Oysters and eelgrass: potential partners in a high pCO₂ ocean

Abstract

Climate change is affecting the health and physiology of marine organisms and altering species interactions. Ocean acidification (OA) threatens calcifying organisms such as the Pacific oyster, Crassostrea gigas. In contrast, seagrasses, such as the eelgrass Zostera marina, can benefit from the increase in available carbon for photosynthesis found at a lower seawater pH. Seagrasses can remove dissolved inorganic carbon from OA environments, creating local daytime pH refugia. Pacific oysters may improve the health of eelgrass by filtering out pathogens such as Labyrinthula zosterae (LZ), which causes eelgrass wasting disease (EWD). We examined how co-culture of eelgrass ramets and juvenile oysters affected the health and growth of eelgrass and the mass of oysters under different pCO exposures. In Phase I, each species was cultured alone or in co-culture at 12°C across ambient, medium, and high pCO conditions, (656, 1,158 and 1,606 μatm pCO , respectively). Under high pCO , eelgrass grew faster and had less severe EWD (contracted in the field prior to the experiment). Co-culture with oysters also reduced the severity of EWD. While the presence of eelgrass decreased daytime pCO , this reduction was not substantial enough to ameliorate the negative impact of high pCO on oyster mass. In Phase II, eelgrass alone or oysters and eelgrass in co-culture were held at 15°C under ambient and high pCO conditions, (488 and 2,013 μatm pCO , respectively). Half of the replicates were challenged with cultured LZ. Concentrations of defensive compounds in eelgrass (total phenolics and tannins), were altered by LZ exposure and pCO treatments. Greater pathogen loads and increased EWD severity were detected in LZ exposed eelgrass ramets; EWD severity was reduced at high relative to low pCO . Oyster presence did not influence pathogen load or EWD severity; high LZ concentrations in experimental treatments may have masked the effect of this treatment. Collectively, these results indicate that, when exposed to natural concentrations of LZ under high pCO conditions, eelgrass can benefit from co-culture with oysters. Further experimentation is necessary to quantify how oysters may benefit from co-culture with eelgrass, examine these interactions in the field and quantify context-dependency.

A halo of reduced dinoflagellate abundances in and around eelgrass beds

“…However, our work demonstrates that Z. marina habitat may have a protective effect against harmful dinoflagellates within these buffer zones, reducing the potential for shellfish to accumulate HAB toxins from the surrounding waters. Likewise, filter feeders can mitigate microbial disease in adjacent environments, and Magallana (Crassostrea) gigas, in particular, has recently been shown to lessen the effects of eelgrass wasting disease on Z. marina (Groner et al, 2018). Eelgrass and oysters may thus provide critical support to one another in changing marine ecosystems worldwide.…”

Peer Review #1 of "A halo of reduced dinoflagellate abundances in and around eelgrass beds (v0.1)"

“…However, our work demonstrates that Z. marina habitat may have a protective effect against harmful dinoflagellates within these buffer zones, reducing the potential for shellfish to accumulate HAB toxins from the surrounding waters. Likewise, filter feeders can mitigate microbial disease in adjacent environments, and Magallana (Crassostrea) gigas, in particular, has recently been shown to lessen the effects of eelgrass wasting disease (EWD) on Z. marina (Groner et al, 2018). Eelgrass and oysters may thus provide critical support to one another in changing marine ecosystems worldwide.…”

Sand Supplementation to Eutrophic Sediments Improves the Growth and Survival of Seagrass Thalassia Hemprichii: Implication for Seagrass Restoration and Management

“…Similarly, a decrease in the total phenolic concentrations in Z. marina was also found when grown in high pCO 2 waters (Arnold et al 2014). This might attributed to a reallocation of carbon to other pathways (Groner et al 2018). Phenolic compounds are regarded as storage compounds for carbohydrates, which are only produced when the plants cannot convert the carbohydrates into growth (Cannac et al 2006;Waterman et al 1984).…”