Thomas, AC, et al 2017 Seasonal trends and phenology shifts in sea surface temperature on the North American northeastern continental shelf. Elem Sci Anth, 5: 48, DOI: https://doi.org/10.1525/elementa.240 Introduction Sea surface temperatures (SST) on the North American continental shelf from Cape Hatteras to Nova Scotia (Figure 1) (hereinafter referred to as the northeastern shelf) exhibit one of the strongest warming trends of the global ocean (Burrows et al., 2011;Pershing et al., 2015; Saba et al., 2015), and the region has recently been subjected to a strong heat wave (Mills et al., 2013; Scannell et al., 2016). The warming trend has been implicated in shifts in the distribution of marine species (Lucey and Nye, 2010;Pinsky et al., 2013), many of which are of commercial importance (Nye et al., 2009;Pinsky and Fogarty, 2012), and some of which are invasive species able to exploit new ranges (e.g. Maynard et al., 2016; Stephenson et al., 2009). Such trends impose serious challenges for fisheries and fisheries management (e.g. Pinsky and Fogarty, 2012;Pershing et al., 2015). However, temperature interactions with species distributions and behaviors occur not only through trends in temperatures, latitudinal shifts in isotherms, or even in episodic events such as heat waves, but also through shifts in phenology, the timing within temperature seasonal cycles (Asch, 2015;Burrows et al., 2011). Friedland and Hare (2007) ). Winter (January-April) trends are relatively weak, and even negative in some areas; early summer (May-June) trends are positive everywhere, and later summer (July-September) trends are strongest (~1.0°C decade -1). These seasonal differences shift the phenology of many metrics of the SST cycle. The yearday on which specific temperature thresholds (8° and 12°C) are reached in spring trends earlier, most strongly over the Scotian Shelf and Gulf of Maine (~ -0.5 days year ). Three metrics defining the warmest summer period show significant trends towards earlier summer starts, later summer ends and longer summer duration over the entire study region. Trends in start and end dates are strongest (~1 day year -1 ) over the Gulf of Maine and Scotian Shelf. Trends in increased summer duration are >2.0 days year -1 in parts of the Gulf of Maine. Regression analyses show that phenology trends have regionally varying links to the North Atlantic Oscillation, to local spring and summer atmospheric pressure and air temperature and to Gulf Stream position. For effective monitoring and management of dynamically heterogeneous shelf regions, the results highlight the need to quantify spatial and seasonal differences in SST trends as well as trends in SST phenology, each of which likely has implications for the ecological functioning of the shelf.

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The first 4 years of SeaWiFS ocean color data (September 1997-August 2001 provide the first synoptic quantification of seasonal and interannual phytoplankton chlorophyll variability in the Gulf of Maine. Climatological monthly means show spatial patterns associated with the annual cycle. Concentrations are elevated throughout the year in coastal regions and over shallow banks (Georges Bank, Nantucket Shoals and Browns Bank) with a spring and fall bloom superimposed. Over deeper basins and the Scotia Shelf, a canonical North Atlantic seasonal cycle is present with low (o 1 mg m À3 ) winter (December-February) concentrations, an annual maximum in March-April (>2 mg m À3 ), reduced concentrations in summer and a fall bloom beginning as early as September in Jordan Basin but in OctoberNovember over other regions. Strong interannual variability over the 4-year time series shows the climatological seasonal features are often a biased picture of both timing and magnitude. The clearest interannual signal is of reduced chlorophyll concentrations throughout 1998, including weak spring and fall blooms. A connection between low concentrations in 1998 and local wind forcing is not evident. However, the low concentrations are coincident with negative anomalies in satellite surface temperature fields and follow the intrusion of relatively cold, low salinity slope water into the Northeast Channel which previous authors have argued is linked to changes in Labrador slope water transport induced by the North Atlantic Oscillation. Reduced concentrations in 1998 are consistent with both lower nitrate/nitrite concentrations in the intruding water as well as reduced subsurface stratification which would delay or reduce the onset of the spring bloom. r

Understanding the dispersal processes that influence genetic structure in marine species requires estimating gene flow in a dynamic, fluid environment that is often poorly characterized at scales relevant to multiple dispersive stages (e.g. spores, gametes, zygotes, larvae, adults). We examine genetic structure in the marine alga Fucus vesiculosus L., which inhabits moderately exposed shores in the northern Atlantic but releases gametes only under sunny, calm conditions. We predicted genetic structure would correlate with coastal topography because weather frequently varies across coastal promontories on the Maine shore when F. vesiculosus is reproductive, which causes one side to experience high levels of water motion (= no gamete release) while one side is calm (= gamete release). Furthermore, we expected that the effect of low dispersal capacities of gametes and zygotes would result in spatial genetic structure over short distances. Using surface drifters, we characterized near-shore circulation patterns around the study sites to investigate whether directionality of gene flow was correlated with directionality of currents. We found significant genetic differentiation among sites sampled at two different peninsulas, but patterns of differentiation were unrelated to coastal topography and there was no within-site spatial structuring. Our genetic and near-shore circulation data, combined with an examination of gamete longevity, support the dependency of gene flow on storm-detached, rafting, reproductive adults. This study highlights the significance of rafting as a mechanism for structuring established populations of macroalgae and associated biota and demonstrates the importance of coupling population genetics' research with relevant hydrodynamic studies.

Remote sensing data is useful for selection of aquaculture sites because it can provide water-quality products mapped over large regions at low cost to users. However, the spatial resolution of most ocean color satellites is too coarse to provide usable data within many estuaries. The Landsat 8 satellite, launched February 11, 2013, has both the spatial resolution and the necessary signal to noise ratio to provide temperature, as well as ocean color derived products along complex coastlines. The state of Maine (USA) has an abundance of estuarine indentations (∼3,500 miles of tidal shoreline within 220 miles of coast), and an expanding aquaculture industry, which makes it a prime casestudy for using Landsat 8 data to provide products suitable for aquaculture site selection. We collected the Landsat 8 scenes over coastal Maine, flagged clouds, atmospherically corrected the top-of-the-atmosphere radiances, and derived time varying fields (repeat time of Landsat 8 is 16 days) of temperature (100 m resolution), turbidity (30 m resolution), and chlorophyll a (30 m resolution). We validated the remote-sensing-based products at several in situ locations along the Maine coast where monitoring buoys and programs are in place. Initial analysis of the validated fields revealed promising new areas for oyster aquaculture. The approach used is applicable to other coastal regions and the data collected to date show potential for other applications in marine coastal environments, including water quality monitoring and ecosystem management.