Hypoxia is a mounting problem affecting the world's coastal waters, with severe consequences for marine life, including death and catastrophic changes. Hypoxia is forecast to increase owing to the combined effects of the continued spread of coastal eutrophication and global warming. A broad comparative analysis across a range of contrasting marine benthic organisms showed that hypoxia thresholds vary greatly across marine benthic organisms and that the conventional definition of 2 mg O(2)/liter to designate waters as hypoxic is below the empirical sublethal and lethal O(2) thresholds for half of the species tested. These results imply that the number and area of coastal ecosystems affected by hypoxia and the future extent of hypoxia impacts on marine life have been generally underestimated.
Uniform CO2 during human evolution (180 to 280 ppm) resulted, because of the role of the CO2-bicarbonate buffer in regulating pH, in rather constant pH (7.35 to 7.45) in human fluids, cells and tissues, determining, in turn, the narrow pH range for optimal functioning of the human proteome. Here we hypothesize that chronic exposure to elevated pCO2 with increasing atmospheric CO2 (>400 ppm) and extended time spent in confined, crowded indoor atmospheres (pCO2 up to 5,000 ppm) with urban lifestyles may be a major, largely overlooked, driver of changes in the performance of the human proteome. The reduced pH (downregulated from 0.1 to 0.4 units below the optimum pH) of extant humans chronically exposed to elevated CO2 is likely to lead to proteome malfunction due to protein misfolding, aggregation, charge distribution and altered interaction with other molecules (e.g. nucleic acids, metals, proteins, and drugs). Such alterations would have systemic effects helping explain the prevalence of syndromes (obesity, diabetes, respiratory diseases, osteoporosis, cancer, and neurological disorders) characteristic of the modern lifestyle. The risks chronic exposure to elevated CO2 poses to human health are too profound to be ignored and require testing with fit-for-purpose equipment and protocols along with indoor carbon capture technologies to bring CO2 levels to those (180 to 280 ppm) under which the humans proteome evolved.
During the past several decades, high numbers of gelatinous zooplankton species have been reported in many estuarine and coastal ecosystems. Coupled with media-driven public perception, a paradigm has evolved in which the global ocean ecosystems are thought to be heading toward being dominated by “nuisance” jellyfish. We question this current paradigm by presenting a broad overview of gelatinous zooplankton in a historical context to develop the hypothesis that population changes reflect the human-mediated alteration of global ocean ecosystems. To this end, we synthesize information related to the evolutionary context of contemporary gelatinous zooplankton blooms, the human frame of reference for changes in gelatinous zooplankton populations, and whether sufficient data are available to have established the paradigm. We conclude that the current paradigm in which it is believed that there has been a global increase in gelatinous zooplankton is unsubstantiated, and we develop a strategy for addressing the critical questions about long-term, human-related changes in the sea as they relate to gelatinous zooplankton blooms.
Abstract Climate change impact syntheses, such as those by the Intergovernmental Panel on Climate Change, consistently assert that limiting global warming to 1.5 °C is unlikely to safeguard most of the world’s coral reefs. This prognosis is primarily based on a small subset of available models that apply similar ‘excess heat’ threshold methodologies. Our systematic review of 79 articles projecting coral reef responses to climate change revealed five main methods. ‘Excess heat’ models constituted one third (32%) of all studies but attracted a disproportionate share (68%) of citations in the field. Most methods relied on deterministic cause-and-effect rules rather than probabilistic relationships, impeding the field’s ability to estimate uncertainty. To synthesize the available projections, we aimed to identify models with comparable outputs. However, divergent choices in model outputs and scenarios limited the analysis to a fraction of available studies. We found substantial discrepancies in the projected impacts, indicating that the subset of articles serving as a basis for climate change syntheses may project more severe consequences than other studies and methodologies. Drawing on insights from other fields, we propose methods to incorporate uncertainty into deterministic modeling approaches and propose a multi-model ensemble approach to generating probabilistic projections for coral reef futures.
The mean (±SE) depth‐integrated gross production (P) of 2,600 ± 271 mg O 2 m −2 d −1 derived from a compilation of data from nine cruises conducted between 1991–2000 in the subtropical NE Atlantic was found to be significantly lower (t‐test, P = 0.005, N = 33) than the mean (±SE) community respiration (R) of 3,821 ± 276 mg O 2 m −2 d −1 . Two‐thirds of the stations investigated were heterotrophic, and the P/R ratio of the communities tended to increase as P increased, such that communities where P < 3,000 mg O 2 m −2 d −1 tended to be heterotrophic. The tendency for R to exceed P (P/R , 1.0) was statistically significant (Wilcoxon ranked sign test, P < 0.05) in the upper and deep layers of the photic zone, with an overall balance between P and R at intermediate depths. These results provide evidence that the subtropical NE Atlantic is a heterotrophic ecosystem, where planktonic communities respire more organic carbon than they produce, thereby acting as net sources of CO 2 .
Abstract. Diatoms are generally the dominant contributors to the Arctic Ocean spring bloom, which is a key event in regional food webs in terms of capacity for secondary production and organic matter export. Dissolved silicic acid is an obligate nutrient for diatoms and has been declining in the European Arctic. The lack of regional silicon cycling information precludes understanding the consequences of such changes for diatom productivity during the Arctic spring bloom. This study communicates the results from a cruise in the European Arctic around Svalbard reporting the first concurrent data on biogenic silica production and export, diatom cellular export, the degree of kinetic limitation by ambient silicic acid, and diatom contribution to primary production. Regional biogenic silica production rates were significantly lower than those achievable in the Southern Ocean and silicic acid concentration limited the biogenic silica production rate in 95 % of samples. Compared to diatoms in the Atlantic subtropical gyre, regional diatoms are less adapted for silicic acid uptake at low substrate, and at some stations during the present study, silicon limitation may have been intense enough to limit diatom growth. Thus, silicic acid can play a critical role in diatom spring bloom dynamics. Diatom contribution to primary production was variable, ranging from
Abstract. The metabolism of the Arctic Ocean is marked by extreme pronounced seasonality and spatial heterogeneity associated with light conditions, ice cover, water masses and nutrient availability. Here we report the marine planktonic metabolic rates (Net Community Production, Gross Primary Production and Community Respiration) along three different seasons of the year for a total of eight cruises along the western sector of the European Arctic (Fram Strait – Svalbard region) in the Arctic Ocean margin: one at the end of 2006 (fall/winter), two in 2007 (early spring and summer), two in 2008 (early spring and summer), one in 2009 (late spring–early summer) and one in 2010 (spring). The results show that metabolisms of the western sector of the European Arctic varies throughout the year, depending mostly on the stage of bloom, which is mainly determined by availability of light and nutrients. Here we report metabolic rates for the different periods, including the spring bloom, summer and the dark period, increasing considerably the empirical basis on metabolic rates in the Artic Ocean, and especially in the European Arctic corridor. We also report a rough annual metabolic balance for this area of the Arctic Ocean, resulting in a Net Community Production of 108 g C m−2 yr−1.
Seagrass meadows often appear to the casual observer as static landscapes. However, seagrass meadows are subject to intense dynamics involving the continuous loss and replacement of shoots in the population, which, when in balance, maintain a dynamic equilibrium. Such apparent steady-state conditions can be maintained over extended time periods, leading to long-lived seagrass meadows, such as some Posidonia oceanica meadows, which possibly may persist for > 4000 years in the Mediterranean (e.g. Mateo et al., 1997), and Zostera marina meadows exceeding a millennium in age (Reusch et al., 1999).
