Differential decomposition patterns of marine and terrestrial biomass in a coastal lagoon

Abstract. Lagoons are ecosystems where freshwater and marine organisms converge together with lagoonal specialists to form a mixed community that may vary spatially along a salinity gradient. Many organisms can only survive within relatively narrow bands of salinity. As a result of marine and freshwater inflows, together with exposure to variable salinity levels, dead marine and terrestrial biomass is accumulated in lagoons where it enters the detritic pathway. This study examined the in situ decomposition of marine (Fucus vesiculosus) and terrestrial (Alder glutinosa) biomass in Cuskinny Lagoon, South West Ireland. F. vesiculosus decayed rapidly and uniformly across the lagoon. A. glutinosa biomass loss varied throughout the lagoon, with the greatest loss occurring near the freshwater inflow. Thus, the spatial pattern of A. glutinosa decomposition differs from that of F. vesiculosus decomposition. Invertebrate abundances were not related to the amount of biomass loss of the marine and terrestrial material. This study demonstrates the differential decomposition patterns of marine and terrestrial biomass in the dynamic environment of a coastal lagoon. Abbreviations: ppt (parts per thousand); AFDW (ash free dry weight