MEPS prepress abstract  -  DOI: https://doi.org/10.3354/meps12513

Nutrient production in rhodolith beds: impact of a foundation species and its associates

L. A. McConnico*, G. Hernández Carmona, R. Riosmena Rodríguez†

*Email: Laurie_mcconnico@cuesta.edu

ABSTRACT: Foundation species harboring associated fauna and micro-organisms provide an opportunity to explore nutrient contributions from excretion and decomposition (recycled nutrients) relative to new inputs. Rhodoliths, free-living non-geniculate coralline algae, support diverse cryptofaunal and microbial assemblages which could supply regenerated nutrients to their host, but studies of such nutrient dynamics are limited. We assessed temporal variability in concentrations of dissolved inorganic nutrients (ammonium: NH4+, nitrate + nitrite: NOx, and orthophosphate: PO43) associated with rhodolith beds on the Gulf and Pacific sides of Baja California Sur, México and considered potential sources of nutrient enrichment from cryptofauna, microbes and allochthonous inputs. Data suggest rhodoliths and/or sediments provide NH4+, NOx and PO43 in excess of water column availability, regardless of season or year. Cryptofaunal biomass was positively correlated with rhodolith diameter at all sites, and in some cases so was nutrient concentration. Ammonium and PO43 enrichment in rhodoliths may be attributed to cryptofaunal excretion or decomposition by micro-organisms. While seasonal delivery of new nutrients (NOx) via wind-induced water motion occurred in the Gulf, NOx in the Pacific was likely impacted by microbial mediated nitrification. Light and Dark incubations showed rhodolith assemblages may initially uptake NH4+ over NOx, but all nutrients were consumed in the presence and absence of light. This study highlights the importance of rhodoliths in coastal and estuarine environments not only as foundation species, but also for their role in nutrient cycling especially in areas of seasonal nutrient limitation.