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Environmental stresses reshuffle ocean food webs, making them less secure

Published 10 September 2020 Media coverage Closed

New experiments show important food web redundancies get left behind

May Law / Pexels

We are often taught about the relationships between organisms as a one-lane, one-way street: the grass is eaten by the rabbit, which is eaten by the snake, which is eaten by the hawk. In reality, this food chain model drastically oversimplifies the complex web of interactions between species. Healthy ecosystems contain numerous species that can fill the same role. Instead of the rabbits only being eaten by a snake, for example, they might be eaten by a snake or a fox or a hawk. This built-in redundancy in ecological roles makes ecosystems more resilient to change.

New research published in Science suggests that marine ecosystems may not have enough redundancy in their food webs to combat the cocktail of changes they could see in the near future.

Researchers set up large-scale ecological experiments called “mesocosms” to test how ecosystems responded to ocean acidification, ocean warming, and a combination of both acidification and warming.

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Contrasting marine carbonate systems in two fjords in British Columbia, Canada: seawater buffering capacity and the response to anthropogenic CO2 invasion

Published 9 September 2020 Science Closed
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The carbonate system in two contrasting fjords, Rivers Inlet and Bute Inlet, on the coast of British Columbia, Canada, was evaluated to characterize the mechanisms driving carbonate chemistry dynamics and assess the impact of anthropogenic carbon. Differences in the character of deep water exchange between these fjords were inferred from their degree of exposure to continental shelf water and their salinity relationships with total alkalinity and total dissolved inorganic carbon, which determined seawater buffering capacity. Seawater buffering capacity differed between fjords and resulted in distinct carbonate system characteristics with implications on calcium carbonate saturation states and sensitivity to increasing anthropogenic carbon inputs. Saturation states of both aragonite and calcite mineral phases of calcium carbonate were seasonally at or below saturation throughout the entire water column in Bute Inlet, while only aragonite was seasonally under-saturated in portions of the water column in Rivers Inlet. The mean annual saturation states of aragonite in Rivers Inlet and calcite in Bute Inlet deep water layers have declined to below saturation within the last several decades due to anthropogenic carbon accumulation, and similar declines to undersaturation are projected in their surface layers as anthropogenic carbon continues to accumulate. This study demonstrates that the degree of fjord water exposure to open shelf water influences the uptake and sensitivity to anthropogenic carbon through processes affecting seawater buffering capacity, and that reduced uptake but greater sensitivity occurs where distance to ocean source waters and freshwater dilution are greater.

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Responses of coral gastrovascular cavity pH during light and dark incubations to reduced seawater pH suggest species-specific responses to the effects of ocean acidification on calcification

Published 7 September 2020 Science Closed
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Coral polyps have a fluid-filled internal compartment, the gastrovascular cavity (GVC). Respiration and photosynthesis cause large daily excursions in GVC oxygen concentration (O2) and pH, but few studies have examined how this correlates with calcification rates. We hypothesized that GVC chemistry can mediate and ameliorate the effects of decreasing seawater pH (pHSW) on coral calcification. Microelectrodes were used to monitor O2 and pH within the GVC of Montastraea cavernosa and Duncanopsammia axifuga (pH only) in both the light and the dark, and three pHSW levels (8.2, 7.9, and 7.6). At pHSW 8.2, GVC O2 ranged from ca. 0 to over 400% saturation in the dark and light, respectively, with transitions from low to high (and vice versa) within minutes of turning the light on or off. For all three pHSW treatments and both species, pHGVC was always significantly above and below pHSW in the light and dark, respectively. For M. cavernosa in the light, pHGVC reached levels of pH 8.4–8.7 with no difference among pHSW treatments tested; in the dark, pHGVC dropped below pHSW and even below pH 7.0 in some trials at pHSW 7.6. For D. axifuga in both the light and the dark, pHGVC decreased linearly as pHSW decreased. Calcification rates were measured in the light concurrent with measurements of GVC O2 and pHGVC. For both species, calcification rates were similar at pHSW 8.2 and 7.9 but were significantly lower at pHSW 7.6. Thus, for both species, calcification was protected from seawater acidification by intrinsic coral physiology at pHSW 7.9 but not 7.6. Calcification was not correlated with pHGVC for M. cavernosa but was for D. axifuga. These results highlight the diverse responses of corals to changes in pHSW, their varying abilities to control pHGVC, and consequently their susceptibility to ocean acidification.

 

Continue reading ‘Responses of coral gastrovascular cavity pH during light and dark incubations to reduced seawater pH suggest species-specific responses to the effects of ocean acidification on calcification’

International Ocean Acidification Week 8-10 September

Published 7 September 2020 Web sites and blogs Closed

A new program will monitor ocean acidity within marine reserves to get a national picture on how New Zealand’s moana will be affected by climate change.

A diver in a kelp forest at Taputeranga Marine Reservein Wellington.
Credit: Vincent Zinten

8-10th September is International Ocean Acidification Week
Ocean acidification is usually associated with poor ocean health, but this Monday we take the opportunity to celebrate DOC’s contribution to a nation-wide monitoring program that will help us track and respond to ocean acidification. This program is linked to the Global and New Zealand Ocean Acidification Observing Networks (GOA-ON and NZOA-ON), which are international and national collaborative efforts to monitor and understand ocean acidification.

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Event: Commission on ocean acidification

Published 7 September 2020 Events Closed

Date: Friday, September 18, 2020, 12:00 PM Eastern Time

Description: The Special Legislative Commission on Ocean Acidification will convene to discuss the progress of the working groups and discuss planning for the report.

Agenda:
12 – 12:15 — Welcome and Introduction
12:15 – 1:15 — Working Groups: Presentations and Discussion
1:15 – 1:50 — Commission Report: Planning and Discussion
1:50 – 2:00 — Closing Remarks and Scheduling

Meeting location: Virtual via Zoom Public meeting link: https://harvard.zoom.us/j/98992932227

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Paracellular transport to the coral calcifying medium: effects of environmental parameters

Published 4 September 2020 Science Closed
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Coral calcification relies on the transport of ions and molecules to the extracellular calcifying medium (ECM). Little is known about paracellular transport (via intercellular junctions) in corals and other marine calcifiers. Here, we investigated whether the permeability of the paracellular pathway varied in different environmental conditions in the coral Stylophora pistillata. Using the fluorescent dye calcein, we characterised the dynamics of calcein influx from seawater to the ECM and showed that increases in paracellular permeability (leakiness) induced by hyperosmotic treatment could be detected by changes in calcein influx rates. We then used the calcein-imaging approach to investigate the effects of two environmental stressors on paracellular permeability: seawater acidification and temperature change. Under conditions of seawater acidification (pH 7.2) known to depress pH in the ECM and the calcifying cells of S. pistillata, we observed a decrease in half-times of calcein influx, indicating increased paracellular permeability. By contrast, high temperature (31°C) had no effect, whereas low temperature (20°C) caused decreases in paracellular permeability. Overall, our study establishes an approach to conduct further in vivo investigation of paracellular transport and suggests that changes in paracellular permeability could form an uncharacterised aspect of the physiological response of S. pistillata to seawater acidification.

 

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Calcification and organic productivity at the world’s southernmost coral reef

Published 4 September 2020 Science Closed
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Highlights

  • High-latitude coral reefs are hotspots of ocean change and vulnerable to bleaching.
  • Coral ecosystem calcification in winter was lower than most studied ecosystems.
  • The reef was net heterotrophic in the winter and net respiratory in the summer.
  • Detailed bathymetric observations reduce uncertainties in metabolic calculations.
  • Summer calcification was not driven by temperature or aragonite saturation state.

Abstract

Estimates of coral reef calcification and organic productivity provide valuable insight to community functionality and the response of an ecosystem to stress events. High-latitude coral reefs are expected to experience rapid changes in calcification rates and become refugia for tropical species following climate change and increasing bleaching events. Here, we estimate ecosystem-scale calcification and organic productivity at the world’s southernmost coral reef using seawater carbon chemistry observations (Lord Howe Island, Australia). We reduce uncertainties in metabolic calculations by producing a detailed bathymetric model and deploying two current meters to refine residence time and volume estimates. Bathymetry-modelled transect depths ranged from 74% shallower to 20% deeper than depths averaged from reef crest/flat current meters, indicating that higher-resolution depth observations help to reduce uncertainties in reef metabolic calculations. Rates of ecosystem calcification were 56.6 ± 14.8 mmol m−2 d−1 in the winter and 125.3 ± 39.4 mmol m−2 d−1 in the summer. These rates are lower than most other high-latitude reefs according to our compilation of high-latitude coral ecosystem metabolism estimates. Coral cover ranged from 14.7 ± 2.3% in winter to 19.8 ± 2.1% in the summer. A concurrent bleaching event and cyclone occurred during summer sampling (February – March 2019), resulting in 47% of corals bleached at the study site and 2% mortality due to cyclonal damage. Therefore, it is likely that the summertime Gnet rates underestimate baseline calcification. Our results enable future assessments of long-term change, but do not resolve the impact of bleaching at Lord Howe Island.

 

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Palaeoclimate ocean conditions shaped the evolution of corals and their skeletons through deep time

Published 4 September 2020 Science Closed
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Identifying how past environmental conditions shaped the evolution of corals and their skeletal traits provides a framework for predicting their persistence and that of their non-calcifying relatives under impending global warming and ocean acidification. Here we show that ocean geochemistry, particularly aragonite–calcite seas, drives patterns of morphological evolution in anthozoans (corals, sea anemones) by examining skeletal traits in the context of a robust, time-calibrated phylogeny. The lability of skeletal composition among octocorals suggests a greater ability to adapt to changes in ocean chemistry compared with the homogeneity of the aragonitic skeleton of scleractinian corals. Pulses of diversification in anthozoans follow mass extinctions and reef crises, with sea anemones and proteinaceous corals filling empty niches as tropical reef builders went extinct. Changing environmental conditions will likely diminish aragonitic reef-building scleractinians, but the evolutionary history of the Anthozoa suggests other groups will persist and diversify in their wake.

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Configuration and skill assessment of the coupled biogeochemical model for the carbonate system in the Bay of Bengal

Published 3 September 2020 Science Closed
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Highlights

  • A coupled physical-biogeochemical model (ROMS-PISCES) has been set up for the Bay of Bengal region to emulate the carbonate chemistry of this region.
  • The model has been run and rigorously evaluated using the available data sets and 8 statistical indices have been used to evaluate model skills.
  • The effect of wind stress and E-P has been evaluated through two numerical experiments, which uses two different bulk formulae to calculate the wind stresses.
  • The model is excellent in simulating the spatial heterogeneity and temporal variation of all the carbonate parameters thus giving a basis for further studies like the effect of physical dynamics, forecasting, etc.

Abstract

The Bay of Bengal is a semi-enclosed ocean basin situated in the eastern part of the North Indian Ocean. Though the physical dynamical features of the Bay of Bengal have been studied and measured in detail, the carbonate chemistry of this basin has been less explored, and very few reliable data-sets exist. This paucity of data has emerged as a major challenge in modeling and understanding the carbonate system parameters for this region. In this study, a coupled physical-biogeochemical (ROMS-PISCES) model has been configured and run to emulate the surface carbonate system parameters (DIC, TALK, pCO2, and pH) for the Bay of Bengal region. Model skill assessment analysis has been performed using available observational data-sets. Two different numerical experiments have been performed (WB indicating the use of default bulk formulae of ROMS to calculate wind stress and WoB indicating the calculated wind stresses of QuikSCAT climatology product using different bulk formula), to understand which one reproduces the carbonate parameters better. Both the numerical experiments are rigorously compared for physical as well as carbonate system parameters. The numerical experiments have been passed through exhaustive statistical analysis by comparing it with the observed data-sets. The temperature, the primary driver affecting pH and pCO2 has been reproduced by both the experiments excellently, and the correlation value is more than 0.9 with RAMA buoy data (15o N, 90o E). The salinity, when compared with the NIOA climatology data, shows that the WoB experiment has better captured both the spatial and temporal variation of salinity. Both the numerical experiments have been compared individually with three sets of observed carbonate data. The WoB run has been found to emulate carbonate system parameters satisfactorily than the WB run. The pCO2 and pH show a good positive correlation with RAMA data and the values are 0.87, and 0.93, respectively.

 

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Experimental evidence of uncertain future of the keystone ragworm Hediste diversicolor (O.F. Müller, 1776) under climate change conditions

Published 3 September 2020 Science Closed
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Highlights

  • Temperature enhances the impact of acidification on polychaetes survival and burrowing behavior.
  • Regardless the temperature, acidification results in a reduction on polychaetes feeding rate
  • Faster regeneration at the lowest temperature and less regenerated chaetigers at lower pH levels
  • Climate change induced oxidative stress in H. diversicolor
  • Polychaetes metabolic capacity was enhanced in stressed organisms, with no expenditure of energy reserves.

Abstract

It is currently assumed that climate change related factors pose severe challenges to biodiversity maintenance. This paper assesses the multi-stressor effects of elevated temperature (15 °C as control, 25 °C as elevated) and CO2 levels (pH 8.1 as control, 7.5 and 7.0 representing acidifying conditions) on the physiological (survival, and regenerative capacity), behavioral (feeding and burrowing activities), and biochemical changes (metabolic capacity, oxidative status and biotransformation mechanisms) experienced by the keystone polychaete Hediste diversicolor. Temperature rise enlarged the adverse effect of marine acidification on the survival of H. diversicolor, delayed the beginning of the excavation activity, enhancing the negative effects that pH decrease had in the burrowing behavior of this polychaete. Additionally, regardless of the temperature, exposure of H. diversicolor to acidification results in a reduction in the feeding rate. It is the first time that this decreased feeding capacity is found related to seawater acidification in this species. The healing of the wound and the blastemal formation were retarded due to these two climatic factors which hinder the regenerative process of polychaetes. These vital physiological functions of H. diversicolor can be related to the oxidative stress induced by climate change conditions since free radicals overproduced will impair cells functioning affecting species biochemical and physiological performance, including feeding, and tissue regeneration. The present results also demonstrated that although polychaete’s metabolic capacity was enhanced under stress conditions, organisms were still able to increase or maintain their energy reserves. Our findings are of major environmental relevance considering that predicted climate change conditions will affect species vital and ecological and physiological capacities. These can be translated into shrinking not only at the individual and population level but also in microbial and endofaunal diversities, in the detritus processing in estuaries and biogeochemical cycles at the ecosystem level. Thus the conservation of H. diversicolor populations is vital for the normal functioning of estuarine mudflat ecosystems.

Continue reading ‘Experimental evidence of uncertain future of the keystone ragworm Hediste diversicolor (O.F. Müller, 1776) under climate change conditions’

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