The accuracy and precision of ion sensitive field effect transistor (ISFET) pH sensors have been well documented, but primarily by ocean chemistry specialists employing the technology at single locations. Here we examine their performance in a network context through comparison to discrete measurements of pH, using different configurations of the Honeywell DuraFET pH sensor deployed in six coastal settings by operators with a range of experience. Experience of the operator had the largest effect on performance. The average difference between discrete and ISFET pH was 0.005 pH units, but ranged from-0.030 to 0.083 among operators, with more experienced operators within ± 0.02 pH units of the discrete measurement. In addition, experienced operators achieved a narrower range of variance in difference between discrete bottle measurements and ISFET sensor readings compared to novice operators and novice operators had a higher proportion of data failing quality control screening. There were no statistically significant differences in data uncertainty associated with sensor manufacturer or deployment environment (pier-mounted, flowthrough system, and buoy-mounted). The variation we observed among operators highlights the necessity of best practices and training when instruments are to be used in a network where comparison across data streams is desired. However, while opportunities remain for improving the performance of the ISFET sensors when deployed by less experienced operators, the uncertainty associated with their deployment and validation was several-fold less than the observed natural temporal variability in pH, demonstrating the utility of these sensors in tracking local changes in acidification.

Existing descriptions of the sister species Mazzaella splendens and Mazzaella linearis were insufficient to identify all low intertidal Mazzaella thalli along a wave exposure gradient in Barkley Sound, British Columbia. After sampling size classes of sporophytes and gametophytes, uni- and multi-variate analyses indicated that thalli at low and intermediate exposure sites were M. splendens, whereas thalli at the high exposure site were M. linearis. The longer and thicker stipe of M. linearis best distinguishes it from M. splendens, whereas the previously emphasized characters of blade width and angle at the blade base were not useful. The latter characters demonstrated gradual clines, and for the longer size class, blade width was not isomorphic between phases. The species alternated with each other along the shoreline depending on how rock topography influenced the arrangement of low, intermediate, and high wave exposure sites. Regressions that used an indicator of water motion (i.e., sucrose candy weight loss) to predict morphological variation were often significant. These regressions suggest that some factors affecting the distribution of M. splendens and M. linearis along the gradient are the degree of wave exposure itself as well as light and nutrient availability. Keywords: Mazzaella, Iridaea, cline, wave exposure, gametophyte, sporophyte.

Managers need to predict how animals will respond to habitat redistributions caused by climate change. Our objective was to model the effects of sea level rise on total eelgrass (Zostera marina) habitat area and on the amount of that area that is accessible to Brant geese (Branta bernicla), specialist grazers of eelgrass. Digital elevation models were developed for seven estuaries from Alaska, Washington, California (USA), and Mexico. Scenarios of future total eelgrass area were derived from combinations of estuarine specific sediment and tectonic rates (i.e., bottom change rate) with three rates of eustatic sea level rise (ESLR). Percentages of total eelgrass areas that were accessible to foraging Brant were determined for December when the birds overwinter at more southerly sites and in April as they move north to sites where they build body stores on their way to nesting areas in Alaska. The modeling showed that accessible eelgrass area could be lower than total area due to how daytime low-tide height, eelgrass shoot length, and the upper elevation of eelgrass determined Brant-reaching depth. Projections of future eelgrass area indicated that present-day ESLR (2.8 mm/yr) and bottom change rates should sustain the current pattern of estuarine use by Brant except in Morro Bay, where use should decrease because eelgrass is being ejected from this estuary by a positive bottom change rate. Higher ESLR rates (6.3 and 12.7 mm/yr) should result in less Brant use of estuaries at the northern and southern ends of the flyway, particularly during the winter, but more use of mid-latitude estuaries. The capacity of midlatitude estuaries to function as Brant feeding refugia, or for these estuaries and Izembek Lagoon to provide drift rather than attached leaves, is eventually limited by the decrease in total eelgrass area, which is a result of a light extinction affect on the eelgrass, or the habitat being pushed out of the estuary by positive tectonic rates. Management responses are limited to the increase or decrease of sediment supply and the relocation of levees to allow for upslope migration of eelgrass habitat.

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Biomechanical models of red algae have been developed that make predictions about blade survivorship based on tissue strengths, drag coefficients, and blade surface areas. The first 2 objectives of the present field study were therefore to examine actual survivorship of genets (i.e. holdfast + blades) from wide-and narrow-bladed species of Mazzaella G. DeToni f., as well as to compare blade survivorship to predictions of their survival from a previous biomechanics study of the 2 species. The third and fourth objectives were, respectively, to determine the most frequent break location in the genet, and finally to ascertain if surviving blades are likely to be reproductive. Low intertidal transplant sites were established at a wave-sheltered site where the wide-bladed form of Mazzaella splendens (Setchell et Gardner) Fredericq occurs, and in a high wave impact habitat of the narrow-bladed Mazzaella linearis (Setchell et Gardner) Fredericq. Short and long blades size classes (SC1, SC2, respectively) were included for each species because separate population sampling established that SC1 blades are almost never reproductive, whereas SC2 blades are potentially reproductive. Within the high wave impact transplant site, genet survival of experimental (i.e. transplanted to site of the other species) M. splendens was initially lower than for control (i.e. transplanted within native site) M. linearis presumably due to drag on the larger M. splendens blades. As predicted by the biomechanics model, long blades of control M. linearis survive better than those of experimental M. splendens, but not as well as short blades of experimental M. splendens. However, the narrow blade of M. linearis allows it to reach a reproductively mature length, whereas the short, broken survivors of experimental M. splendens are not long enough to be reproductive. In the sheltered transplant site, genet survival for control M. splendens and experimental M. linearis was similar, but replicate M. linearis populations located higher in the intertidal were stressed (i.e. bleached) and more likely to die. Survivorship for SC2 blades of experimental M. linearis was not greater than SC2 blades of control M. splendens as predicted by the biomechanics model; survivorship of these 2 treatments was similar. For both species, the junction between the stipe and holdfast was rarely the most frequent break location as predicted by previous studies of Mazzaella and other red algae. We conclude that M. linearis is more likely to survive and become reproductive at high wave impact sites because its narrow blade can persist in the face of large hydrodynamic forces. In contrast, in a sheltered site the widebladed form of M. splendens is still at a hydrodynamic disadvantage relative to M. linearis, but M. splendens is able to survive long enough to produce wide, potentially reproductive blades because it is apparently more tolerant of abiotic conditions (e.g. high irradiance, desiccation) within these sites.