Safe in My Garden: Reduction of Mainstream Flow and Turbulence by Macroalgal Assemblages and Implications for Refugia of Calcifying Organisms From Ocean Acidification

Macroalgae, with their various morphologies, are ubiquitous throughout the world’s oceans and provide ecosystem services to a multitude of organisms. Water motion is a fundamental physical parameter controlling the mass transfer of dissolved carbon and nutrients to and from the macroalgal surface, but measurements of flow speed and turbulence within and above macroalgal canopies are lacking. This information is becoming increasingly important as macroalgal canopies may act as refugia for calcifying organisms from ocean acidification (OA); and the extent to which they act as refugia is driven by water motion. Here we report on a field campaign to assess the flow speed and turbulence within and above natural macroalgal canopies at two depths (3 and 6 m) and two sites (Ninepin Point and Tinderbox) in Tasmania, Australia in relation to the canopy height and % cover of functional forms. Filamentous groups made up the greatest proportion (75%) at both sites and depth while foliose groups were more prevalent at 3 than at 6 m. Irrespective of background flows, depth or site, flow speeds within the canopies were <0.03 m s–1 – a ∼90% reduction in flow speeds compared to above the canopy. Turbulent kinetic energy (TKE) within the canopies was up to two orders of magnitude lower (<0.008 m2 s–2) than above the canopies, with higher levels of TKE within the canopy at 3 compared to 6 m. The significant damping effect of flow and turbulence by macroalgae highlights the potential of these ecosystems to provide a refugia for vulnerable calcifying species to OA.

Coexistence of the native mussel, Mytilus edulis, and the invasive Pacific oyster, Crassostrea (Magallana) gigas, does not affect their growth or mortality, but reduces condition of both species

Ecological impacts caused by invasive alien species can be severe but may vary depending upon environmental conditions. Many European populations of the native mussel, Mytilus edulis, have been invaded by the Pacific oyster, Crassostrea (Magallana) gigas. Although widespread invasions have occurred, interactions between M. edulis and C. gigas have largely been investigated with regards to competition for space and food as well as effects on species assemblages. Experimental investigation of competitive interactions on physiological responses of the two species requires further exploration. To this end, we used a 12-month field manipulation experiment to examine growth rates, mortality and condition indices of the two species occurring in monospecific and heterospecific groups. Growth rates and mortality of both species were similar in monospecific and heterospecific groups, whereas condition indices were significantly reduced for both species in heterospecific groups. Growth rates and condition indices also differed amongst experimental sites, potentially due to differing water motion. Shell weight-length relationships did not explain the observed differences in condition for either species. We show that coexistence between the two species may occur but could be detrimental for both species. We also provide a preliminary viewpoint that water motion can mediate competitive interactions between these species.

Multiple Metrics of Temperature, Light, and Water Motion Drive Gradients in Eelgrass Productivity and Resilience

Characterizing the response of ecosystems to global climate change requires that multiple aspects of environmental change be considered simultaneously, however, it can be difficult to describe the relative importance of environmental metrics given their collinearity. Here, we present a novel framework for disentangling the complex ecological effects of environmental variability by documenting the emergent properties of eelgrass (Zostera marina) ecosystems across ∼225 km of the Atlantic Coast of Nova Scotia, Canada, representing gradients in temperature, light, sediment properties, and water motion, and evaluate the relative importance of different metrics characterizing these environmental conditions (e.g., means, extremes, variability on different time scales) for eelgrass bioindicators using lasso regression and commonality analysis. We found that eelgrass beds in areas that were warmer, shallower, and had low water motion had lower productivity and resilience relative to beds in deeper, cooler areas that were well flushed, and that higher temperatures lowered eelgrass tolerance to low-light conditions. There was significant variation in the importance of various metrics of temperature, light, and water motion across biological responses, demonstrating that different aspects of environmental change uniquely impact the cellular, physiological, and ecological processes underlying eelgrass productivity and resilience, and contribute synergistically to the observed ecosystem response. In particular, we identified the magnitude of temperature variability over daily and tidal cycles as an important determinant of eelgrass productivity. These results indicate that ecosystem responses are not fully resolved by analyses that only consider changes in mean conditions, and that the removal of collinear variables prior to analyses relating environmental metrics to biological change reduces the potential to detect important environmental effects. The framework we present can help to identify the conditions that promote high ecosystem function and resilience, which is necessary to inform nearshore conservation and management practices under global climate change.

Single Encoding Diffusion MRI: A Probe to Brain Anisotropy

This chapter covers anisotropy in the context of probing microstructure of the human brain using single encoded diffusion MRI. We will start by illustrating how diffusion MRI is a perfectly adapted technique to measure anisotropy in the human brain using water motion, followed by a biological presentation of human brain. The non-invasive imaging technique based on water motions known as diffusion MRI will be further presented, along with the difficulties that come with it. Within this context, we will first review and discuss methods based on signal representation that enable us to get an insight into microstructure anisotropy. We will then outline methods based on modeling, which are state-of-the-art methods to get parameter estimations of the human brain tissue.

Electrical resistivity imaging for monitoring soil water motion patterns under different drip irrigation scenarios

The use of hydrogeophysical methods provides insights for supporting optimal irrigation design and management. In the present study, the electrical resistivity imaging (ERI) was applied for monitoring the soil water motion patterns resulting from the adoption of water deficit scenarios in a micro-irrigated orange orchard (Eastern Sicily, Italy). The relationship of ERI with independent ancillary data of soil water content (SWC), plant transpiration (T) and in situ measurements of hydraulic conductivity at saturation (Ks, i.e., using the falling head method, FH) was evaluated. The soil water motion patterns and the maximum wet depths in the soil profile identified by ERI were quite dependent on SWC (R2 = 0.79 and 0.82, respectively). Moreover, ERI was able to detect T in the severe deficit irrigation treatment (electrical resistivity increases of about 20%), whereas this phenomenon was masked at higher SWC conditions. Ks rates derived from ERI and FH approaches revealed different patterns and magnitudes among the irrigation treatments, as consequence of their different measurement scales and the methodological specificity. Finally, ERI has been proved suitable for identifying the soil wetting/drying patterns and the geometrical characteristics of wet bulbs, which represent some of the most influential variables for the optimal design and management of micro-irrigation systems.