Shrimp farming: Where does the carbon go?

Abstract The muscle tissues of the Litopenaeus vannamei shrimp grown in ponds through organic and traditional (intensive) management show that δ13C values were similar amongst the shrimp. Shrimp grown in the traditional pond were enriched in 13C by 7‰ relative to the carbon isotope ratios of their feed. The differences in the carbon isotope ratios of shrimp and feed in the traditional pond shows that the feed is not the main carbon source for shrimp grown in the traditional intensive management. Using mass balance we calculate that feed in traditional culture contributes at most 13% of the shrimp's carbon biomass

Growth and gas exchange responses of Brazilian pepper (Schinus terebinthifolius) and native South Florida species to salinity

Schinus terebinthifolius Raddi (Schinus) is an invasive exotic species widely found in disturbed and native communities of Florida. This species has been shown to displace native species as well as alter community structure and function. The purpose of this study was to determine if the growth and gas exchange patterns of Schinus, under differing salinity conditions, were different from native species. Two native upland glycophytic species (Rapanea punctata and Randia aculeata) and two native mangrove species (Rhizophora mangle and Laguncularia racemosa) were compared with the exotic. Overall, the exotics morphologic changes and gas exchange patterns were most similar to R. mangle. Across treatments, increasing salinity decreased relative growth rate (RGR), leaf area ratio (LAR) and specific leaf area (SLA) but did not affect root/shoot ratios (R:S). Allocation patterns were however significantly different among species. The largest proportion of Schinus biomass was allocated to stems (47%), resulting in plants that were generally taller than the other species. Schinus also had the highest SLA and largest total leaf area of all species. This meant that the exotic, which was taller and had thinner leaves, was potentially able to maintain photosynthetic area comparable to native species. Schinus response patterns show that this exotic exhibits some physiological tolerance for saline conditions. Coupled with its biomass allocation patterns (more stem biomass and large area of thin leaves), the growth traits of this exotic potentially provide this species an advantage over native plants in terms of light acquisition in a brackish forested ecosystem

Water Uptake Patterns of an Invasive Exotic Plant in Coastal Saline Habitats

Schinus terebinthifolius Raddi (Schinus) is one of the most widely found woody exotic species in South Florida. This exotic is distributed across environments with different hydrologic regimes, from upland pine forests to the edges of sawgrass marshes and into saline mangrove forests. To determine if this invasive exotic had different physiological attributes compared to native species in a coastal habitat, we measured predawn xylem water potentials (Ψ), oxygen stable isotope signatures (δ18O), and sodium (Na+) and potassium (K+) contents of sap water from plants within: (1) a transition zone (between a mangrove forest and upland pineland) and (2) an upland pineland in Southwest Florida. Under dynamic salinity and hydrologic conditions, Ψ of Schinus appeared less subject to fluctuations caused by seasonality when compared with native species. Although stem water δ18O values could not be used to distinguish the depth of Schinus and native species\u27 water uptake in the transition zone, Ψ and sap Na+/K+ patterns showed that Schinus was less of a salt excluder relative to the native upland species during the dry season. This exotic also exhibited Na+/K+ ratios similar to the mangrove species, indicating some salinity tolerance. In the upland pineland, Schinus water uptake patterns were not significantly different from those of native species. Differences between Schinus and native upland species, however, may provide this exotic an advantage over native species within mangrove transition zones

Comparative study of water uptake and photosynthetic gas exchange between scrub and fringe red mangroves, Rhizophora mangle L

The red mangrove (Rhizophora mangle L.) occurs frequently in both scrub and fringe mangrove forests. Our previous study demonstrated that individuals of this mangrove species growing in scrub and fringe forests differ significantly in both morphological and physiological characteristics. To further characterize physiological differences between scrub and fringe mangroves, we compared their differences in water uptake and photosynthetic gas exchange during different seasons. In the wet season (June-October, 1990), scrub mangroves showed lower δD and δO values of stem water than fringe mangroves, indicating more usage of rain-derived freshwater. In the dry season (Jan-April, 1991), however, scrub mangroves utilized the same water source as fringe mangroves, reflected by their similar δD and δO values of stem water. Consistently, there were significant differences in predawn water potentials between scrub and fringe mangroves in the wet season (October 1990) with higher values for scrub mangroves, but no significant differences in the dry season (January 1991). Higher elevation in the scrub forest seems to be the major factor responsible for the shift of water sources in scrub mangroves. On Apr. 27 and Aug. 8, 1990, scrub mangroves showed lower COassimilation rate, stomatal conductance, and intercellular COconcentration than fringe mangroves. There were no differences in these gas exchange characteristics on the other two measuring dates: Oct. 17, 1990 and Jan. 11, 1991. Instantaneous water use efficiency was significantly higher for scrub mangroves than for fringe mangroves on three of the four sampling dates. Similarly, leaf carbon isotope discrimination of scrub mangroves was always significantly lower than that of fringe mangroves, indicating higher long-term water use efficiency. Higher water use efficiency in scrub mangroves is a result of stomatal limitation on photosynthesis, which may entail considerable carbon cost to the plants

Utilization of Freshwater and Ocean Water by Coastal Plants of Southern Florida

The coastal vegetation of southern Florida is undergoing dramatic changes due to the instability of the ocean water-freshwater boundary. These vegetation changes will be determined by the response of each particular species to saline ocean water, particularly whether it can use ocean water or not. In this study, isotopic data were used to determine the relative usage of freshwater or ocean water by plants in the Florida keys. The results indicate that, with some exceptions, plants toward the interior of the keys were using freshwater while those toward the edge were using ocean water. A plot of the hydrogen and oxygen isotopic composition of the plant water yielded a mixing line between typical freshwater values and those of ocean water. In general, the isotopic ratios of stem water for species found in hardwood hammocks were confined to the freshwater end of the line, followed by values of stem water from mangrove margin species. found in mangroves, however, had water with extremely variable isotopic ratios, ranging from values typical of ocean water to values typical of freshwater. This variability is consistent with the hypothesis that mangroves are fully capable of growing in freshwater, but are limited to saline habitats because of competitive exclusion by fast-growing glycophilic plants