Posts Tagged 'South Pacific'

Aerobic performance of two tropical cephalopod species unaltered by prolonged exposure to projected future carbon dioxide levels

Squid and many other cephalopods live continuously on the threshold of their environmental oxygen limitations. If the abilities of squid to effectively take up oxygen are negatively affected by projected future carbon dioxide (CO2) levels in ways similar to those demonstrated in some fish and invertebrates, it could affect the success of squid in future oceans. While there is evidence that acute exposure to elevated CO2 has adverse effects on cephalopod respiratory performance, no studies have investigated this in an adult cephalopod after relatively prolonged exposure to elevated CO2 or determined any effects on aerobic scope. Here, we tested the effects of prolonged exposure (≥20% of lifespan) to elevated CO2 levels (~1000 μatm) on the routine and maximal oxygen uptake rates, aerobic scope and recovery time of two tropical cephalopod species, the two-toned pygmy squid, Idiosepius pygmaeus and the bigfin reef squid, Sepioteuthis lessoniana. Neither species exhibited evidence of altered aerobic performance after exposure to elevated CO2 when compared to individuals held at control conditions. The recovery time of I. pygmaeus under both control and elevated CO2 conditions was less than 1 hour, whereas S. lessoniana required approximately 8 hours to recover fully following maximal aerobic performance. This difference in recovery time may be due to the more sedentary behaviours of I. pygmaeus. The ability of these two cephalopod species to cope with prolonged exposure to elevated CO2 without detriment to their aerobic performance suggests some resilience to an increasingly high CO2 world.

Continue reading ‘Aerobic performance of two tropical cephalopod species unaltered by prolonged exposure to projected future carbon dioxide levels’

Extreme, but not moderate climate scenarios, impart sublethal effects on polyps of the Irukandji jellyfish, Carukia barnesi

• Sublethal effects on Carukia barnesi polyps only manifested in extreme conditions.

• Individual metabolites were suppressed in extreme pH and elevated temperature treatments.

• C. barnesi polyps are unaffected by the most optimistic climate scenario and can survive in extreme conditions.

Ocean acidification and warming, fueled by excess atmospheric carbon dioxide, can impose stress on marine organisms. Most studies testing the effects of climate change on marine organisms, however, use extreme climate projection scenarios, despite moderate projections scenarios being most likely to occur. Here, we examined the interactive effects of warming and acidification on reproduction, respiration, mobility and metabolic composition of polyps of the Irukandji jellyfish, Carukia barnesi, to determine the responses of a cubozoan jellyfish to moderate and extreme climate scenarios in Queensland, Australia. The experiment consisted two orthogonal factors: temperature (current 25 °C and future 28 °C) and pH (current (8.0) moderate (7.9) and extreme (7.7)). All polyps survived in the experiment but fewer polyps were produced in the pH 7.7 treatment compared to pH 7.9 and pH 8.0. Respiration rates were elevated in the lowest pH treatment throughout most of the experiment and polyps were approximately half as mobile in this treatment compared to pH 7.9 and pH 8.0, regardless of temperature. We identified metabolites occurring at significantly lower relative abundance in the lowest pH (i.e. glutamate, acetate, betaine, methylguanidine, lysine, sarcosine, glycine) and elevated temperature (i.e. proline, trigonelline, creatinine, mannose, acetate, betaine, methylguanidine, lysine, sarcosine) treatments. Glycine was the only metabolite exhibiting an interactive effect between pH and temperature. Our results suggest that C. barnesi polyps are unaffected by the most optimistic climate scenario and may tolerate even extreme climate conditions to some extent.

Continue reading ‘Extreme, but not moderate climate scenarios, impart sublethal effects on polyps of the Irukandji jellyfish, Carukia barnesi’

Fifty years of sporadic coral reef calcification estimates at One Tree Island, Great Barrier Reef: is it enough to imply long term trends?

Estimates of coral reef ecosystem calcification (Gnet) and productivity (Pnet) provide insight into coral community health and functionality in response to short- and long-term stressors such as ocean warming and acidification. Here, we investigate spatial variability in calcification and organic production at One Tree Island (OTI) and compare our new observations to sporadic metabolic rates reported over the previous 50 years on the same reef flat. Gnet and Pnet estimates at the nearshore site were 50% and 166% lower than an offshore site with a shift in organic production from net productive to net respiratory. Contrary to expectations, calcification rates in 2017 (145.7 ± 20.2 mmol m-2 d-1) were comparable to the 1970s estimate (125.0 ± 12.5 mmol m-2 d-1) and 400% greater than similar observations in 2014. Our results indicate only weak associations between Gnet and aragonite (Ωar). A local increase in coral cover from 18% in 2014 to 31% in 2017 was the likely driver of increased calcification. A steeper TA–DIC slope in 2017 demonstrates a greater control of calcification on seawater carbonate chemistry than prior years. Overall, these results highlight the importance of site selection and replication when comparing metabolic datasets, and demonstrate major short-term variability in metabolic rates. The predictive capabilities of ecosystem metabolism studies may be constrained by using the available short-term datasets to represent long-term calcification trends.

Continue reading ‘Fifty years of sporadic coral reef calcification estimates at One Tree Island, Great Barrier Reef: is it enough to imply long term trends?’

Resistance to ocean acidification in coral reef taxa is not gained by acclimatization

Ocean acidification (OA) is a major threat to coral reefs, which are built by calcareous species. However, long-term assessments of the impacts of OA are scarce, limiting the understanding of the capacity of corals and coralline algae to acclimatize to high partial pressure of carbon dioxide (pCO2) levels. Species-specific sensitivities to OA are influenced by its impacts on chemistry within the calcifying fluid (CF). Here, we investigate the capacity of multiple coral and calcifying macroalgal species to acclimatize to elevated pCO2 by determining their chemistry in the CF during a year-long experiment. We found no evidence of acclimatization to elevated pCO2 across any of the tested taxa. The effects of increasing seawater pCO2 on the CF chemistry were rapid and persisted until the end of the experiment. Our results show that acclimatization of the CF chemistry does not occur within one year, which confirms the threat of OA for future reef accretion and ecological function.

Continue reading ‘Resistance to ocean acidification in coral reef taxa is not gained by acclimatization’

Surface ocean carbon dioxide variability in South Pacific boundary currents and Subantarctic waters

To improve estimates of the long-term response of the marine carbon system to climate change a better understanding of the seasonal and interannual variability is needed. We use high-frequency multi-year data at three locations identified as climate change hotspots: two sites located close to South Pacific boundary currents and one in the Subantarctic Zone (SAZ). We investigate and identify the main drivers involved in the seasonal an interannual (2012–2016) variability of the carbon system. The seasonal variability at boundary current sites is temporally different and highly controlled by sea surface temperature. Advection processes also play a significant role on the monthly changes of the carbon system at the western boundary current site. The interannual variability at these sites most likely responds to long-term variability in oceanic circulation ultimately related to climatic indices such as the El Niño Southern Oscillation, the Pacific Decadal Oscillation and the Southern Annular Mode (SAM). In the SAZ, advection and entrainment processes drive most of the seasonality, augmented by the action of biological processes in spring. Given the relevance of advection and entrainment processes at SAZ, the interannual variability is most probably modulated by changes in the regional winds linked to the variability of the SAM.

Continue reading ‘Surface ocean carbon dioxide variability in South Pacific boundary currents and Subantarctic waters’

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


• 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.


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’

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Ocean acidification in the IPCC AR5 WG II

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