Ostreopsis spp and benthic diatom interactions in contrasting sites: NW Mediterranean and El Hierro (Canary Islands)

Abstract

Ostreopsis becomes noticeable during blooms, when it can produce high levels of toxins and smother the benthos with polysaccharide. Considerable efforts have been made to identify the abiotic factors associated with blooms, to allow prediction of their occurrence. Locally, blooms are often associated with particular temperature regimes and hydrodynamics. However, the sea conditions associated with blooms are not consistent across the geographical range (e.g. Totti et al. 2010, Berdalet et al. 2017). Overall, abiotic factors may be better regarded as permissive ‘scene-setters‘, allowing rapid growth of Ostreopsis if other undefined conditions are met. Biotic interactions may be important (e.g. Ternon et al. 2018). However, interactions with other microbenthos have been little studied, partly through lack of practical means of identification. In the ECOS project we take advantage of the new possibilities opened by DNA metabarcoding, combined with established microscopical methods, to determine the influence of microeukaryotes on the yearly cycle of Ostreopsis at three contrasting sites: one in the Mediterranean (Llavanares) and two in Canary Islands (El Hierro). Here we present results for the first annual cycle. In each site we have sampled the most abundant substrata (red and brown macroalgae and mixed turfs) at least monthly and characterized the microeukaryotic benthic community by microscopy (diatoms) and DNA metabarcoding using general (V4 18S rDNA) and targeted (rbcL) markers. Preliminary results show an extremely diverse community of photosynthetic microeukaryotes and an interesting, inverse relationship between blooms of Ostreopsis and the centric diatom Actinocyclus, but different Actinocyclus species in the two regions.

Keywords: Ostreopsis, diatoms, metabarcoding

Financing: PID2022-138753OB-C21, PI E. Berdalet (ICM-CSIC); PID2022-138753OB-C22, PI R. Trobajo (IRTA); MICIU, Spain. Grant CEX2024-001494-S funded by AEI 10.13039/501100011033.

Acknowledgments: To the Reserva Marina La Restinga – Mar de Las Calmas, MAPA, and the staff at GESTIÓN DEL MEDIO RURAL DE CANARIAS, Gobierno de Canarias. Rosa Trobajo¹, David G. Mann¹, Emilio Soler-Onis², Adrian Kryk¹, Alba Garriga¹, Sofía I. Homedes³, Ico Martínez², Sofía Huelbes², May Gómez², Ted. T. Packard², Magda Vila³, Marta Estrada³, Elisa Berdalet³