Sandy Wyllie-Echeverria’s research while affiliated with Trinity Washington University and other places

Seed dispersal and burial are important processes in the expansion and restoration of Zostera marina (eelgrass) meadows. The depth at which seeds are buried is a significant factor contributing to the success of seedling survival. If seeds are buried below 6 cm, it is unlikely that viable seedlings will develop, while shallow burials protect seeds from predation on the sediment surface. Burrowing behavior of infaunal organisms is one factor that contributes to seed burial with a potentially positive or negative influence on seedling survival. In this study, we designed a laboratory experiment to determine the relationship between lugworm (Abarenicola pacifica) density and eelgrass seed burial. Three treatments (no worms, low-density, and high-density of worms) with three replicates each were used to quantify seed burial. Each replicate was seeded with a blend of seed mimics and real seeds. After 25 days, three cores were extracted from each replicate and the depths of the seeds recorded. In the high-density worm treatments, most of the seeds and mimics were buried below the 6 cm critical depth, while in the low-density treatments most seeds were found shallower than 3 cm. These results agree with previous work on the burying capacity of infaunal organisms, and strongly suggest that the presence and activity of infauna can determine the success of Z. marina meadow expansion and restoration.

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 pCO2 exposures. In Phase I, each species was cultured alone or in co‐culture at 12°C across ambient, medium, and high pCO2 conditions, (656, 1158 and1606 μatm pCO2, respectively). Under high pCO2, 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 pCO2, this reduction was not substantial enough to ameliorate the negative impact of high pCO2 on oyster mass. In Phase II, eelgrass alone or oysters and eelgrass in co‐culture were held at 15°C under ambient and high pCO2 conditions, (488 and 2013 μatm pCO2, 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 pCO2 treatments. Greater pathogen loads and increased EWD severity were detected in LZ exposed eelgrass ramets; EWD severity was reduced at high relative to low pCO2. 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 pCO2 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. This article is protected by copyright. All rights reserved.

Infectious marine diseases can decimate populations and are increasing among some taxa due to global change and our increasing reliance on marine environments. Marine diseases become emergencies when significant ecological, economic or social impacts occur. We can prepare for and manage these emergencies through improved surveillance, and the development and iterative refinement of approaches to mitigate disease and its impacts. Improving surveillance requires fast, accurate diagnoses, forecasting disease risk and real-time monitoring of disease-promoting environmental conditions. Diversifying impact mitigation involves increasing host resilience to disease, reducing pathogen abundance and managing environmental factors that facilitate disease. Disease surveillance and mitigation can be adaptive if informed by research advances and catalysed by communication among observers, researchers and decision-makers using information-sharing platforms. Recent increases in the awareness of the threats posed by marine diseases may lead to policy frameworks that facilitate the responses and management that marine disease emergencies require.

Seagrasses are ecosystem engineers of essential marine habitat. Their populations are rapidly declining worldwide. One potential cause of seagrass population declines is wasting disease, which is caused by opportunistic pathogens in the genus Labyrinthula. While infection with these pathogens is common in seagrasses, theory suggests that disease only occurs when environmental stressors cause immunosuppression of the host. Recent evidence suggests that host factors may also contribute to disease caused by opportunistic pathogens. In order to quantify patterns of disease, identify risk factors, and investigate responses to infection, we surveyed shoot density, shoot length, epiphyte load, production of plant defenses (phenols), and wasting disease prevalence in eelgrass Zostera marina across 11 sites in the central Salish Sea (Washington state, USA), a region where both wasting disease and eelgrass declines have been documented. Wasting disease was diagnosed by the presence of necrotic lesions, and Labyrinthula cells were identified with histology. Disease prevalence among sites varied from 6 to 79%. The probability of a shoot being diseased was higher in longer shoots, in patches of higher shoot density, and in shoots with higher levels of biofouling from epiphytes. Phenolic concentration was higher in diseased leaves. We hypothesize that this results from the induction of phenols during infection. Additional research is needed to evaluate whether phenols are an adaptive defense against Labyrinthula infection. The high site-level variation in disease prevalence emphasizes the potential for wasting disease to be causing some of the observed decline in eelgrass beds.

Indigenous Peoples of the Northwest Coast Cultural Area of North America managed plant populations of many of the 100–200 species used for food and other purposes, through cultivation and selective harvesting. Eelgrass (Zostera marina, L.; Zosteraceae) was one of these species. The Kwakwaka’wakw harvested its sweet rhizomes in the springtime. Directed by the traditional knowledge of Clan Chief Adam Dick, whose hereditary name is Kwaxsistalla, of the Tsawataineuk First Nation of Kingcome Inlet (one of the many communities of Kwakwaka’wakw, or Kwak’wala speaking Indigenous peoples of the West Coast of British Columbia), we investigated the protocols of traditional harvesting and tending on typical Z. marina populations in the Discovery Islands area. We interviewed 18 Kwakwaka’wakw knowledge holders and conducted six harvesting demonstrations to determine traditional harvesting protocols. Based on traditional protocols and traditional Z. marina management inferences, we developed an in situ, subtidal, Complete Randomized Block Design removal experiment in an eelgrass meadow on Quadra Island, BC. In a first exploratory study, we removed Z. marina shoots at three different intensities using SCUBA in defined quadrats in the springtime. Shoots were counted at the end of summer to examine shoot recruitment post treatment over the growing season. Our preliminary results showed no significant difference between treatments. However, with more replicates, we might have strengthened the tendency of more shoots in the harvested quadrats. Here our main intention is to describe our unique study of a marine plant resource harvested in traditional times by Kwakwaka’wakw peoples and to outline a new experimental methodology to examine ecological rationale behind traditional knowledge. We hope to stimulate new and important avenues of research on this topic.

Marine diseases can decimate populations and can have substantial ecological, economic, and social impacts. Recent disease outbreaks in marine mammals, shellfish, sponges, seagrasses, crustaceans, corals, and fishes demonstrate the potential for catastrophic effects, including reduced biodiversity,

Environmental heterogeneity can promote coexistence, and is therefore predicted to increase invasibility of communities, but decrease invasion impacts. We examined the role of local-scale environmental heterogeneity in promoting the coexistence of the invasive seagrass, Z. japonica, and its native congener Z. marina in a patch mosaic. In its introduced range, Z. japonica often co-occurs with the native Z. marina in a patch mosaic associated with intertidal microtopography (centimeter to decimeter relief over meter to decameter distances). Here, Z. marina inhabits depressions that retain water during low tides, and Z. japonica inhabits well-drained mounds. Transplant experiments revealed that Z. marina suppressed Z. japonica shoot densities, more so in pools than on mounds. Z. marina suppressed Z. japonica above-ground and below-ground biomass by 47% and 19% respectively, on mounds, and by over 60% in pools. Z. marina shoot densities and biomass were 40% and 95% lower, respectively, on mounds, regardless of Z. japonica presence. Topographic context remained the most influential predictor of Z. marina responses, even when we transplanted Z. marina into higher densities of Z. japonica. These results indicate that the native Z. marina is physiologically restricted from mounds and competitively excludes the introduced Z. japonica from pools. We provide empirical evidence of local-scale heterogeneity promoting coexistence of an invasive and a native macrophyte, supporting the hypothesis that environmental heterogeneity increases invasibility and decreases invasion impacts. Furthermore, active control of the invader in mixed beds is unlikely to benefit the native.

Eelgrass (Zostera marina) forms the foundation of an important shallow coastal community in protected estuaries and bays. Widespread population declines have stimulated restoration efforts, but these have often overlooked the importance of maintaining the evolutionary potential of restored populations by minimizing the reduction in genetic diversity that typically accompanies restoration. In an experiment simulating a small-scale restoration, we tested the effectiveness of a buoy-deployed seeding technique to maintain genetic diversity comparable to the seed source populations. Seeds from three extant source populations in San Francisco Bay were introduced into eighteen flow-through baywater mesocosms. Following seedling establishment, we used seven polymorphic microsatellite loci to compare genetic diversity indices from 128 shoots to those found in the source populations. Importantly, allelic richness and expected heterozygosity were not significantly reduced in the mesocosms, which also preserved the strong population differentiation present among source populations. However, the inbreeding coefficient F IS was elevated in two of the three sets of mesocosms when they were grouped according to their source population. This is probably a Wahlund effect from confining all half-siblings within each spathe to a single mesocosm, elevating F IS when the mesocosms were considered together. The conservation of most alleles and preservation of expected heterozygosity suggests that this seeding technique is an improvement over whole-shoot transplantation in the conservation of genetic diversity in eelgrass restoration efforts.