Macrophyte Community Response to Nitrogen Loading and Thermal Stressors in Rapidly Flushed Mesocosm Systems.

A mesocosm system was developed to simulate estuarine conditions characteristic of short water-residence time ecosystems of the Pacific Coast of North America, and used to evaluate the response of multiple macrophyte metrics to gradients of NO3 loading and temperature. Replicated experiments found that few responses could be directly attributed to NO3 loading up to 6 x ambient. Some response metrics exhibited weak relationships with nutrient loading but could not be resolved with available statistical power. While direct nutrient responses were found for some species-specific metrics (e.g. green macroalgal growth and biomass, tissue N%, etc.), many patterns were confounded with temperature. Temperature generally had a larger effect on response metrics than did nutrient load. Experimental macrophyte communities exhibited community shifts consistent with the predicted effects of nutrient loading at 20 °C, but there was no evidence of other eutrophication symptoms (phytoplankton blooms or hypoxia) due to the short system-residence time. The Z. marina Nutrient Pollution Index (NPI) tracked the NO3 gradient at 10 °C, but exhibited no response at 20 °C, which may limit the utility of this metric in areas with marked thermal seasonality. Results suggest that teasing apart the influence of temperature and nutrients on the expression of eutrophication symptoms will require complex multi-stressor experiments and the use of indicators that are sensitive across a broad range of conditions.

Science and management of the introduced seagrass Zostera japonica in North America.

Healthy seagrass is considered a prime indicator of estuarine ecosystem function. On the Pacific coast of North America, at least two congeners of Zostera occur: native Zostera marina, and introduced, Zostera japonica. Z. japonica is considered "invasive" and therefore, ecologically and economically harmful by some, while others consider it benign or perhaps beneficial. Z. japonica does not appear on the Federal or the Oregon invasive species or noxious weed lists. However, the State of California lists it as both an invasive and noxious weed; Washington State recently listed it as a noxious weed. We describe the management dynamics in North America with respect to these congener species and highlight the science and policies behind these decisions. In recent years, management strategies at the state level have ranged from historical protection of Z. japonica as a priority habitat in Washington to eradication in California. Oregon and British Columbia, Canada appear to have no specific policies with regard to Z. japonica. This fractured management approach contradicts efforts to conserve and protect seagrass in other regions of the US and around the world. Science must play a critical role in the assessment of Z. japonica ecology and the immediate and long-term effects of management actions. The information and recommendations provided here can serve as a basis for providing scientific data in order to develop better informed management decisions and aid in defining a uniform management strategy for Z. japonica.

Comparison of metals in eelgrass (Zostera marina L.) and the environment across the North Pacific Ocean: Environmental processes drive source delivery.

Seagrass beds play a critical role in biodiversity maintenance, serving as nursery habitats for fisheries, and aiding in carbon and sediment sequestration in the ecosystem. These habitats receive dissolved and particulate material inputs, like nutrients and heavy metals, affecting both plant health and the ecosystem. Eelgrass (Zostera marina L.), sediments, and water were randomly collected at twenty sites along the temperate North Pacific coasts of Asia and North America to assess heavy metals concentrations (Cr, Cu, Zn, Cd, and Pb). This aimed to understand heavy metal distribution and accumulation patterns in eelgrass tissues, revealing crucial factors influencing metal accumulation. The sampling included various areas, from pristine marine reserves to human-influenced zones, covering industrial, agricultural, and aquaculture regions, enabling a thorough analysis. This study's uniqueness lies in comparing heavy metal distributions in eelgrass tissues with sediments, uncovering unique accumulation patterns. Aboveground eelgrass tissues mainly accumulated Cd, Zn, and Cu, while belowground tissues stored Cr and Pb. Aboveground eelgrass tissues proved reliable in indicating Cd and Pb concentrations in sediments. However, the correlation between Cu, Zn, and Cr in eelgrass tissues and environmental concentrations seemed less direct, requiring further investigation into factors affecting metal accumulation in seagrass. Human activities are probable major contributors to heavy metal presence in Asian marine environments, whereas oceanographic processes serve as primary metal sources in North American Pacific estuaries. Critical discoveries emphasize the necessity for ongoing research on phytotoxic thresholds and in-depth studies on the complex connections between seagrass physiology and environmental metal concentrations. Understanding these dynamics is crucial for evaluating the broader impact of heavy metal pollution on coastal ecosystems and developing effective conservation measures.

Population genetic patterns across the native and invasive range of a widely distributed seagrass: Phylogeographic structure, invasive history and conservation implications.

Aim: The seagrass Zostera japonica is a dramatically declined endemic species in the Northwestern Pacific from the (sub)tropical to temperate areas, however, it is also an introduced species along the Pacific coast of North America from British Columbia to northern California. Understanding the population's genetic patterns can inform the conservation and management of this species. Location: North Pacific. Methods: We used sequences of the nuclear rDNA internal transcribed spacer (ITS) and chloroplast trnK intron maturase (matK), and 24 microsatellite loci to survey 34 native and nonnative populations (>1000 individuals) of Z. japonica throughout the entire biogeographic range. We analysed the phylogeographic relationship, population genetic structure and genetic diversity of all populations and inferred possible origins and invasion pathways of the nonnative ones. Results: All markers revealed a surprising and significant deep divergence between northern and southern populations of Z. japonica in the native region separated by a well-established biogeographical boundary. A secondary contact zone was found along the coasts of South Korea and Japan. Nonnative populations were found to originate from the central Pacific coast of Japan with multiple introductions from at least two different source populations, and secondary spread was likely aided by waterfowl. Main Conclusions: The divergence of the two distinct clades was likely due to the combined effects of historical isolation, adaptation to distinct environments and a contemporary physical barrier created by the Yangtze River, and the warm northward Kuroshio Current led to secondary contact after glacial separation. Existing exchanges among the nonnative populations indicate the potential for persistence and further expansion. This study not only helps to understand the underlying evolutionary potential of a widespread seagrass species following global climate change but also provides valuable insights for conservation and restoration.

First record of Phytomyxid infection of the non-native seagrass Halophila stipulacea in Puerto Rico.

Halophila stipulacea is an invasive seagrass in the Caribbean Sea that also harbors a phytomyxid endoparasite. Phytomyxean parasites are known to cause disease in agricultural crops and are documented to form galls in some seagrass species. Here we make the first report of phytomyxid infection of Halophila stipulacea in the Bahía de Jobos in Salinas, Puerto Rico. We found phytomyxid infected H. stipulacea at 3 of 5 sites examined; expanding the documented range of the Marinomyxa marina phytomyxid infection by almost 400 km from where it was first documented in 2018. Presence of the endoparasite has not impeded H. stipulacea dispersal and continued expansion of H. stipulacea will likely spread both the host seagrass and the endoparasite.

Carbon limitation in response to nutrient loading in an eelgrass mesocosm: influence of water residence time.

Altered primary productivity associated with eutrophication impacts not only ecosystem structure but also the biogeochemical cycling of oxygen and carbon. We conducted laboratory experiments to empirically determine how residence time (1, 3, 10 d) influences eutrophication responses in a simplified Pacific Northwest Zostera marina-green macroalgal community. We expected long-residence time (RT) systems to exhibit eutrophication impairments. Instead, we observed an accumulation of nutrients at all RTs and a shift in the dissolved inorganic carbon speciation away from CO2 (aq) with unexpected consequences for eel grass plant condition, including shoot mortality. Most metrics responded more strongly to temperature treatments than to RT treatments. No dramatic shifts in the relative abundance of Z. marina and green macro algae were detected. Z. marina shoot density proliferated in cool temperatures (12°C) with a modest decline at 20°C. Eelgrass loss was associated with high total scale pH (pHT) and CO2 (aq) concentrations of <10 µmol kg-1 CO2 (aq), but not with high nutrients. Z. marina δ13C values support the hypo thesis that carbon availability was greater at short RT. Further, very low leaf sugar concentrations are consistent with extreme photosynthetic CO2 (aq) limitation. We suggest that the effects of extremely low environ mental car bon concentrations (CO2 (aq)) and increased respiration at warm temperatures (20°C) and other physiological processes can lead to internal carbon limitation and shoot mortality. Eutrophication responses to nutrient loading are more nuanced than just light limitation of eelgrass and require additional research on the interaction of the biogeochemical environment and plant physiology to better understand estuarine ecosystem disruption.