Archive for the 'Science' Category



Effects of environmental stressors on a habitat forming macroalga over evolutionary and ecological time scales

Fucus vesiculosus is a keystone species in the North Atlantic and Baltic Sea; any changes in its distribution or physical structure could have broad-reaching implications on many coastal ecosystems. It is therefore important to understand both how this important species has evolved in the past and adapted to historical changes in the environment but also how future environmental stress and changes will affect this species. When stress, for example from environmental change, affects a population, traits that make individuals more likely to survive will remain in the population. This is the fundamental basis of evolution, occurring over both short and long time scales. Climate change is
liable to exert a strong selective pressure on many species as it changes the environment inhabited by those species.

Continue reading ‘Effects of environmental stressors on a habitat forming macroalga over evolutionary and ecological time scales’

Seasonal carbonate chemistry dynamics on southeast Florida coral reefs: localized acidification hotspots from navigational inlets

Seawater carbonate chemistry varies across temporal and spatial scales. Shallow-water environments can exhibit especially dynamic fluctuations as biological and physical processes operate on a smaller water volume relative to open ocean environments. Water was collected on a bi-monthly basis from seven sites off of southeast Florida (Miami-Dade and Broward counties), including four reefs, and three closely-associated inlets. Significant seasonal fluctuations in carbonate chemistry were observed on reef sites, with elevated pCO2 in the warmer wet season. Inlets demonstrated a more dynamic range, with periodic pulses of acidified water contributing to, on average, more advanced acidification conditions than those found at nearby reefs. Within inlet environments, there was a significant negative correlation between seawater salinity and both total alkalinity (TA) and dissolved inorganic carbon (DIC), which was in contrast to the patterns observed on reefs. Elevated TA and DIC in low salinity waters likely reflect carbonate dissolution as a result of organic matter decomposition. Together, these data highlight the important role that inlets play on shallow-water carbonate chemistry dynamics within southeast Florida waters and underscore the degree to which engineered freshwater systems can contribute to coastal acidification on localized scales.

Continue reading ‘Seasonal carbonate chemistry dynamics on southeast Florida coral reefs: localized acidification hotspots from navigational inlets’

Changing structure of benthic foraminiferal communities due to declining pH: results from laboratory culture experiments

The ocean absorbs large amounts of CO2 emitted from human activities, which results in a decrease in seawater pH. Marine calcifying organisms such as foraminifera, are most likely to be affected by this declining pH. In this study, we collected sediments from five stations of different depths (34–73 m) in a continental shelf of the Yellow Sea. The entire benthic foraminiferal communities together with sea sediments were cultured under three constant pHs (8.3, 7.8, and 7.3) for 6 and 12 weeks in the laboratory to study their responses to pH or incubation time. The microcosm’s experimental results obtained showed that most of the foraminiferal community parameters (abundance, species richness, Margalef index, and Shannon-Wiener diversity) decreased significantly (p<0.05) with the decline in pH in all the tested stations. The responses of foraminifera to the decline in pH were species-specific, for instance, Protelphidium tuberculatum and Cribroelphidiumfrigidum were highly sensitive to declining pH and were finally eliminated at low pH, while some species (e.g., Lagenammina atlantica, Verneuilinulla advena, V. propinqua, Haplophragmoides applanata, and H. canariensis) could tolerate low pH and acted as pH-tolerant species. In addition, the proportion of hyaline taxa showed a significant (p<0.05) positive correlation with pH, while agglutinated type showed a negative response. Furthermore, different incubation times (6 and 12 weeks) showed significant effects on the nearshore communities other than the offshore treatments, which were, however, entirely declined after 6 weeks’ incubation under low pH manipulation. Our results indicated that nearshore foraminiferal communities showed rather a resilience to the declining pH and the offshore foraminifera, especially those in the central area of the Yellow Sea Cold Water Mass were found to be more sensitive to the decline in pH in the continental shelf sediments of the Yellow Sea.

Continue reading ‘Changing structure of benthic foraminiferal communities due to declining pH: results from laboratory culture experiments’

Common Caribbean corals exhibit highly variable responses to future acidification and warming

We conducted a 93-day experiment investigating the independent and combined effects of acidification (280−3300 µatm pCO2) and warming (28°C and 31°C) on calcification and linear extension rates of four key Caribbean coral species (Siderastrea sidereaPseudodiploria strigosaPorites astreoidesUndaria tenuifolia) from inshore and offshore reefs on the Belize Mesoamerican Barrier Reef System. All species exhibited nonlinear declines in calcification rate with increasing pCO2. Warming only reduced calcification in Ps. strigosa. Of the species tested, only S. siderea maintained positive calcification in the aragonite-undersaturated treatment. Temperature and pCO2 had no effect on the linear extension of S. siderea and Po. astreoides, and natal reef environment did not impact any parameter examined. Results suggest that S. siderea is the most resilient of these corals to warming and acidification owing to its ability to maintain positive calcification in all treatments, Ps. strigosa and U. tenuifolia are the least resilient, and Po. astreoides falls in the middle. These results highlight the diversity of calcification responses of Caribbean corals to projected global change.

Continue reading ‘Common Caribbean corals exhibit highly variable responses to future acidification and warming’

Cues for metamorphosis in the invasive gastropod Crepidula fornicata and the effects of ocean acidification on larval development and cue perception

Chemical cues that induce larval metamorphosis in marine invertebrates contribute to the distribution and success of many species, including the marine gastropod Crepidula fornicata. As a markedly successful invasive species in Europe since the 1800’s, C. fornicata poses economic and environmental threats in its invasive range. Its behavior is therefore of great interest to fisheries, aquaculturists, and conservationists. In light of the changing global environment, and that of ocean acidification in particular, much is unknown about how chemical signals and their connected behaviors may shift. In my thesis, I aimed to identify the sources of cues that induce metamorphosis in competent C. fornicata larvae. I also examined the impact of reduced pH, which indicates increased acidity, on larval growth and the ability of larvae to perceive metamorphic cues to assess the potential impact of future ocean acidification levels on larval metamorphosis and early development in this particular species.

Continue reading ‘Cues for metamorphosis in the invasive gastropod Crepidula fornicata and the effects of ocean acidification on larval development and cue perception’

Ocean acidification causes mortality in the medusa stage of the cubozoan Carybdea xaymacana

Ocean pH is decreasing due to anthropogenic activities, and the consequences of this acidification on marine fauna and ecosystems are the subject of an increasing number of studies. Yet, the impact of ocean acidification (OA) on several abundant and ecologically important taxa, such as medusozoans, is poorly documented. To date there have been no studies on the effect of post-2050 OA projections on the medusa stage of jellyfish. As medusae represent the reproductive stage of cnidarians, negative impacts on adult jellyfish could severely impact the long-term survival of this group. Using a laboratory experiment, we investigated the effect of 2300 OA projections (i.e. pH of 7.5) on the mortality rate of the medusa-stage of the cubozoan species Carybdea xaymacana, compared to ambient seawater pH conditions (i.e. pH of 8.1). After a 12-h exposure to OA, Cxaymacana medusae suffered higher mortality rates compared to ambient conditions. This study represents the first evidence of the potential lethal effects of post-2050 OA projections on jellyfish. The higher metabolic rates of cubozoans compared to other cnidarians might make box jellyfish more vulnerable to OA. A decrease in the density of cnidarians could lead to harmful ecological events, such as algal blooms.

Continue reading ‘Ocean acidification causes mortality in the medusa stage of the cubozoan Carybdea xaymacana’

Geochemistry of hot-springs at the SuSu Knolls Hydrothermal Field, Eastern Manus Basin: advanced argillic alteration and vent fluid acidity

SuSu Knolls is an area of ongoing magmatic activity and recent volcanism located in the back-arc spreading environment of the Manus Basin in the Bismarck Sea, Papua New Guinea. In 2006, hydrothermal fluids were collected from three areas of submarine hot-spring venting and analyzed for the chemical and isotopic composition of major and trace species. Fluids were characterized by temperatures that varied from 226 to 325 °C, and formed grey to black smoke as they mixed with bottom seawater. The compositions of seawater derived vent fluids are regulated by the relative contributions of fluid-rock and fluid-sediment interaction, phase separation, and the addition of volatiles from magmatic degassing. In addition to phase separation, leaching of Cl from felsic rocks that compose the lithosphere in back-arc environments may produce measured Cl concentrations in excess of seawater values.

The measured pH25°C of SuSu Knolls smoker fluids varied from 1.5 to 3.7, a range that includes values substantially more acidic than typically observed in fluids at mid-ocean ridge spreading centers. Late stage addition of magmatic volatiles in the shallow seafloor is directly responsible for the most acidic fluids (pH25°C values below 2). In contrast, the acidity of vent fluids characterized by pH25°C values between 2 and 3 is not the direct result of the direct addition of magmatically-derived acidic species. Instead, the pH of these fluids likely reflects reaction with rocks that were previously altered by highly acidic magmatic fluids to an advanced argillic alteration assemblage containing quartz-illite-pyrophyllite-anhydrite±alunite in hydrothermal upflow zones. Fluids that do not react with advanced argillic alteration assemblages during upflow have measured pH25°Cvalues between 3 and 4.

Continue reading ‘Geochemistry of hot-springs at the SuSu Knolls Hydrothermal Field, Eastern Manus Basin: advanced argillic alteration and vent fluid acidity’


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