteroides, Dictyota (genus), Flabelliapetiolata, Halopteris (genus), Halopterisscoparia, Jania (genus), Osmundariavolubilis, Padina pavonica and Peyssonneliasquamaria.The videos also showed that the invasive algae Caulerpacylindracea has spread between 2016 and 2019 and that more focused studies should be held in the Bay to assess the actual reach and possible impacts of this invasion.Finally, our ROV video transects have also underlined the significant presence of particular benthic macroalgae communities over habitat zones described as "soft-bottom" on benthic habitat maps. Although the biomass per unit area of these communities is probably lower than for most coastal rocky bottoms, this widely-spread habitat type holds a contribution to primary production to be considered in coastal ecosystem models.
Highlights
As macroalgae play an essential role in benthic ecosystems, it can be very important to monitor their cover rates and study their community structures
The analysis of the cover rates of different macroalgae, often used as bioindicators of environmental disturbance, in particular the genus Cystoseira, allows us to assess the impacts and pressures of environmental changes in the Bay of Calvi. Such approaches already exist for Cystoseira in the Mediterranean (Sales Villalonga et al 2010), as for complete shallow macroalgae communities (Leduc et al 2017, Sirjacobs et al 2019)
The data we provide can be used to study the evolution of macroalgae distributions on a 40 year-span and to explore additional ones, including in sedimentary habitats. This could give interesting insights on how water quality improved after installation of a dedicated plant to treat wastewater discharges in the Bay of Calvi (Clarisse 1984, Janssens et al 1993) and how this affected benthic communities
Summary
Macroalgae play a structuring role in benthic ecosystems, which makes it very important to monitor their cover rates and study their community structures and changes in time. Such studies are usually led by autonomous divers and often do not generate sufficient data to provide enough material for strategically-sound conservation plans. In order to allow future uses, such as monitoring the status of colonisation of the invasive algae Caulerpa cylindracea, the ROV was sent to some deeper transects on sedimentary habitats (40 m) below the Posidonia meadows lower limits. The biomass per unit area of these communities is probably lower than for most coastal rocky bottoms, this widely-spread habitat type holds a contribution to primary production to be considered in coastal ecosystem models
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