Priming effect of benthic gastropod mucus on sedimentary organic matter remineralization

Mucous gels are produced by benthic animals rapidly and in copious amounts, and consequently they are a possible priming substrate whose addition in modest amounts may affect sedimentary organic matter (SOM) remineralization. The priming effect of benthic infaunal mucus was tested using mucus of the common gastropod Neverita duplicata as model substrate. Its composition is typical of marine molluscan mucus, consisting primarily of water (> 96% by weight). Salt-free dry weight constitutes 0.7% of total mucus. Relationships between C, N, and S content show the presence of N-free and S-free fractions, indicative of mucopolysaccharides, that account for approximately half of the total C present. The C/N ratios of the N-containing fraction (6.1 and 8.75 for pedal and hypobranchial mucus, respectively) are indicative of a carbohydrate-protein complex. Relatively low C/S ratios for the S-containing fraction (21.8 and 10.5 for pedal and hypobranchial mucus, respectively) and positive staining with Alcian Blue dye are indicative of S-ester and alkyl- SO^2- ₄ groups bridging mucopolysaccharide and glycoprotein components. Anaerobic incubations of pedal mucus, sediment, and mucus-sediment mixture resulted in the generation of ΣCO₂ and NH⁺ ₄ at ratios lower than substrate C/N ratios, indicating the preferential decomposition of N-rich components. Production rates of ΣCO₂ and NH⁺ ₄ in mucus-sediment incubations are higher, by 9% ± 16% and 29% ± 11%, respectively, than those predicted from linear addition of mucus-only and sediment-only rates. The accelerated remineralization rate of N in the presence of modest mucus contribution suggests that benthic mucus addition can affect SOM remineralization processes through a “priming” effect.