Posts Tagged 'morphology'

The pH dependency of the boron isotopic composition of diatom opal (Thalassiosira weissflogii)

The high latitude oceans are key areas of carbon and heat exchange between the atmosphere and the ocean. As such, they are a focus of both modern oceanographic and palaeoclimate research. However, most palaeoclimate proxies that could provide a long-term perspective are based on calcareous organisms, such as foraminifera, that are scarce or entirely absent in deep-sea sediments south of 50° latitude in the Southern Ocean and north of 40° in the North Pacific. As a result, proxies need to be developed for the opal-based organisms (e.g. diatoms) that are found at these high latitudes, and which dominate the biogenic sediments that are recovered from these regions. Here we present a method for the analysis of the boron (B) content and isotopic composition (δ11B) of diatom opal. We also apply it for the first time to evaluate the relationship between seawater pH and δ11B and B concentration ([B]) in the frustules of the diatom Thalassiosira weissflogii, cultured at a range of pCO2/pH. In agreement with existing data, we find that the [B] of the cultured diatom frustules increases with increasing pH (Mejia et al., 2013). δ11B shows a relatively well-defined negative trend with increasing pH; a completely distinct relationship from any other biomineral previously measured. This relationship not only has implications for the magnitude of the isotopic fractionation that occurs during boron incorporation into opal, but also allows us to explore the potential of the boron-based proxies for palaeo-pH and palaeo-CO2 reconstruction in high latitude marine sediments that have, up until now, eluded study due to the lack of suitable carbonate material.

Continue reading ‘The pH dependency of the boron isotopic composition of diatom opal (Thalassiosira weissflogii)’

Net heterotrophy and carbonate dissolution in two subtropical seagrass meadows

The net ecosystem productivity (NEP) of two contrasting seagrass meadows within one of the largest seagrass ecosystems in the world, Florida Bay, was assessed using direct measurements over consecutive diel cycles. We report significant differences between NEP determined by dissolved inorganic carbon (NEPDIC) and by dissolved oxygen (NEPDO), likely driven by differences in air-water gas exchange and contrasting responses to variations in light intensity. In this first direct determination of NEPDIC in seagrasses, we found that both seagrass ecosystems were net heterotrophic, on average, despite large differences in seagrass net aboveground primary productivity. Net ecosystem calcification (NEC) was also negative, indicating that both sites were net dissolving of carbonate minerals. We suggest that a combination of carbonate dissolution and respiration in sediments exceeded seagrass primary production and calcification, supporting our negative NEP and NEC measurements. Furthermore, a simple budget analysis indicates that these two seagrass meadows have contrasting impacts on pH buffering of adjacent systems, due to variations in the TA : DIC export ratio. The results of this study highlight the need for better temporal resolution, as well as accurate carbonate chemistry accounting in future seagrass metabolism studies.

Continue reading ‘Net heterotrophy and carbonate dissolution in two subtropical seagrass meadows’

Calcification and distribution of extant coccolithophores across the Drake Passage during late austral summer 2016

Coccolithophores are globally distributed microscopic marine algae that exert a major influence on the global carbon cycle through calcification and primary productivity. There is recent interest in coccolithophore polar communities, however field observations regarding their biogeographic distribution are scarce for the Southern Ocean. This study documents the latitudinal variability in the coccolithophore assemblage composition and the coccolith mass variation of the ecologically dominant Emiliania huxleyi across the Drake Passage. Ninety-six water samples were taken between 10 and 150 m water depth from 18 stations during POLARSTERN Expedition PS97 (February–April, 2016). A minimum of 200 coccospheres per sample were classified in scanning electron microscope and coccolith mass was estimated with light microscopy, using the C-Calcita software. We find that coccolithophore abundance and diversity decrease southwards marking different oceanographic fronts as ecological boundaries. We characterize three zones: (1) the Chilean margin, where E. huxleyi type A (normal and overcalcified) and type R are present; (2) the Subantarctic Zone (SAZ), where E. huxleyi reaches maximum values of 212.5×103cells/L and types B/C, C, O are dominant. (3) The Polar Front Zone (PFZ), where E. huxleyi types B/C and C dominate. We link the decreasing trend in E. huxleyi coccolith mass to the poleward latitudinal succesion from type A to type B group. Remarkably, we find that coccolith mass is strongly anticorrelated to total alkalinity, total CO2, bicarbonate ion and pH. We speculate that low temperatures are a greater limiting factor than carbonate chemistry in the Southern Ocean. However, further in situ oceanographical data is needed to verify the proposed relationships. We hypothesize that assemblage composition and calcification modes of E. huxleyi in the Drake Passage will be strongly influenced by the ongoing climate change.

Continue reading ‘Calcification and distribution of extant coccolithophores across the Drake Passage during late austral summer 2016’

Sub-weekly coral linear extension measurements in a coral reef

Highlights

• 5-day coral skeletal liner extension growth was measured in the field using calcein.

• Linear extension was measured for three consecutive 5-day growth periods spanning a tidal cycle.

• Liner extension measurements were made on petrographically thin-sectionedskeletons with a confocal microscope.

• Skeletal linear extension was consistent through time despite large variation in environmental conditions.

Abstract

Coral growth rates are often used as a metric of coral health and are measured extensively in the laboratory under controlled conditions to better understand the potential impacts of future climate change scenarios. However, in the field, corals live in dynamic environments, which can be subjected to multiple types of stressors that can not be mimicked in the laboratory. Furthermore, the temporal scales over which many environmental conditions can vary in the reef, such as extreme temperature anomalies, tidal fluctuations, and point source pollution events are far shorter than most field estimates of coral growth, which are generally at annual or seasonal scales. To measure the impact to coral growth of environmental variables that vary on time scales of less than a year or a few months requires developing new growth measurement techniques. With the goal of measuring coral growth at sub-weekly scales in the field, we developed a technique to measure 5-day linear extension growth rates. We tested our approach on colonies of Acropora hyacinthus living in a shallow back-reef ecosystem with routine extreme daily fluctuations in temperature, pH, and dissolved oxygen saturation. Using serial skeletal staining and petrographic thin sectioning we measured linear extension in A. hyacinthus during three consecutive 5-day growth periods that had differing amounts of environmental variability. At our field site in American Samoa, the second growth period had the largest tidal swings, resulting in higher variability: within a day temperature ranged up to 5.4 °C (reaching a maximum of 31.9 °C) and pH ranged up to 0.41 units (with a minimum of pH 7.78). We tested whether corals are able to maintain even linear extension rates across these short periods of time or not. After confocal microscopy analysis of stained skeletal samples we found that linear extension rates were similar across the three growth periods. Our fine-scale measurements suggest that during periods with different magnitudes of tidally driven environmental variability, but constant mean conditions, short-term linear extension growth rates remain consistent.

Continue reading ‘Sub-weekly coral linear extension measurements in a coral reef’

Effects of ocean acidification on life parameters and antioxidant system in the marine copepod Tigriopus japonicus

Highlights

• Exposure of OA to copepod resulted in reduction in the growth rate with decreased fecundity and body length.

• GST and GR activities were increased in response to OA-induced oxidative stress while GPx and SOD activities were decreased in a pH-dependent manner.

• GSTs2b was significantly up-regulated in response to OA.

Abstract

Ocean acidification (OA) is caused by alteration of global ocean carbon chemistry due to the increased pCO2 in the atmosphere and caused deleterious impacts on the marine ecosystem. Although various detrimental effects of OA were reported in marine organisms, the potential impact of OA on aquatic invertebrates still remains largely unknown. Here, we examined changes in life parameters and antioxidant system in response to low pH (7.5 and 7) in the marine copepod Tigriopus japonicus. Exposures to lower pHs (pH 7.5 and 7.0) of copepods resulted in lengthening of the developmental time with decreased fecundity and body length. Also, they showed increased reactive oxygen species contents with enhanced glutathione S-transferase and glutathione reductase activities but decreased glutathione peroxidase and superoxide dismutase activities in pH-dependent manner, indicating that OA exposure caused disturbance of the redox system in T. japonicus. Among several oxidative stress-related genes, GSTs2b was significantly up-regulated in response to OA. These findings will be helpful for a better understanding on the potential impact of OA on life parameters and antioxidant system in the marine copepod T. japonicus.

Continue reading ‘Effects of ocean acidification on life parameters and antioxidant system in the marine copepod Tigriopus japonicus’

Proteomic responses to ocean acidification of the marine diazotroph Trichodesmium under iron-replete and iron-limited conditions

Growth and dinitrogen (N2) fixation of the globally important diazotrophic cyanobacteria Trichodesmium are often limited by iron (Fe) availability in surface seawaters. To systematically examine the combined effects of Fe limitation and ocean acidification (OA), T. erythraeum strain IMS101 was acclimated to both Fe-replete and Fe-limited concentrations under ambient and acidified conditions. Proteomic analysis showed that OA affected a wider range of proteins under Fe-limited conditions compared to Fe-replete conditions. OA also led to an intensification of Fe deficiency in key cellular processes (e.g., photosystem I and chlorophyll a synthesis) in already Fe-limited T. erythraeum. This is a result of reallocating Fe from these processes to Fe-rich nitrogenase to compensate for the suppressed N2 fixation. To alleviate the Fe shortage, the diazotroph adopts a series of Fe-based economic strategies (e.g., upregulating Fe acquisition systems for organically complexed Fe and particulate Fe, replacing ferredoxin by flavodoxin, and using alternative electron flow pathways to produce ATP). This was more pronounced under Fe-limited-OA conditions than under Fe limitation only. Consequently, OA resulted in a further decrease of N2- and carbon-fixation rates in Fe-limited T. erythraeum. In contrast, Fe-replete T. erythraeum induced photosystem I (PSI) expression to potentially enhance the PSI cyclic flow for ATP production to meet the higher demand for energy to cope with the stress caused by OA. Our study provides mechanistic insight into the holistic response of the globally important N2-fixing marine cyanobacteria Trichodesmium to acidified and Fe-limited conditions of future oceans.

Continue reading ‘Proteomic responses to ocean acidification of the marine diazotroph Trichodesmium under iron-replete and iron-limited conditions’

Adaptive responses and local stressor mitigation drive coral resilience in warmer, more acidic oceans

Coral reefs have great biological and socioeconomic value, but are threatened by ocean acidification, climate change and local human impacts. The capacity for corals to adapt or acclimatize to novel environmental conditions is unknown but fundamental to projected reef futures. The coral reefs of Kāne‘ohe Bay, Hawai‘i were devastated by anthropogenic insults from the 1930s to 1970s. These reefs experience naturally reduced pH and elevated temperature relative to many other Hawaiian reefs which are not expected to face similar conditions for decades. Despite catastrophic loss in coral cover owing to human disturbance, these reefs recovered under low pH and high temperature within 20 years after sewage input was diverted. We compare the pH and temperature tolerances of three dominant Hawaiian coral species from within Kāne‘ohe Bay to conspecifics from a nearby control site and show that corals from Kāne‘ohe are far more resistant to acidification and warming. These results show that corals can have different pH and temperature tolerances among habitats and understanding the mechanisms by which coral cover rebounded within two decades under projected future ocean conditions will be critical to management. Together these results indicate that reducing human stressors offers hope for reef resilience and effective conservation over coming decades.

Continue reading ‘Adaptive responses and local stressor mitigation drive coral resilience in warmer, more acidic oceans’


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Ocean acidification in the IPCC AR5 WG II

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