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Archive for changing marine ecosystems – Page 3

Warming counteracts acidification in temperate crustose coralline algae communities

Posted by mmaheigan

· Friday, November 6th, 2020

Seawater carbonate chemistry has been altered by dramatic increases in anthropogenic CO₂ release and global temperatures, leading to significant changes in rocky shore habitats and the metabolism of most marine organisms. There has been recent interest in how these anthropogenic stresses affect crustose coralline algae (CCA) communities because CCA photosynthesis and calcification are directly influenced by seawater carbonate chemistry. CCA is a foundation species in temperate macroalgal communities, where species succession and rocky shore community structure are particularly susceptible to anthropogenic disturbance. In particular, the disappearance of turf and foliose macroalgae caused by climate change and herbivore pressure results in the dominance of CCA (Figure 1a).

Figure 1: (a) Examples of crustose coralline algae (CCA)-dominated seaweed bed in the East Sea of Korea showing barren ground dominated by CCA (bright white and pink color on the rock; see arrows) on a rocky subtidal zone grazed by sea urchins. (b) Specific growth rate of marginal encrusting area under future climate conditions.

In a recent study published in Marine Pollution Bulletin, the authors conducted a mesocosm experiment to investigate the sensitivity of temperate CCA Chamberlainium sp. to future climate stressors, as simulated by three experimental treatments: 1) Acidification: doubled CO₂; 2) Warming: +5ºC; and 3) Greenhouse: doubled CO₂ and +5ºC. After a 47-day acclimation period, when compared with present-day (control: 490 μatm and 20ºC) conditions, the Acidification treatment showed decreased photosynthesis rates of Chamberlainium sp, whereas the Warming treatment showed increased photosynthesis. The Acidification treatment also showed reduced encrusting growth rates relative to the Control, but when acidification was combined with warming in the Greenhouse treatment, encrusting growth rates increased substantially (Figure 1b). Taken together, these results suggest that the negative ecophysiological responses of Chamberlainium sp to acidification are ameliorated by elevated temperatures in a greenhouse world. In other words, if the foliose macroalgal community responses negatively in the greenhouse environment, the dominance of CCA will increase further, and the biodiversity of the algae community will be reduced.

Authors:
Ju-Hyoung Kim (Faculty of Marine Applied Biosciences, Kunsan National University)
Il-Nam Kim (Department of Marine Science, Incheon National University)

Austral summer vertical migration patterns in Antarctic zooplankton

Posted by mmaheigan

· Thursday, October 15th, 2020

Sunrise and sunset are the main cues driving zooplankton diel vertical migration (DVM) throughout the world’s oceans. These marine animals balance the trade-off between feeding in surface waters at night and avoiding predation during the day at depth. Near-constant daylight during polar summer was assumed to dampen these daily migrations. In a recent paper published in Deep-Sea Research I, authors assessed austral summer DVM patterns for 15 taxa over a 9-year period. Despite up to 22 hours of sunlight, a diverse array of zooplankton – including copepods, krill, pteropods, and salps – continued DVM.

Figure caption: Mean day (orange) and night (blue) abundance of (A) the salp Salpa thompsoni, (B) the krill species Thysanoessa macrura, (C) the pteropod Limacina helicina, and (D) chaetognaths sampled at discrete depth intervals from 0-500m. Horizontal dashed lines indicate weighted mean depth (WMD). N:D is the night to day abundance ratio for 0-150 m. Error bars indicate one standard error. Sample size n = 12 to 22. Photos by Larry Madin, Miram Gleiber, and Kharis Schrage.

The Palmer Antarctica Long-Term Ecological Research (LTER) Program conducted this study using a MOCNESS (Multiple Opening/Closing Net and Environmental Sensing System) to collect depth-stratified samples west of the Antarctic Peninsula. The depth range of migrations during austral summer varied across taxa and with daylength and phytoplankton biomass and distribution. While most taxa continued some form of DVM, others (e.g., carnivores and detritivores) remained most abundant in the mesopelagic zone, regardless of photoperiod, which likely impacted the attenuation of vertical carbon flux. Given the observed differences in vertical distribution and migration behavior across taxa, ongoing changes in Antarctic zooplankton assemblages will likely impact carbon export pathways. More regional, taxon-specific studies such as this are needed to inform efforts to model zooplankton contributions to the biological carbon pump.

Authors:
John Conroy (VIMS, William & Mary)
Deborah Steinberg (VIMS, William & Mary)
Patricia Thibodeau (VIMS, William & Mary; currently University of Rhode Island)
Oscar Schofield (Rutgers University)

Marine heatwave implications for future phytoplankton blooms

Posted by mmaheigan

· Thursday, October 15th, 2020

Ocean temperature extreme events such as marine heatwaves are expected to intensify in coming decades due to anthropogenic warming. Although the effects of marine heatwaves on large plants and animals are becoming well documented, little is known about how these warming events will impact microbes that regulate key biogeochemical processes such as ocean carbon uptake and export, which represent important feedbacks on the global carbon cycle and climate.

Figure caption: Relationship between phytoplankton bloom response to marine heatwaves and background nitrate concentration in the 23 study regions. X-axis denotes the annual-mean sea-surface nitrate concentration based on the model simulation (1992-2014; OFAM3, blue) and the in situ climatology (WOA13, orange). Y-axis denotes the mean standardised anomalies (see Equation 1 of the paper) of simulated sea-surface phytoplankton nitrogen biomass (1992-2014; OFAM3, blue) and observed sea-surface chlorophyll a concentration (2002-2018; MODIS, orange) during the co-occurrence of phytoplankton blooms and marine heatwaves.

In a recent study published in Global Change Biology, authors combined model simulations and satellite observations in tropical and temperate oceanographic regions over recent decades to characterize marine heatwave impacts on phytoplankton blooms. The results reveal regionally‐coherent anomalies depicted by shallower surface mixed layers and lower surface nitrate concentrations during marine heatwaves, which counteract known light and nutrient limitation effects on phytoplankton growth, respectively (Figure 1). Consequently, phytoplankton bloom responses are mixed, but derive from the background nutrient conditions of a study region such that blooms are weaker (stronger) during marine heatwaves in nutrient-poor (nutrient-rich) waters.

Given the projected expansion of nutrient-poor waters in the 21st century ocean, the coming decades are likely to see an increased occurrence of weaker blooms during marine heatwaves, with implications for higher trophic levels and biogeochemical cycling of key elements.

Authors:
Hakase Hayashida (University of Tasmania)
Richard Matear (CSIRO)
Pete Strutton (University of Tasmania)

Will global change “stress out” ocean DOC cycling?

Posted by mmaheigan

· Tuesday, September 29th, 2020

The dissolved organic carbon (DOC) pool is vital for the functioning of marine ecosystems. DOC fuels marine food webs and is a cornerstone of the earth’s carbon cycle. As one of the largest pools of organic matter on the planet, disruptions to marine DOC cycling driven by climate and environmental global changes can impact air-sea CO2 exchange, with the added potential for feedbacks on Earth’s climate system.

Figure 1. Simplified view of major dissolved organic carbon (DOC) sources (black text) and sinks (yellow text) in the ocean.

Since DOC cycling involves multiple processes acting concurrently over a range of time and space scales, it is especially challenging to characterize and quantify the influence of global change. In a recent review paper published in Frontiers in Marine Science, the authors synthesize impacts of global change-related stressors on DOC cycling such as ocean warming, stratification, acidification, deoxygenation, glacial and sea ice melting, inflow from rivers, ocean circulation and upwelling, and atmospheric deposition. While ocean warming and acidification are projected to stimulate DOC production and degradation, in most regions, the outcomes for other key climate stressors are less clear, with much more regional variation. This synthesis helps advance our understanding of how global change will affect the DOC pool in the future ocean, but also highlights important research gaps that need to be explored. These gaps include for example a need for studies that allow to understand the adaptation of degradation/production pathways to global change stressors, and their cumulative impacts (e.g. temperature with acidification).

Authors:
C. Lønborg (Aarhus University)
C. Carreira (CESAM, Universidade de Aveiro)
Tim Jickells (University of East Anglia)
X.A. Álvarez-Salgado (CSIC, Instituto de Investigacións Mariñas)

Little big exporters

Posted by mmaheigan

· Wednesday, April 8th, 2020

In the Southern Ocean, coccolithophores are thought to account for a major fraction of marine carbonate production and export to the deep sea. Despite their importance in the ocean carbon cycle, we lack fundamental information about Southern Ocean coccolithophore abundance, species composition, and contribution to carbonate export.

Figure caption: Heliscosphaera carteri (left), Coccolithus pelagicus (right) and Emiliania huxleyi (bottom right, partially behind C. pelagicus) coccospheres retrieved from the subantarctic waters south of Tasmania. Image Ruth Eriksen, courtesy AAD EMU.

A recent study in Biogeosciences has generated annual observations of coccolithophore species composition and contribution to calcium carbonate fluxes at two sites that are representative of a large portion of the Subantarctic zone. Coccolithophores account for roughly half of the annual calcium carbonate exported to the deep sea. Notably, it is not the most abundant species (Emiliania huxleyi), but rather the less abundant and larger species (e.g. Calcidiscus leptoporus, Helicosphaera carteri and Coccolithus pelagicus) that make the greatest contribution to carbonate export to the deep sea. Since these larger species exhibit substantially different ecological traits from the opportunistic E. huxleyi, predictions of future response of Southern Ocean coccolithophore communities should not be based on the physiological results from experiments with E. huxleyi. Rather, new physiological response experiments of those less abundant, larger coccolithophore species are urgently needed to constrain responses of these important carbonate exporters to environmental change in the Southern Ocean. This study underscores the importance of phytoplankton ecological traits on the regulation of the marine carbon cycle and emphasizes the need for more species-specific studies to improve predictions of marine ecosystem response to ongoing climate change.

Authors
Andrés S. Rigual Hernández (Universidad de Salamanca)
Thomas W. Trull (CSIRO and ACE CRC)
Scott D. Nodder (NIWA)
José A. Flores (Universidad de Salamanca)
Helen Bostock (University of Queensland,)
Fátima Abrantes (Portuguese Institute for Sea and Atmosphere and CCMAR)
Ruth S. Eriksen (CSIRO and IMAS)
Francisco J. Sierro (Universidad de Salamanca)
Diana M. Davies (CSIRO and ACE CRC)
Anne-Marie Ballegeer (Universidad de Salamanca)
Miguel A. Fuertes (Universidad de Salamanca)
Lisa C. Northcote (NIWA)

Chasing Sargassum in the Atlantic Ocean

Posted by mmaheigan

· Wednesday, March 25th, 2020

The pelagic brown alga Sargassum forms a habitat that hosts a rich diversity of life, including other algae, crustaceans, fish, turtles, and birds in both the Gulf of Mexico and the area of the Atlantic Ocean known as the Sargasso Sea. However, high abundances of Sargassum have been appearing in the tropical Atlantic, in some cases 3,000 miles away from the Sargasso Sea. This is a new phenomenon. Nearly every year since 2011, thick mats of Sargassum have blanketed the coastlines of many countries in tropical Africa and the Americas. When masses of Sargassum wash ashore, the seaweed rots, attracts insects, and repels beachgoers, with adverse ecological and socioeconomic effects. A new study in Progress in Oceanography sheds light on the mystery.

Figure 1. The hypothesized route of Sargasso Sea Sargassum to the tropical Atlantic and the Caribbean Sea. The solid black lines indicate the climatological surface flow, the dashed black lines indicate areas where there was variability from the average conditions.

The authors analyzed reams of satellite data and used computer models of the Earth’s winds and ocean currents to try to understand why these large mats started to arrive in coastal areas in 2011. A strengthening and southward shift of the westerlies in the winter of 2009-2010 caused ocean currents to move the Sargassum toward the Iberian Peninsula, then southward in the Canary Current along Africa, where it entered the tropics by the middle of 2010 (Figure 1). The tropical Atlantic provided ample sunlight, warmer sea temperatures, and nutrients for the algae to flourish. In 2011, Sargassum spread across the entire tropical Atlantic in a massive belt north of the Equator, along the Intertropical Convergence Zone (ITCZ), and these blooms have appeared nearly every year since. Utilizing international oceanographic studies done in the Atlantic since the 1960s, and multiple satellite sensors combined with Sargassum distribution patterns, the authors discovered that the trade winds aggregate the Sargassum under the ITCZ and mix the water deep enough to bring new nutrients to the surface and sustain the bloom.

Improved understanding and predictive capacity of Sargassum bloom occurrence will help us better constrain and quantify its impacts on our ecosystems, which can inform management of valuable fisheries and protected species.

Authors:
Elizabeth Johns (NOAA AMOL)
Rick Lumpkin (NOAA AMOL)
Nathan Putman (LGL Ecological Research Associates)
Ryan Smith (NOAA AMOL)
Frank Muller-Karger (University of South Florida)
Digna Rueda-Roa (University of South Florida)
Chuanmin Hu (University of South Florida)
Mengqiu Wang (University of South Florida)
Maureen Brooks (University of Maryland Center for Environmental Science)
Lewis Gramer (NOAA AMOL and University of Miami)
Francisco Werner (NOAA Fisheries)

Where the primary production goes determines whether you catch tuna or cod

Posted by mmaheigan

· Friday, September 6th, 2019

Fishes are incredibly diverse, fill various roles in their ecosystems, and are an important resource—economically, socially, and nutritionally. The relationship between primary productivity and fish catches is not straightforward; fisheries oceanographers and managers have long struggled to predict abundances and fully understand the controls of cross-ecosystem differences in fish abundances and assemblages. A recent study in Progress in Oceanography modeled the relationships between fish abundances and assemblages and ecosystem factors such as physical properties and plankton productivity.

The mechanistic model simulated feeding, growth, reproduction, and mortality of small pelagic forage fish, large pelagic fish, and demersal (bottom-dwelling) fish in the global ocean using plankton food web estimates and ocean conditions from a high-resolution earth system model of the 1990s. Modeled fish assemblages were more related to the separation of secondary production into pelagic zooplankton or benthic fauna secondary production than to primary productivity. Specifically, the ratio of pelagic to benthic production drove spatial differences in dominance by large pelagic fish or by demersal fish. Similarly, demersal fish abundance was highly sensitive to the efficiency of energy transfer from exported surface production to benthic fauna.

The model results offer a systematic understanding of how marine fish communities are structured by spatially varying environmental conditions. With global climate change, the expected decrease in exported primary production would lead to fewer demersal fish around the world. This model provides a framework for testing the effect of changing conditions on fish communities at a global scale, which can also help inform managers of potential impacts on economic, social, and nutritional resources worldwide.

Figure 1: (A) Sample food web with three fish types, two habitats, two prey categories, and feeding interactions (arrows). Dashed arrow denotes feeding only occurs in shelf regions with depth <200 m. (B) Fraction of large pelagic vs. demersal fishes (LP/(LP+D)) as a function of the ratio of zooplankton production lost to higher predation (Zoop) to detritus flux to the seafloor (Bent) averaged over large marine ecosystems. Solid line: predicted linear model response, dashed lines: standard error. (Lower panels) Circles=mean biomasses (g m^-2) and lines=fluxes of biomass (g m^-2 d^-1) through the pelagic (top 100m) and benthic components of the food webs at two test locations, (C) Peruvian Upwelling (PUP) ecosystem and (D) Eastern Bering Sea (EBS) shelf ecosystem. Circles and lines scale with the modeled biomasses and fluxes. Circle color key: Gray=net primary productivity (NPP); yellow=medium and large zooplankton; red=forage fish; blue=large pelagic fish; brown=benthos; green=demersal fish.

Authors:
Colleen M. Petrik (Princeton University, Texas A&M University)
Charles A. Stock (NOAA Geophysical Fluid Dynamics Laboratory)
Ken H. Andersen (Technical University of Denmark)
P. Daniël van Denderen (Technical University of Denmark)
James R. Watson (Oregon State University)

Predicting marine ecosystem futures

Posted by mmaheigan

· Wednesday, September 4th, 2019

Earth System Models (ESMs) are powerful and effective tools for exploring and predicting marine ecosystem response to environmental change, including biogeochemical processes that underlie threats to ocean health such as ocean acidification, deoxygenation, and changes in productivity. Seasonal to interannual marine biogeochemical predictions with ESMs hold great promise for exploring links between climate and marine resources such as fisheries but have thus far been challenged by limitations associated with observational initialization, model structure, and computational availability. In a recent study published in Science, authors integrated the Geophysical Fluid Dynamics Laboratory’s (GFDL) COBALT (Carbon, Ocean Biogeochemistry and Lower Trophics) marine biogeochemical model with seasonal to multi-annual climate predictions from GFDL’s CM2.1 climate model to examine marine ecosystem futures on these shorter time scales. The global biogeochemical forecasts were initialized on the first of each month between 1991 and 2017 with 12 ensemble members in each prediction, creating a database of nearly 4000 forecasts and 8000 simulation years. The model skillfully predicted seasonal to multi-annual chlorophyll fluctuations in many ocean regions (Figure 1).

Figure 1: Prediction skill in reproducing observed variations of monthly chlorophyll anomaly. (Top) Correlation coefficient between predicted and observed chlorophyll at 1-3 month lead time during the period 1997-2017. Stippled areas indicate that the correlation is significantly greater than 0 with 95% confidence. Areas with less than 80% satellite chlorophyll coverage are masked in grey. (Lower panels) Correlation coefficient between predicted and observed chlorophyll as a function of forecast initialization month (x-axis) and lead time (y-axis) in tropical Pacific, Indian, North Atlantic, North Pacific, and South Pacific oceans. In all panels, the darker the red, the higher the correlation up to a perfect correlation of 1.0. White indicates no correlation, while blue indicates negative correlation.

These results suggest that annual fish catches in selected large marine ecosystems can be predicted from chlorophyll and sea surface temperature anomalies up to 2-3 years in advance. Given that fisheries predictions sometimes failed to the point of commercial stock collapse in the past, this prediction capacity could be vital for fisheries managers. Biogeochemical prediction systems can extend beyond sea surface temperature and chlorophyll to include other potential drivers (e.g., oxygen, acidity, net primary production, zooplankton, etc.) as highly valuable tools for marine resource managers of dynamic and changing ecosystems.

Authors:
Jong-Yeon Park (Princeton Univ, NOAA GDFL, Chonbuk National Univ., Korea)
Charles A. Stock, John P. Dunne, Xiaosong Yang, and Anthony Rosati (NOAA GFDL)

Zooplankton-fueled carbon export is changing in the North Atlantic Ocean

Posted by mmaheigan

· Monday, June 10th, 2019

Zooplankton-mediated carbon export is an important, but variable and relatively unconstrained part of the biological carbon pump—the processes that fix atmospheric carbon dioxide in organic material and transport it from the upper sunlit ocean to depth. Changes in the biological pump impact the climate system, but are challenging to quantify because such analyses require spatially and temporally explicit information about biological, chemical, and physical properties of the ocean, where empirical observations are in short supply.

A recent study in Nature, Ecology and Evolution focused on copepods in the northern half of the North Atlantic Ocean, where the Continuous Plankton Recorder (CPR) time series program has documented surface plankton abundance and taxonomic composition for nearly six decades. Copepods transport carbon passively by producing sinking fecal pellets while feeding near the sea surface, and actively via daily and seasonal migrations to deeper waters where carbon is released through respiration, defecation, and mortality. Using allometry, metabolic theory, and an optimal behavior model, the authors examined patterns of passive and active carbon transport from 1960 to 2014 and sensitivity of carbon export to different model inputs.

Figure caption: Spatial distribution and change, from 1960 to 2014, of modeled copepod-mediated carbon flux: top left – mean passive carbon flux (sinking fecal pellets), bottom left – change in passive carbon flux, top right – mean active carbon flux (respiration plus fecal pellets produced during diel vertical migration), bottom right – change in active carbon flux.

The authors observed that from southern Iceland to the Gulf of Maine, copepod-mediated carbon transport has increased over the last six decades, with the highest rates around 30 mgC m^-2 y^-1 each decade for passive flux, and 4 mgC m^-2 y^-1 each decade for active flux. Meanwhile, it has decreased across much of the more temperate central northern North Atlantic with highest rates around 69 mgC m^-2 y^-1 each decade for passive flux and 8 mgC m^-2 y^-1 each decade for active flux. This pattern is largely driven by changes in copepod population distributions and community structure, specifically the distributions of large and abundant species (e.g. Calanus spp.). These results suggest that shifts in species distributions driven by a changing global climate are already impacting ecosystem function across the northern North Atlantic Ocean. These shifts are not latitudinally uniform, thus highlighting the complexity of marine ecosystems. This study demonstrates the importance of these sustained plankton measurements and how plankton-mediated carbon fluxes can be mechanistically implemented in next-generation biogeochemical models.

Authors:
Philipp Brun (Technical University of Denmark and Swiss Federal Research Institute)
Karen Stamieszkin (University of Maine, Bigelow Lab and Virginia Institute of Marine Science)
Andre W. Visser (Technical University of Denmark)
Priscilla Licandro (Sir Alister Hardy Foundation for Ocean Science, Plymouth Marine Laboratory, and Stazione Zoologica Anton Dohrn, Italy)
Mark R. Payne (Technical University of Denmark)
Thomas Kiørboe (Technical University of Denmark)

Also see OCB2019 plenary session: The effect of size on ocean processes (allometry) and implications for export (Thursday, June 27, 2019)

Ocean microbes drive fluctuating nutrient loss

Posted by mmaheigan

· Tuesday, May 28th, 2019

The removal of bioavailable nitrogen (N) by anaerobic microbes in the ocean’s oxygen deficient zones (ODZs) is thought to vary over time primarily as a result of climate impacts on ocean circulation and primary production. However, a recent study in PNAS using a data-constrained model of the microbial ecosystem in the world’s largest ODZ revealed that internal species oscillations cause local- to basin-scale fluctuations in the rate of N loss, even in a completely stable physical environment. Such ecosystem oscillations have been hypothesized for nearly a century in idealized models, but are rarely shown to persist in a three-dimensional ocean circulation model.

Figure caption. Ecological variability in the basin-scale rate of nitrogen loss over time (left) and in the local-scale contribution of autotrophic anammox to total N loss (right) in a model with unchanging ocean circulation. In the left panel, colors represent model simulations with different biological parameters. In the right panel, colors represent distinct locations within the ODZ in the standard model simulation.

These emergent ecosystem dynamics arise at the oxic-anoxic interface from O₂-dependent resource competition between aerobic and anaerobic microbes, and leave a unique geochemical fingerprint: infrequent spikes in ammonium that are observable in nutrient measurements from the ODZ. Non-equilibrium ecosystem behavior driven by competition among aerobic nitrifiers, anaerobic denitrifiers, and anammox bacteria also generates fluctuations in the balance of autotrophic versus heterotrophic N loss pathways that help reconcile conflicting field observations.

These internally driven fluctuations in microbial community structure partially obscure a direct correspondence between the chemical environment and microbial rates, a universal assumption in biogeochemical models. Because of the fundamental nature of the underlying mechanism, similar dynamics are hypothesized to occur across wide-ranging microbial communities in diverse habitats.

Authors:
Justin L. Penn (University of Washington)
Thomas Weber (University of Rochester),
Bonnie X. Chang (University of Washington, NOAA)
Curtis Deutsch (University of Washington)

See also the OCB2019 plenary session: Anthropogenic changes in ocean oxygen: Coastal and open ocean perspectives (Monday, June 24, 2019)

Funding for the Ocean Carbon & Biogeochemistry Project Office is provided by the National Science Foundation (NSF) and the National Aeronautics and Space Administration (NASA). The OCB Project Office is housed at the Woods Hole Oceanographic Institution.

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