Multispecies approach shows high tolerance of temperate marine sponges to nitrogenous fertiliser

Excessive use of nitrogen fertilisers increases crop yields but leads to nutrient run-off into coastal habitats causing harmful algal blooms (HABs) and eutrophication. The mechanisms by which organisms respond to nitrogen input are poorly understood in sessile filter feeders. Despite their ecological importance, there is a paucity of research on how marine sponges respond to fertiliser inputs. In this study, seven temperate marine sponge species from two oceans were exposed to fertiliser for 13 days (NE Atlantic Ocean: Cliona celata, Stelligera stuposa, Axinella dissimilis, and Suberites carnosus) and 10 days (SW Pacific Ocean: Crella incrustans, Suberites australiensis, and Tethya bergquistae). In both oceans, sponges were exposed to three locally relevant environmental treatments. In the NE Atlantic (Lough Hyne, Ireland), concentrations included ambient seawater without fertiliser, 4–6 mg L⁻¹ NO₃-N (286–426 μM NO₃), and 16–19 mg L⁻¹ NO₃-N (1143–1357 μM NO₃). In the SW Pacific (Wellington, Central New Zealand), concentrations included ambient seawater without fertiliser, 1 mg L⁻¹ NO₃-N (71 μM NO₃), and 5–7 mg L⁻¹ NO₃-N (357–500 μM NO₃). Sponges showed high survival rates (>95 %) in both experiments and only one species, Cliona celata, showed evidence of health effects. Respiration rates in NE Atlantic sponges were variable, with no consistent patterns across species or treatments. In contrast, there were no differences in respiration rates between control and treatment sponges from the SW Pacific. Overall, our results show that temperate sponges have a high tolerance to fertiliser exposure, regardless of study site, which is consistent with studies of tropical sponge species.