Maria T. Kavanaugh

Spatial and Spectral Resolution Considerations for Imaging Coastal Waters

Current ocean color sensors, for example SeaWiFS and MODIS, are well suited for sampling the open ocean. However, coastal environments are spatially and optically more complex and require more frequent sampling and higher spatial resolution sensors with additional spectral channels. We have conducted experiments with data from Hyperion and airborne hyperspectral imagers to evaluate these needs for a variety of coastal environments. Here we present results from an analysis of airborne hyperspectral data for a Harmful Algal Bloom in Monterey Bay. Based on these results and earlier studies we recommend increased frequency of sampling, increased spatial sampling and additional spectral channels for ocean color sensors for coastal environments.

Human impacts on connectivity in marine and freshwater ecosystems assessed using graph theory: a review

Human activities are altering the processes that connect organisms within and among habitats and populations in marine and freshwater (aquatic) ecosystems. Connectivity can be quantified using graph theory, where habitats or populations are represented by ‘nodes’ and dispersal is represented by ‘links’. This approach spans discipline and systemic divides, facilitating identification of generalities in human impacts. We conducted a review of studies that have used graph theory to quantify spatial functional connectivity in aquatic ecosystems. The search identified 42 studies published in 2000–14. We assessed whether each study quantified the impacts of (1) habitat alteration (loss, alteration to links, and gain), (2) human movements causing species introductions, (3) overharvesting and (4) climate change (warming temperatures, altered circulation or hydrology, sea-level rise) and ocean acidification. In freshwater systems habitat alteration was the most commonly studied stressor, whereas in marine systems overharvesting, in terms of larval dispersal among protected areas, was most commonly addressed. Few studies have directly assessed effects of climate change, suggesting an important area of future research. Graph representations of connectivity revealed similarities across different impacts and systems, suggesting common strategies for conservation management. We suggest future research directions for studies of aquatic connectivity to inform conservation management of aquatic ecosystems.

Variability in the mechanisms controlling Southern Ocean phytoplankton bloom phenology in an ocean model and satellite observations

A coupled global numerical simulation (conducted with the Community Earth System Model) is used in conjunction with satellite remote sensing observations to examine the role of top-down (grazing pressure) and bottom-up (light, nutrients) controls on marine phytoplankton bloom dynamics in the Southern Ocean. Phytoplankton seasonal phenology is evaluated in the context of the recently proposed ‘disturbance-recovery’ hypothesis relative to more traditional, exclusively ‘bottom-up’ frameworks. All blooms occur when phytoplankton division rates exceed loss rates to permit sustained net population growth, however the nature of this decoupling period varies regionally in CESM. Regional case studies illustrate how unique pathways allow blooms to emerge despite very poor division rates or very strong grazing rates. In the Subantarctic, southeast Pacific small spring blooms initiate early co-occurring with deep mixing and low division rates, consistent with the ‘disturbance-recovery’ hypothesis. Similar systematics are present in the Subantarctic, southwest Atlantic during the spring, but are eclipsed by a subsequent, larger summer bloom that is coincident with shallow mixing and the annual maximum in division rates, consistent with a ‘bottom-up’, light limited framework. In the model simulation, increased iron stress prevents a similar summer bloom in the southeast Pacific. In the simulated Antarctic zone (70°S - 65°S) seasonal sea ice acts as a dominant phytoplankton-zooplankton decoupling agent, triggering a delayed but substantial bloom as ice recedes. Satellite ocean color remote sensing and ocean physical reanalysis products do not precisely match model predicted phenology, but observed patterns do indicate regional variability in mechanism across the Atlantic and Pacific.

Satellite sensor requirements for monitoring essential biodiversity variables of coastal ecosystems

Abstract The biodiversity and high productivity of coastal terrestrial and aquatic habitats are the foundation for important benefits to human societies around the world. These globally distributed habitats need frequent and broad systematic assessments, but field surveys only cover a small fraction of these areas. Satellite‐based sensors can repeatedly record the visible and near‐infrared reflectance spectra that contain the absorption, scattering, and fluorescence signatures of functional phytoplankton groups, colored dissolved matter, and particulate matter near the surface ocean, and of biologically structured habitats (floating and emergent vegetation, benthic habitats like coral, seagrass, and algae). These measures can be incorporated into Essential Biodiversity Variables (EBVs), including the distribution, abundance, and traits of groups of species populations, and used to evaluate habitat fragmentation. However, current and planned satellites are not designed to observe the EBVs that change rapidly with extreme tides, salinity, temperatures, storms, pollution, or physical habitat destruction over scales relevant to human activity. Making these observations requires a new generation of satellite sensors able to sample with these combined characteristics: (1) spatial resolution on the order of 30 to 100‐m pixels or smaller; (2) spectral resolution on the order of 5 nm in the visible and 10 nm in the short‐wave infrared spectrum (or at least two or more bands at 1,030, 1,240, 1,630, 2,125, and/or 2,260 nm) for atmospheric correction and aquatic and vegetation assessments; (3) radiometric quality with signal to noise ratios (SNR) above 800 (relative to signal levels typical of the open ocean), 14‐bit digitization, absolute radiometric calibration <2%, relative calibration of 0.2%, polarization sensitivity <1%, high radiometric stability and linearity, and operations designed to minimize sunglint; and (4) temporal resolution of hours to days. We refer to these combined specifications as H4 imaging. Enabling H4 imaging is vital for the conservation and management of global biodiversity and ecosystem services, including food provisioning and water security. An agile satellite in a 3‐d repeat low‐Earth orbit could sample 30‐km swath images of several hundred coastal habitats daily. Nine H4 satellites would provide weekly coverage of global coastal zones. Such satellite constellations are now feasible and are used in various applications.

Implications of future northwest Atlantic bottom temperatures on the American lobster (Homarus americanus) fishery

Sea surface temperatures of the northwest Atlantic have warmed dramatically over the last several decades, while benthic temperatures have increased at a slower pace. Here we analyze a subset of the CMIP5 global Earth system model ensemble using a statistical downscaling approach to determine potential future changes in benthic temperatures on the northwest Atlantic continental shelf and slope (<500 m). We put future changes in the context of possible impacts of ocean warming on the high-value, wild-caught American Lobster (Homarus americanus) fishery. Future bottom temperatures of the northwest Atlantic under a business-as-usual (RCP8.5) and a climate-policy (RCP4.5) scenario are projected to increase by 0–1.58C and 1.2–2.48C by 2050 and 0–1.98C and 2.3–4.38C by the end of the century for RCP4.5 and RCP8.5, respectively. H. americanus experiences thermal stress at temperatures above 208C, and projected increases in temperature is likely to result in changes in the distribution of optimal thermal egg hatching and settlement indicators. Inshore regions of southern New England, where H. americanus biomass and catch have been declining historically, will likely become inhospitable under either future scenario, while thermal egg hatching and settlement indicators will expand offshore and in the Gulf of Maine. These changes imply that members of the fishery based in southern New England may need to recapitalize to larger vessels to prepare for potential changes brought on by future climate warming. Results from the downscaling presented here can be useful in preparing for potential changes to other fisheries or in future climate vulnerability analyses.

Atmospheric and Fluvial Nutrients Fuel Algal Blooms in the East China Sea

Chinese coastal waters support vast fisheries and vital economies, but their productivity is threatened by increasingly frequent harmful algal blooms (HABs). Here we provide direct experimental evidence that atmospheric deposition, along with riverine input, opens new niches for bloom-forming dinoflagellates and diatoms in the East China Sea (ECS) by increasing the ratio of nitrogen to phosphorus (N:P), inducing severe P limitation, and altering trace metal micronutrient inventories. Remote sensing analysis of blooms in the region showed that dinoflagellate blooms were associated with increased aerosol optical thickness and decreased sea surface temperature, whereas diatom blooms were primarily associated with seasonally decreased temperature (e.g. during spring blooms). Bottle incubation experiments revealed that aerosol additions approximating 10 days of strong deposition increased iron availability and intensified P limitation, which together promoted dinoflagellate growth in offshore waters. Diatom growth was correlated with elevated trace metal and nutrient content from aerosols. Aerosols did not induce phytoplankton growth at a station within the Yangtze River plume where light was limiting, consistent with remote sensing observations that aerosol effects are stronger in offshore waters. Eutrophication and trace metal enrichment from Yangtze River discharge together with atmospheric deposition may underlie the transition from diatom-dominated spring blooms toward more frequent spring and summer dinoflagellate blooms that has occurred over the past three decades in the ECS.

Thirty-Three Years of Ocean Benthic Warming Along the U.S. Northeast Continental Shelf and Slope: Patterns, Drivers, and Ecological Consequences

Abstract The U.S. Northeast Continental Shelf is experiencing rapid warming, with potentially profound consequences to marine ecosystems. While satellites document multiple scales of spatial and temporal variability on the surface, our understanding of the status, trends, and drivers of the benthic environmental change remains limited. We interpolated sparse benthic temperature data along the New England Shelf and upper Slope using a seasonally dynamic, regionally specific multiple linear regression model that merged in situ and remote sensing data. The statistical model predicted nearly 90% of the variability of the data, resulting in a synoptic time series spanning over three decades from 1982 to 2014. Benthic temperatures increased throughout the domain, including in the Gulf of Maine. Rates of benthic warming ranged from 0.1 to 0.4°C per decade, with fastest rates occurring in shallow, nearshore regions and on Georges Bank, the latter exceeding rates observed in the surface. Rates of benthic warming were up to 1.6 times faster in winter than the rest of the year in many regions, with important implications for disease occurrence and energetics of overwintering species. Drivers of warming varied over the domain. In southern New England and the mid‐Atlantic shallow Shelf regions, benthic warming was tightly coupled to changes in SST, whereas both regional and basin‐scale changes in ocean circulation affect temperatures in the Gulf of Maine, the Continental Shelf, and Georges Banks. These results highlight data gaps, the current feasibility of prediction from remotely sensed variables, and the need for improved understanding on how climate may affect seasonally specific ecological processes.

ALOHA From the Edge: Reconciling Three Decades of in Situ Eulerian Observations and Geographic Variability in the North Pacific Subtropical Gyre

Global analyses of satellite-and modeled data suggest decreased phytoplankton abundance and primary productivity in oligotrophic gyres as they expand in response to increased surface temperatures, shoaling of surface mixed layers, and decreased supply of subsurface macronutrients. However, concomitant changes have not been evident in situ at Hawaii Ocean Time-series (HOT) Station ALOHA, suggesting physiological or structural reorganization not observed from space, uncharacterized spatiotemporal variability, or uncorrected sensor drift. To address the spatiotemporal variability hypothesis, we compared interannual patterns of in situ data to gyre geography based on multiple metrics including dynamic topography, satellite surface chlorophyll (chl a), and multivariate seascapes using modelled or satellite data. There was only weak evidence of secular increases in the extent of the subtropical gyre; rather, interannual oscillations were evident in physical, biological, and multivariate biophysical definitions of the gyre. Modelled and satellite-based multivariate seascapes agreed well in terms of expansion (surface area of seascapes) and isolation of Station ALOHA (distance to seascape boundary) resulting in combined data record of nearly three decades. Isolation was associated positively with the North Pacific Gyre Oscillation (NPGO), and negatively with Multivariate ENSO Index (MEI) and Pacific Decadal Oscillation (PDO); the converse was true for the gyre’s expansion. This expansion followed a shoaling and freshening of the surface mixed layer and declines in in situ 14C assimilation rates measured over 12 hours in ambient light suggesting that Station ALOHA may serve as an leading indicator of gyre biogeographic patterns. Lags between geographic indicators and in situ conditions appear to partially explain past observed discrepancies between patterns from satellite remote sensing and those from in situ conditions at Station ALOHA appear to be partially explained by lags between geographic indicators and in situ conditions as well as satellite sensor drift and data record length.

Advancing Toward Professorship in Biology, Ecology, and Earth System Sciences

Multiple factors may interact with gender to convince women to opt out of careers as tenure track faculty. Rates of attrition in academia are particularly pronounced in science, technology, engineering, and mathematics (STEM) disciplines, which include biology, ecology and earth system sciences, or collectively, BEESS. In addition to the stressors that affect other STEM careers, paths in BEESS fields are unique in that they are inherently interdisciplinary, often require field work, and involve interactions with a broad range of stakeholders. We designed and conducted a workshop for an at-risk population of BEESS scientists—postdoctoral and tenure track, but pre-tenured scientists—who may not already have access to targeted professional development. We also conducted longitudinal research to determine the perceptions of career preparation and challenges of our participants, as well as to quantify the effect of our programming on those perceptions.