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, 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. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2017. / FAU Electronic Theses and Dissertations Collection

The ecophysiology of the red alga Gelidium pristoides (Turner) Kuetzing was investigated in an effort to establish a technique for commercial cultivation. The seaweed is of commercial importance in South Africa where it is harvested from the intertidal zone rocky shores along the coast. It is dried and exported abroad for the extraction of agar. Yields and quality could be improved by cultivation in commercial systems. However, attempts at growing the seaweed in experimental systems have all ended in failure. This study aimed to describe the conditions in which the seaweed grows naturally; and investigate its physiological response to selected physical conditions in the laboratory in order to determine suitable conditions for mariculture. Ecological studies showed that G. pristoides grew above the spring low tide water level. The upper limit of the seaweed’s vertical distribution range, as well as its abundance, was largely dependent on wave exposure. The zone normally inhabited by G. pristoides was dominated by coralline turf in sheltered areas, while the abundance of G. pristoides increased towards more exposed rocky shore sites. The seaweed occurred among species such as Pattelid limpets and barnacles, but was usually the dominant macroalga in this zone, with coralline turf and encrusting algae being the only others. Physical conditions in the part of the intertidal zone inhabited by G. pristoides were highly variable. During low tide temperatures could vary by as much as 10°C within the three hours between tidal inundation of the seaweed population, while salinity varied by up to 9 ppt, and light intensity by as much as 800 μmol m-2 s-1. During these exposure periods the seaweed suffered up to 20% moisture loss. Laboratory experiments on the seaweed’s response to these conditions indicated that it was well adapted to such fluctuations. It had a broad salinity (20 and 40 ppt), and temperature tolerance range (18 to 24°C), with an o ptimum of temperature of 21°C for photosynthesis, while there was no difference in the photosynthetic rate of the alga within the 20 to 40 ppt salinity range. The alga had a low saturating irradiance (ca. 45 – 80 μmol m-2 s-1) equipping it well for photosynthesis in turbulent environments, with high light attenuation, but poorly to unattenuated light conditions. Exposure resulted in an initial increase in photosynthetic rate followed by a gradual decrease thereafter. pH drift experiments showed that low seawater pH, and associated increased carbon dioxide availability, resulted in an increase in photosynthetic rate. This response suggests that the seaweed has a high affinity for carbon dioxide, while the reduction in photosynthetic rate in response to bicarbonate use inhibition indicates that it also has the capacity for bicarbonate use. The high affinity of Gelidium pristoides for carbon dioxide as an inorganic carbon source appears to be the primary reason for the low abundance of the alga on sheltered rocky shore areas, and also explains the failure of the alga to grow in tank or open-water mariculture systems. Exposed rocky shores have experience heavy wave action, and the resultant aeration and mixing of nearshore waters increases the availability of carbon dioxide, which is considered a limiting resource. The absence of such mixing and aeration at sheltered site makes this less suitable habitat for G. pristoides. Periodic exposure also makes high levels of atmospheric carbon dioxide available from which the seaweed benefits. The traditional mariculture systems in which attempts have been made to cultivate the seaweed failed to satisfy either of the above conditions.

Macroalgal blooms are responses to nutrient enrichment in shallow seagrass ecosystems like the Indian River Lagoon (IRL), Florida. Little is known about nitrogen (N) and phosphorus (P) limitation or the importance of morphological/physiological characteristics of bloom-forming macroalgae (Ulva lactuca, Hypnea musciformis, and Gracilaria tikvahiae) in the IRL. We hypothesized: 1) all species would proliferate in nutrient-rich Titusville, 2) opportunistic U. lactuca would dominate, 3) Rapid Light Curves (RLCs) would assess nutrient status, and 4) nutrient concentrations would regulate growth more than N:P ratios. Field studies showed rapid biomass doubling times of 2 days (U. lactuca; November 2012) in urbanized Titusville. RLCs in a guano-enriched island off Big Pine Key (BPK) and Titusville (Ulva spp.) were similar due to P-saturation. Laboratory studies showed three-fold higher RLCs and two-fold faster growth at high nutrient concentrations of N and P. Reductions of both N and P will be required to moderate future blooms. / by Lisa N.A. Vlaming. / Thesis (M.S.)--Florida Atlantic University, 2013. / Includes bibliography. / Mode of access: World Wide Web. / System requirements: Adobe Reader.