Oyster aquaculture impacts Zostera marina epibiont community composition in Akkeshi-ko estuary, Japan

Abstract

Coastal fisheries are in decline worldwide, and aquaculture has become an increasingly popular way to meet seafood demand. While finfish aquaculture can have substantial adverse effects on coastal ecosystems due mostly to necessary feed inputs, bivalves graze on natural phytoplankton and are often considered for their positive ecosystem services. We conducted two independent studies to investigate the effects of long-line Crassostrea gigas oyster aquaculture on Zostera marina seagrass beds and associated epibiont communities in Akkeshi-ko estuary, Japan. Results from both studies yielded no evidence of an effect of oyster aquaculture on the morphology, density, or biomass of Z. marina, but significant differences were apparent in the epibiont community. Reference seagrass beds located away from aquaculture had higher seagrass epiphyte loads and higher abundances of amphipods. Conversely, seagrass beds below aquaculture lines had higher sessile polychaete biomass and higher isopod abundances. Our results suggest that the presence of oyster aquaculture may have indirect effects on seagrass by changing epibiont community composition and relative abundances of species. One proposed mechanism is that cultured oysters feed on epiphytic diatoms and epiphyte propagules before they can settle on the seagrass, which reduces epiphyte loads and influences subsequent faunal settlement. If carefully implemented and monitored, long-line oyster aquaculture may be a sustainable option to consider as bivalve aquaculture expands to meet global seafood demand, but further work is needed to fully assess and generalize the community-level effects on seagrass epibionts.

Monitoring oyster culture rafts and seagrass meadows in Nagatsura-ura Lagoon, Sanriku Coast, Japan before and after the 2011 tsunami by remote sensing: their recoveries implying the sustainable development of coastal waters

“…In Akkeshi Lake, Hokkaido, Smith et al (2018) found that the cultured oysters fed on epiphytic diatoms and epiphyte propagules before they settled on seagrass, which reduced epiphyte loads and influenced subsequent faunal settlements. As a result, the presence of cultured oysters might indirectly affect seagrass by changing the composition and relative abundance of species such as sessile polychaetes, gastropods, and amphipods.…”

Restoration potential of Asian oysters on heavily developed coastlines

“…There are 30 recorded extant Osteridae species in Asia, including 11 species of Crassostrea . Although most known natural oyster populations are reported to be over‐harvested and have since been maintained by aquaculture in Asia, Crassostrea species have been reported to form natural beds and reefs along Asian intertidal shorelines, including northern China (Quan et al 2012), Thailand (Brohmanonda et al 1988), and Japan (Smith et al 2018). Given their wide range of distribution and high diversity within Asia, they have the potential to provide ecosystem services that are valuable to the health and sustainability of coastal waters.…”

The overlooked role of taphonomy in ecology: post‐mortem processes can outweigh recruitment effects on community functions

“…The dynamics shown relate only to such communities, but these can be vitally important for understanding general ecological theory (Connell ). Particularly when small calcareous domiciles are counted as components of larger species assemblages, domicile abundances are commonly reported without information on whether any were dead and what the proportion may be (Clark et al , McGowan and Iyengar , Krzemińska and Kuklinski , Smith et al , Traiger and Konar , among other recent examples). The diagram shows the ecological processes (R = recruitment, M = mortality, T = taphonomic degradation) that may be considered to cause a hypothetical distributional pattern of differing density of domicile structures, depending on whether information is known about the status of occupancy.…”