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Title: Effects of elevated pCO2 and light on growth, photosynthesis and calcification in Halimeda discoidea.
Creator: Peach, Katherine, Koch, Marguerite, Blackwelder, Patricia, Graduate College
Abstract/Description: We hypothesized that ocean acidification OA effects on calcifying benthic macroalgae are inextricably linked to light availability. To address this supposition, we examined OA and light effects on the calcifying green macroalga Halimeda discoidea, an important carbonate sediment producer in tropical reef ecosystems. An aquaria experiment was conducted to examine elevated pCO2 and light saturating vs. sub-saturating effects on photosynthesis, growth, calcification and crystal morphology....
Show moreWe hypothesized that ocean acidification OA effects on calcifying benthic macroalgae are inextricably linked to light availability. To address this supposition, we examined OA and light effects on the calcifying green macroalga Halimeda discoidea, an important carbonate sediment producer in tropical reef ecosystems. An aquaria experiment was conducted to examine elevated pCO2 and light saturating vs. sub-saturating effects on photosynthesis, growth, calcification and crystal morphology. Photosynthetic rates were enhanced under elevated pCO2 and saturating light. This upregulation of photosynthesis did not enhance calcification of new segments or the number of new segments produced. The lowest number of new segments was produced in the saturating light treatment. Scanning electron microscopy of new segments confirmed net calcification and production of aragonite crystals at 2100 pCO2 levels. Aragonite crystal size and abundance were unaffected by CO2 or light treatments. We also examined dissolution of nonliving segments and observed that without photosynthesis dead segments experienced greater dissolution and possessed smaller crystals under elevated pCO2. Our findings support the hypothesis that light plays a crucial role in calcifying macroalgal responses to OA. We further suggest that H. discoidea will maintain its role as a dominant reef sediment producer under year 2100 pCO2 levels.
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Date Issued: 2015
PURL: http://purl.flvc.org/fau/fd/FA00005906
Format: Document (PDF)

Title: Biotic Control of Surface pH and Evidence of Light-Induced H+ Pumping and Ca2+-H+ Exchange in a Tropical Crustose Coralline Alga.
Creator: Hofmann, Laurie C., Koch, Marguerite, de Beer, Dirk, Chin, Wei-Chun
Abstract/Description: Presently, an incomplete mechanistic understanding of tropical reef macroalgae photosynthesis and calcification restricts predictions of how these important autotrophs will respond to global change. Therefore, we investigated the mechanistic link between inorganic carbon uptake pathways, photosynthesis and calcification in a tropical crustose coralline alga (CCA) using microsensors. We measured pH, oxygen (O2), and calcium (Ca^2+) dynamics and fluxes at the thallus surface under ambient (8.1)...
Show morePresently, an incomplete mechanistic understanding of tropical reef macroalgae photosynthesis and calcification restricts predictions of how these important autotrophs will respond to global change. Therefore, we investigated the mechanistic link between inorganic carbon uptake pathways, photosynthesis and calcification in a tropical crustose coralline alga (CCA) using microsensors. We measured pH, oxygen (O2), and calcium (Ca^2+) dynamics and fluxes at the thallus surface under ambient (8.1) and low (7.8) seawater pH (pHSW) and across a range of irradiances. Acetazolamide (AZ) was used to inhibit extracellular carbonic anhydrase (CAext), which mediates hydrolysis of HCO3-, and 4,40 diisothiocyanatostilbene- 2,2'-disulphonate (DIDS) that blocks direct HCO3- uptake by anion exchange transport. Both inhibited photosynthesis, suggesting both diffusive uptake of CO2 via HCO3- hydrolysis to CO2 and direct HCO3- ion transport are important in this CCA. Surface pH was raised approximately 0.3 units at saturating irradiance, but less when CAext was inhibited. Surface pH was lower at pHSW 7.8 than pHSW 8.1 in the dark, but not in the light. The Ca^2+ fluxes were large, complex and temporally variable, but revealed net Ca2+ uptake under all conditions. The temporal variability in Ca^2+ dynamics was potentially related to localized dissolution during epithallial cell sloughing, a strategy of CCA to remove epiphytes. Simultaneous Ca^2+ and pH dynamics suggest the presence of Ca^2+/H^+ exchange. Rapid light-induced H^+ surface dynamics that continued after inhibition of photosynthesis revealed the presence of a light-mediated, but photosynthesis-independent, proton pump. Thus, the study indicates metabolic control of surface pH can occur in CCA through photosynthesis and light-inducible H^+ pumps. Our results suggest that complex light-induced ion pumps play an important role in biological processes related to inorganic carbon uptake and calcification in CCA.
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Date Issued: 2016-07-26
PURL: http://purl.flvc.org/fau/fd/FAUIR000029
Format: Citation

Title: Nest placement by three species of sea turtles in southeast Florida, USA.
Creator: Wood, Lawrence D., Florida Atlantic University, Koch, Marguerite
Abstract/Description: Studies of loggerhead, leatherback and green turtle nest distribution across beaches (between water and dune) have revealed conflicting random versus non-random patterns of nest placement. I examined nest placement on a southeast Florida beach (Juno and Jupiter) with average beach widths of 30 (natural) and 90 m (nourished beach) and tested slope as a proximal cue for nesting using long-term data sets and GPS technology. All three species had similar species-specific crawl lengths and nest...
Show moreStudies of loggerhead, leatherback and green turtle nest distribution across beaches (between water and dune) have revealed conflicting random versus non-random patterns of nest placement. I examined nest placement on a southeast Florida beach (Juno and Jupiter) with average beach widths of 30 (natural) and 90 m (nourished beach) and tested slope as a proximal cue for nesting using long-term data sets and GPS technology. All three species had similar species-specific crawl lengths and nest sites relative to distance from water, regardless of beach width. Loggerheads and leatherbacks crawled and nested significantly shorter median distances (8--14 m) relative to the water compared to greens (15 m), corresponding to sites of maximum productivity measured as percent hatchling success. The observed consistencies of crawl distance across all beach profiles suggest a strong evolutionary selection for a non-random crawl length at this study site, regardless of beach width and slight shifts in slope.
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Date Issued: 2004
PURL: http://purl.flvc.org/fcla/dt/13185
Subject Headings: Sea turtles--Florida--Palm Beach County, Loggerhead turtle--Florida, Sea turtles--Nests--Florida
Format: Document (PDF)

Title: Phosphorus uptake kinetics of the tropical seagrass Thalassia testudinum.
Creator: Gras, Amy Frances, Florida Atlantic University, Koch, Marguerite
Abstract/Description: Recent evidence indicates P-limitation in tropical seagrass beds, but to date no data are available on P kinetics of the dominant tropical seagrass Thalassia testudinum. In this study, T. testudinum leaves and roots exhibited Michaelis-Menten saturation kinetics under high (0.5 to 25 muM SRP) and low (0.5 to 5 muM SRP) P concentrations. Leaf Vmax was similar under light and dark conditions. Root Vmax under the high range was slightly lower (30%) in the dark and 2 to 3-fold lower than leaves...
Show moreRecent evidence indicates P-limitation in tropical seagrass beds, but to date no data are available on P kinetics of the dominant tropical seagrass Thalassia testudinum. In this study, T. testudinum leaves and roots exhibited Michaelis-Menten saturation kinetics under high (0.5 to 25 muM SRP) and low (0.5 to 5 muM SRP) P concentrations. Leaf Vmax was similar under light and dark conditions. Root Vmax under the high range was slightly lower (30%) in the dark and 2 to 3-fold lower than leaves in the light and dark. Leaf and root P uptake rates were similar at low substrate concentrations. A two-phase kinetic system appears to be functioning with lower values of leaf Vmax and Km at low P levels, indicating a higher affinity for P by leaves at lower P concentrations. In conclusion, T. testudinum leaf and root tissues may contribute similarly to plant P uptake at low concentrations.
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Date Issued: 2001
PURL: http://purl.flvc.org/fcla/dt/12767
Subject Headings: Thalassia, Seagrasses, Plants--Effect of phosphorus on
Format: Document (PDF)

$Sediment phosphorus fractionation in calcium carbonate sediments of northeastern Florida Bay$

Title: Sediment phosphorus fractionation in calcium carbonate sediments of northeastern Florida Bay.
Creator: Benz, Robert E., Jr., Florida Atlantic University, Koch, Marguerite
Abstract/Description: Different physiochemical processes control phosphorus storage in subtropical versus temperate estuaries; however, few studies are available on sediment phosphorus storage from the subtropics. In this study, solid-phase phosphorus pools of northeastern Florida Bay's sediments were examined by sequential chemical extractions, separating phosphorus into exchangeable, iron-bound, calcium-bound, and residual organic fractions. Calcium-bound phosphorus was the dominant fraction, accounting for...
Show moreDifferent physiochemical processes control phosphorus storage in subtropical versus temperate estuaries; however, few studies are available on sediment phosphorus storage from the subtropics. In this study, solid-phase phosphorus pools of northeastern Florida Bay's sediments were examined by sequential chemical extractions, separating phosphorus into exchangeable, iron-bound, calcium-bound, and residual organic fractions. Calcium-bound phosphorus was the dominant fraction, accounting for approximately 60% of the total phosphorus and 93% of the inorganic phosphorus. Residual organic phosphorus was the second dominant fraction, accounting for 37% of the total phosphorus. In contrast to calcium-bound and residual organic phosphorus, the concentration of iron-bound phosphorus was low, indicating a limited role of iron in long-term phosphorus storage. The fine-grained carbonate sediments of Florida Bay probably account for the large pool of calcium-bound phosphorus, while the proximity of the mangroves to the northeastern section of the Bay may account for the high residual organic pool of phosphorus.
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Date Issued: 2000
PURL: http://purl.flvc.org/fcla/dt/15763
Subject Headings: Water--Phosphorus content, Marine sediments--Florida--Florida Bay, Calcium carbonate, Florida Bay (Fla )--Environmental conditions
Format: Document (PDF)

Title: Seagrass (Thalassia testudinum) Nutrient Recycling in Florida Bay, a Carbonate-Dominated Shallow Estuary.
Creator: Rosch, Kara Baca, Koch, Marguerite, Florida Atlantic University
Abstract/Description: Nitrogen (N) and phosphorus (P) senescent leaf retention, as a measure of resorption, and the subsequent decay of senescent leaves, roots and rhizomes were examined for the dominant tropical seagrass species, Thalassia testudinum, across a nutrient gradient in Florida Bay. Leaf nutrient loss while still attached to the short shoot, from both resorption and decay, was highest at the nutrient-rich (88% P; 51% N) compared to nutrient-poor site ( 49% P; 25% N). High nutrient loss rates by...
Show moreNitrogen (N) and phosphorus (P) senescent leaf retention, as a measure of resorption, and the subsequent decay of senescent leaves, roots and rhizomes were examined for the dominant tropical seagrass species, Thalassia testudinum, across a nutrient gradient in Florida Bay. Leaf nutrient loss while still attached to the short shoot, from both resorption and decay, was highest at the nutrient-rich (88% P; 51% N) compared to nutrient-poor site ( 49% P; 25% N). High nutrient loss rates by attached leaves (0.37-2.5 mg P and 6.5-34 mg N m^-2 d^-1) represented significant recycling (46-87% P and 17-48% N) oftotal estimated external nutrient loads to the bay. In contrast, senescent leaf, rhizome and root nutrient loss rates were > 1 00-fold lower than intact leaves. In tropical /subtropical estuaries dominated by T testudinum, seagrasses may be acting as nutrient pumps, translocating high porewater nutrients to the overlying waters and promoting phytoplankton blooms in the bay.
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Date Issued: 2007
PURL: http://purl.flvc.org/fau/fd/FA00000822
Subject Headings: Estuarine ecology--Florida--Florida Bay, Seagrasses--Florida--Florida Bay, Stream ecology--Methodology, Climatic changes
Format: Document (PDF)

Title: Response of tropical marine macroalgae to thermal stress.
Creator: Anderson, Brent C., Florida Atlantic University, Koch, Marguerite
Abstract/Description: Short-term increases in temperatures above 31°C have been shown to influence the structure and diversity of coral reefs through coral bleaching episodes, but quantitative information on how these thermal events affect macroalgae on coral reef communities has rarely been described. Using laboratory mesocosm experiments, I examined six species of commonly occurring macroalgae from two functional form groups on the Florida Keys reef tract to determine their temperature thresholds, quantified by...
Show moreShort-term increases in temperatures above 31°C have been shown to influence the structure and diversity of coral reefs through coral bleaching episodes, but quantitative information on how these thermal events affect macroalgae on coral reef communities has rarely been described. Using laboratory mesocosm experiments, I examined six species of commonly occurring macroalgae from two functional form groups on the Florida Keys reef tract to determine their temperature thresholds, quantified by the point at which photosynthesis, quantum yield (Fv/Fm), and mortality rates were significantly affected. Red crustose coralline sp., classified in the calcareous group, showed no significant changes in Fv/Fm, and experienced no mortality at elevated temperatures of 34°C. However, Halimeda incrassata, another calcareous species showed significant changes in photosynthesis at thermal treatments of 32°C, and experienced 75% mortality at 34°C. Sargassum fluitans, a branching fleshy macroalgae maintained photosynthetic rates up to 32°C, but at 34°C succumbed to 100% mortality. Laurencia chondroides, also a branching fleshy macroalgal form experienced 50% mortality at 34°C. My results, among the first high temperature experiments on dominant tropical macroalgae, indicate that macroalgae are more robust than corals (∼32°C) in their thermal tolerance, but have varying thresholds among species.
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Date Issued: 2006
PURL: http://purl.flvc.org/fcla/dt/13394
Subject Headings: Marine algae--Florida--Florida Keys, Coral reef ecology--Florida--Florida Keys
Format: Document (PDF)

Title: Kinetic parameters and organic phosphorus remineralization potential of alkaline phosphatase activity in the tropical seagrass Thalassia testudinum and associated epiphyton.
Creator: Evans, Samantha Lorraine., Florida Atlantic University, Koch, Marguerite
Abstract/Description: Tropical carbonate estuaries are P-limited due to high carbonate sorption of DIP, therefore alternative P sources may represent an important contribution to the nutrient requirements of submerged aquatic vegetation. Alkaline phosphatase (AP'ase) is a cell-surface enzyme that allows aquatic plants to utilize the organic-P pool, and its activity (APA) may generate a significant portion of plant P-requirements in oligotrophic environments. Seasonal APA of the seagrass Thalassia testudinum and...
Show moreTropical carbonate estuaries are P-limited due to high carbonate sorption of DIP, therefore alternative P sources may represent an important contribution to the nutrient requirements of submerged aquatic vegetation. Alkaline phosphatase (AP'ase) is a cell-surface enzyme that allows aquatic plants to utilize the organic-P pool, and its activity (APA) may generate a significant portion of plant P-requirements in oligotrophic environments. Seasonal APA of the seagrass Thalassia testudinum and its epiphytic community was measured in NE Florida Bay. APA was higher for T. testudinum leaves with intact epiphytes (TTE) than for T. testudinum leaves alone (TT) in all seasons, and the spring growing season elicited the highest activities. Based on in situ PME levels (0.117--0.387muM), AP'ase P-remineralization rates were 0.326--2.181 for TTE and 0.237--0.823 for TT (mumol g-1 AFDW day-1), representing 26% and 4% of P-uptake, respectively. Therefore, APA may be an important P source to the seagrass-epiphyte consortium in tropical carbonate estuaries.
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Date Issued: 2000
PURL: http://purl.flvc.org/fcla/dt/12714
Subject Headings: Alkaline phosphatase, Thalassia
Format: Document (PDF)

Title: Sulfur-35 incorporation in the seagrass Thalassia testudinum under oxic and anoxic conditions.
Creator: Peters, Jasmine Star., Florida Atlantic University, Koch, Marguerite
Abstract/Description: Currently, there is a great deal of interest in the role of sulfur in the seagrass ecosystems and for sulfide, a known phytotoxin, in particular. This research used a 35S tracer technique to examine sulfur metabolism in the seagrass Thalassia testudinum. The uptake of the 35S radiotracer was documented at similar rates under both oxic and anoxic treatments. The highest total radioactivity was in root and rhizome tissue, as compared to the leaves. 35S translocation from roots to leaves was...
Show moreCurrently, there is a great deal of interest in the role of sulfur in the seagrass ecosystems and for sulfide, a known phytotoxin, in particular. This research used a 35S tracer technique to examine sulfur metabolism in the seagrass Thalassia testudinum. The uptake of the 35S radiotracer was documented at similar rates under both oxic and anoxic treatments. The highest total radioactivity was in root and rhizome tissue, as compared to the leaves. 35S translocation from roots to leaves was found to be more efficient in young versus mature leaves. Total sulfur uptake was estimated and found to be significantly different between root and rhizome tissue under oxic conditions. In the anoxic treatment, 1 mM sulfide may have been a threshold, at which the seagrass showed reduced uptake of 35S into the below-ground tissue. While the plants assisted in the production of sulfide in this experiment, sulfide accumulation may inhibit 35S uptake. This is counter to the idea of increased sulfide intrusion under sediment hypoxia. This study represents the first attempt to use 35S to trace sulfur incorporation into seagrass; further research will be required to understand the complex sulfur biochemistry of these important marine plants using this method.
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Date Issued: 2006
PURL: http://purl.flvc.org/fcla/dt/13385
Subject Headings: Seagrasses--Ecology, Sulfates--Physiological effect, Plant morphology, Marine sediments
Format: Document (PDF)

Title: Sulfide effects on Thalassia testudinum carbon balance and adenylate energy charge.
Creator: Erskine, James M., Florida Atlantic University, Koch, Marguerite
Abstract/Description: Sulfide accumulation in carbonate sediments of tropical seagrass communities may be responsible for widespread die-back of Thalassia testudinum in Florida Bay. Root hydroponic chambers were used to determine the effects of below-ground exposure to 0.0, 2.0, 4.0, 6.0, and 10.0 mM sulfides. T. testudinum ATP, energy charge, photosynthesis and growth responses were determined after 48 h under light saturation. Root ATP, energy charge and adenylate ratios were all significantly reduced (P
Show moreSulfide accumulation in carbonate sediments of tropical seagrass communities may be responsible for widespread die-back of Thalassia testudinum in Florida Bay. Root hydroponic chambers were used to determine the effects of below-ground exposure to 0.0, 2.0, 4.0, 6.0, and 10.0 mM sulfides. T. testudinum ATP, energy charge, photosynthesis and growth responses were determined after 48 h under light saturation. Root ATP, energy charge and adenylate ratios were all significantly reduced (P < 0.05) when exposed to 2.0-10.0 mM sulfides. Leaf elongation rates declined by an average of 43% in the 2.0-6.0 mM treatments and 63% in the 10.0 mM treatment. Although root energy charge, ATP production and leaf elongation rates declined after sulfide exposure, concentrations up to 10.0 mM failed to produce visual signs of sulfide toxicity or mortality. Photosynthesis and leaf EC remained high after sulfide treatments, suggesting a resilience of T. testudinum to short-term sulfide exposure.
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Date Issued: 1999
PURL: http://purl.flvc.org/fcla/dt/15672
Subject Headings: Adenylate cyclase, Hydrocharitaceae, Sulfates--Physiological effect, Photosynthesis
Format: Document (PDF)

Title: Alkaline Phosphatase Activity of Seagrass and Water Column Fractions in Florida Bay.
Creator: Kletou, Demetris, Koch, Marguerite, Florida Atlantic University, Charles E. Schmidt College of Science, Department of Biological Sciences
Abstract/Description: Few phosphorus (P) depleted coastal marine ecosystems have been examined for their capacity to hydrolyze phosphomonoesters (PMEs). The purpose of this study was to examine seasonal APA partitioning between water column fractions (phytoplankton, bacteria and freely dissolved) and benthic autotrophs in Florida Bay, a P limited shallow estuary using low fluorescent substrate (MUF-P) concentrations (≤2.0 μm). APA was higher at the western and northcentral (751 and 695 nmol L^-1 h^-1) sites and...
Show moreFew phosphorus (P) depleted coastal marine ecosystems have been examined for their capacity to hydrolyze phosphomonoesters (PMEs). The purpose of this study was to examine seasonal APA partitioning between water column fractions (phytoplankton, bacteria and freely dissolved) and benthic autotrophs in Florida Bay, a P limited shallow estuary using low fluorescent substrate (MUF-P) concentrations (≤2.0 μm). APA was higher at the western and northcentral (751 and 695 nmol L^-1 h^-1) sites and driven by cyanobacterial blooms, compared to the P limited northeastern (359 nmol L^-1 h^-1) site The free dissolved fraction (<0.2 μm) accounted for the most APA (~50%), followed by the phytoplankton (>1 μm; 30%) and bacteria fraction (<0.2-> 1.2 μm; 8%). Thaiassia testudinum leaves with their associated epiphytes contributed modestly to water column APA (14 and 20%), and only during non-bloom conditions. Rapid hydrolysis of PMEs (undetected in most samplings) in Florida Bay is probably driven by high concentration of organic substrates for microbial and cyanobacterial activity which results from the close association of the shallow water column with the underlying seagrass community and adjacent Everglades wetlands.
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Date Issued: 2007
PURL: http://purl.flvc.org/fau/fd/FA00000780
Subject Headings: Coastal ecology--Florida, Coastal zone management--Florida, Estuarine sediments--Florida--Florida Bay, Aquaculture--Environmental aspects--Florida
Format: Document (PDF)

Title: CLIMATE CHANGE AND OCEAN ACIDIFICATION EFFECTS ON TROPICAL REEF MACROALGAE.
Creator: McNicholl, Conall, Koch, Marguerite S., Florida Atlantic University, Department of Biological Sciences, Charles E. Schmidt College of Science
Abstract/Description: Tropical marine macroalgae perform an essential role in coral reef function and health, however, their persistence in a rapidly changing ocean remains uncertain. The rise in sea surface temperatures and decrease in pH (ocean acidification = OA) are predicted to have damaging effects on marine calcifiers. Calcifying macroalgae have varied, often negative, responses to these conditions, however our lack of understanding about the mechanisms involved with calcification prevent us from...
Show moreTropical marine macroalgae perform an essential role in coral reef function and health, however, their persistence in a rapidly changing ocean remains uncertain. The rise in sea surface temperatures and decrease in pH (ocean acidification = OA) are predicted to have damaging effects on marine calcifiers. Calcifying macroalgae have varied, often negative, responses to these conditions, however our lack of understanding about the mechanisms involved with calcification prevent us from interpreting these results fully. Thus, I conducted a series of experiments on five calcifying species, utilizing microsensors, radioisotopes, and mesocosms, in an attempt to define biotic and abiotic mechanisms involved in calcification and dissolution under OA. Microsensor work demonstrated that all species elevate the thalli surface pH 2-3X higher under OA, which promoted calcification. The use of a photosynthetic inhibitor revealed species-specific light-triggered thalli pH control that stimulated calcification, indicating strong biotic control over calcification. When exposed to OA conditions, stronger organismal control over calcification was shown to maintain calcification in the light. A major gap in our understanding of calcification under OA is whether it affects organismal capacity to form new calcium carbonate, or if dissolution occurs, reducing calcification rates. Using radioisotopes, I found that the ability to form new calcium carbonate under OA in the light was not affected in any species. This suggested that species with reduced net calcification were actually experiencing dissolution. This study also highlighted that all species were experiencing dissolution in the dark under OA. Finally, in a short-term growth experiment, I examined the combined effects of OA and increased temperature and found complex responses in species that are negatively affected by OA. This included a crustose coralline that appears to have an additive negative effect where temperature enhances the effect of OA but also a species that exhibited a negative effect which was evidently offset with increased temperature. Here, I define distinct abiotic (light, temperature, dissolution) and biotic (proton pump & photosynthesis), that are essential for understanding macroalgae persistence on future coral reefs.
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Date Issued: 2019
PURL: http://purl.flvc.org/fau/fd/FA00013397
Subject Headings: Coral reefs, Seaweed, Climate Change, Ocean acidification
Format: Document (PDF)

Title: Elevated pCO2 effects on the macroalgal genus Halimeda: Potential roles of photophysiology and morphology.
Creator: Peach, Katherine, Koch, Marguerite, Florida Atlantic University, Charles E. Schmidt College of Science, Department of Biological Sciences
Abstract/Description: While ocean acidification (OA) is predicted to inhibit calcification in marine macroalgae, species whose photosynthesis is limited by current dissolved inorganic carbon (DIC) levels may benefit. Furthermore, variations in macroalgal morphology will likely give rise to a range of OA tolerance in calcifying macroalgae. One genus of calcifying macroalgae that has shown varying species’ tolerance to OA is Halimeda, a major carbonate sediment producer on tropical reefs. Species within this genus...
Show moreWhile ocean acidification (OA) is predicted to inhibit calcification in marine macroalgae, species whose photosynthesis is limited by current dissolved inorganic carbon (DIC) levels may benefit. Furthermore, variations in macroalgal morphology will likely give rise to a range of OA tolerance in calcifying macroalgae. One genus of calcifying macroalgae that has shown varying species’ tolerance to OA is Halimeda, a major carbonate sediment producer on tropical reefs. Species within this genus occupy a range of habitats within tropical environments (reefs and lagoons), illustrating their ability to adapt to diverse environmental conditions (e.g. carbonate chemistry, irradiance). To date it is not clear if morphological and photophysiological diversity in Halimeda will translate to different tolerances to OA conditions (elevated pCO2 and lower pH).
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Date Issued: 2016
PURL: http://purl.flvc.org/fau/fd/FA00004621
Subject Headings: Coral reef ecology., Chemical oceanography., Halimeda., Environmental mapping., Plants--Effect of light on., Plant physiology., Photobiology., Carbon cycle (Biogeochemistry)
Format: Document (PDF)

Title: Ocean Acidification Effects on Photosynthesis in Tropical Marine Macroalgae.
Creator: Zweng, Regina C., Koch, Marguerite, Florida Atlantic University, Charles E. Schmidt College of Science, Department of Biological Sciences
Abstract/Description: Field data from CO2 vents, a current model of future ocean acidification conditions, show a positive correlation between elevated seawater pCO2 and fleshy macroalgal abundance, as well as a negative correlation between elevated seawater pCO2 and calcareous macroalgal abundance on coral reefs. One underlying physiological mechanism for increases of fleshy macroalgae species in response to greater pCO2 could be an increase in their photosynthesis. Furthermore, inorganic carbon use mechanisms,...
Show moreField data from CO2 vents, a current model of future ocean acidification conditions, show a positive correlation between elevated seawater pCO2 and fleshy macroalgal abundance, as well as a negative correlation between elevated seawater pCO2 and calcareous macroalgal abundance on coral reefs. One underlying physiological mechanism for increases of fleshy macroalgae species in response to greater pCO2 could be an increase in their photosynthesis. Furthermore, inorganic carbon use mechanisms, irradiance and depth may influence species-specific responses to ocean acidification. Therefore, this thesis aimed to discern carbon use strategies and photosynthetic responses to elevated pCO2 of dominant tropical fleshy and calcareous macroalgae. All species studied were able to utilize HCO3 - for photosynthesis. 33% of calcifying macroalgae and 80% of fleshy macroalgae had increased photosynthetic rates in response to lower pH. Thus, future conditions of OA may perpetuate or exacerbate the abundance of fleshy seaweeds at the expense of calcareous species.
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Date Issued: 2017
PURL: http://purl.flvc.org/fau/fd/FA00004879, http://purl.flvc.org/fau/fd/FA00004879
Subject Headings: Marine algae--Ecophysiology., Algal communities--Monitoriing., Coral reef ecology.
Format: Document (PDF)

Title: Tropical crustose coralline algal community and individual growth responses to light and elevated pCO2.
Creator: Dutra, Elizabeth A., Koch, Marguerite, Florida Atlantic University, Charles E. Schmidt College of Science, Department of Biological Sciences
Abstract/Description: Crustose coralline algae (CCA) are important reef stabilizers and their susceptibility to anthropogenic climate change and ocean acidification (OA) is of concern. Ocean acidification effects on benthic algal communities were determined by the response of CCA, fleshy macroalgae and microalgae to the interaction of pCO2 and light. I examined if elevated pCO2 and light influences CCA dominance by assessing their growth, recruitment and calcification. Elevated pCO2 under natural reef diurnal CO2...
Show moreCrustose coralline algae (CCA) are important reef stabilizers and their susceptibility to anthropogenic climate change and ocean acidification (OA) is of concern. Ocean acidification effects on benthic algal communities were determined by the response of CCA, fleshy macroalgae and microalgae to the interaction of pCO2 and light. I examined if elevated pCO2 and light influences CCA dominance by assessing their growth, recruitment and calcification. Elevated pCO2 under natural reef diurnal CO2 cycles did not significantly affect CCA percent cover, calcification rates or survival of adult CCA lobes. No significant community pCO2 effects were observed, rather light controlled dominance. The percent cover of microalgae increased in highlight, while CCA increased in the shade. My results indicate that algal response to irradiance is a more significant driver of reef benthic algal change than pCO2 levels predicted for 2100; however, this conclusion should be corroborated in longer-term and in field experiments.
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Date Issued: 2015
PURL: http://purl.flvc.org/fau/fd/FA00004365, http://purl.flvc.org/fau/fd/FA00004365
Subject Headings: Marine algae, Algal communities--Monitoring, Coral reef ecology
Format: Document (PDF)

Title: Mechanisms Controlling Distribution of Cosmopolitan Submerged Aquatic Vegetation: A Model Study of Ruppia maritima L. (widgeongrass) at the Everglades-Florida Bay Ecotone.
Creator: Strazisar, Theresa, Koch, Marguerite, Florida Atlantic University, Charles E. Schmidt College of Science, Department of Biological Sciences
Abstract/Description: Aquatic plants and submerged aquatic vegetation (SAV) are some of the most wide-ranging species and create important habitat for fish and wildlife in many ecosystems, including highly variable coastal ecotones. Mechanistically understanding factors controlling current distributions of these species is critical to project future distribution and abundance under increasing variability and climate change. I used a population-based approach to quantify the effects of spatial and temporal...
Show moreAquatic plants and submerged aquatic vegetation (SAV) are some of the most wide-ranging species and create important habitat for fish and wildlife in many ecosystems, including highly variable coastal ecotones. Mechanistically understanding factors controlling current distributions of these species is critical to project future distribution and abundance under increasing variability and climate change. I used a population-based approach to quantify the effects of spatial and temporal variability on life history transitions of the SAV Ruppia maritima L. (widgeongrass) in the highly dynamic Everglades-Florida Bay ecotone as a model to (1) examine which life history stages were most constrained by these conditions and (2) determine how management can promote life history development to enhance its distribution, an Everglades restoration target. Ruppia maritima life history transitions were quantified in a series of laboratory and field experiments encompassing a ra nge of abiotic and biotic factors known to affect seagrass and SAV (salinity, salinity variability, temperature, light and nutrients and seed bank recruitment and competition). These studies revealed that R. maritima life history varied east to west across the Everglades ecotone, driven by multiple gradients in abiotic factors that constrained different life history transitions in distinct ways. Based on this examination, persistence of SAV populations from dynamic coastal environments is highly dependent on large reproductive events that produce high propagule densities for recruitment. Large productive meadows of SAV also depend on high rates of clonal reproduction where vegetation completely regenerates in a short amount of time. Therefore, in hydrologically variable systems, maintenance or increases in SAV reproduction is required for population persistence through recruitment. However, SAV communities that do not experience high rates of sexual reproduction are dependent on successful seed germination, seedling and adult survival and clonal reproduction for biomass production and maintenance. Seedling survival and to a lesser extent, adult survival, are bottlenecks that can limit life history transitions under highly variable hydrological conditions. To ensure long-term survival in these communities, management activities that increase survival and successful life history development through these critical stages will be beneficial. If not, SAV populations may become highly reduced and ephemeral, providing less productive habitat.
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Date Issued: 2015
PURL: http://purl.flvc.org/fau/fd/FA00004549, http://purl.flvc.org/fau/fd/FA00004549
Subject Headings: Coastal zone management, Ruppia maritima -- Ecology -- Everglades National Park (Fla.), Ruppia maritima -- Ecology -- Florida Bay (Fla.), Seagrasses -- Everglades National Park (Fla.), Seagrasses -- Florida Bay (Fla.), Wetland ecology -- Everglades National Park (Fla.), Wetland ecology -- Florida Bay (Fla.)
Format: Document (PDF)

Title: The role of symbiotic dinoflagellates in the temperature-induced bleaching response of Aiptasia pallida.
Creator: Perez, Santiago F., Florida Atlantic University, Marsh, G. Alex, Cook, Clayton B., Brooks, W. Randy, Koch, Marguerite
Abstract/Description: Bleaching of reef corals and other cnidarians symbiotic with zooxanthellae can be attributed to the stress response of the host, algae or both. To determine if zooxanthellae are involved in the bleaching process, I infected a single strain of sea anemone, Aiptasia pallida with zooxanthellae from different hosts. I measured expulsion of the algae from the host during 24-hour incubations at 25, 32 and 34C, as well as photosynthetic rates at these temperatures. Photosynthesis and expulsion of...
Show moreBleaching of reef corals and other cnidarians symbiotic with zooxanthellae can be attributed to the stress response of the host, algae or both. To determine if zooxanthellae are involved in the bleaching process, I infected a single strain of sea anemone, Aiptasia pallida with zooxanthellae from different hosts. I measured expulsion of the algae from the host during 24-hour incubations at 25, 32 and 34C, as well as photosynthetic rates at these temperatures. Photosynthesis and expulsion of zooxanthellae were inversely and directly proportional to elevated temperatures, respectively. Photosynthesis and expulsion of zooxanthellae isolated from Condylactis gigantea showed the greatest sensitivity to elevated temperature when compared to other zooxanthellae tested. These results suggest that zooxanthellae have a function in the bleaching process and that this function may be related to their photosynthetic response. Thus, the differential tolerance of zooxanthellae to stress could partly explain the spatial variability characteristic of coral-bleaching episodes.
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Date Issued: 1999
PURL: http://purl.flvc.org/fcla/dt/15698
Subject Headings: Dinoflagellates, Sea anemones, Coral reef ecology, Seawater--Thermal properties
Format: Document (PDF)

Title: Trophic linkages of primary producers and consumers in fringing mangroves of tropical lagoons.
Creator: Kieckbusch, David Keith, Florida Atlantic University, Koch, Marguerite, Charles E. Schmidt College of Science, Department of Biological Sciences
Abstract/Description: Stable carbon and nitrogen isotope ratios were analyzed to investigate the trophic linkages between primary producers and consumers in fringing mangrove ecosystems of The Bahamas and Biscayne Bay, Florida. The isotope ratios, in conjunction with stomach content analysis, were used to trace the flow of organic matter from the primary organic sources (mangroves, seagrass and macro-algae) to primary consumers and ultimately to the gray snapper (Lutjanus griseus). We found the mean delta^13C...
Show moreStable carbon and nitrogen isotope ratios were analyzed to investigate the trophic linkages between primary producers and consumers in fringing mangrove ecosystems of The Bahamas and Biscayne Bay, Florida. The isotope ratios, in conjunction with stomach content analysis, were used to trace the flow of organic matter from the primary organic sources (mangroves, seagrass and macro-algae) to primary consumers and ultimately to the gray snapper (Lutjanus griseus). We found the mean delta^13C value of the primary consumers (-17.1%) to be closely related to the mean values of the macro-algal material (-16.7%) and the seagrass (-10.5%) with very little correlation to the carbon signature of mangroves (mean = -27.4%). Our results suggest the ultimate source of carbon for the primary and secondary consumers, located at our study sites, is algal and seagrass material, individually or possibly as a mixture, and that mangroves are not the sole source of carbon in these systems.
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Date Issued: 2001
PURL: http://purl.flvc.org/fcla/dt/12754
Subject Headings: Mangrove ecology, Food chains (Ecology)
Format: Document (PDF)

Title: SUSCEPTIBILITY OF RECRUITING SEAGRASS (THALASSIA TESTUDINUM) TO POREWATER H2S IN FLORIDA BAY.
Creator: MacLeod, Kasey, Koch, Marguerite, Florida Atlantic University, Department of Biological Sciences, Charles E. Schmidt College of Science
Abstract/Description: This study investigated the influence of high concentrations of porewater H2S (~100 μM) on recruitment of the tropical dominant seagrass species, Thalassia testudinum, following mortality events or "die-offs" in Florida Bay. Major seagrass die-off events (>50 km2) are occurring globally in coastal regions with mortality frequently linked to hypoxia and sediment-derived hydrogen sulfide (H2S) exposure, a well-known phytotoxin. In tropical carbonate environments, such as Florida Bay, low iron...
Show moreThis study investigated the influence of high concentrations of porewater H2S (~100 μM) on recruitment of the tropical dominant seagrass species, Thalassia testudinum, following mortality events or "die-offs" in Florida Bay. Major seagrass die-off events (>50 km2) are occurring globally in coastal regions with mortality frequently linked to hypoxia and sediment-derived hydrogen sulfide (H2S) exposure, a well-known phytotoxin. In tropical carbonate environments, such as Florida Bay, low iron in sediments promote H2S accumulation and subsequent intrusion into seagrass meristematic tissue through roots, and root-shoot junctions. While H2S intrusion into meristematic tissue is a leading hypothesis for large-scale seagrass mortality events, it is less clear if H2S contributes to a decline in seagrass recruitment following large-scale seagrass die-off events. Herein, I examined tissue stable sulfur isotope signatures (d34S), belowground tissue biomass partitioning, and internal O2/H2S dynamics of newly recovering shoots over seasons at a western Florida Bay site with recurrent die-off events. Tissue results showed less H2S accumulation in tissue samples of shoots recruiting into bare sediment patches compared to tissue samples from adjacent T. testudinum and H. wrightii seagrass meadows. Additionally, internal gas dynamics of recruits showed high pO2 during the day, and no detection of meristematic H2S intrusion, despite meristem hypoxia for several hours during the night. Recruiting shoots consistently have low root biomass, likely contributing to a lack of meristem H2S intrusion, as young, minimally developed, or lack of roots in recruiting shoots limit H2S intrusion. These results lead me to suggest that high H2S levels in porewater of western Florida Bay does not limit T. testudinum recruitment into open bare patches following major die-off events, supported by the recovery, albeit slow, of this species based long-term monitoring of seagrass in the Bay.
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Date Issued: 2022
PURL: http://purl.flvc.org/fau/fd/FA00014030
Subject Headings: Thalassia testudinum, Seagrasses, Hydrogen sulfide, Pore water
Format: Document (PDF)

Title: INTERNAL OXYGEN DYNAMICS AND RHIZOSPHERE OXIDATION IN TROPICAL SEAGRASS, THALASSIA TESTUDINUM.
Creator: Winn, Nathaniel, Koch-Rose, Marguerite, Florida Atlantic University, Department of Environmental Sciences, Charles E. Schmidt College of Science
Abstract/Description: Large-scale seagrass mortality events have been linked to internal hypoxia and exposure to phytotoxins in the sediment, such as hydrogen sulfide (H2S). Although seagrasses can transport oxygen (O2) to belowground tissues (rhizomes and roots) and into surrounding sediment to prevent H2S intrusion, reoccurring seagrass mortality events from H2S exposure continue. In the present study, I examined the potential of tropical seagrass Thalassia testudinum to transport O2 effectively to belowground...
Show moreLarge-scale seagrass mortality events have been linked to internal hypoxia and exposure to phytotoxins in the sediment, such as hydrogen sulfide (H2S). Although seagrasses can transport oxygen (O2) to belowground tissues (rhizomes and roots) and into surrounding sediment to prevent H2S intrusion, reoccurring seagrass mortality events from H2S exposure continue. In the present study, I examined the potential of tropical seagrass Thalassia testudinum to transport O2 effectively to belowground tissues and diffuse O2 into Florida Bay sediment around the root rhizosphere or sediment-root interface to constrain H2S diffusion into the roots. My approach was to (1) examine the spatial distribution of O2 in the rhizosphere during the light and dark with 2-D planar optode sensors, (2) examine patterns of root O2 loss (ROL) with O2 dye tracing experiments, and (3) measure O2 and H2S dynamics in internal tissues and rhizospheres. My results indicate that T. testudinum effectively sustains oxidation in belowground tissues to constrain H2S, but minimal evidence of ROL into the rhizosphere.
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Date Issued: 2023
PURL: http://purl.flvc.org/fau/fd/FA00014365
Subject Headings: Turtle grass Seagrasses, Thalassia testudinum, Hydrogen sulfide--Environmental aspects, Rhizosphere
Format: Document (PDF)

FAU Theses and Dissertations (18)	+ -
FAU College Collections (2)	+ -
FAU Graduate Student Research (1)	+ -

Coral reef ecology (2)	+ -
Coral reef ecology. (2)	+ -
Seagrasses (2)	+ -
Sulfates--Physiological effect (2)	+ -
Thalassia (2)	+ -

Thalassia testudinum (2)	+ -
Adenylate cyclase (1)	+ -
Algal communities--Monitoriing. (1)	+ -
Algal communities--Monitoring (1)	+ -
Alkaline phosphatase (1)	+ -
Aquaculture--Environmental aspects--Florida (1)	+ -
Calcium carbonate (1)	+ -
Carbon cycle (Biogeochemistry) (1)	+ -
Chemical oceanography. (1)	+ -
Climate Change (1)	+ -
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Coastal ecology--Florida (1)	+ -
Coastal zone management (1)	+ -
Coastal zone management--Florida (1)	+ -
Coral reef ecology--Florida--Florida Keys (1)	+ -
Coral reefs (1)	+ -
Dinoflagellates (1)	+ -
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Estuarine ecology--Florida--Florida Bay (1)	+ -
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Florida Bay (Fla )--Environmental conditions (1)	+ -
Food chains (Ecology) (1)	+ -
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Hydrogen sulfide (1)	+ -

Electronic Thesis or Dissertation (18)	+ -
article (1)	+ -
poster (1)	+ -
report (1)	+ -

Koch, Marguerite (19)	+ -
Florida Atlantic University (18)	+ -
Charles E. Schmidt College of Science (10)	+ -
Department of Biological Sciences (8)	+ -
Peach, Katherine (2)	+ -

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