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Passive ocean color remote sensing has revolutionized our ability to quantify the horizontal distribution of phytoplankton across the ocean surface. Lidar technology can provide remotely sensed estimates of the vertical distribution of optical properties and suspended particles in natural waters, significantly improving our ability to model upper ocean biogeochemical processes. In this study, we constructed and deployed a ship-based lidar system to measure laser backscattering and linear depolarization profiles in the coastal Mid-Atlantic ranging from estuarine to oceanic conditions, and across the Gulf of Maine (GoM). The instrument identified layers with different backscattering intensity in stratified waters of the coastal Mid-Atlantic and produced system attenuation coefficients (Ksys) approximating the absorption coefficient (apg) of particulate + dissolved matter. The linear depolarization ratio was strongly related to in situ measurements of the particulate backscattering ratio (bbp/bp). Measurements of Ksys and linear depolarization made across the GoM corresponded well with simultaneous in situ observations performed aboard the M/V Nova Star and by an autonomous glider deployed along the transect. The relationship between Ksys and apg differed between sampling schemes, likely due to differences in the deployment geometries (e.g., height, nadir angle). These results support the proposition that ship-based lidar systems can provide a powerful tool for remotely measuring the vertical distributions of optical properties and geochemical constituents (e.g., particles) in the upper ocean. Continued development of compact lidar systems for deployment on ships, moorings, and autonomous platforms has the potential to greatly improve the quality and scope of a variety of oceanographic investigations.

The proximity of seagrass meadows to centers of human activity makes them vulnerable to a variety of habitat degrading insults. Physical scarring has long been recognized as an important but difficult-to-quantify source of habitat fragmentation and seagrass loss. We present a pixel-based algorithm to detect seafloor propeller seagrass scars in shallow water that promises to automate the detection and measurement of scars across the submarine landscape. 1 We applied the algorithm to multispectral and panchromatic images captured at the Deckle Beach, Florida using the WorldView-2 commercial satellite. The algorithm involves four steps using spectral and spatial information from radiometrically calibrated multispectral and panchromatic images. First, we fused multispectral and panchromatic images using a principal component analysis (PCA)-based pan-sharpening method to obtain multispectral pan-sharpened bands. In the second step, we enhanced the image contrast of the pan-sharpened bands for better scar detection. In the third step, we classified the contrast enhanced image pixels into scar and non-scar categories based on a sparse coding algorithm that produced an initial scar map in which false positive scar pixels were also present. In the fourth step, we applied post-processing techniques including a morphological filter and local orientation to reduce false positives. Our results show that the proposed method may be implemented on a regular basis to monitor changes in habitat characteristics of coastal waters.

The absorption of solar energy by colored dissolved organic material (CDOM) in Arctic surface waters during the springtime is increasingly recognized as having profound impacts on seasonal retreat of ice from the Arctic Ocean. This study observed the production of CDOM within first year landfast sea ice, its contribution to light absorption within the water column and its photoreactivity, at a location near Ellef Ringnes Island in the Canadian Archipelago during the spring of 2011. CDOM was the optically dominant component of non-water absorption, increasing the energy absorption and heating potential in the top 8 m by 30% over pure seawater. CDOM absorption within sea ice brine channels increased with solar-stimulated ice algae production. This ice algal mediated production of CDOM exceeded photooxidation rates, potentiating a net delivery of CDOM to the immediately underlying water column from brine channels in the ice. The rates of production and loss of CDOM in Arctic waters during the early spring quantified here will help constrain a major uncertainty in modeling light absorption by surface waters that contributes to sea ice loss in the Arctic.

Satellite remote sensing offers an effective remedy to challenges in ground-based and aerial mapping that have previously impeded quantitative assessments of global seagrass extent. Commercial satellite platforms offer fine spatial resolution, an important consideration in patchy seagrass ecosystems. Currently, no consistent protocol exists for image processing of commercial data, limiting reproducibility and comparison across space and time. Additionally, the radiometric performance of commercial satellite sensors has not been assessed against the dark and variable targets characteristic of coastal waters. This study compared data products derived from two commercial satellites: DigitalGlobe's WorldView-2 and Planet's RapidEye. A single scene from each platform was obtained at St. Joseph Bay in Florida, USA, corresponding to a November 2010 field campaign. A reproducible processing regime was developed to transform imagery from basic products, as delivered from each company, into analysis-ready data usable for various scientific applications. Satellite-derived surface reflectances were compared against field measurements. WorldView-2 imagery exhibited high disagreement in the coastal blue and blue spectral bands, chronically overpredicting. RapidEye exhibited better agreement than WorldView-2, but overpredicted slightly across all spectral bands. A deep convolutional neural network was used to classify imagery into deep water, land, submerged sand, seagrass, and intertidal classes. Classification results were compared to seagrass maps derived from photointerpreted aerial imagery. This study offers the first radiometric assessment of WorldView-2 and RapidEye over a coastal system, revealing inherent calibration issues in shorter wavelengths of WorldView-2. Both platforms demonstrated as much as 97% agreement with aerial estimates, despite differing resolutions. Thus, calibration issues in WorldView-2 did not appear to interfere with classification accuracy, but could be problematic if estimating biomass. The image processing routine developed here offers a reproducible workflow for WorldView-2 and RapidEye imagery, which was tested in two additional coastal systems. This approach may become platform independent as more sensors become available.

The estuaries and continental shelf system of the United States Mid-Atlantic are subject to ocean acidification driven by atmospheric CO2, and coastal acidification caused by nearshore and land-sea interactions that include biological, chemical, and physical processes. These processes include freshwater and nutrient input from rivers and groundwater; tidally-driven outwelling of nutrients, inorganic carbon, alkalinity; high productivity and respiration; and hypoxia. Hence, these complex dynamic systems exhibit substantial daily, seasonal, and interannual variability that is not well captured by current acidification research on Mid-Atlantic organisms and ecosystems. We present recommendations for research priorities that target better understanding of the ecological impacts of acidification in the U. S. Mid-Atlantic region. Suggested priorities are: 1) Determining the impact of multiple stressors on our resource species as well as the magnitude of acidification; 2) Filling information gaps on major taxa and regionally important species in different life stages to improve understanding of their response to variable temporal scales and sources of acidification; 3) Improving experimental approaches to incorporate realistic environmental variability and gradients, include interactions with other environmental stressors, increase transferability to other systems or organisms, and evaluate community and ecosystem response; 4) Determining the capacity of important species to acclimate or adapt to changing ocean conditions; 5) Considering multi-disciplinary, ecosystem-level research that examines acidification impacts on biodiversity and biotic interactions; and 6) Connecting potential acidification-induced ecological impacts to ecosystem services and the economy. These recommendations, while developed for the Mid-Atlantic, can be applicable to other regions will help align research towards knowledge of potential larger-scale ecological and economic impacts.

Recent warming of surface waters, accompanied by reduced ice thickness and extent may have significant consequences for climate-driven changes of primary production (PP) in the Arctic Ocean (AO). However, it has been difficult to obtain a robust benchmark estimate of pan-Arctic PP necessary for evaluating change. This paper provides an estimate of pan-Arctic PP prior to significant warming from a synthetic analysis of the ARCSS-PP database of in situ measurements collected from 1954 to 2007 and estimates derived from satellite-based observations from 1998 to 2007. Vertical profiles of in situ chlorophyll a (Chl a ) and PP revealed persistent subsurface peaks in biomass and PP throughout the AO during most of the summer period. This was contradictory with the commonly assumed exponential decrease in PP with depth on which prior satellite-derived estimates were based. As remotely sensed Chl a was not a good predictor of integrated water column Chl a , accurate satellite-based modeling of vertically integrated primary production (IPP sat ), requires knowledge of the subsurface distribution of phytoplankton, coincident with the remotely sensed ocean color measurements. We developed an alternative approach to modeling PP from satellite observations by incorporating climatological information on the depths of the euphotic zone and the mixed layer that control the distribution of phytoplankton that significantly improved the fidelity of satellite derived PP to in situ observations. The annual IPP of the Arctic Ocean combining both in situ and satellite based estimates was calculated here to be a minimum of 466 ± 94 Tg C yr −1 and a maximum of 993 ± 94 Tg C yr −1 , when corrected for subsurface production. Inflow shelf seas account for 75% of annual IPP, while the central basin and Beaufort northern sea were the regions with the lowest annual integrated productivity, due to persistently stratified, oligotrophic and ice-covered conditions. Although the expansion of summertime ice retreat should stimulate photosynthesis by exposing more of the AO to solar irradiance, total PP is ultimately limited by nutrient availability. Therefore, changes in AO PP will be forced by the balance between stratification and mixing, the effects of which are not yet quantified.

The Arctic Ocean, including its regional shelf seas, is assumed to play an important role in the global carbon cycle. However, the true magnitude of annual production is unknown, as in situ data are sparse in time and space. Remote sensing technology has the potential to provide large scale estimates of phytoplankton biomass at much higher frequency and spatial coverage than shipboard observations in this remote region. Subsurface peaks in both biomass and primary production (PP), which are the characteristics of the Arctic, are shown to limit the reliability of ocean color based integrated PP (IPP) models in the Chukchi Sea. Here we report that the retrievals of IPP from remotely sensed ocean color data were accurate only when limited to 1.2 optical depths, which severely constrains the utility of ocean color remote sensing for the assessment of Arctic Ocean dynamics. Active sensors such as LIDAR, can, in combination with passive ocean color, dramatically improve our ability to estimate IPP for the Arctic. IPP retrievals were improved to within a factor of 2–3 of the measured values, when the vertical distribution of Chl a was determined to a resolution of 1 m using modeled LIDAR retrievals of the beam attenuation coefficient. This was far better than models using only passive ocean color. The instrument specifications of the current NASA spaceborne LIDAR (CALIOP) allow for the retrieval of K d at a depth resolution of 23 m. Even with this constraint, however, the accuracy of the modeled IPP was improved over passive ocean color retrievals to approximately a factor of 3. The Arctic is a perfect location to merge ocean color and LIDAR measurements as the polar orbit of CALIOP provides complete grid coverage of the area every 8 days, crossing the horizontal gradients in Chl a already known to exist from passive ocean color observations.

Refractive, rhomboidal, intracellular crystals were identified in leaves of Thalassia testudinum Banks ex Konig (turtlegrass) from the Bahamas (Lee Stocking Island); Florida (Key Largo and Key West); and Texas (Laguna Madre). At all four collection sites, crystals were present in leaves of all ages and in most but not all epidermal cells. Crystals were not found in mesophyll cells. Epidermal cells generally contained a single, large crystal, but leaves collected from Key West frequently exhibited cells containing two or more conjoined crystals. Crystals dissolved in concentrated HCl and were partially soluble in concentrated NaOH. Transmission electron microscopy showed that crystals were contained within a vacuole. The size (as large as 12 μm × 6 μm), morphology, and distribution of crystals in turtlegrass leaves are similar to proteinaceous crystals described in marine red and brown macroalgae, but histology and spectroscopy results suggest a closer affinity to calcium oxalate crystals found in flowering plants. Although crystalline inclusions within plant cells have been linked to (inter alia) deterrence of herbivory and regulation of intracellular calcium ion concentrations, their function within leaves of turtlegrass remains to be determined.

Although seagrasses possess numerous adaptations for life underwater, they lack the specialized accessory pigments for the efficient harvesting of green light that dominates many aquatic environments. Without these specialized pigments, photoacclimation by seagrasses is likely to result in a severe package effect, i.e. the loss of linearity between light harvesting efficiency and pigment loading. Here, we investigated the optical constraints imposed by the package effect on photoacclimation in seagrass leaves. Pigment concentrations and optical properties (absorptances, absorption coefficients and optical cross-sections) of turtlegrass ( Thalassia testudium) leaves from Lee Stocking Island (LSI; Bahamas) and eelgrass (Zostera marina) leaves from Monterey Bay, CL, USA were measured at different times of the year. Chlorophyll concentrations and optical cross-sections differed by a factor of five across sampling dates and populations. Increases in leaf-specific absorption among seagrass leaves were greatest in the green (500–600 nm), while the package effect, as measured by a decrease in leaf optical cross-section, was most severe in the blue (400–500 nm) and red (600–700 nm). Consequently, the five-fold range in pigment concentration resulted in similar photosynthetic light harvest efficiencies ( φL ≈ 50% of incident PAR) for intact seagrass leaves in their native light environments. Although the package effect has significant impacts on the optical properties of seagrass leaves, chlorophyll use efficiency does not appear to play a strong role in the ecology or evolution of seagrasses. © 2002 Elsevier Science B.V. All rights reserved.

Annual variations in density, morphology, pigment levels, carbohydrate levels and photosynthetic characteristics of Zostera marina L. (eelgrass) from a coastal lagoon and from an unprotected area in the open coast were compared to understand the environmental regulation of this species growing near the southern limit of its distribution in the eastern Pacific. From January to April of 1997, light attenuation coefficients at the lagoon and the open coast increased six-fold as a result of sediment resuspension caused by storms in the area. During the storms, in situ irradiance was reduced two-fold at the lagoon. Irradiance values at the open coast, however, were reduced to nearly zero for >3 weeks, promoting the disappearance of the open coast population. At the open coast, eelgrass shoots died after sugar and starch content in the leaves decreased by approximately 85% after 3 weeks of light limitation. The re-appearance of eelgrass seedlings at the open coast coincided with the end of the winter storms in the area and decreasing water column turbidity. Maximum photosynthesis values of eelgrass from the open coast were two-fold greater than those from lagoon plants, except during March–June when seeds germinated at the open coast. Similarly, survival and leaf carbohydrate content of eelgrass from both sites decreased by >90% when incubated for 3 weeks in darkness. Collectively, these results indicate that the disappearance of eelgrass at the open coast is regulated by irradiance and not by an endogenous cycle. Although eelgrass can succeed in the open coast given sufficient light during the year, the accumulation and mobilization of carbon reserves appear to play a key role in the dynamics of eelgrass survival in temporally variable environments.

Survival, metabolism and growth of Zostera marina L. transplants were examined along depth gradients in Keil Cove and Paradise Cove in the extremely turbid San Francisco Bay estuary. Water transparency was unusually high throughout 1989–1990 for San Francisco Bay. Transplant survival was strongly depth-dependent at Paradise Cove but not at Keil Cove. All transplants were lost below − 1.0 m depth within 1 year at Paradise Cove, but survived to depths of − 1.5 m at Keil Cove. Half the transplants growing in shallow water survived the first year at both sites. Shoot photosynthesis, respiration, growth, and sugar content did not differ between sites. Daily periods of irradiance-saturated photosynthesis (Hsat) were over 6 h all year. Seasonal photosynthetic acclimation to light availability maintained long Hsat periods and high ratios of daily whole-plant production to respiration through the winter, indicating a potential for net carbon gain throughout the year. Winter growth was 50% of the summer rate. Despite high initial losses, surviving transplants have persisted at both sites through 1994. Although eelgrass transplants can succeed in San Francisco Bay given sufficient light availability, the role of carbon reserves and transplant timing may influence transplant survival.

p-(sulphooxy) Cinnamic acid was isolated as a natural product for the first time from the seagrass Zostera marina (eelgrass) and was found to prevent attachment of marine bacteria and barnacles to artificial surfaces at nontoxic concentrations. Analogous synthetic sulphate esters had similar antifouling properties, while the non-sulphated phenolic acid precursors were ineffective. The antifouling properties of phenolic acid sulphates are consistent with an emerging pattern of biological activity exhibited by other sulphate esters isolated from a variety of marine organisms, and their low toxicity offers promise for the development of environmentally benign antifouling agents to protect structures in aquatic environments.

The relationship between turbidity and light availability, and its subsequent effect on the depth distribution of Zostera marina L. (eelgrass) in San Francisco Bay was explored. The average daily period of irradiance-saturated photosynthesis (Hsat) required for the maintenance of whole plant carbon balance and growth, based on measured rates of photosynthesis and respiration as well as data available in the literature, were estimated to be between 3 and 5 h. Estimates of average Hsat availability in the field were determined from laboratory measurements of the phytosynthesis vs. irradiance (P vs. I) response and from field observations of light attenuation measured at five sites in San Francisco Bay. Although plants were found to be low-light adapted with regard to their P vs. I response, they were limited to depths shallower than −2 m mean lower low water (MLLW) at all sites. The −2 m depth limit corresponded fairly well to predicted Hsat requirements at two sites where turbidity was relatively low and constant, but depth limits of eelgrass were less than 1.5 m at three sites subjected to extremely turbid and variable light environments, much shallower than predicted from calculations of mean daily carbon requirements and Hsat availability. Thus, in addition to the mean light environment, periods of extreme light attenuation that last from days to weeks may be important in controlling eelgrass growth and productivity in highly turbid and dynamic estuaries such as San Francisco Bay.

Thermal acclimation in eelgrass Zostera marina L. was investigated in laboratory experiments after growing plants at 10 and 20°C for 21 days under a 12:12 L:D regime. Metabolic rates showed significant shifts in short-term response to temperature in leaves and roots. Growth rates, tissue carbohydrate concentrations and metabolic rates measured at the two growth temperatures were statistically identical, indicating that thermal acclimation was essentially complete at these temperatures. When measured at pO2 values high enough to achieve capacity rates of respiration, thermal responses of respiration (Q10) were lower than previously reported while the thermal response of photosynthesis (measured at pO2 below air saturation) was similar to previous reports. Daily C budgets constructed from metabolic rate data indicated that Hsat periods required for photosynthesis to balance C demand can vary from 3 to > 12 h, depending on the ratios of net photosynthesis: respiration (Pnet: R) and shoot: root. Since Z. marina. shows evidence of thermal acclimation, seasonal changes in ambient temperature may not significantly affect Hsat requirements and whole-plant C balance. Rapid mortality at high temperatures during summer may result instead from thermal disruption of metabolism while internal C reserves may be important in meeting C demand during winter periods of low light availability, particularly among high-latitude populations.