Pacific oysters are a sink and a potential source of the eelgrass pathogen, Labyrinthula zosterae

Abstract

Oyster aquaculture and seagrasses often co-occur and are each vital to the ecological and economic value of coastal ecosystems. Global declines in seagrasses, including Zostera marina, have recently been observed in association with multiple factors, including infection with diseases such as seagrass wasting disease (SWD), caused by the protist Labyrinthula zosterae. Protection of seagrasses has led to restrictions on oyster aquaculture due to perceived negative impacts on seagrass beds; however, positive impacts may also occur. An important aquaculture species, the Pacific oyster Crassostrea gigas, can filter L. zosterae from the water, potentially reducing pathogen transmission, although oysters may vector infection if they accumulate and release live L. zosterae into the water. We investigated whether oyster presence decreases lesion severity and infection intensity in eelgrass, or acts as a vector of L. zosterae, via laboratory and field experiments. In the laboratory, oysters and eelgrass were exposed to L. zosterae for 24 h and kept at 11°C or 18°C for 13 d. In the field, eelgrass ramets were deployed with and without oysters for 28 d adjacent to eelgrass known to have SWD. In the laboratory experiment, the presence of oysters significantly decreased lesion severity and infection intensity, but oysters previously exposed to L. zosterae did transmit the pathogen to naïve eelgrass. Temperature did not affect oyster ability to mitigate SWD; however, increased temperature significantly increased lesion severity. Oysters had no effect on SWD in the field. Further research is needed regarding the potential for oysters to vector L. zosterae and to quantify when oysters reduce SWD in the field.

Manipulation of the seagrass‐associated microbiome reduces disease severity

“…Lz‐inoculated leaves ( n = 57; bleached and untreated) were placed in individual WhirlPaks with 99 mL FSW and 1 mL of Lz inoculum. The inoculum was made with Lz strain 4JB‐MVA, which was originally isolated from diseased eelgrass from Fourth of July Beach, San Juan Island, WA (Agnew et al, 2022); the final inoculum had a cell concentration of 1.2 × 10 6 cells/mL. The inoculum was pipetted directly into each WhirlPak, rather than nicking the surface of eelgrass leaves and pipetting it directly onto eelgrass tissue, to more accurately mimic natural infection mechanisms.…”

Influence of seagrass on juvenile Pacific oyster growth in two US west coast estuaries with different environmental gradients

“…Both seagrass and oyster habitats have other attributes and provide numerous ecosystem services at the seascape scale, including carbon sequestration, sediment/shoreline stabilization, and habitat provision, that will also change under future 2011, Plummer et al 2013, Lemasson et al 2017, Unsworth et al 2018, Ricart et al 2020, Barrett et al 2022. Finally, co-culture has been shown to benefit seagrass as well (Groner et al 2021, Agnew et al 2022, and this interaction should continue to be evaluated. initial review of water quality data.…”

Marine herbivores facilitate transmission of a seagrass pathogen

“…We filled control Whirl-Paks with 100 mL filtered, UV-sterilized seawater and treatment Whirl-Paks with 99 mL filtered, UV-sterilized seawater and 1 mL concentrated Lz inoculum (3.51 x 10 6 cells/mL for isopods, 2.86 x 10 6 cells/mL for snails), following established protocols for controlled Lz inoculations (Dawkins et al, 2018;Groner et al, 2018). We made the inoculum using a virulent strain of Lz (strain 4JB), which was originally isolated from diseased eelgrass from the same meadow as the snails and asymptomatic eelgrass (Agnew et al, 2022). Following inoculations, we gently agitated all Whirl-Paks to distributed the inoculum and seawater.…”