Posts Tagged 'bryozoans'

Volcanic CO2 seep geochemistry and use in understanding ocean acidification

Ocean acidification is one of the most dramatic effects of the massive atmospheric release of anthropogenic carbon dioxide (CO2) that has occurred since the Industrial Revolution, although its effects on marine ecosystems are not well understood. Submarine volcanic hydrothermal fields have geochemical conditions that provide opportunities to characterise the effects of elevated levels of seawater CO2 on marine life in the field. Here, we review the geochemical aspects of shallow marine CO2-rich seeps worldwide, focusing on both gas composition and water chemistry. We then describe the geochemical effects of volcanic CO2 seepage on the overlying seawater column. We also present new geochemical data and the first synthesis of marine biological community changes from one of the best-studied marine CO2 seep sites in the world (off Vulcano Island, Sicily). In areas of intense bubbling, extremely high levels of pCO2 (> 10,000 μatm) result in low seawater pH (< 6) and undersaturation of aragonite and calcite in an area devoid of calcified organisms such as shelled molluscs and hard corals. Around 100–400 m away from the Vulcano seeps the geochemistry of the seawater becomes analogous to future ocean acidification conditions with dissolved carbon dioxide levels falling from 900 to 420 μatm as seawater pH rises from 7.6 to 8.0. Calcified species such as coralline algae and sea urchins fare increasingly well as sessile communities shift from domination by a few resilient species (such as uncalcified algae and polychaetes) to a diverse and complex community (including abundant calcified algae and sea urchins) as the seawater returns to ambient levels of CO2. Laboratory advances in our understanding of species sensitivity to high CO2 and low pH seawater, reveal how marine organisms react to simulated ocean acidification conditions (e.g., using energetic trade-offs for calcification, reproduction, growth and survival). Research at volcanic marine seeps, such as those off Vulcano, highlight consistent ecosystem responses to rising levels of seawater CO2, with the simplification of food webs, losses in functional diversity and reduced provisioning of goods and services for humans.

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Plastic responses of bryozoans to ocean acidification

Phenotypic plasticity has the potential to allow organisms to respond rapidly to global environmental change, but the range and effectiveness of these responses are poorly understood across taxa and growth strategies. Colonial organisms might be particularly resilient to environmental stressors, as organizational modularity and successive asexual generations can allow for distinctively flexible responses in the aggregate form. We performed laboratory experiments to examine the effects of increasing dissolved carbon dioxide (i.e. ocean acidification) on the colonial bryozoan Celleporella cornuta sampled from two source populations within a coastal upwelling region of the northern California coast. Bryozoan colonies were remarkably plastic under these carbon dioxide (CO2) treatments. Colonies raised under high CO2 grew more quickly, investing less in reproduction and producing lighter skeletons when compared to genetically identical clones raised under current atmospheric values. Bryozoans held in high CO2 conditions also changed the Mg/Ca ratio of skeletal calcite and increased the expression of organic coverings in new growth, which may serve as protection against acidified water. We also observed strong differences between populations in reproductive investment and organic covering reaction norms, consistent with adaptive responses to persistent spatial variation in local oceanographic conditions. Our results demonstrate that phenotypic plasticity and energetic trade-offs can mediate biological responses to global environmental change, and highlight the broad range of strategies available to colonial organisms.

Continue reading ‘Plastic responses of bryozoans to ocean acidification’

Growth rates, age determination and calcification levels in Flustra foliacea (L.) (Bryozoa: Cheilostomata): preliminary assessment – Morphology, growth and calcification levels in Flustra foliacea (L.)

Potential consequences for species distribution, abundances and diversity and their imprint in food chains and ecosystems call for more studies of the short and long term impacts of ocean acidification. Bryozoans have been overlooked in this respect even though they play an important role in benthic temperate ecosystems. Flustra foliacea colonies from the North and Baltic Seas were used to assess morphology, growth rates, wall structure and preservation aiming to build up a baseline to use this species as a ‘sentinel’ of acidification levels. Though no significant differences in mean zooid size among the studied basins were found, North Sea colonies show periodic oscillations across generations in mean frontal area index and zooid density. Preliminary geochemistry analyzes show: (1) similar carbon contents (TC, TIC, TOC) in both basins; (2) skeletal walls composed of IMC; (3) over 50% weight loss in dissolution experiments during the first hour. A winter growth stop marked by growth-check lines is postulated. Experimental data are needed to calibrate results and assess collections done over the last 200 years.

Continue reading ‘Growth rates, age determination and calcification levels in Flustra foliacea (L.) (Bryozoa: Cheilostomata): preliminary assessment – Morphology, growth and calcification levels in Flustra foliacea (L.)’

Being a bimineralic bryozoan in an acidifying ocean – Ocean acidification and bryozoans

Strongly controlled calcification by bryozoans means that some species maintain complex skeletons formed of more than one mineral. Whether they are mainly intermediate-Mg calcitic with up to 50% aragonite, mainly aragonitic with small amounts of high-Mg calcite (>8 wt.% MgCO3), or formed of both high- and low-Mg calcites, preservation of sediments formed of these bimineralic bryozoan skeletons may be more at risk from ocean acidification than the majority of bryozoan sediments formed of monomineralic skeletons. An acid-bath immersion experiment on seven species reveals that three (Adeonella sp., Adeonella patagonica, and Adeonellopsis sp.) are more resistant to dissolution than the other four. Skeletal carbonate mineralogy appears to influence dissolution history very little: the most soluble aragonite and high-Mg calcite species, Adeonellopsis sp., was more highly resistant to dissolution than species dominated by low-Mg calcite. In the context of ocean acidification, it is likely that bryozoan skeletons with high surface area and small delicate morphologies are at greatest risk of dissolution, irrespective of mineralogical composition.

Continue reading ‘Being a bimineralic bryozoan in an acidifying ocean – Ocean acidification and bryozoans’

Patterns of Magnesium-calcite distribution in the skeleton of some polar bryozoan species – Mineralogy of polar bryozoan skeletons

Polar marine environments are already starting to exhibit the effects of climate change. The Arctic is the most rapidly warming place on Earth, and changes of the seawater chemistry of polar oceans have been recorded. Calcifying Bryozoa have diverse skeletal mineralogies making them an ideal model for investigating differences caused by environmental change. The aim of this study is to quantify the skeletal mineralogical diversity of polar bryozoans using X-ray diffraction (XRD). Six species of erect Bryozoa were analysed, three Arctic and three Antarctic species. Within each of the three species from each region, one has a cemented attachment point, one has flexible growth and the third is attached by chitinous rootlets. The analysis shows no significant difference in Mg-calcite distribution along the length of the six species but does show species-specific variation in both the consistency of Mg-calcite distribution along the length of a colony and the relationship between concentration of Mg-calcite in the root and growing tip. Analysis shows a statistically significant trend of increasing Mg-calcite concentration with increasing temperature. This adds further data to a growing body of published evidence for this mineralogy trend. The results of this study suggest that if bryozoan species are to be used as indicators of environmental change then it will be critical to have robust, replicated data of species-specific profiles for Mg-calcite distribution. This data, viewed alongside published mineralogy trends, may allow the use of skeletal mineralogy as a register of environmental effects and may enable monitoring of future impacts of climate change in marine benthic ecosystems.

Continue reading ‘Patterns of Magnesium-calcite distribution in the skeleton of some polar bryozoan species – Mineralogy of polar bryozoan skeletons’


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