Download Retrospective analysis of ecological changes in the Laurentian

Retrospective analysis of ecological changes in the Laurentian
ecosystem using sclerochronology
– ARCHivES –
Ph.D. research proposal – Ecole Doctorale des Sciences de la Mer et du Littoral
Supervisor: Dr. Laurent Chauvaud, senior scientist CNRS (HDR)
Email: [email protected]
Co-supervisor: Dr. Julien Thébault, associate professor UBO
Email: [email protected]
Website: http://pagesperso.univ-brest.fr/~jthebaul/
Doctoral school:
Ecole Doctorale des Sciences de la Mer et du Littoral
Research unit: Laboratoire des sciences de l’environnement marin (LEMAR UMR6539 CNRS / UBO /
IRD / Ifremer), Institut Universitaire Européen de la Mer (IUEM), rue Dumont d’Urville, 29280 Plouzané
Research team: Equipe DISCOVERY (Diversité, structure et dynamique des populations et des communautés) – LEMAR
Abstract
The Laurentian ecosystem spreads all along the River, the Estuary and the Gulf of St. Lawrence (Canada)
and is one of the greatest and most productive aquatic systems worldwide. Increasing anthropization of
this continuum since two centuries had still poorly assessed ecological consequences. Environmental and
ecological observatory networks are now monitoring with accuracy a large set of hydrobiological parameters
but the oldest data only go back to the late 1990s. This is insufficient to get insights about the impacts
of mankind and global change on this ecosystem. In this context, the main goal of the project ARCHivES
is to build annually-resolved chronologies of multi-decadal to multi-centennial variations in environmental
parameters (temperature, phytoplankton dynamics, pollution). This goal will be achieved by deciphering
the structural and geochemical information archived in shells of long-lived (> 100 years) bivalve species.
Eight freshwater and marine species will be collected (both live and dead) from Montreal to Saint-Pierreet-Miquelon and analyzed for their growth patterns and geochemical composition. This sclerochronological
approach will provide insights about spatial and temporal variability of anthropogenic impacts. It will
therefore go towards overcoming the scarcity of long-term observation time-series that are, yet, essential for
accurate regional-scale climate predictions.
Scientific background
General context – At the eve of the 21st century, Crutzen & Stoermer (2000) proposed using the neologism "Anthropocene" to emphasize the significant global impact that mankind started to have on Earth’s
geology and ecology. Nowadays, there is a consensus in the international scientific community, stating that
human activities have, or will shortly have, consequences on the structure and functioning of all the Earth’s
ecosystems, especially in the marine realm. In the world ocean, coastal areas and estuaries are definitely
amongst the marine ecosystems that are/will be the most affected by anthropogenic activities and global
change (Millennium Ecosystem Assessment 2005). These systems lie among the most dynamic interfaces of
the biosphere. Therefore, they hold an important place along the land-sea continuum. For instance, estuaries
play a major role in filtering pollutants before waters reach the coastal areas. They also provide shelter,
1
Ph.D. research proposal – Ecole Doctorale des Sciences de la Mer et du Littoral – LEMAR UMR6539
Figure 1: Map of the River, Estuary and Gulf of St. Lawrence (REGSL)
breeding and feeding grounds for many species (birds, fish, marine mammals, etc.). The most significant
anthropogenic impacts affecting these ecosystems are related to changes in continental freshwater discharge,
inputs of sediment, organic and inorganic pollutants, and nutrients. The latter can induce changes of trophic
conditions and disturbances in phytoplankton dynamics, keystone of the functioning of coastal ecosystems
(Cloern 2001), up to eutrophication. All these anthropogenic changes also frequently induce (chronic) hypoxia events, and losses of habitats and biodiversity (Smith 2006).
The St. Lawrence continuum, an anthropogenically-altered ecosystem — The River, Estuary
& Gulf of Saint Lawrence (REGSL) continuum is one of the greatest and most productive aquatic systems
worldwide. The St. Lawrence River (1200 km long, draining area of 1 344 000 km2 ) begins at the outflow of
the Great Lakes and widens into a large and deep estuary that starts at the mouth of the Saguenay River
and ends in the Gulf of St. Lawrence, a large (240 000 km2) semi-enclosed sea connected to the Atlantic
Ocean by Cabot Strait to the south and the Strait of Belle-Isle to the north (Figure 1). The gulf is also
influenced by ocean and climate variability in the North Atlantic, especially by the Laborador Current.
Temporal variability of Labrador Current inflow and St. Lawrence River runoff creates large spatial and
temporal variations in environmental conditions. The REGSL system also provides a seaway to the heart
of North America, which encouraged the settlement and development of much of Canada and Central USA.
Over the past two centuries, the transformation of the St. Lawrence River and estuary has sped up, with
an intensive colonization of the riverbanks. Nowadays, the St. Lawrence marine ecosystem is exposed to a
wide variety of human pressures and uses that pose significant threats to its integrity and sustainable use:
fisheries, navigation, mariculture, oil and gas exploration, etc. It is also affected by industrial and municipal
activities, agriculture, etc. In addition, large–scale modifications resulting from climate change already have
significant effects on the ecology the REGSL, with changes in timing and volume of freshwater inputs, in
surface temperatures, in the strength and inflow of the Labrador current, in the duration of summer stratification, in the nutrient availability, etc. (Dufour & Ouellet 2007).
Relevance of biological recorders of environmental variability – This global vision of anthropogenic impacts on terrestrial and aquatic ecosystems conceals temporal and spatial disparities. The problem
is that "conventional" monitoring time-series (electronic instruments, periodic water sampling) are relatively
sparse, scattered, poorly replicated and often very short. Moreover, they do not encompass low frequency
cycles of natural variations, especially in marine environments (Jackson 2001). And yet, long-term oceanic
variability time-series are fundamental to comprehend global change impacts on marine ecosystems (Ducklow
et al. 2009). Multi-decadal long datasets are also essential to disentangle climate change signals from natural
variability (Doney et al. 2012). The Fourth Assessment Report of the IPCC (IPCC 2007) recognised the
2
Ph.D. research proposal – Ecole Doctorale des Sciences de la Mer et du Littoral – LEMAR UMR6539
need to generate high-resolution marine proxy records in order to reduce uncertainty in climate simulations:
"[. . . ] there are important limitations due to a lack of [. . . ] ocean records"
"Lastly, this assessment would be improved with extensive networks of proxy data that run right
up to the present day. This would help measure how the proxies responded to the rapid global
warming observed in the last 20 years [. . . ]"
In this context, biological records of environmental variability (biogeochemical archives) appear as relevant tools (i) to extend conventional records over time periods long enough to decouple the respective roles of
natural variability and anthropogenic activities in the current changes in structure and functioning of coastal
ecosystems, and (ii) to gain insights into the spatial variability of ecosystem’s responses to global change.
These biological records are obtained by deciphering environmental tracers (so-called "proxies") incorporated
within biogenic archives during their growth (e.g., corals, sclerosponges, mollusk shells, rhodoliths). These
organisms form their external calcium carbonate (CaCO3 ) skeleton periodically, which leads to the formation
of growth lines (e.g. daily striae, annual bands) that can be used as chronological landmarks (sclerochronology, the aquatic equivalent to dendrochronology). In addition, some minor, trace and ultra-trace elements
can be trapped/included within the shell matrix during biomineralization (e.g. Sr, Mg, Mn, Ba, Li, Pb, U,
heavy metals), in quantities that are dependent upon (i) a large panel of environmental parameters (e.g.
temperature, phytoplankton, hypoxia events, pH), and (ii) the physiology of these organisms. Over the past
ten years, bivalve mollusk shell analysis led to many environmental reconstructions of seawater temperature
(Walliser et al. 2016), phytoplankton dynamics (Thébault & Chauvaud 2013), pollutions (Holland et al.
2014), or biogeochemical processes in the water column or at the sediment-water interface (Freitas et al.
2016).
Questions & Objectives of the project
The intensity and the spatio-temporal dynamics of the environmental and ecological changes that occurred
in the REGSL system still remains unknown and better predictive models are needed. In this context,
looking back to the past is essential to better understand the present and predict the future. In 2005, the
St. Lawrence Global Observatory (SLGO) was created and now provides an access to the most accurate
and complete data and information about the REGSL ecosystem through clustering and networking of data
producers. Thousands of data are available back to 1999. What happened before? How fast did the REGSL
ecosystem change over the past two centuries? What about the spatial disparities of this dynamics? A stateof-the-art clearly highlights (i) that there is definitely a need for long-term time-series of environmental
conditions in the REGSL system, and (ii) that despite their outstanding potential, bivalve shells have never
been used as paleo-environmental archives in this ecosystem. In this context, the main objectives of this
research project are:
• to calibrate environmental proxies by comparing structural and geochemical patterns archived in bivalve shells with high-frequency environmental variables measured in the REGSL over the past 20
years (access through SLGO);
• to reconstruct past variations (100-200 years, a minima) of environmental parameters (temperature,
phytoplankton dynamics, pollution) in the REGSL by looking at growth patterns and geochemical
composition of bivalve mollusk shells (in both dead and live collected specimens). Combined use
of different bivalve species at a given location (multi-proxy approach) will increase the quality and
strength of these reconstructions as already outlined by Black et al. (2009);
• to get insights about spatial variability of anthropogenic impacts by analyzing freshwater and marine
shells from several species that cover most of the river-estuary-gulf continuum from Montreal to SaintPierre-et-Miquelon.
Research methodologies
Our investigations will focus on several locations, chosen for their physical/chemical/biological characteristics between the St. Lawrence River and the outer part of the Gulf of St. Lawrence, and therefore covering
the entire continuum between freshwater and typically marine waters. This area is exceptional as it hosts,
3
Ph.D. research proposal – Ecole Doctorale des Sciences de la Mer et du Littoral – LEMAR UMR6539
Figure 2: Pictures of the different long-lived bivalve species selected for this project (scale bar = 1 cm).
like no other place in the world, many bivalve species that can live over 100 years (Figure 2). The river portion (and its tributaries) from Montreal to Québec City is an interesting area as it is densely populated and
therefore affected by different kind of effluents. Target bivalve species in that area belong to the Unionoida
order: freshwater pearl mussels Margaritifera margaritifera (lifespan of up to 280 years; Dunca et al. 2011),
eastern elliptios Elliptio complanata (149 years; Anthony et al. 2001), fatmuckets Lampsilis siliquoidea (167
years; Anthony et al. 2001) and giant floaters Pyganodon grandis (95 years; Anthony et al. 2001). These
species will be collected in close collaboration with SurVol Benthos, a volunteer monitoring program of rivers
and streams using benthic macroinvertebrates (including bivalves) as bioindicators.
In the estuary and the gulf, some bivalves are already available thanks to a giant oceanographic campaign
carried out each summer between 2006 and 2009 (755 stations between 25 and 512 m water depth; Moritz
et al. 2013). In addition, Laval University coordinates since 2016 (collaboration with Fisheries and Oceans
Canada) an annual oceanographic campaign covering the entire area from the mouth of the Saguenay to
Newfoundland (110 stations between 30 m and 340 m water depth). Three locations in the gulf will be
particularly investigated:
• the mouth of the Saguenay River, as this area is the geographic boundary between the Upper and the
Lower Estuary;
• Sept-Iles. This city is located on the north shore of the St. Lawrence Estuary. It hosts the largest
primary aluminum smelter in the Americas, and the 3rd largest port of Québec (> 22 millions metric
tons in 2016), with potential impacts of coastal ecosystems;
• Old Harry oil field. Located north of Cabot Strait, between Newfoundland and Magdalen Islands, it
is a large 30 km x 12 km field, at a depth of 450 m, with a potential of 2 billion barrels. It is not
exploited yet which means that sclerochronological and geochemical analyses of shells from that area
will provide a reference baseline that could be useful if its exploitation starts in a near future.
In the southern part of the gulf, samples will be collected around the Magdalen Islands thanks to a
collaboration with Dr. C. McKindsey (Fisheries and Oceans Canada). At the southeastern tip of the gulf,
bivalves will be sampled around the French archipelago of Saint-Pierre-et-Miquelon in the framework of
the MATISSE research project (launched in 2016 and funded by the French National Center for Scientific
Research – CNRS; PI: Dr. L. Chauvaud). Target species in the Estuary/Gulf area will be the ocean quahog
Arctica islandica (lifespan of up to 507 years; Butler et al. 2013), the Arctic surfclam Mactromeris polynyma
(92 years; DFO 2012), the arctic saxicave Hiatella arctica (126 years; Sejr et al. 2002) and the astarte
Astarte spp. (over 100 years; Gaillard et al. in prep.).
After collection, shells will be prepared using conventional sclerochronological techniques in the sclerochronology lab at LEMAR. After measurements of annual growth increment width, geochemical analyses
will be performed at the European Institute for Marine Sciences (IUEM) using facilities of its spectrometry
platform (Pôle Spectrométrie Océan – PSO; http://www.pso-brest.org): stable isotope composition on
4
Ph.D. research proposal – Ecole Doctorale des Sciences de la Mer et du Littoral – LEMAR UMR6539
an IR-MS MAT 253 equipped with a Kiel IV device (carbon, oxygen) and elemental composition on a HRICP-MS Thermo Element2 coupled to a laser ablation unit (Mg, Sr, Ba, Mn, Mo, Li, U, Pb). Radiocarbon
dating analyses of dead-collected specimens will be subcontracted to a private company (Beta Analytic, UK;
http://www.radiocarbon.com).
International collaborations
This project lies in the framework of the BeBEST International Associated Laboratory (Benthic Biodiversity
Ecology Sciences and Technologies; https://www.liabebest.org), created in 2016 for 5 years by the National Center for Scientific Research (CNRS, France – PI: Dr. L. Chauvaud) and the Université du Québec à
Rimouski (UQAR, Quebec, Canada – PI: Prof. P. Archambault). This “laboratory without walls” currently
gathers 19 French and Canadian scientists around the development of bioindicators that could help diagnosing past and current changes in marine ecosystems, by using tools such as sclerochronology, accelerometry,
and passive acoustics.
Cited references
Anthony et al. (2001). Freshwater Biology 46: 1349-1359
Black et al. (2009). Palaeogeography Palaeoclimatology Palaeoecology 278: 40-47
Butler et al. (2013). Palaeogeography Palaeoclimatology Palaeoecology 373: 141-151
Cloern (2001). Marine Ecology Progress Series 210: 223-253
Crutzen & Stoermer (2000). IGBP Newsletter 41: 17-18
DFO (2012). DFO Canadian Science Advisory Secretariat Science Advisory Reports 2011/068
Doney et al. (2012). Annual Review of Marine Science 4: 11-37
Ducklow et al. (2009). Annual Review of Marine Science 1: 279-302
Dufour & Ouellet (2007). Canadian Technical Report of Fisheries and Aquatic Sciences 2744E
Dunca et al. (2011). Ferrantia 64: 48-58
Freitas et al. (2016). Geochimica et Cosmochimica Acta 194: 266-278
Holland et al. (2014). Marine Pollution Bulletin 87: 104-116
IPCC (2007). Contribution of WG I to the 4th Assessment Report of the IPCC, Solomon et al. (Eds.),
Cambridge University Press
Jackson. (2001). Proceedings of the National Academy of Sciences of the USA 98: 5411-5418
Millennium Ecosystem Assessment (2005). Ecosystems and Human Well-being: Biodiversity Synthesis.
World Resources Institute
Moritz et al. (2013). Journal of Sea Research 78: 75-84
Sejr et al. (2002). Marine Ecology Progress Series 244: 163-169
Smith (2006). Limnology and Oceanography 51: 377-384
Thébault & Chauvaud (2013). Palaeogeography Palaeoclimatology Palaeoecology 373: 108-122
Walliser et al. (2016). Palaeogeography Palaeoclimatology Palaeoecology 459: 552-569
5