This dataset includes body characteristic measurements of sand dollar larvae (Dendraster excentricus) reared in different pCO2 conditions as part of a laboratory experiment to investigate the behavioral effects of ocean acidification on this species in July 2017.

This dataset reports water quality data and Olympia oyster abundance counts from depthspecific sampling collected by boat in Fidalgo Bay, WA, during July 2017.

This dataset is a time series of horizontal and vertical current profiles collected from an upward-facing acoustic Doppler current profiler in Fidalgo Bay, WA during July 2017. These data were published in the following Masters Thesis: McIntyre, Brooke A., "Vertical Distribution of Olympia oyster (Ostrea lurida) larvae in Fidalgo Bay, WA" (2018). WWU Graduate School Collection. 694. https://cedar.wwu.edu/wwuet/694 For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/752803

This datasets includes pH data measures from larval rearing jars as part of a laboratory experiment to investigate the behavioral effects of ocean acidification on sand dollar larvae (Dendraster excentricus) in July 2017. For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/752999

The relationship between seagrasses and pore-water hydrogen sulfide in the sediment is complex due to the opposing effects of the seagrass root system, which can reduce sulfide concentration by promoting its oxidation to sulfate, and the burial of organic matter from the plant itself, which can increase sulfide concentration by stimulating anaerobic sulfate reduction. Here, field samples of pore-water sulfide were collected in areas with and without Zostera marina shoots using Diffusive Gradients in Thin-Films (DGTs) to obtain two-dimensional visualizations of sulfide concentrations within the sediment in relation to location of eelgrass detritus and the rhizosphere. To decouple the effects of leaf detritus and the eelgrass rhizosphere on sulfide, manipulative laboratory studies were conducted over 4 weeks using 10 aquaria with or without eelgrass and different quantities of eelgrass detritus planted at 4 cm and 11 cm depths. Spatial distribution of pore-water sulfide was again measured via DGT. We found high spatial variation in pore-water sulfide concentration depending on the location analyzed relative to the rhizosphere or detritus. In the field study, pore-water sulfide concentration was greater in samples with eelgrass present, and the presence of leaf detritus accounted for higher than average sulfide concentrations in the sediment. In the laboratory experiment, sulfide concentrations localized around the leaf detritus increased with higher mass of added detritus, and sediment within the rhizosphere exhibited reduced sulfide concentrations. These results suggest that on the large scale the presence of eelgrass increases sulfide concentration, but on the smaller scale the pattern varies, with higher concentrations near buried detritus and lower concentrations near root tips.

In the Salish Sea, the magnitude of ocean acidification varies greatly due to CO2 enrichment from upwelling and CO2 uptake by primary producers. Eelgrass meadows have been identified as potential mitigators of ocean acidification because eelgrass takes up dissolved CO 2 and bicarbonate through photosynthesis, is carbon limited, and can increase its photosynthetic rate under elevated pCO 2 conditions. However, eelgrass morphology and density varies from site to site in the Salish Sea, and photosynthesis varies diurnally. In this study, we experimentally investigated the effect of eelgrass shoot density and irradiance on eelgrass’ ability to alter carbonate chemistry under conditions of moderate and high pCO 2 . We found no difference in carbon drawdown rate between pCO 2 treatments. However, increasing shoot density led to greater increases in pH, but only up to a point. Above a threshold shoot density, the increase in pH was not as high, possibly due to self-shading. In the absence of light, eelgrass density decreased pH, most likely due to cellular respiration. These results imply that eelgrass may exacerbate ocean acidification if light is limiting. We propose further study of eelgrass density under a gradation of irradiance levels. By quantifying the changes in carbonate chemistry due to varying eelgrass densities and varying irradiances, our research will help identify characteristics of eelgrass habitats that could provide refugia for marine organisms from ocean acidification.

By changing ecosystem processes and altering the physical landscape, invasive ecosystem engineers can have substantial impacts on ecosystem functions and human economies and may facilitate other non-native species. Eradication programs in terrestrial and aquatic systems aim to reverse the impacts of invasive species and return the system to its pre-invasion conditions. Despite an extensive focus on the impacts of both native and non-native ecosystem engineers, the consequences of removing invasive ecosystem engineers, particularly in coastal ecosystems, are largely unknown. In this study, we quantified changes in a benthic community following the eradication of the invasive ecosystem engineer, hybrid cordgrass Spartina, in San Francisco Bay, California. We used field experimental manipulations to test for persistent effects of both aboveground and belowground structural modifications of the invasive plant on the benthic community. We found significant effects of the invasive plant more than four years following eradication. Experimental modification of the above- vs. belowground structure of this ecosystem engineer revealed taxonomic specific effects resulting in hysteresis in the recovery of the benthic food webs. We found that these "legacy effects" resulted from two specific mechanisms: (1) delayed breakdown of belowground structures (stems, roots) and (2) persistence of other invasive species whose invasion was facilitated by the ecosystem engineer. Both of these mechanisms are likely to occur in similar systems where belowground structures breakdown more slowly or where other associated long-lived invaders persist. Our work is among the first to quantify the slow rate of change in food web and community processes and the persistent legacy effects of an invasive ecosystem engineer in a coastal ecosystem. We suggest that this delayed transition to pre-invasion conditions could resemble an alternate state that would be misidentified without a sufficient monitoring interval or recovery duration, with consequences for future management and restoration activity planning.

Photosynthesis and respiration are vital biological processes that shape the diurnal variability of carbonate chemistry in nearshore waters, presumably ameliorating (daytime) or exacerbating (nighttime) short-term acidification events, which are expected to increase in severity with ocean acidification (OA). Biogenic habitats such as seagrass beds have the capacity to reduce CO2 concentration and potentially provide refugia from OA. Further, some seagrasses have been shown to increase their photosynthetic rate in response to enriched total CO2 (TCO2). Therefore, the ability of seagrass to mitigate OA may increase as concentrations of TCO2 increase. In this study, we exposed native Zostera marina and non-native Zostera japonica seagrasses from Padilla Bay, WA (USA) to various levels of irradiance and TCO2. Our results indicate that the average maximum net photosynthetic rate (P-max) for Z japonica as a function of irradiance and TCO2 was 3x greater than Z. marina when standardized to chlorophyll (360 +/- 33 pmol TCO2 mg chl(-1) h(-1) and 113 +/- 10 mu mol TCO2 mg chl(-1) h(-1), respectively). Additionally, Z. japonica increased its P-max similar to 50% when TCO2 increased from similar to 1,770 to 2,051 mu mol TCO2 kg(-1). In contrast, Z. marina did not display an increase in P-max with higher TCO2, possibly due to the variance of photosynthetic rates at saturating irradiance within TCO2 treatments (coefficient of variation: 30-60%) relative to the range of TCO2 tested. Our results suggest that Z japonica can affect the OA mitigation potential of seagrass beds, and its contribution may increase relative to Z. marina as oceanic TCO2 rises. Further, we extended our empirical results to incorporate various biomass to water volume ratios in order to conceptualize how these additional attributes affect changes in carbonate chemistry. Estimates show that the change in TCO2 via photosynthetic carbon uptake as modeled in this study can produce positive diurnal changes in pH and aragonite saturation state that are on the same order of magnitude as those estimated for whole seagrass systems. Based on our results, we predict that seagrasses Z. marina and Z. japonica both have the potential to produce short-term changes in carbonate chemistry, thus offsetting anthropogenic acidification when irradiance is saturating.

By definition, ecosystem engineers can have large effects on resource flows and habitat structure, with impacts on other organisms ranging from facilitative to inhibitory. The stress gradient hypothesis posits that facilitative interactions predominate in conditions of environmental stress and switch to competitive interactions in benign environments. We conducted an empirical test of the stress gradient hypothesis for a marine ecosystem engineer, eelgrass Zostera marina L., across a hydrodynamic gradient. Eelgrass meadows perform important functions in coastal ecosystems and have experienced contemporary declines worldwide with variable recruitment success. In this study, we first determine whether eelgrass modified the local hydrodynamic conditions and then how the presence of an adult eelgrass canopy affected the plants' own relative seedling success over the hydrodynamic gradient. Eelgrass reduced water motion significantly, which provided a positive feedback on survival and growth for conspecific seedlings, but only at the stressful end of the hydrodynamic gradient. By contrast, adult conspecifics negatively impacted seedling recruitment and growth in calmer environments, presumably due to intraspecific competition. Thus, eelgrass ecosystem engineering does not always facilitate the plant's own performance, and our results support the stress gradient hypothesis as an explanation for this context dependence. The balance of these complex interactions may provide a mechanism for delayed or failed recovery of eelgrass in habitats exposed to high hydrodynamic exposure.

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.

Because photosynthesis requires CO 2 , carbon limitation in aquatic environments could restrict primary production and provide signals in tissue chemistry. We took advantage of spatial variability of aqueous [CO 2 ] in estuaries to examine within-estuary variation in biometrics of intertidal eelgrass ( Zostera marina ) during peak summer production. As expected from the sensitivity of carbonate equilibria to pH, aqueous [CO 2 ] increased along an ocean-to-river gradient in Willapa Bay, WA, USA. The scale of pH variability also changed, reflecting weather-driven upwelling near the ocean, tidal advection near rivers, and reduced diel fluctuation up-estuary. Z. marina studied at eight sites in the bay integrated across these different temporal fluctuations in water chemistry to exhibit increased tissue carbon and depleted δ 13 C up-estuary. However, seagrass production did not change as expected from aqueous [CO 2 ]. Instead, small standing biomass occurred at sites with organic-rich sediments or high wave energy, investment in branching showed trends along the estuarine gradient that changed seasonally, and specific growth rates based on leaf extension did not shift with the estuarine gradient or with standing biomass. These results reinforce that estuarine seagrasses are likely to experience modified mean pH and variability due not only to ocean acidification in the strict sense (anthropogenic CO 2 absorbed from the atmosphere) but also from land use, upwelling, and feedbacks from biological processes. However, responses via productivity may be less evident than in tissue chemistry.

Seagrasses are a critical marine habitat and are in decline worldwide. Previous studies have demonstrated that factors such as sediment conditions, resource availability, and desiccation can influence life history transitions and morphology in intertidal eelgrass (Zostera marina L.) and therefore potential for recovery after a disturbance. We combined these factors in an exploratory path model linking environmental conditions to eelgrass vegetative (shoot size and density) and reproductive traits (branching, flowering, seedling recruitment). In this construction, significant path coefficients reveal factors influencing recovery potential. To test the path model, we collected abiotic and eelgrass data at 17 sites in the southern Salish Sea (Washington, USA) and assessed model fit with structural equation modeling. Significant path coefficients linked sediment organic content to shoot size and seedling recruitment, tidal amplitude to reduced flowering, and shoot size and density were inversely correlated. We found no significant links between any morphological or life history trait and nutrient availability, possibly reflecting consistently high nutrients across sites. Variable rates of asexual reproduction and a trade-off between shoot size and density may reflect light limitation in eelgrass' intertidal range, where light is not expected to be strongly limiting. Overall, structural equation modeling identified organic-rich sediments as relatively more important than desiccation and nutrient conditions for resilience potential of intertidal eelgrass populations in this region. Life history and morphological traits provide eelgrass with recovery mechanisms from disturbance where sediments are muddy, which has implications for both conservation and restoration.

Humans are the dominant ecological and evolutionary force on the planet today, transforming habitats, polluting environments, changing climates, introducing new species, and causing other species to decline in number or go extinct. These worrying anthropogenic impacts, collectively termed global change, are often viewed as a confounding factor to minimize in basic studies and a problem to resolve or quantify in applied studies. However, these ‘accidental experiments’ also represent opportunities to gain fundamental insight into ecological and evolutionary processes, especially when they result in perturbations that are large or long in duration and difficult or unethical to impose experimentally. We demonstrate this by describing important fundamental insights already gained from studies which utilize global change factors as accidental experiments. In doing so, we highlight why accidental experiments are sometimes more likely to yield insights than traditional approaches. Next, we argue that emerging environmental problems can provide even more opportunities for scientific discovery in the future, and provide both examples and guidelines for moving forward. We recommend 1) a greater flow of information between basic and applied subfields of ecology and evolution to identify emerging opportunities; 2) considering the advantages of the ‘accidental experiment’ approach relative to more traditional approaches; and 3) planning for the challenges inherent to uncontrolled accidental experiments. We emphasize that we do not view the accidental experiments provided by global change as replacements for scientific studies quantifying the magnitude of anthropogenic impacts or outlining strategies for mitigating impacts. Instead, we believe that accidental experiments are uniquely situated to provide insights into evolutionary and ecological processes that ultimately allow us to better predict and manage change on our human‐dominated planet.SynthesisHumans have an increasingly large impact on the planet. In response, ecologists and evolutionary biologists are dedicating increasing scientific attention to global change, largely with studies documenting biological effects and testing strategies to avoid or reverse negative impacts. In this article, we analyze global change from a different perspective, and suggest that human impacts on the environment also serve as valuable ‘accidental experiments’ that can provide fundamental scientific insight. We highlight and synthesize examples of studies taking this approach, and give guidance for gaining future insights from these unfortunate ‘accidental experiments’.