Posts Tagged 'South Pacific'

Simulated future conditions of ocean warming and acidification disrupt the microbiome of the calcifying foraminifera Marginopora vertebralis across life stages

Foraminifera host diverse microbial communities that can shift in response to changing environmental conditions. To characterize climate change impacts on the foraminifera microbiome across life stages, we exposed adult Marginopora vertebralis (Large Benthic Foraminifera) to pCO2 and temperature scenarios representing present day, 2050 and 2100 levels and raised juveniles under present day and 2050 conditions. While treatment condition had no significant effect on the seawater microbial communities, exposure to future scenarios significantly altered both adult and juvenile microbiomes. In adults, divergence between present day and 2050 or 2100 conditions was primarily driven by a reduced relative abundance of Oxyphotobacteria under elevated temperature and pCO2. In juveniles, the microbial shift predominantly resulted from changes in the proportion of Proteobacteria. Indicator species analysis identified numerous treatment‐specific indicator taxa, most of which were indicative of present day conditions. Oxyphotobacteria, previously reported as putative symbionts of foraminifera, were indicative of present day and 2050 conditions in adults, but of present day conditions only in juveniles. Overall, we show that the sensitivity of the M. vertebralis microbiome to climate change scenarios extends to both life stages and primarily correlates with declines in Oxyphotobacteria and shifts in Proteobacteria under elevated temperature and pCO2.

Continue reading ‘Simulated future conditions of ocean warming and acidification disrupt the microbiome of the calcifying foraminifera Marginopora vertebralis across life stages’

Diel vertical migration into anoxic and high-pCO2 waters: acoustic and net-based krill observations in the Humboldt Current

A select group of marine organisms can enter the Oxygen Minimum Zones (OMZs) and even anoxic waters, while performing diel vertical migration (DVM). DVM of the euphausiid Euphausia eximia off northern Chile in the spring of 2015 was documented based on acoustic measurements using an echo sounder along with net samplings. Dissolved oxygen (DO) concentrations were obtained using a vertical profiler, and water samples were collected to obtain in situ nitrite (NO2) concentrations as well as pHT, total alkalinity (AT), and therefore carbon dioxide partial pressure (pCO2) was estimated. Krill were found to migrate up to the surface (0–50 m) during the night and returned to ca. 200–300 m depth during the day, spending between 11 and 14 h at these layers. At the surface, DO and NO2 concentrations were 208 and 0.14 μM respectively, while pHT was 8.04 and 405 μatm pCO2. In contrast, at the deeper layers (200–300 m), DO and NO2 were < 3 and 6.3 μM respectively, with pHT 7.53 and 1490 μatm pCO2. The pHT and high pCO2 values at depths represent the conditions predicted for open ocean waters in a worst-case global warming scenario by 2150. The acoustic scatter suggested that > 60% of the krill swarms enter the OMZ and anoxic waters during the daytime. These frequent migrations suggest that krill can tolerate such extreme conditions associated with anoxic and high-pCO2 waters. The inferences drawn from the observation of these migrations might have strong implications for the current oceanic carbon pump models, highlighting the need for understanding the molecular and physiological adaptations allowing these migrations.

Continue reading ‘Diel vertical migration into anoxic and high-pCO2 waters: acoustic and net-based krill observations in the Humboldt Current’

Early development and metabolic rate of the sea louse Caligus rogercresseyi under different scenarios of temperature and pCO2

Highlights

  • The temperature has a significant effect on the hatching time of C. royercresseyi.

  • Combination of pCO2 and temperature has a significant effect on survival in C. rogercresseyi.

  • The combination of pCO2 and temperature had no impact on the size of nauplius I, nauplius II and copepodid stage.

  • Only the temperature has a significant effect on oxygen consumption rate of C. royercresseyi.

Abstract

Anthropogenic CO2 emissions have led to ocean acidification and a rise in the temperature. The present study evaluates the effects of temperature (10, 15 and 20 °C) and pCO2 (400 and 1200 μatm) on the early development and oxygen consumption rate (OCR) of the sea louse Caligus rogercresseyi. Only temperature has an effect on the hatching and development times of nauplius I. But both factors affected the development time of nauplius II (<temperature = longer development time). Copepodid survival time was also affected by temperature and pCO2, at 10 °C and 400 μatm, survival was 30 and 44% longer than at 15 and 20 °C. OCRs were impacted by temperature but not by pCO2. In all treatments, OCR was lower for nauplius II than for the copepodid. Our results show the need to further evaluate the effects of a combination of environmental drivers on the performance of C. rogercresseyi, in a changing and uncertain future.

Continue reading ‘Early development and metabolic rate of the sea louse Caligus rogercresseyi under different scenarios of temperature and pCO2’

Temperature affects the reproductive outputs of coral-eating starfish Acanthaster spp. after adult exposure to near-future ocean warming and acidification

Highlights

  • It is possible to keep adult COTS in modified conditions for several months with minimal losses.

  • The natural peak of reproduction for COTS in New Caledonia is around the end of the calendar year.

  • A +2 °C warming exposure of 3–4 months have detrimental effects on quality and quantity of COTS eggs along with fertilisation success.

  • During sub-optimal spawning season, COTS fertilisation success drops by 3-fold for animals exposed to elevated temperature.

Abstract

Outbreaks of the coral-eating crown-of-thorns starfish Acanthaster spp. (COTS) have become to be amongst the most severe threats to coral reefs worldwide. Although most research has focused on COTS early development, it remains unclear how COTS populations will keep pace with changing ocean conditions. Since reproduction is a key process contributing to outbreaks, we investigated the reproductive success of adult COTS acclimated for 3–4 months to different treatment combinations of ambient conditions, ocean warming (+2 °C) and acidification (−0.35 pH). Our results suggest that the optimal breeding season in New Caledonia is concentrated around the end of the calendar year, when water temperature reaches >26 °C. We found negative effects of temperature on egg metrics, fertilisation success, and GSI, conflicting with previously documented effects of temperature on echinoderm reproductive outputs. Fertilisation success dropped drastically (more than threefold) with elevated temperature during the late breeding season. In contrast, we detected no effects of near-future acidification conditions on fertilisation success nor GSI. This is the first time that COTS reproduction is compared among individuals acclimated to different conditions of warming and acidification. Our results highlight the importance of accounting for adult exposure to better understand how COTS reproduction may be impacted in the face of global change.

Continue reading ‘Temperature affects the reproductive outputs of coral-eating starfish Acanthaster spp. after adult exposure to near-future ocean warming and acidification’

Coastal acidification and deoxygenation enhance settlement but do not influence movement behavior of creeping polyps of the irukandji jellyfish, Alatina alata (cubozoa)

Highlights

  • Deoxygenation enhanced the survival of the creeping polyps of Alatina alata.

  • More creeping polyps settled under low pH and low dissolved O2 (DO) treatments than under normal pH and DO conditions.

  • Exposure to low pH and DO did not influence the number of tentacles, mobility or movement velocity of the creeping polyps.

  • The Irukandji jellyfish may persist in coastal areas with coastal deoxygenation and acidification.

Abstract

Deoxygenation and acidification co-occur in many coastal ecosystems because nutrient enrichment produces excess organic matter that intensifies aerobic respiration during decomposition, thereby depleting O2, increasing CO2 and lowering pH. Despite this link between coastal deoxygenation (CD) and acidification (CA), and evidence that both stressors pose a risk to marine fauna, few studies have examined the effects of these drivers in combination on marine animals including invertebrates. Here, we studied the individual and combined effects of CD (∼1.5 mg L−1 O2) and CA (∼7.7 pH) on the survival, number of tentacles, settlement and movement behaviours of creeping polyps of the Irukandji jellyfish, Alatina alata. Low DO increased the survival rate (17% more) of the creeping polyps. 12% more creeping polyps settled in low pH than ambient pH and 16.7% more settled in low DO than ambient DO treatment. Exposure to CA and CD did not influence the number of tentacles, mobility or movement velocity of the creeping polyps, but after 4 h exposure to the treatments, they moved approximately half as fast. Our results indicate that CD can enhance survival and settlement success, but CA does not intensify these outcomes on A. alata creeping polyps.

Continue reading ‘Coastal acidification and deoxygenation enhance settlement but do not influence movement behavior of creeping polyps of the irukandji jellyfish, Alatina alata (cubozoa)’

Remnant kelp bed refugia and future phase-shifts under ocean acidification

Ocean warming, ocean acidification and overfishing are major threats to the structure and function of marine ecosystems. Driven by increasing anthropogenic emissions of CO2, ocean warming is leading to global redistribution of marine biota and altered ecosystem dynamics, while ocean acidification threatens the ability of calcifying marine organisms to form skeletons due to decline in saturation state of carbonate Ω and pH. In Tasmania, the interaction between overfishing of sea urchin predators and rapid ocean warming has caused a phase-shift from productive kelp beds to overgrazed sea urchin barren grounds, however potential impacts of ocean acidification on this system have not been considered despite this threat for marine ecosystems globally. Here we use automated loggers and point measures of pH, spanning kelp beds and barren grounds, to reveal that kelp beds have the capacity to locally ameliorate effects of ocean acidification, via photosynthetic drawdown of CO2, compared to unvegetated barren grounds. Based on meta-analysis of anticipated declines in physiological performance of grazing urchins to decreasing pH and assumptions of nil adaptation, future projection of OA across kelp-barrens transition zones reveals that kelp beds could act as important pH refugia, with urchins potentially becoming increasingly challenged at distances >40 m from kelp beds. Using spatially explicit simulation of physicochemical feedbacks between grazing urchins and their kelp prey, we show a stable mosaicked expression of kelp patches to emerge on barren grounds. Depending on the adaptative capacity of sea urchins, future declines in pH appear poised to further alter phase-shift dynamics for reef communities; thus, assessing change in spatial-patterning of reef-scapes may indicate cascading ecological impacts of ocean acidification.

Continue reading ‘Remnant kelp bed refugia and future phase-shifts under ocean acidification’

Cross‐generational effects of climate change on the microbiome of a photosynthetic sponge

Coral reefs are facing increasing pressure from rising seawater temperatures and ocean acidification. Sponges have been proposed as possible winners in the face of climate change; however, little is known about the mechanisms underpinning their predicted tolerance. Here we assessed whether microbiome‐mediated cross‐generational acclimatization could enable the photosynthetic sponge Carteriospongia foliascens to survive under future climate scenarios. To achieve this, we first established the potential for vertical (cross‐generational) transmission of symbionts. Sixty‐four amplicon sequence variants accounting for >90% of the total C. foliascens microbial community were present across adult, larval and juvenile life stages, showing that a large proportion of the microbiome is vertically acquired and maintained. When C. foliascens were exposed to climate scenarios projected for 2050 and 2100, the host remained visibly unaffected (i.e. no necrosis/bleaching) and the overall microbiome was not significantly different amongst treatments in adult tissue, the respective larvae or recruits transplanted amongst climate treatments. However, indicator species analysis revealed that parental exposure to future climate scenarios altered the presence and abundance of a small suite of microbial taxa in the recruits, thereby revealing the potential for microbiome‐mediated cross‐generational acclimatization through both symbiont shuffling and symbiont switching within a vertically acquired microbiome.

Continue reading ‘Cross‐generational effects of climate change on the microbiome of a photosynthetic sponge’

Coral reef sediment dissolution in a changing ocean: insights from a temporal field study

Calcium carbonate sediments form an essential part of coral reefs yet have often been overlooked when studying the effects of future ocean acidification (OA). This original field-based research aims to assess the temporal variability of organic and inorganic sediment metabolism under ambient and elevated pCO2. OA caused a shift from net precipitation to net dissolution, but the sensitivity to OA varied seasonally, depending on interactions with temperature and benthic productivity. A slack-water approach of net ecosystem calcification revealed that sediments can play an important role in carbonate budgets, particularly at night, and become increasingly important as the oceans continue acidifying.

Continue reading ‘Coral reef sediment dissolution in a changing ocean: insights from a temporal field study’

Warming and ocean acidification may decrease estuarine dissolved organic carbon export to the ocean

Estuaries make a disproportionately large contribution of dissolved organic carbon (DOC) to the global carbon cycle, but it is unknown how this will change under a future climate. As such, the response of DOC fluxes from microbially dominated unvegetated sediments to individual and combined future climate stressors of warming (from Δ−3 °C to Δ+5 °C on ambient mean temperatures) and ocean acidification (OA, ~2 times the current partial pressure of CO2, pCO2) was investigated ex situ. Warming alone increased sediment heterotrophy, resulting in a proportional increase in sediment DOC uptake, with sediments becoming net sinks of DOC (3.5 to 8.8 mmol-C m−2 d−1) at warmer temperatures (Δ+3 °C and Δ+5 °C, respectively). This temperature response changed under OA conditions, with sediments becoming more autotrophic and a greater sink of DOC (1 to 4 times greater than under current-pCO2). This response was attributed to the stimulation of heterotrophic bacteria with the autochthonous production of labile organic matter by microphytobenthos. Extrapolating these results to the global area of unvegetated subtidal estuarine sediments, the future climate of warming (Δ+3 °C) and OA may decrease the estuarine export of DOC by ~80 % (~150 Tg-C yr−1) and have a disproportionately large impact on the global DOC budget.

Continue reading ‘Warming and ocean acidification may decrease estuarine dissolved organic carbon export to the ocean’

Bigfin reef squid demonstrate capacity for conditional discrimination and projected future carbon dioxide levels have no effect on learning capabilities

Anthropogenic carbon dioxide (CO2) emissions are being absorbed by the oceans, a process known as ocean acidification, and risks adversely affecting a variety of behaviours in a range of marine species, including inhibited learning in some fishes. However, the effects of elevated CO2 on learning in advanced invertebrates such as cephalopods are unknown. Any impacts to the learning abilities of cephalopods could have far-reaching consequences for their populations and the communities they inhabit. Cephalopods have some of the most advanced cognitive abilities among invertebrates and are one of the few invertebrate taxa in which conditional discrimination has been demonstrated, though the trait has not been demonstrated in any species of squid. Here, we tested for the first time the capacity for conditional discrimination in a squid species (Sepioteuthis lessoniana). Furthermore, we investigated the effects of projected future CO2 levels (1,084 µatm) on conditional discrimination and learning more generally. A three-task experiment within a two-choice arena was used to test learning and conditional discrimination. Learning was measured by improvements in task completion in repeated trials over time and the number of trials required to pass each task. Squid exhibited significant learning capabilities, with an increase in correct choices over successive trials and a decrease in the number of trials needed to complete the successive tasks. Six of the 12 squid tested successfully passed all three tasks indicating a capacity for conditional discrimination in the species. Elevated CO2 had no effect on learning or on the capacity for conditional discrimination in squid. This study highlights the remarkable cognitive abilities of S. lessoniana, demonstrated by their capacity for conditional discrimination, and suggests that ocean acidification will not compromise learning abilities. However, other behavioural traits in the species have been shown to be altered at comparable elevated CO2 conditions. It is not clear why some ecologically important behaviours are altered by elevated CO2 whereas others are unaffected. Future research should focus on the physiological mechanism responsible for altered behaviours in squid at elevated CO2.

Continue reading ‘Bigfin reef squid demonstrate capacity for conditional discrimination and projected future carbon dioxide levels have no effect on learning capabilities’


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