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Disentangling Arctica islandica's environmental archive: Ecological drivers of its feeding behavior and growth
Ballesta-Artero, I. (2018). Disentangling Arctica islandica's environmental archive: Ecological drivers of its feeding behavior and growth. PhD Thesis. Vrije Universiteit Amsterdam: Amsterdam. ISBN 978-94-028-11599. 210 pp. https://hdl.handle.net/1871/55781

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Documenttype: Doctoraat/Thesis/Eindwerk

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  • Ballesta-Artero, I., meer

Abstract
    In these times of global and fast climate change, there is a need to further develop the research fieldof sclerochronology. This relatively new discipline uses the annual banding in the shells of long-livedmollusks to develop long timelines or chronologies. These chronologies can be coupled with localenvironmental records, in the same way as growth rings of trees are used in dendrochronology (Jones,1980; Witbaard et al., 1994; Karney et al., 2011). As such they provide insight into past and presentocean climatic conditions (Schöne et al., 2003; Witbaard et al., 2003; Butler et al., 2013; Mette et al.,2016). Continuous long-term (>50 years) instrumental records of environmental conditions are sparsein the marine environment. Thus, proxy-based environmental reconstructions are needed to improveregional and temporal coverage and to understand past marine climate variability (Jones et al. 2009;Wanamaker et al., 2011; Mette et al., 2016; Steinhardt et al., 2016).The boreal species Arctica islandica (Mollusca, Bivalvia) is an example of a great marine bioarchivedue to its wide distribution and extreme long-life (up to five centuries). This species' shell presentsannual growth increments (or growth bands) which provides dated environmental information by wayof variable growth increments, and microstructural and geochemical properties. However, theduration, timing, and main environmental forces regulating A. islandica ’s growing season still neededfurther study. The combined role of temperature and food in regulating activity patterns and shellgrowth of this bivalve had to be disentangled.Chapter 1 of this thesis describes the main characteristics of the species and the aim of my research.Chapter 2 reports about a fieldwork in situ experiment where we discovered that A. islandica gapingactivity in northern Norway has an eight months long active season in which valve movements aremainly regulated by food availability. Active gaping periods appear to coincide with periods of growth,indicating that A. islandica records their environment when its valves are open.A series of food and temperature experiments (Chapter 3 and Chapter 4), where the microstructuralproperties of A. islandica shells were studied, showed that temperature, but not food, induced achange in the crystallographic orientation of the biomineral units, indicating that this microstructuralproperty may be a potential proxy for seawater temperature. This change in crystallographicorientation was only detected by confocal Raman microscopy (CRM), not by scanning electronmicroscopy (SEM).Chapter 4 explores the combined effects of temperature and food availability on the shell and tissuegrowth of A. islandica under laboratory conditions. It appeared that the concentration of algal food is the main factor driving siphon activity and with that shell and tissue growth. Thus, these experimentaloutcomes support the results from Chapter 2, where in situ gaping activity was most closely correlatedwith the concentration of chlorophyll-a and to a lesser degree with the seawater temperature.We used a subsample of specimens from above laboratory growth experiment (Chapter 4) to studythe role of environmental and biological controls on trace elemental incorporation of A. islandica shells(Chapter 5). We found that all trace element-to-calcium ratios (Mg, Sr, Na, and Ba) were significantlyaffected by growth rate. This indicates that physiological processes seem to dominate the controls ofelement incorporation into A. islandica shells.Chapter 6 describes the energy use of A. islandica based on a Dynamic Energy Budget model. Ourresults indicate that A. islandica 's extreme longevity arises from its low somatic maintenance cost[?̇?] and low ageing acceleration ℎ̈?. We could not find a direct relationship between food availabilityand lifespan (theory of caloric restriction) in the eight North Atlantic populations studied.Nevertheless, food estimates based on the DEB’s scaled functional response can be a good foodindicator, sometimes the only one, of the benthic food conditions at A. islandica localities.The main conclusions of this thesis are that (1) A. islandica gaping and growing season seems to belimited to 8 months of the year, and that food availability and not temperature is the main driver ofthis gaping and growth behavior, (2) some microstructural and geochemical properties of A. islandica shell contain environmental information, but further study still need to be done to use them as areliable environmental proxy, and (3) the extreme longevity of the species is due to its low somaticmaintenance cost and low accumulation of waste that provokes ageing.

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