Non-indigenous f ouling organisms settling onto artificial and natural hard substrata in estuaries can negatively impact native species via space competition, predation, or other mechanisms. The effects of Amathia verticillatum, and other fouling organisms on the recruitment of Ostrea lurida, were studied to determine whether their presence, biomass, and abundance affect oyster recruitment.
Terracotta tiles, proxies for available hard substrata, were deployed in Newport Bay, California at tidal elevations between -0.4 and +0.1 feet MLLW, April-October 2020, during the oyster’s spawning and recruitment season. F ive treatment groups (n=5 replicates per tile) were established to examine the effects of A. verticillata and other fouling organisms on recruitment of O. lurida : unmanipulated controls, A . verticillat a removals, A . verticillat a plus other fouler removals, other fouler removals with A . verticillatum additions, and other fouler removals with 2X A . verticillat a additions. The treatment groups were maintained by adding or removing A . verticillat a foulers as appropriate per treatment; all removals were quantified via volume displacement as a proxy for biomass. During tile retrieval, the volume displacement and wet weight of A. verticillata and other foulers were recorded. Oysters recruiting to the tiles were measured for length and width, identified, and counted. Percent cover of all species recruiting to the tiles using point contact techniques was recorded.
Results suggest that A. verticillata is facilitating O. lurida recruitment as A. verticillata removals had lower oyster recruitment . Some non-indigenous fouling organisms may not be as problematic as predicted when restoring native species in estuarine communities.