The importance of blue carbon as a food source to oysters (Saccostrea cucullata) inside a tropical pristine Australian estuary

This study investigated the importance of blue carbon (carbon captured from the atmosphere by algae, mangrove and seagrass leaves) as a component of particulate organic matter (POM) along the pristine King George River (Kimberley region, Australia), and how this modulates the diet of common suspension feeding bivalves (Mussels: Brachidontes sp. and Oysters: Saccostrea cucullata). These species utilise a range of different carbon sources (e.g., mangrove and seagrass detritus and plankton), which dictate the composition of locally available POM), which could then be used to evaluate shifts in consumer diet away from blue carbon within the estuary, to an increasing reliance on marine phytoplankton in offshore areas. The differences in δ¹³C of different organs (i.e., mantle, gill and adductor muscle) of oysters further affirm a greater discrepancy between ‘slow-turnover’ muscle and ‘fast-turnover’ gill and mantle tissue at offshore sites, when compared to inner estuarine sites. We foundthe importance of organic material from a blue carbon origin (and its assimilation by organisms) is proportional to the dominance of these ecosystems in various zones within of the King George River, and moreover that any changes in the structure of subtidal landscapes may affect invertebrate assemblages by modifying the availability and or quality of food resources. The use of stable isotope mixing models also shows that the contribution of POM transitions from mangrove-dominated to seagrass or phytoplankton dominated material along a gradient from inshore to offshore and that carbon inputs may be more predictable inside of estuaries, compared to offshore sites exposed to more variable inputs.