Andrew M. Fischer

Variation beneath the surface: Quantifying complex thermal environments on coral reefs in the Caribbean, Bahamas and Florida

Analysis of in situ temperature records collected on six coral reefs in the Caribbean, Bahamas, and Florida Keys reveal significant variability across a range of temporal and spatial scales from minutes to seasons, across depths, and among sites. Subsurface variability occurring at daily and faster frequencies is prevalent across the region, likely driven by combinations of diurnal heating and cooling, wind driven advection, and internal waves at tidal and faster frequencies. This high frequency variability is not detected in records of remotely-sensed sea surface temperature alone. Diurnal variability likely caused by diurnal solar heating and cooling and possibly by advection associated with diurnal winds (daily sea breeze) was significant at all sites and showed greatest magnitude of variation at shallowest depths. Temperature fluctuations at tidal and faster frequencies were common at 5 out of the 6 sites. The magnitude of this variability is not well explained by measured vertical temperature stratification combined with oscillations of the water column associated with barotropic surface tides. Rather, the magnitude and nature of the temperature changes point to the presence of internal waves generated at tidal and faster frequencies. Power spectra calculated seasonally show greatest variability within both diurnal and semi-diurnal frequency bands in Spring and Summer at Florida, Bahamas, Jamaica, and St. Croix. Variability within the semi-diurnal frequency band at Belize and Bonaire was greatest in Winter. Warming in Summer estimated as degree-hours per day above 29.0°C increased with increasing latitude and varied significantly among sites and depths in a manner not predictable from remotely sensed SST data alone. Site latitude was directly related to the amplitude of the seasonal thermal variability, but was not tightly related to variability at daily and faster frequencies which was greatest at the highest and lowest latitude sites. The interactions of depth, site, and season across the study region are associated with distinct signals of thermal variability, and have significant implications for the physiology and ecology of corals and other reef organisms.

Characterizing estuarine plume discharge into the coastal ocean using fatty acid biomarkers and pigment analysis.

The transformation of estuaries by human activities continues to alter the biogeochemical balance of the coastal ocean. The disruption of this balance can negatively impact the provision of goods and services, including fisheries, commerce and transportation, recreation and esthetic enjoyment. Here we examine a link, between the Elkhorn Slough and the coastal ocean in Monterey Bay, California (USA) using a novel application of fatty acid and pigment analysis. Fatty acid analysis of filtered water samples showed biologically distinct water types between the Elkhorn Slough plume and the receiving waters of the coastal ocean. A remarkable feature of the biological content of the plume entering the coastal ocean was the abundance of bacteria-specific fatty acids, which correlated well with concentrations of colored dissolved organic matter (CDOM). Pigment analysis showed that plume waters contained higher concentrations of diatoms and cryptophytes, while the coastal ocean waters showed higher relative concentrations of dinoflagellates. Bacteria and cryptophytes can provide a source of labile, energy-rich organic matter that may be locally important as a source of food for pelagic and benthic communities. Surface and depth surveys of the plume show that the biogeochemical constituents of the slough waters are injected into the coastal waters and become entrained in the northward flowing, nearshore current of Monterey Bay. Transport of these materials to the northern portion of the bay can fuel a bloom incubator, which exists in this region. This study shows that fatty acid markers can reveal the biogeochemical interactions between estuaries and the coastal ocean and highlights how man-made changes have the potential to influence coastal ecological change.

Axisymmetric circulation driven by marginal heating in ice‐covered lakes

Below the temperature of maximum density (TMD) in freshwater lakes, heating at the lateral margins produces gravity currents along the bottom slope, akin to katabatic winds in the atmosphere and currents on continental shelves. We describe axisymmetric basin-scale circulation driven by heat flux at the shorelines in polar Lake Kilpisjarvi. A dense underflow originating near the shore converges toward the lake center, where it produces warm upwelling and return flow across the bulk of lake water column. The return flow, being subject to Coriolis force, creates a lake-wide anticyclonic gyre with velocities of 2–4 cm s-1. While warm underflows are common on ice-covered lakes, the key finding is the basin-scale anticyclonic gyre with warm upwelling in the core. This circulation mechanism provides a key to understanding transport processes in (semi) enclosed basins subject to negative buoyancy flux due to heating (or cooling at temperatures above TMD) at their lateral boundaries.

Performance of the MODIS FLH algorithm in estuarine waters: a multi-year 2003–2010 analysis from Tampa Bay, Florida USA

Although satellite technology promises great usefulness for the consistent monitoring of chlorophyll-α concentration in estuarine and coastal waters, the complex optical properties commonly found in these types of waters seriously challenge the application of this technology. Blue–green ratio algorithms are susceptible to interference from water constituents, different from phytoplankton, which dominate the remote-sensing signal. Alternatively, modelling and laboratory studies have not shown a decisive position on the use of near-infrared (NIR) algorithms based on the sun-induced chlorophyll fluorescence signal. In an analysis of a multi-year (2003–2010) in situ monitoring data set from Tampa Bay, Florida (USA), as a case, this study assesses the relationship between the fluorescence line height (FLH) product from the Moderate Resolution Imaging Spectrometer (MODIS) and chlorophyll-α.

Mining and other industry contributions to employment leakage in Australia's Northern Territory

Leakage of employment income is a pressing issue in the economic development of regional and remote communities. It can draw income away from regional economies but also inject new revenue from outside. Using Australian Bureau of Statistics 2011 census employment data by place of usual residence and place of work, we identify for all 17 Local Government Areas (LGAs) of the Northern Territory (NT), workers commuting out of and into each LGA. Using summary graphs and geospatial visualizations we find that while there is substantial leakage out of most LGAs there are also gains from those leaving an LGA to work and then returning home with their income. Overall, for most LGAs and all remote LGAs there is net leakage. In contrast, Wagait, Palmerston, Litchfield and Alice Springs experience net gains from work commuting. Core-Periphery staples theory (Carson 2011) helps explain these net gaining LGAs, but cannot be used to consistently explain net leakage or net gain for population centers and nearby periphery LGAs. Darwin, including parts of Unincorporated NT, together act as a net leakage core to surrounding commuter LGAs such as Palmerston, Litchfield and Wagait. Katherine also acts as a net leakage core for surrounding peripheral LGAs despite receiving some offsetting employment income gains through mining. In addition to Katherine, Mining and the supporting Construction industry are also delivering net employment income gains to the core centers of Darwin, Palmerston, and Litchfield from periphery and typically remote LGAs. For remote mining commuters, these core centers offer preferred places to live. In contrast to Darwin and Katherine, Alice Springs acts as an employment income sink drawing on net employment gains from periphery remote LGAs. Our geospatial visualizations also help to identify the leakage vulnerability of remote LGAs dependent on mining like Central Desert and East Arnhem. Of all the remote LGAs, East Arnhem has the highest average net leakage of income across the most diversified distribution of industries, primarily derived from mining and its supporting construction and upstream manufacturing industries. Combined, these factors make East Arnhem particularly vulnerable to mining related downturns. Also, Alice Springs and Coomalie are highly vulnerable to commuting in Business Services and Public and Personal Services respectively. However, these vulnerabilities also cloak hidden flexibilities to deal with job losses during downturns. Undertaking our analysis for a number of census years could help decision makers build scenarios for future economic development and employment.

Inter-annual variation in the density of anthropogenic debris in the Tasman Sea

An increasing number of studies highlight the risk of plastic pollution in the marine environment. However, systematic longitudinal data on the distribution and abundance of plastic debris remain sparse. Here we present the results of a two-year study of plastic pollution within the Tasman Sea, contrasted with a further year of data from the same region, in order to document how the density of debris varies across years in this area. Surface net tows were collected between Hobart, Tasmania and Sydney, Australia during the spring of 2013 and 2014 and compared with a subset of data from autumn 2012 from the same region. Substantial inter-annual variation in mean plastic abundance was observed over the three year period, ranging from to 248.04-3711.64pieceskm-2, confirming the need for multiple years of sampling to fully estimate the extent of, and trends in, plastic pollution.

Chlorophyll-a Estimation Around the Antarctica Peninsula Using Satellite Algorithms: Hints from Field Water Leaving Reflectance

Ocean color remote sensing significantly contributes to our understanding of phytoplankton distribution and abundance and primary productivity in the Southern Ocean (SO). However, the current SO in situ optical database is still insufficient and unevenly distributed. This limits the ability to produce robust and accurate measurements of satellite-based chlorophyll. Based on data collected on cruises around the Antarctica Peninsula (AP) on January 2014 and 2016, this research intends to enhance our knowledge of SO water and atmospheric optical characteristics and address satellite algorithm deficiency of ocean color products. We collected high resolution in situ water leaving reflectance (±1 nm band resolution), simultaneous in situ chlorophyll-a concentrations and satellite (MODIS and VIIRS) water leaving reflectance. Field samples show that clouds have a great impact on the visible green bands and are difficult to detect because NASA protocols apply the NIR band as a cloud contamination threshold. When compared to global case I water, water around the AP has lower water leaving reflectance and a narrower blue-green band ratio, which explains chlorophyll-a underestimation in high chlorophyll-a regions and overestimation in low chlorophyll-a regions. VIIRS shows higher spatial coverage and detection accuracy than MODIS. After coefficient improvement, VIIRS is able to predict chlorophyll a with 53% accuracy.

Environmental correlates of phenotypic variation: do variable tidal regimes influence morphology in intertidal seaweeds?

Seaweed morphology is often shaped by the hydrodynamic environment. However, exposure to air at low tide represents an additional factor potentially affecting the morphology of intertidal species. Here, we examined the relationships between the morphology of Hormosira banksii, an important intertidal habitat‐forming seaweed in southern Australia, and environmental factors across multiple spatial scales around the island of Tasmania, Australia. Tasmania is surrounded by a diverse coastline with differences in wave exposure, tidal parameters, and temperature. We sampled Hormosira from four regions (100s km apart), three sites (10s km apart) within each region, and two zones (meters apart; eulittoral and sublittoral) at each site, and measured multiple morphological variables to test for differences in morphology at those different spatial scales. Thirteen environmental variables reflecting wave exposure, tidal conditions, and temperature for each site were generated to assess the relationship between Hormosira morphology and environmental variation. Morphology varied at all spatial scales examined. Most notably, north coast individuals had a distinct morphology, generally having smaller vesicles and shorter fronds, compared to other regions. Tidal conditions were the main environmental factors separating north coast sites from other sites and tidal regime was identified as the best predictor of morphological differences between regions. In contrast to other studies, we found little evidence that wave exposure was associated with morphological variation. Overall, our study emphasizes the role of tidal conditions, associated with emersion stress during low tide, in affecting the morphology of intertidal seaweeds.

Improved Management Effectiveness of a Marine Protected Area through Prioritizing Performance Indicators

ABSTRACT The management success of a marine protected area (MPA) is essentially a social construct because people have differing views on what defines success. Conflicting opinions between stakeholders need to be identified and resolved to ensure these factors do not interfere with successful functioning of MPAs. This study looked at developing and prioritizing performance indicators for Maria Island Marine Nature Reserve (MIMNR), Australia. Performance indicators were developed for MIMNR based on an expert-led, structured framework and then prioritized using the Analytic Hierarchy Process (AHP), with respect to input from key informants of stakeholder groups. Results showed that all stakeholder groups agreed that management of MIMNR should first focus on “abundance and size of native species,” and that managers, fishers, and environmental nongovernmental organizations place a significantly higher priority on ecological over socioeconomic and governance performance indicators. Researchers placed even emphasis across all priorities. Results suggest that MIMNR should first focus on monitoring “abundance and size of native species” and demonstrates the capacity of the AHP to increase management effectiveness and improve the decision-making process. Furthermore, by identifying where discrepancies in preferences exist, the outcomes of this research can be used to enhance collaboration among stakeholders.

Fluorescence-based approach to estimate the chlorophyll-a concentration of a phytoplankton bloom in Ardley Cove (Antarctica)

A phytoplankton bloom occurred in Ardley Cove, King George Island in January 2016, during which maximum chlorophyll-a reached 9.87 mg/m3. Records show that blooms have previously not occurred in this area prior to 2010 and the average chlorophyll-a concentration between 1991 and 2009 was less than 2 mg/m3. Given the lack of in situ measurements and the poor performance of satellite algorithms in the Southern Ocean and Antarctic waters, we validate and assess several chlorophyll-a algorithms and apply an improved baseline fluorescence approach to examine this bloom event. In situ water properties including in vivo fluorescence, water leaving radiance, and solar irradiance were collected to evaluate satellite algorithms and characterize chlorophyll-a concentration, as well as dominant phytoplankton groups. The results validated the nFLH fluorescence baseline approach, resulting in a good agreement at this high latitude, high chlorophyll-a region with correlation at 59.46%. The dominant phytoplankton group within the bloom was micro-phytoplankton, occupying 79.58% of the total phytoplankton community. Increasing sea ice coverage and sea ice concentration are likely responsible for increasing phytoplankton blooms in the recent decade. Given the profound influence of climate change on sea-ice and phytoplankton dynamics in the region, it is imperative to develop accurate methods of estimating the spatial distribution and concentrations of the increasing occurrence of bloom events.