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Impacts of ocean acidification on calcifying macroalgae: Padina sp. as a test case – a review
Abstract
Since the Industrial Revolution, increasing atmospheric CO2 has been causing a rise in the concentration of carbon dioxide dissolved in seawater. This process results in seawater acidification, which has a major impact on the physical and chemical parameters of the oceans, consequently affecting the numerous calcifying organisms in the marine environment. Calcifying organisms secrete calcium carbonate in their inner or outer skeleton and include plankton (e.g. coccolithophores and foraminifera), corals, mussels and some of the macroalgae. Calcifying macroalgae make a critical contribution to the structure and function of marine ecosystems in several coastal biotas, providing food and shelter to diverse organisms. The present review summarizes the current information about the brown alga Padina sp. and its ecophysiology, focusing on the environmental control of the calcification process; suggests possible benefits that seaweeds may derive from their calcium carbonate cover, and discuss different future Intergovernmental Panel on Climate Change scenarios of ocean acidification and their likely impact on calcifying algae and on the ecosystems in which they are a key component.
... Thus, it is imperative to investigate acute acidic stress in coastal areas, characterized by large daily pH variations. Rapid changes in seawater pH have the potential to directly or indirectly affect the growth and development of marine organisms [16]. Increasing studies have demonstrated that even fish with a relatively well-developed acid-base balance regulation system would be negatively impacted by decreases in pH, particularly during the early developmental stages [17,18]. ...
Simple Summary
The reduction in seawater pH as a consequence of ocean acidification has resulted in a considerable challenge for the adaptation of fish. The effects of pH fluctuations in coastal regions on offshore fish are not fully understood in terms of their behavioral and physiological responses. In the present study, we aimed to examine the consequences of a brief period of reduced pH levels on the behavioral and physiological performance of juvenile black rockfish (Sebastes schlegelii). The findings revealed that juvenile black rockfish could withstand changes in pH, but there was a significant impact on their activity state and metabolic levels. The present study will enhance our understanding of the behavioral and physiological responses of costal fish (the black rockfish, in this case) to acidic conditions.
Abstract
Coastal areas are subject to greater pH fluctuation and more rapid pH decline as a result of both natural and anthropogenic influences in contrast to open ocean environments. Such variations in pH have the potential to pose a threat to the survival and physiological function of offshore fishes. With the aim of evaluating the impact of short-term pH reduction on the behavioral performance and physiological response of costal fish, the black rockfish (Sebastes schlegelii), one of the principal stock-enhanced species, was examined. In the present study, juveniles of the black rockfish with a mean body length of 6.9 ± 0.3 cm and weight of 8.5 ± 0.5 g were exposed to a series of pHs, 7.0, 7.2, 7.4, 7.6, 7.8, and normal seawater (pH 8.0) for 96 h. At the predetermined time points post-exposure (i.e., 0, 12, 24, 48, and 96 h), fish movement behavior was recorded and the specimens were sampled to assess their physiological responses. The results indicate that the lowered pH environment (pH 7.0–7.8) elicited a significant increase in highly mobile behavior, a decrease in immobile behavior, and a significant rise in the metabolic levels of the black rockfish juveniles. Specifically, carbohydrate metabolism was significantly elevated in the pH 7.2 and 7.4 treatments, while lipid metabolism was significantly increased in the pH 7.0, 7.4, and 7.8 treatments. The results of the present study indicate that short-term reductions in pH could ramp up boldness and boost energy expenditure in the black rockfish juveniles, leading to an increased metabolic cost. Additionally, the present investigation revealed that the black rockfish juveniles were capable of adapting to a short-term pH reduction. The findings may provide insight into the underlying physiological mechanisms that govern fish responses to potential decreases in seawater pH in the future.
... In addition to altering pH, OA also reduces the availability of carbonate ions by decreasing the saturation state of calcium carbonate (CaCO 3 ) (Kleypas et al., 1999). Therefore, most studies investigating the physiological effects of OA have been conducted with calcifying organisms such as corals, echinoderms, and bivalve mollusks (Fine and Tchernov, 2007;Havenhand et al., 2008;Gazeau et al., 2010;Reuter et al., 2011;Hofmann and Bischof, 2014;Bhadury, 2015;Segman et al., 2016). However, the effects of OA on other marine species such as fishes remain poorly understood to date. ...
In recent years, ocean acidification caused by oceanic absorption of anthropogenic carbon dioxide (CO2) has drawn worldwide concern over its physiological and ecological effects on marine organisms. However, the behavioral impacts of ocean acidification and especially the underlying physiological mechanisms causing these impacts are still poorly understood in marine species. Therefore, in the present study, the effects of elevated pCO2 on foraging behavior, in vivo contents of two important neurotransmitters, and the expression of genes encoding key modulatory enzymes from the olfactory transduction pathway were investigated in the larval black sea bream. The results showed that larval sea breams (length of 4.71 ± 0.45 cm) reared in pCO2 acidified seawater (pH at 7.8 and 7.4) for 15 days tend to stall longer at their acclimated zone and swim with a significant slower velocity in a more zigzag manner towards food source, therefore taking twice the amount of time than control (pH at 8.1) to reach the food source. These findings indicate that the foraging behavior of the sea bream was significantly impaired by ocean acidification. In addition, compared to a control, significant reductions in the in vivo contents of γ-aminobutyric acid (GABA) and Acetylcholine (ACh) were detected in ocean acidification-treated sea breams. Furthermore, in the acidified experiment groups, the expression of genes encoding positive regulators, the olfaction-specific G protein (Golf) and the G-protein signaling 2 (RGS2) and negative regulators, the G protein-coupled receptor kinase (GRK) and arrestin in the olfactory transduction pathway were found to be significantly suppressed and up-regulated, respectively. Changes in neurotransmitter content and expression of olfactory transduction related genes indicate a significant disruptive effect caused by ocean acidification on olfactory neural signal transduction, which might reveal the underlying cause of the hampered foraging behavior.
Understanding long-term persistence and variability in species populations can help to predict future survival, growth and distribution; however, sustained observations are exceedingly rare. We examine and interpret a remarkable record of the calcareous brown alga Padina pavonica (Phaeophyceae) at its northern limit on the south coast of England (50°N, 1–3°W) from 1680 to 2014, which is probably the longest compilation and review of any marine algal species. Over this period, which extends from the middle of the Little Ice Age to the present, there has been considerable variability in temperature and storminess. We identified a significant number of site extinctions in the second half of the nineteenth century, which coincided with cooler conditions and stormier weather. To interpret these changes, we measured recruitment, growth and production of tetraspores at sheltered and exposed sites in 2012–2014, years which had low and high spring temperatures. Potential spore production was greater at the sheltered site due to a longer growing period and survival of larger fronds. Delayed growth in the cooler spring resulted in smaller fronds and lower potential production of tetraspores by early summer. Yet in the warmer year, rapid initial growth caused higher sensitivity to damage and dislodgement by summer storms, which also limited potential spore production. Antagonistic responses to multiple stressors and disturbances make future predictions of survival and distribution difficult. Fronds of Padina
pavonica are sensitive to both temperature and physical disturbances, yet vegetative perennation appears to have enabled population persistence and explained the longevity of remaining populations.
Since the industrial revolution, anthropogenic CO2 emissions have caused ocean acidification, which particularly affects calcified organisms. Given the fan-like calcified fronds of the brown alga Padina pavonica, we evaluated the acute (short-term) effects of a sudden pH drop due to a submarine volcanic eruption (October 2011-early March 2012) affecting offshore waters around El Hierro Island (Canary Islands, Spain). We further studied the chronic (long-term) effects of the continuous decrease in pH in the last decades around the Canarian waters. In both the observational and retrospective studies (using herbarium collections of P. pavonica thalli from the overall Canarian Archipelago), the percent of surface calcium carbonate coverage of P. pavonica thalli were contrasted with oceanographic data collected either in situ (volcanic eruption event) or from the ESTOC marine observatory data series (herbarium study). Results showed that this calcified alga is sensitive to acute and chronic environmental pH changes. In both cases, pH changes predicted surface thallus calcification, including a progressive decalcification over the last three decades. This result concurs with previous studies where calcareous organisms decalcify under more acidic conditions. Hence, Padina pavonica can be implemented as a bio-indicator of ocean acidification (at short and long time scales) for monitoring purposes over wide geographic ranges, as this macroalga is affected and thrives (unlike strict calcifiers) under more acidic conditions.
Ocean acidification is expected to alter marine systems, but there is uncertainty about its effects due to the logistical difficulties of testing its large-scale and long-term effects. Responses of biological communities to increases in carbon dioxide can be assessed at CO2 seeps that cause chronic exposure to lower seawater pH over localised areas of seabed. Shifts in macroalgal communities have been described at temperate and tropical pCO2 seeps, but temporal and spatial replication of these observations is needed to strengthen confidence our predictions, especially because very few studies have been replicated between seasons. Here we describe the seawater chemistry and seasonal variability of macroalgal communities at CO2 seeps off Methana (Aegean Sea). Monitoring from 2011 to 2013 showed that seawater pH decreased to levels predicted for the end of this century at the seep site with no confounding gradients in Total Alkalinity, salinity, temperature or wave exposure. Most nutrient levels were similar along the pH gradient; silicate increased significantly with decreasing pH, but it was not limiting for algal growth at all sites. Metal concentrations in seaweed tissues varied between sites but did not consistently increase with pCO2. Our data on the flora are consistent with results from laboratory experiments and observations at Mediterranean CO2 seep sites in that benthic communities decreased in calcifying algal cover and increased in brown algal cover with increasing pCO2. This differs from the typical macroalgal community response to stress, which is a decrease in perennial brown algae and proliferation of opportunistic green algae. Cystoseira corniculata was more abundant in autumn and Sargassum vulgare in spring, whereas the articulated coralline alga Jania rubens was more abundant at reference sites in autumn. Diversity decreased with increasing CO2 regardless of season. Our results show that benthic community responses to ocean acidification are strongly affected by season.
[1] A simple model of the CaCO3 saturation state of the ocean is presented. It can be solved analytically and is intended to identify the fundamental controls on ocean carbonate ion concentration. It should also attract researchers unfamiliar with complex biogeochemical models. Despite its limitations, the model-calculated CaCO3 saturation state of today's ocean agrees well with observations. In general, the model reveals three distinctly different modes of operation: The “Strangelove Ocean” of high supersaturation which is dominated by inorganic CaCO3 precipitation, (2) the “Neritan Ocean” of indefinite saturation dominated by biogenic shallow-water CaCO3 precipitation, and (3) the “Cretan Ocean” of low saturation dominated by biogenic pelagic CaCO3 precipitation. In the latter mode, the deep ocean [CO32−] is remarkably stable, provided that the biogenic production of CaCO3 exceeds the riverine flux of Ca2+ and CO32−. This explains the overall constancy of the saturation state of the ocean documented over the last 100 Ma. The model is then used to address diverse questions. One important result is that the recovery of the oceanic carbonate chemistry from fossil fuel neutralization in the future will be accelerated due to expected reduced biogenic calcification.
In development since 1996, AlgaeBase (http://www.algaebase.org) is an on-line database providing free access to authoritative taxonomic, distributional and nomenclatural information of more than 135,000 names of species and infraspecific taxa of algae set in the context of a taxonomic hierarchy. The project was initially funded by the Higher Education Authority, Department of Education and Science (Ireland) and the European Union (the SeaweedAfrica Project), and more recently by an industry sponsor in Ireland (Ocean Harvest Technology) and various phycological societies and organisations. The database currently includes more than 50,000 bibliographic references and incorporates the entire contents of the main phycological journals in addition to taxonomic, ecological, physiological and biochemical references in current and classical works. Nearly 10,000 PDFs are included, many of them of 19th-century taxonomic works that are rare and difficult to obtain. The data are searchable at all taxonomic levels from kingdom to species (and infraspecific names), and AlgaeBase strives to provide citations of the original publications of all taxa. For any of the 145,000 taxa (names of genera and above included), all subordinate taxa at the next lowest rank are indicated along with the number of species for each. Within each genus the species and infraspecies taxa are listed along with the current taxonomic status of each name. Nearly 17,000 images are provided for downloading and use in teaching or research, with copyright and other rights being retained by the original contributors or by AlgaeBase. This database is being used by 2,000-3,000 individual visitors each day with nearly 100,000 requests a day and receives over 7 million “hits” each year, increasing at about 20% per annum. A brief description of other main on-line algal resources such as Index Nominum Algarum, the Catalogue of Diatoms Names, CyanoDB, and AlgaTerra is provided.
Marine macroalgae are very rich source of phenolic compounds endowed with antioxidant and antimicrobial properties. The aim of this study was to evaluate the bioactivity composition of three selected green, brown and red algae - viz., Halimeda opuntia, Padina pavonica and Halymenia sp., respectively from Jeddah coast in Saudi Arabia. The antimicrobial properties against pathogenic Grame positive, Grame negative bacteria and fungi were tested. In vitro antioxidant activities including 1, 1-Diphenyl -2-picrylhydrazyl (DPPH) radical scavenging, antityrosenase activity and lipid peroxidation activity were studied. The highest amount of phenolic compound was found in the extract obtained from Padina pavonica this extract also showed good antioxidant activity expressed by its capacity to scavenge superoxide anion and to inhibit lipid peroxidation. Halimeda opuntia, Padina pavonica exhibited good antioxidant activity when compared to Halymenia sp. The maximum antimicrobial activity was shown by the extract of Halimeda opuntia, Padina pavonica against Klebsiella pneumoniae ATCC 27736 (32mm). The results showed that marine macroalgae exhibited varying degrees of antioxidant and antimicrobial properties.
Calcified macroalgae are distributed in marine habitats from polar to tropical latitudes and from intertidal shores to the deepest reaches of the euphotic zone. These algae play critical ecological roles including being key to a range of invertebrate recruitment processes, functioning as autogenic ecosystem engineers through provision of three-dimensional habitat structure, as well as contributing critical structural strength in coral reef ecosystems. Calcified macroalgae contribute significantly to the deposition of carbonates in coastal environments. These organisms are vulnerable to human-induced changes resulting from land and coastal development, such as altered patterns of sedimentation, nutrient enrichment through sewage and agricultural run-off, and are affected by coastal dredging and aquaculture. The consequences of increasing sea surface temperatures and fundamental changes in the carbon chemistry of seawater due to CO2 emissions from anthropogenic activities will have serious impacts on calcifying macroalgae. It is not yet understood how interactions between a range of variables acting at local and global scales will influence the viability of calcifying macroalgae and associated ecosystems. Research is urgently needed on all aspects of the taxonomy, biology and functional ecology of calcifying macroalgae. Without an understanding of the species present, measurement of change and understanding species-specific responses will not be possible.
This special issue compiles 37 manuscripts investigating the biological impacts and societal relevance of ocean acidification. It includes important considerations regarding experimental design, new methods and how ocean acidification science can contribute to society through education and socioeconomic assessment. Altogether, this special issue constitutes a snapshot of recent ocean acidification research. This paper aims at summarizing the key findings and highlights future challenges and research priorities.
The dominant macroalgae growing at a rocky site on the Israeli coast were examined. While all algae apparently grew under light-saturating conditions, Enteromorpha compressa and Ulva lactuca, which occupy the uppermost level of the zone, were very tolerant to high and low temperatures as well as desiccation and varying salinity levels. They were also saturated both by HCO3- (while submerged) and atmospheric CO2 (during emergence). In contrast, four of the species dominating the middle and lower parts of the intertidal showed a narrower temperature response, could not tolerate exposure to high temperatures for prolonged time periods and were more sensitive to desiccation and salinity changes. In Acanthophora najadiformis and Hypnea musciformis, the sensitivity to desiccation in combination with the much higher rates of photosynthesis in air than in water might explain their growth in the mid intertidal. -from Authors
Grazing preferences of two species of Diadema and two species of Echinothrix, including two colour morphs of Echinothrix calamaris, were investigated by gut contents analysis, in situ feeding observations, and grazing preferences trials in aquaria. Grazing preferences were compared to the distribution and abundance of diadematid sea urchins and the percentage cover of algal and seagrass species throughout Sosoikula Reef and Nukubuco Reef, Fiji. Results showed that grazing was selective, with distinct preferences between sea urchin genera, species, and colour morphs of E. calamaris. Preferred species of algae were non-calcareous, with reportedly low concentrations of tannins, phenols and bioactive compounds. Both Diadema savignyi and D. setosum selected Codium geppiorum as their most preferred species, followed by Hydroclathrus clathratus. All Echinothrix favoured Hy. clathratus, with both colour morphs of E. calamaris next selecting Padina pavonica and E. diadema selecting green filamentous algae. The seagrass species Syringodium isoetifolium was only grazed in significant quantities by E. calamaris (b) and E. diadema. This reflected species distributions in the seagrass bed. Peak abundances of diadematid sea urchins coincided with many of their grazing preferences at their maximum percentage cover. However, only E. diadema and D. savignyi had significant correlations with preferred algal/seagrass species (E. diadema with Co. geppiorum, and D. savignyi with G. marginata) throughout the subhabitats identified on the reefs.
Ocean acidification, the drop in seawater pH associated with the ongoing
enrichment of marine waters with carbon dioxide from fossil fuel
burning, may seriously impair marine calcifying organisms. Our present
understanding of the sensitivity of marine life to ocean acidification
is based primarily on short-term experiments, in which organisms are
exposed to increased concentrations of CO2. However,
phytoplankton species with short generation times, in particular, may be
able to respond to environmental alterations through adaptive evolution.
Here, we examine the ability of the world's single most important
calcifying organism, the coccolithophore Emiliania huxleyi, to evolve in
response to ocean acidification in two 500-generation selection
experiments. Specifically, we exposed E. huxleyi populations founded by
single or multiple clones to increased concentrations of CO2.
Around 500 asexual generations later we assessed their fitness. Compared
with populations kept at ambient CO2 partial pressure, those
selected at increased partial pressure exhibited higher growth rates, in
both the single- and multiclone experiment, when tested under ocean
acidification conditions. Calcification was partly restored: rates were
lower under increased CO2 conditions in all cultures, but
were up to 50% higher in adapted compared with non-adapted cultures. We
suggest that contemporary evolution could help to maintain the
functionality of microbial processes at the base of marine food webs in
the face of global change.
Three species of the phaeophycean genus Padina were investigated with the electron microscope. Calcification is initiated in P. japonica and P. pavonica at the inrolled thallus margin which contains chloroplasts and acts as a semi-enclosed space. In these species, the apical cells are covered with a pilose layer with which small aragonite crystals are associated. The non-calcareous P. arborescens has a similar anatomy but here the apical and young cells possess a smooth cuticular layer instead of a pilose layer and it is suggested that nucleation of aragonite is inhibited by this layer.In P. pavonica, carbonate deposition continues at the thallus surface and reaches a maximum, on a percentage dry weight basis, approximately mid-way along the lamina (mean CaCO3 content 9·3% dry wt). The deposits show concentric banding, but this could not be correlated with differences in photosynthetic activity associated with tetrasporangium production.
The Codiacean green algae Halimeda and Penicillus and the brown alga Padina are important producers of both calcium carbonate and organic matter in shallow water tropical and subtropical areas1,2. Estimates of algal contribution to shallow water carbonate deposition range from 0 to 61%3–5. However, direct observations on algal carbonate production are very rare. Available data include short-term measurements of calcium and carbon uptake6–9, observations of growth of aquarium specimens10 and periodic observations of death rate for a year at fixed stations11. I report here on in situ measurements taken in Harrington Sound, Bermuda, a shallow subtropical lagoon. Production rates were ~50 (Halimeda incrassata), 30 (Penicillus capitatus) and 240 Padina sanctae-crucis) g m−2 yr−1 calcium carbonate. The measured growth rates suggest that the algae renew their standing stock approximately once every month (Halimeda and Padina) or once every one and a half months (Penicillus) during their growing season.
Today's surface ocean is saturated with respect to calcium carbonate, but increasing atmospheric carbon dioxide concentrations are reducing ocean pH and carbonate ion concentrations, and thus the level of calcium carbonate saturation. Experimental evidence suggests that if these trends continue, key marine organisms—such as corals and some plankton—will have difficulty maintaining their external calcium carbonate skeletons. Here we use 13 models of the ocean–carbon cycle to assess calcium carbonate saturation under the IS92a 'business-as-usual' scenario for future emissions of anthropogenic carbon dioxide. In our projections, Southern Ocean surface waters will begin to become undersaturated with respect to aragonite, a metastable form of calcium carbonate, by the year 2050. By 2100, this undersaturation could extend throughout the entire Southern Ocean and into the subarctic Pacific Ocean. When live pteropods were exposed to our predicted level of undersaturation during a two-day shipboard experiment, their aragonite shells showed notable dissolution. Our findings indicate that conditions detrimental to high-latitude ecosystems could develop within decades, not centuries as suggested previously.
A coral reef represents the net accumulation of CaCO3 produced by corals and other calcifying organisms. If calcification declines, then reef-building capacity also declines. Coral reef calcification depends on the saturation state of the carbonate mineral aragonite of surface waters. By the middle of next century, increased CO2 concentration will decrease aragonite saturation state in the tropics by 30%, and biogenic aragonite precipitation by 14–30%. Coral reefs are particularly threatened, since reef-building organisms secrete metastable forms of CaCO3, but the biogeochemical consequences on other calcifying marine ecosystems may be equally severe.
Anthropogenic elevation of atmospheric carbon dioxide (pCO(2)) is making the oceans more acidic, thereby reducing their degree of saturation with respect to calcium carbonate (CaCO3). There is mounting concern over the impact that future CO2-induced reductions in the CaCO3 saturation state of seawater will have on marine organisms that construct their shells and skeletons from this mineral. Here, we present the results of 60 d laboratory experiments in which we investigated the effects of CO2-induced ocean acidification on calcification in 18 benthic marine organisms. Species were selected to span a broad taxonomic range (crustacea, cnidaria, echinoidea, rhodophyta, chlorophyta, gastropoda, bivalvia, annelida) and included organisms producing aragonite, low-Mg calcite, and high-Mg calcite forms of CaCO3. We show that 10 of the 18 species studied exhibited reduced rates of net calcification and, in some cases, net dissolution under elevated pCO(2). However, in seven species, net calcification increased under the intermediate and/or highest levels of pCO(2), and one species showed no response at all. These varied responses may reflect differences amongst organisms in their ability to regulate pH at the site of calcification, in the extent to which their outer shell layer is protected by an organic covering, in the solubility of their shell or skeletal mineral, and in the extent to which they utilize photosynthesis. Whatever the specific mechanism(s) involved, our results suggest that the impact of elevated atmospheric pCO(2) on marine calcification is more varied than previously thought.
An encrusting brown alga from subtidal habitats around the island of Oahu (Hawaiian Islands) represents only the second genus of the class Phaeophyceae to form calcium carbonate, which it deposits primarily as both extracellular and intracellular aragonite, admixed with small (3.3%) amounts of calcite. Plants form expanses 15–100+ cm in extent consisting of horizontally aligned imbricating tiers of distromatic blades 1–4 mm in diameter that are separated from one another by cementing layers of extracellular aragonite, the tiers forming stacks of dozens of laminae and anchored to coral substrata by a basement layer that adheres tightly without haptera or rhizoids. The hypodermal layer of each blade consists of lightly pigmented rectilinear cells bearing either one or two smaller deeply pigmented epidermal cells in cross-sectional profiles and three or four in long-sectional profiles, the cells of both layers becoming encased in rigid carbonate skeletons laid down in their outer wall matrices. The successive tiers become stacked by either overgrowing marginal proliferations or new blade primordia that arise from the hypodermal layer of surface laminae and initially spread centrifugally by means of continuous marginal meristems. Neither plurilocular nor unilocular reproductive structures are known. The alga is described as the new genus and species Newhousia imbricata Kraft, G.W. Saunders, Abbott et Haroun and is assigned on the basis of small subunit rDNA gene sequence analyses to the order Dictyotales, family Dictyotaceae, within a strongly supported monophyletic clade that includes Distromium, Lobophora, and Zonaria.
Experiments have shown that ocean acidification due to rising atmospheric carbon dioxide concentrations has deleterious effects on the performance of many marine organisms. However, few empirical or modelling studies have addressed the long-term consequences of ocean acidification for marine ecosystems. Here we show that as pH declines from 8.1 to 7.8 (the change expected if atmospheric carbon dioxide concentrations increase from 390 to 750ppm, consistent with some scenarios for the end of this century) some organisms benefit, but many more lose out. We investigated coral reefs, seagrasses and sediments that are acclimatized to low pH at three cool and shallow volcanic carbon dioxide seeps in Papua New Guinea. At reduced pH, we observed reductions in coral diversity, recruitment and abundances of structurally complex framework builders, and shifts in competitive interactions between taxa. However, coral cover remained constant between pH 8.1 and ~7.8, because massive Porites corals established dominance over structural corals, despite low rates of calcification. Reef development ceased below pH 7.7. Our empirical data from this unique field setting confirm model predictions that ocean acidification, together with temperature stress, will probably lead to severely reduced diversity, structural complexity and resilience of Indo-Pacific coral reefs within this century.
There are high levels of uncertainty about how coastal ecosystems will be affected by rapid ocean acidification caused by anthropogenic CO2, due to a lack of data. The few experiments to date have been short-term (< 1 year) and reveal mixed responses depending on the species examined and the culture conditions used. It is difficult to carry out long-term manipulations of CO2 levels, therefore areas with naturally high CO2 levels are being used to help understand which species, habitats and processes are resilient to the effects of ocean acidification, and which are adversely affected. Here we describe the effects of increasing CO2 levels on macroalgal communities along a pH gradient caused by volcanic vents.
Structural features of marine macrophytes are generally believed to act as defences against herbivores by reducing the ability of herbivores to consume the plants. Thallus form and calcification in particular have been considered structural defences that act by reducing the probability of consumption of tissue by herbivores. Studies directly measuring the mechanical resistance of a variety of marine algae (tropical and temperate) to herbivores of two important feeding types, rasping herbivores (docoglossan limpets) and a biting herbivore (an herbivorous crab), do not support this hypothesis. I suggest that thallus form and calcification may play a more important role in minimizing the impact of herbivores by reducing the probability of subsequent tissue loss due to herbivore-induced damage. For some algal species, tissue lost subsequent to herbivore damage may greatly exceed loss due to direct consumption by herbivores. I suggest that calcification and thallus properties resulting in preferential tear directions reduce the probability of tissue loss subsequent to herbivore damage rather than prevent herbivores from removing tissue as has been suggested in the past.
The UV-absorbing mycosporine-like amino acids (MAAs) are hypothesized to protect organisms against harmful UV radiation (UVR).
Since the physiology and metabolism of these compounds are unknown, the induction and kinetics of MAA biosynthesis by various
natural radiation conditions were investigated in the marine red alga Chondrus crispus collected from Helgoland, Germany. Three photosynthetically active radiation (PAR, 400–700 nm) treatments without UVR and
three UV-A/B (290–400 nm) treatments without PAR were given. Chondrus crispus collected from 4–6 m depth contained only traces of the MAA palythine. After 24 h exposure to 100% ambient PAR, traces of
three additional MAAs, shinorine, palythinol and palythene, were detected, and their concentrations increased strongly during
a one-week exposure to all PAR treatments. The concentration of all MAAs varied directly with PAR dose, with palythine and
shinorine being four- to sevenfold higher than palythinol and palythene. Likewise, naturally high doses of both UV-A and UV-B
resulted in a strong accumulation of all MAAs, in particular shinorine. While shinorine accumulation was much more stimulated
by UVR, the content of all other MAAs was more affected by high PAR, indicating an MAA-specific induction triggered by UVR
or PAR.
In marine ecosystems, rising atmospheric CO2 and climate change are associated with concurrent shifts in temperature, circulation, stratification, nutrient input, oxygen content, and ocean acidification, with potentially wide-ranging biological effects. Population-level shifts are occurring because of physiological intolerance to new environments, altered dispersal patterns, and changes in species interactions. Together with local climate-driven invasion and extinction, these processes result in altered community structure and diversity, including possible emergence of novel ecosystems. Impacts are particularly striking for the poles and the tropics, because of the sensitivity of polar ecosystems to sea-ice retreat and poleward species migrations as well as the sensitivity of coral-algal symbiosis to minor increases in temperature. Midlatitude upwelling systems, like the California Current, exhibit strong linkages between climate and species distributions, phenology, and demography. Aggregated effects may modify energy and material flows as well as biogeochemical cycles, eventually impacting the overall ecosystem functioning and services upon which people and societies depend.
Preferences of the sea urchin Diadema
antillarum (Echinodermata: Echinoidea) feeding on five species of brown macroalgae (Padina
pavonica, Dyctiota
dychotoma, Cystoseira
abies-marina, Lobophora
variegata and Halopteris
filicina) have been studied using caging field experiments on Gran Canaria Island during August to October 2000. Results of three assays of both single and multiple diet experiments rejected the null hypothesis that Diadema does not feed selectively on the five selected algal species. In the multiple diet assays, Diadema consumed an average of 68–98 mg algae urchin−1 h−1 and 4–120 mg algae urchin−1 h−1 in the single diet experiments. On the basis of consumption, the five species of algae eaten can be divided into three groups. Thus Halopteris, Lobophora and Dyctiota were considered preferred algae, while Padina was considered an intermediate alga. Finally Cystoseira was significantly the less preferred and consumed seaweed in all sets of assays.
Low seawater pH can be harmful to many calcifying marine organisms, but the calcifying macroalgae Padina spp. flourish at natural submarine carbon dioxide seeps where seawater pH is low. We show that the microenvironment created by the rolled thallus margin of Padina australis facilitates supersaturation of CaCO3 and calcifi-cation via photosynthesis-induced elevated pH. Using microsensors to investigate oxygen and pH dynamics in the microenvironment of P. australis at a shallow CO2 seep, we found that, under saturating light, the pH inside the microenvironment (pHME) was higher than the external seawater (pHSW) at all pHSW levels investigated, and the difference (i.e., pHME − pHSW) increased with decreasing pHSW (0.9 units at pHSW 7.0). Gross photosynthesis (Pg) inside the microenvironment increased with decreasing pHSW, but algae from the control site reached a threshold at pH 6.5. Seep algae showed no pH threshold with respect to Pg within the pHSW range investigated. The external carbonic anhydrase (CA) inhibitor, acetazolamide, strongly inhibited Pg of P. australis at pHSW 8.2, but the effect was diminished under low pHSW (6.4–7.5), suggesting a greater dependence on membrane-bound CA for the dehydration of HCO3− ions during dissolved inorganic carbon uptake at the higher pHSW. In comparison, a calcifying green alga, Halimeda cuneata f. digitata, was not inhibited by AZ, suggesting efficient bicarbonate transport. The ability of P. australis to elevate pHME at the site of calcification and its strong dependence on CA may explain why it can thrive at low pHSW.
Ocean acidification causes biodiversity loss, alters ecosystems, and may impact food security, as shells of small organisms dissolve easily in corrosive waters. There is a suggestion that photosynthetic organisms could mitigate ocean acidification on a local scale, through seagrass protection or seaweed cultivation, as net ecosystem organic production raises the saturation state of calcium carbonate making seawater less corrosive. Here, we used a natural gradient in calcium carbonate saturation, caused by shallow-water CO2 seeps in the Mediterranean Sea, to assess whether seaweed that is resistant to acidification (Padina pavonica) could prevent adverse effects of acidification on epiphytic foraminifera. We found a reduction in the number of species of foraminifera as calcium carbonate saturation state fell and that the assemblage shifted from one dominated by calcareous species at reference sites (pH ~8.19) to one dominated by agglutinated foraminifera at elevated levels of CO2 (pH ~7.71). It is expected that ocean acidification will result in changes in foraminiferal assemblage composition and agglutinated forms may become more prevalent. Although Padina did not prevent adverse effects of ocean acidification, high biomass stands of seagrass or seaweed farms might be more successful in protecting epiphytic foraminifera.
Population density of the limpet Acmaea testudinalis is highest on the crustose coralline alga Clathromorphum circumscriptum in both tide pool and subtidal environments in the Gulf of Maine. Juvenile limpets recruit to C. circumscriptum and both juveniles and adults preferentially feed on this species (not its epibionts) over a choice of other corallines, foliose algae, microalgae (diatoms), and detritus. The fitness of both organisms may be increased by the association. Acmaea testudinalis possesses a radula apparently adapted to eat efficiently C. circumscriptum, a food of low caloric value; C. circumscriptum requires grazing to remove potentially lethal epiphytes, but is not harmed by limpet grazing since it possesses a thick protective tissue over the region of growth. Reproductive structures of C. circumscriptum develop in winter and are buried below the surface so the effects of grazing on them are minimal. Over a wide range of depths, the rate of cell removal by limpets matches the rate of cell production by Clathromorphum. A coevolved interdependency is implied. -from Author
Six fan-shaped, striated species of Padina Adanson were collected from northernmost part of the Arabian Sea and taxonomically investigated. This the first detailed taxonomic study of the algal genus from the coast of Pakistan, based on a large survey (1989-1996) of different coastal areas of Karachi. This study revealed two new records from Pakistan et al,. P. fraseri (Greville) Greville and P. vickersiae Hoyt and two new species i.e. P. afaqhusainii Aisha et Shameel and P. nizamuddinii Aisha et Shameel. Padina pavonica (L.) Thivy and P. vickersiae were found to exhibit an unusual phenomenon, syntagmatic in situ germination, i.e. all the species dividing and merging into one outgrowth.
Anthropogenic CO2 is a major driver of present environmental change in most ecosystems1, and the related ocean acidification is threatening marine biota2. With increasing pCO2, calcification rates of several species decrease3, although cases of upregulation are observed4. Here, we show that biological control over mineralization relates to species abundance along a natural pH gradient. As pCO2 increased, the mineralogy of a scleractinian coral (Balanophyllia europaea) and a mollusc (Vermetus triqueter) did not change. In contrast, two calcifying algae (Padina pavonica and Acetabularia acetabulum) reduced and changed mineralization with increasing pCO2, from aragonite to the less soluble calcium sulphates and whewellite, respectively. As pCO2 increased, the coral and mollusc abundance was severely reduced, with both species disappearing at pH < 7.8. Conversely, the two calcifying and a non-calcifying algae (Lobophora variegata) showed less severe or no reductions with increasing pCO2, and were all found at the lowest pH site. The mineralization response to decreasing pH suggests a link with the degree of control over the biomineralization process by the organism, as only species with lower control managed to thrive in the lowest pH.
The effects of elevated CO2 and temperature on photosynthesis and calcification in the calcifying algae Halimeda macroloba and Halimeda cylindracea and the symbiont-bearing benthic foraminifera Marginopora vertebralis were investigated through exposure to a combination of four temperatures (28 degrees C, 30 degrees C, 32 degrees C, and 34 degrees C) and four CO2 levels (39, 61, 101, and 203 Pa; pH 8.1, 7.9, 7.7, and 7.4, respectively). Elevated CO2 caused a profound decline in photosynthetic efficiency (F-V : F-M), calcification, and growth in all species. After five weeks at 34 degrees C under all CO2 levels, all species died. Chlorophyll (Chl) a and b concentration in Halimeda spp. significantly decreased in 203 Pa, 32 degrees C and 34 degrees C treatments, but Chl a and Chl c(2) concentration in M. vertebralis was not affected by temperature alone, with significant declines in the 61, 101, and 203 Pa treatments at 28 degrees C. Significant decreases in F-V : F-M in all species were found after 5 weeks of exposure to elevated CO2 (203 Pa in all temperature treatments) and temperature (32 degrees C and 34 degrees C in all pH treatments). The rate of oxygen production declined at 61, 101, and 203 Pa in all temperature treatments for all species. The elevated CO2 and temperature treatments greatly reduced calcification (growth and crystal size) in M. vertebralis and, to a lesser extent, in Halimeda spp. These findings indicate that 32 degrees C and 101 Pa CO2, are the upper limits for survival of these species on Heron Island reef, and we conclude that these species will be highly vulnerable to the predicted future climate change scenarios of elevated temperature and ocean acidification.
Twenty-one studies on the effects of pH on marine phytoplankton were found and are herein reviewed. Under laboratory conditions, the optimum pH for growth is between pH 6.3 and 10. Some species can grow well at a wide range of pH, while others have growth rates that vary greatly over a 0.5 to 1 pH unit change. Different clones of the same species were found to have slightly to strikingly different relationships between pH and growth rate. The pH in typical coastal environments may vary by 1 or more pH units, with over 10% of observations being more than 0.5 units above or below equilibrium pH. This range is great enough, relative to the observed pH effect on growth rate for many species, for seawater pH to affect the growth rate, and hence the timing and abundance of coastal marine phytoplankton species. Effects of pH are not limited to extreme pH conditions. The growth rates of some species are influenced significantly by changes in pH near the equilibrium pH of coastal seawater. Care must be taken in growth experiments with phytoplankton to avoid effects due to pH of the culture media. Eutrophication of coastal waters may amplify the range of pH found in coastal environments.
The influence of elevated CO2 concentrations on growth and photosynthesis ofGracilaria sp. andG. chilensis was investigated in order to procure information on the effective utilization of CO2. Growth of both was enhanced by CO2 enrichment (air + 650 ppm CO2, air + 1250 ppm CO2, the enhancement being greater inGracilaria sp. Both species increased uptake of NO3− with CO2 enrichment. Photosynthetic inorganic carbon uptake was depressed inG. chilensis by pre-culture (15 days) with CO2 enrichment, but little affected inGracilaria sp. Mass spectrometric analysis showed that O2 uptake was higher in the light than in the dark for both species and in both cases was higher inGracilaria sp. The higher growth enhancement inGracilaria sp. was attributed to greater depression of photorespiration by the enrichment of CO2 in culture.
Although seagrasses and marine macroalgae (macro-autotrophs) play critical ecological roles in reef, lagoon, coastal and open-water ecosystems, their response to ocean acidification (OA) and climate change is not well understood. In this review, we examine marine macro-autotroph biochemistry and physiology relevant to their response to elevated dissolved inorganic carbon [DIC], carbon dioxide [CO2 ], and lower carbonate [CO3 (2-) ] and pH. We also explore the effects of increasing temperature under climate change and the interactions of elevated temperature and [CO2 ]. Finally, recommendations are made for future research based on this synthesis. A literature review of >100 species revealed that marine macro-autotroph photosynthesis is overwhelmingly C3 (≥ 85%) with most species capable of utilizing HCO3 (-) ; however, most are not saturated at current ocean [DIC]. These results, and the presence of CO2 -only users, lead us to conclude that photosynthetic and growth rates of marine macro-autotrophs are likely to increase under elevated [CO2 ] similar to terrestrial C3 species. In the tropics, many species live close to their thermal limits and will have to up-regulate stress-response systems to tolerate sublethal temperature exposures with climate change, whereas elevated [CO2 ] effects on thermal acclimation are unknown. Fundamental linkages between elevated [CO2 ] and temperature on photorespiration, enzyme systems, carbohydrate production, and calcification dictate the need to consider these two parameters simultaneously. Relevant to calcifiers, elevated [CO2 ] lowers net calcification and this effect is amplified by high temperature. Although the mechanisms are not clear, OA likely disrupts diffusion and transport systems of H(+) and DIC. These fluxes control micro-environments that promote calcification over dissolution and may be more important than CaCO3 mineralogy in predicting macroalgal responses to OA. Calcareous macroalgae are highly vulnerable to OA, and it is likely that fleshy macroalgae will dominate in a higher CO2 ocean; therefore, it is critical to elucidate the research gaps identified in this review.
Bicarbonate-based photosynthesis requires equal numbers of proton equivalents. Aquatic plants and photosynthetic symbioses can scavenge protons from ambient solutions, or they can manufacture protons through calcification. Both mechanisms are widely employed. This review examines how aquatic photoautotrophs couple calcification to photosynthesis, and the advantages and limitations of this physiology.Key words: calcification, calcium, carbonate, bicarbonate, photosynthesis, aquatic.
A crystallization pathway describes the movement of ions from their source to the final product. Cells are intimately involved in biological crystallization pathways. In many pathways the cells utilize a unique strategy: They temporarily concentrate ions in intracellular membrane-bound vesicles in the form of a highly disordered solid phase. This phase is then transported to the final mineralization site, where it is destabilized and crystallizes. We present four case studies, each of which demonstrates specific aspects of biological crystallization pathways: seawater uptake by foraminifera, calcite spicule formation by sea urchin larvae, goethite formation in the teeth of limpets, and guanine crystal formation in fish skin and spider cuticles. Three representative crystallization pathways are described, and aspects of the different stages of crystallization are discussed. An in-depth understanding of these complex processes can lead to new ideas for synthetic crystallization processes of interest to mate...
ABSTRACT: Since pre-industrial times, uptake of anthropogenic CO2 by surface ocean waters has
caused a documented change of 0.1 pH units. Calcifying organisms are sensitive to elevated CO2
concentrations due to their calcium carbonate skeletons. In temperate rocky intertidal environments,
calcifying and noncalcifying macroalgae make up diverse benthic photoautotrophic communities.
These communities may change as calcifiers and noncalcifiers respond differently to
rising CO2 concentrations. In order to test this hypothesis, we conducted an 86 d mesocosm
ex periment to investigate the physiological and competitive responses of calcifying and noncalcifying
temperate marine macroalgae to 385, 665, and 1486 μatm CO2. We focused on comparing 2
abundant red algae in the Northeast Atlantic: Corallina officinalis (calcifying) and Chondrus crispus
(noncalcifying). We found an interactive effect of CO2 concentration and exposure time on
growth rates of C. officinalis, and total protein and carbohydrate concentrations in both species.
Photosynthetic rates did not show a strong response. Calcification in C. officinalis showed a parabolic
response, while skeletal inorganic carbon decreased with increasing CO2. Community structure
changed, as Chondrus crispus cover increased in all treatments, while C. officinalis cover
decreased in both elevated-CO2 treatments. Photochemical parameters of other species are also
presented. Our results suggest that CO2 will alter the competitive strengths of calcifying and noncalcifying
temperate benthic macroalgae, resulting in different community structures, unless
these species are able to adapt at a rate similar to or faster than the current rate of increasing seasurface
CO2 concentrations.
The various estimates of the amount of anthropogenic CO2 taken up by the ocean that have been published in recent years are evaluated. It is shown that the estimate of Tans et al. (1990) neglects several important processes, and it is concluded that available evidence to date supports an annual mean uptake of about 2 Gt C/yr. Having established a 'best guess' for the oceanic CO2 uptake, one can then show that the total accumulation of CO2 in the atmosphere and ocean from 1980 to 1989 is significantly less than current estimates of the total CO2 emitted during that period. This implies either that the CO2 release from tropical deforestation is much smaller than currently estimated or that there is indeed a 'missing sink' for the CO2, albeit smaller than the one proposed by Tans et al.
Predicting the impacts of ocean acidification on coastal ecosystems requires an understanding of the effects on macro-algae and their grazers, as these underpin the ecology of rocky shores. Whilst calcified coralline algae (Rhodophyta) appear to be especially vulnerable to ocean acidification, there is a lack of information concerning calcified brown algae (Phaeophyta), which are not obligate calcifiers but are still important producers of calcium carbonate and organic matter in shallow coastal waters. Here, we compare ecological shifts in subtidal rocky shore systems along CO 2 gradients created by volcanic seeps in the Mediterranean and Papua New Guinea, focussing on abundant macro-algae and grazing sea urchins. In both the temperate and tropical systems the abundances of grazing sea urchins declined dramatically along CO 2 gradients. Temperate and tropical species of the calcifying macroalgal genus Padina (Dictyoaceae, Phaeophyta) showed reductions in CaCO 3 content with CO 2 enrichment. In contrast to other studies of calcified macroalgae, however, we observed an increase in the abundance of Padina spp. in acidified conditions. Reduced sea urchin grazing pressure and significant increases in photosynthetic rates may explain the unexpected success of decalcified Padina spp. at elevated levels of CO 2 . This is the first study to provide a comparison of ecologi-cal changes along CO 2 gradients between temperate and tropical rocky shores. The similarities we found in the responses of Padina spp. and sea urchin abundance at several vent systems increases confidence in predictions of the ecological impacts of ocean acidification over a large geographical range.
Previous studies have shown that increasing atmospheric CO2 concentrations affect calcification in some planktonic and macroalgal calcifiers due to the changed carbonate chemistry of seawater. However, little is known regarding how calcifying algae respond to solar UV radiation (UVR, UVA+UVB, 280–400 nm). UVR may act synergistically, antagonistically or independently with ocean acidification (high CO2/low pH of seawater) to affect their calcification processes. We cultured the articulated coralline alga Corallina sessilis Yendo at 380 ppmv (low) and 1000 ppmv (high) CO2 levels while exposing the alga to solar radiation treatments with or without UVR. The presence of UVR inhibited the growth, photosynthetic O2 evolution and calcification rates by13%, 6% and 3% in the low and by 47%, 20% and 8% in the high CO2 concentrations, respectively, reflecting a synergistic effect of CO2 enrichment with UVR. UVR induced significant decline of pH in the CO2-enriched cultures. The contents of key photosynthetic pigments, chlorophyll a and phycobiliproteins decreased, while UV-absorptivity increased under the high pCO2/low pH condition. Nevertheless, UV-induced inhibition of photosynthesis increased when the ratio of particulate inorganic carbon/particulate organic carbon decreased under the influence of CO2-acidified seawater, suggesting that the calcified layer played a UV-protective role. Both UVA and UVB negatively impacted photosynthesis and calcification, but the inhibition caused by UVB was about 2.5–2.6 times that caused by UVA. The results imply that coralline algae suffer from more damage caused by UVB as they calcify less and less with progressing ocean acidification.
Abstract The effects of elevated partial pressure of CO2 (pCO2) and temperature, alone and in combination, on survival, calcification and dissolution were investigated in the crustose coralline alga Lithophyllum cabiochae. Algae were maintained in aquaria during 1 year at near-ambient conditions of irradiance, at ambient or elevated temperature (+3 °C) and at ambient [ca. 400 parts per million (ppm)] or elevated pCO2 (ca. 700 ppm). Algal necroses appeared at the end of summer under elevated temperature first at 700 ppm (60% of the thallus surface) and then at 400 ppm (30%). The death of algae was observed only under elevated temperature and was two- to threefold higher under elevated pCO2. During the first month of the experiment, net calcification was significantly reduced under elevated pCO2. At the end of the summer period, net calcification decreased by 50% when both temperature and pCO2 were elevated while no effect was found under elevated temperature and elevated pCO2 alone. In autumn and winter, net calcification in healthy algae increased with increasing temperature, independently of the pCO2 level, while necroses and death in the algal population caused a net dissolution at elevated temperature and pCO2. The dissolution of dead algal thalli was affected by elevated pCO2, being two- to fourfold higher than under ambient pCO2. These results suggest that net dissolution is likely to exceed net calcification in L. cabiochae by the end of this century. This could have major consequences in terms of biodiversity and biogeochemistry in coralligenous communities dominated by these algae.
Calcification in the marine environment is the basis for the accretion of carbonate in structures such as coral reefs, algal ridges and carbonate sands. Among the organisms responsible for such calcification are the Corallinaceae (Rhodophyta), recognised as major contributors to the process world-wide. Hydrolithon sp. is a coralline alga that often forms rhodoliths in the Western Indian Ocean. In Zanzibar, it is commonly found in shallow lagoons, where it often grows within seagrass beds and/or surrounded by green algae such as Ulva sp. Since seagrasses in Zanzibar have recently been shown to raise the pH of the surrounding seawater during the day, and since calcification rates are sensitive to pH, which changes the saturation state of calcium carbonate, we measured the effects of pH on photosynthetic and calcification rates of this alga. It was found that pH had significant effects on both calcification and photosynthesis. While increased pH enhanced calcification rates both in the light and in the dark at pH >8.6, photosynthetic rates decreased. On the other hand, an increase in dissolved CO2 concentration to ∼26 μmol kg−1 (by bubbling with air containing 0.9 mbar CO2) caused a decrease in seawater pH which resulted in 20% less calcification after 5 days of exposure, while enhancing photosynthetic rates by 13%. The ecological implications of these findings is that photosynthetically driven changes in water chemistry by surrounding plants can affect calcification rates of coralline algae, as may future ocean acidification resulting from elevated atmospheric CO2.
Predictions of an evolutionary model were examined for 43 tropical macroalgae using a functional-form group approach. The ranking from high to low primary producers (Sheet- and Filamentous-Groups > Coarsely Branched- and Thick Leathery-Groups > Jointed Calcareous- and Crustose-Groups), and data from the literature, support the hypothesis that persistent forms which allocate resources for environmental resistance, interference competition or antiherbivory defenses do so at the cost of lower primary production rates. The results for percent thallus lost to fish grazing over a 24 h period support the hypothesis that members of the Thick Leathery-, Jointed Calcareous- and Crustose-Groups have evolved antipredator defenses, with a tendency for decreasing herbivore resistance toward the Sheet- and Filamentous-Groups. The most heavily-calcified species (e.g. crustose corallines) ranked among the most grazer resistant as did the thick rubbery or leathery species. The ranking of functional-form group means for resistance to predation was as follows: Filamentous-Group (62% lost-24 h−1), Sheet-Group (42%), Coarsely Branched-Group (33%), Jointed Calcareous-Group (10%), Thick Leathery-Group (7%) and Crustose-Group (0%), in accordance with the hypothesis. The algal groups generally showed an increase in mean penetration toughness from filaments (
The biosphere's great carbonate deposits, from caliche soils to deep-sea carbonate oozes, precipitate largely as by-products of autotrophic nutrient acquisition physiologies. Protons constitute the critical link: Calcification generates protons, which plants and photosynthetic symbioses use to assimilate bicarbonate and nutrients.A calcium ATPase-based “trans” mechanism underlies most biological calcification. This permits high calcium carbonate supersaturations and rapid carbonate precipitation.The competitive advantages of calcification become especially apparent in light and nutrient-deficient alkaline environments. Calcareous plants often dominate the lower euphotic zone in both the benthos and the plankton. Geographically and seasonally, massive calcification concentrates in nutrient-deficient environments including alkaline soils, coral reefs, cyanobacterial mats and coccolithophorid blooms. Structural and defensive uses for calcareous skeletons are sometimes overrated.