Ocean time-series near Bermuda: Hydrostation S and the US JGOFS Bermuda Atlantic time-series study

Bermuda is the site of two ocean time-series programs. At Hydrostation S, the ongoing biweekly profiles of temperature, salinity and oxygen now span 37 years. This is one of the longest open-ocean time-series data sets and provides a view of decadal scale variability in ocean processes. In 1988, the U.S. JGOFS Bermuda Atlantic Time-series Study began a wide range of measurements at a frequency of 14-18 cruises each year to understand temporal variability in ocean biogeochemistry. On each cruise, the data range from chemical analyses of discrete water samples to data from electronic packages of hydrographic and optics sensors. In addition, a range of biological and geochemical rate measurements are conducted that integrate over time-periods of minutes to days. This sampling strategy yields a reasonable resolution of the major seasonal patterns and of decadal scale variability. The Sargasso Sea also has a variety of episodic production events on scales of days to weeks and these are only poorly resolved. In addition, there is a substantial amount of mesoscale variability in this region and some of the perceived temporal patterns are caused by the intersection of the biweekly sampling with the natural spatial variability. In the Bermuda time-series programs, we have added a series of additional cruises to begin to assess these other sources of variation and their impacts on the interpretation of the main time-series record. However, the adequate resolution of higher frequency temporal patterns will probably require the introduction of new sampling strategies and some emerging technologies such as biogeochemical moorings and autonomous underwater vehicles

Acute and Sub-Acute Toxicity of the Polycyclic Aromatic Hydrocarbon 1-Methylnaphthalene to the Shallow-Water Coral Porites divaricata: Application of a Novel Exposure Protocol

Previous research evaluating hydrocarbon toxicity to corals and coral reefs has generally focused on community-level effects, and results often are not comparable between studies because of variability in hydrocarbon exposure characterization and evaluation of coral health and mortality during exposure. Toxicity of the polycyclic aromatic hydrocarbon 1-methylnaphthalene to the coral Porites divaricata was assessed in a constant exposure toxicity test utilizing a novel toxicity testing protocol uniquely applicable to shallow-water corals, which considered multiple assessment metrics and evaluated the potential for post-exposure mortality and/or recovery. Acute and subacute effects (gross morphological changes, photosynthetic efficiency, mortality, and histologic cellular changes) were evaluated during pre-exposure (4 wk), exposure (48 h), and post-exposure recovery (4 wk) periods. Coral condition scores were used to determine a 48-h median effective concentration of 7442 μg/L. Significant physical and histological changes resulted from exposure to 640 μg/L and 5427 μg/L 1-methylnaphthalene, with a 1-d to 3-d delay in photosynthetic efficiency effects (ΔF/Fm). Pigmented granular amoebocyte area was found to be a potentially useful sublethal endpoint for this species. Coral mortality was used to estimate a 48-h median lethal concentration of 12 123 μg/L

The Effects of Oil and Oil Dispersants on the Skeletal Growth of the Hermatypic Coral Diploria strigosa

Specimens of the hermatypic coral species Diploria strigosa were exposed to various concentrations (1–50 ppm) of oil or oil plus dispersant for 6–24 h periods in four laboratory and two field experiments. After dosing, corals were transplanted to, or left in, the field and recollected approximately one year later for extension (linear) growth analysis by the alizarin stain method. The experiments were designed to assess the long-term effects of brief low-level concentrations of chemically dispersed oil and oil alone on corals in a situation, for example, where an oil slick (treated and non-treated with dispersants) passes over a reef. No significant differences between extension growth parameters (Septa increase, Columella increase) and a calical shape parameter (New Endotheca Length) of treated corals versus controls were found in any of the experiments. In two summer experiments calical relief (Fossa length) was found to be depressed in corals of some of the experimental treatments

Behavioural Effects of Chemically Dispersed Oil and Subsequent Recovery in Diploria strigosa (Dana)

Survival and behaviour of the hermatypic coral Diploria strigosa was studied during 6–24 h doses with water-accomodated fractions of chemically dispersed crude oil, and for a subsequent recovery period of 1 month. Experiments utilized a flow-through laboratory dosing procedure and incorporated petroleum hydrocarbon measurements in order to simulate a major but short-term oil spill in shallow subtidal benthic reef environments. Chemically dispersed oil treatments consisted of Arabian Light Crude oil with Corexit 9527 or BP1100WD at 1–20 ppm concentrations of oil. In general, effects observed were sub-lethal, temporary, and associated with the highest concentrations tested. Responses to the presence of dispersed oil at 20ppm for 24 h included mesenterial filament extrusion, extreme tissue contraction, tentacle retraction and localized tissue rupture. The nature and severity of reactions during the dosing phase varied between colonies and treatments, but colonies typically resumed normal behaviour within 2 h to 4 d of the recovery period. It therefore seems unlikely that observed biological effects would impair long-term viability

Summer diatom blooms in the eastern North Pacific gyre investigated with a long-endurance autonomous surface vehicle

Satellite chlorophyll a (chl a) observations have repeatedly noted summertime phytoplankton blooms in the North Pacific subtropical gyre (NPSG), a region of open ocean that is far removed from any land-derived or Ekman upwelling nutrient sources. These blooms are dominated by N2-fixing diatom-cyanobacteria associations of the diatom genera Rhizosolenia Brightwell and Hemiaulus Ehrenberg. Their nitrogen fixing endosymbiont, Richelia intracellularis J.A. Schmidt, is hypothesized to be critical to the development of blooms in this nitrogen limited region. However, due to the remote location and unpredictable duration of the summer blooms, prolonged in situ observations are rare outside of the Station ALOHA time-series off of Hawai’i. In summer, 2015, a proof-of-concept mission using the autonomous vehicle, Honey Badger (Wave Glider SV2; Liquid Robotics, a Boeing company, Sunnyvale, CA, USA), collected near-surface (<20 m) observations in the NPSG using hydrographic, meteorological, optical, and imaging sensors designed to focus on phytoplankton abundance, distribution, and physiology of this bloom-forming region. Hemiaulus and Rhizosolenia cell abundance was determined using digital holography for the entire June–November mission. Honey Badger was not able to reach the 30°N subtropical front region where most of the satellite chl a blooms have been observed, but near-real time navigational control allowed it to transect two blooms near 25°N. The two taxa did not co-occur in large numbers, rather the blooms were dominated by either Hemiaulus or Rhizosolenia. The August 2–4, 2015 bloom was comprised of 96% Hemiaulus and the second bloom, August 15–17, 2015, was dominated by Rhizosolenia (75%). The holograms also imaged undisturbed, fragile Hemiaulus aggregates throughout the sampled area at ∼10 L−1. Aggregated Hemiaulus represented the entire observed population at times and had a widespread distribution independent of the summer export pulse, a dominant annual event suggested to be mediated by aggregate fluxes. Aggregate occurrence was not consistent with a density dependent formation mechanism and may represent a natural growth form in undisturbed conditions. The photosynthetic potential index (Fv:Fm) increased from ∼0.4 to ∼0.6 during both blooms indicating a robust, active phytoplankton community in the blooms. The diel pattern of Fv:Fm (nocturnal maximum; diurnal minimum) was consistent with macronutrient limitation throughout the mission with no evidence of Fe-limitation despite the presence of nitrogen fixing diatom-diazotroph assemblages. During the 5-month mission, Honey Badger covered ∼5,690 km (3,070 nautical miles), acquired 9,336 holograms, and reliably transmitted data onshore in near real-time. Software issues developed with the active fluorescence sensor that terminated measurements in early September. Although images were still useful at the end of the mission, fouling of the LISST-Holo optics was considerable, and appeared to be the most significant issue facing deployments of this duration

Short-Term Toxicity of 1-Methylnaphthalene to Americamysis bahia and 5 Deep-Sea Crustaceans

There are few studies that have evaluated hydrocarbon toxicity to vertically migrating deep-sea micronekton. Crustaceans were collected alive using a 9-m2 Tucker trawl with a thermally insulated cod end and returned to the laboratory in 10 °C seawater. Toxicity of the polycyclic aromatic hydrocarbon 1-methylnaphthalene to Americamysis bahia, Janicella spinacauda, Systellaspis debilis, Sergestes sp., Sergia sp., and a euphausiid species was assessed in a constant exposure toxicity test utilizing a novel passive dosing toxicity testing protocol. The endpoint of the median lethal concentration tests was mortality, and the results revealed high sensitivity of the deep-sea micronekton compared with other species for which these data are available. Threshold concentrations were also used to calculate critical target lipid body burdens using the target lipid model

Characterizing the weather band variability of the Texas shelf current

Considering the benefits of understanding the circulation patterns of the shelf, it is not surprising that there are numerous studies of the Texas Shelf circulation patterns. Given that previous studies were focused on the low-frequency variability of the circulation which is upcoast (northeast flow) in the summer and downcoast (southwest flow) especially on the inner shelf in the non-summer seasons, this study investigates the weather band (2–15 days) variability of the Texas Shelf near-surface circulation pattern. Current meter data at 1.5 m below the sea surface from the inner, mid, and outer shelves were analyzed. This study demonstrated that there are high-frequency current reversals within the weather band in each season. From the estimated persistence of the currents during reversals, the inner and mid shelf currents are predominantly downcoast in the non-summer seasons and upcoast in the summer season whereas the outer shelf currents are mostly upcoast all year round. The Wavelets analysis of the currents revealed that most of the variabilities on the inner and mid shelf regions were within the 4-12-day band whereas on the outer shelf the dominant variability was within the 3–8-day band. From the cross-spectra analysis of both the currents and wind data, it was determined that the influence of the wind was more dominant on the inner and mid shelf regions at the 8–15-day band than on the outer shelf where the contribution of the wind is prevalent at the 2–4-day band

The Role of Microbial Exopolymers in Determining the Fate of Oil and Chemical Dispersants in the Ocean

The production of extracellular polymeric substances (EPS) by planktonic microbes can influence the fate of oil and chemical dispersants in the ocean through emulsification, degradation, dispersion, aggregation, and/or sedimentation. In turn, microbial community structure and function, including the production and character of EPS, is influenced by the concentration and chemical composition of oil and chemical dispersants. For example, the production of marine oil snow and its sedimentation and flocculent accumulation to the seafloor were observed on an expansive scale after the Deepwater Horizon oil spill in the Northern Gulf of Mexico in 2010, but little is known about the underlying control of these processes. Here, we review what we do know about microbially produced EPS, how oil and chemical dispersant can influence the production rate and chemical and physical properties of EPS, and ultimately the fate of oil in the water column. To improve our response to future oil spills, we need a better understanding of the biological and physiochemical controls of EPS production by microbes under a range of environmental conditions, and in this paper, we provide the key knowledge gaps that need to be filled to do so