The potential impacts of global climate change on marine protected areas

The potential effects of global climate changeon marine protected areas do not appear to havebeen addressed in the literature. This paperexamines the literature on protected areas,conservation biology, marine ecology,oceanography, and climate change, and reviewssome of the relevant differences between marineand terrestrial environments. Frameworks andclassifications systems used in protected areadesign are discussed. Finally, a frameworkthat summarizes some of the importantoceanographic processes and their links to thefood chain are reviewed. Species abundance anddistribution are expected to change as a resultof global climate change, potentiallycompromising the efficacy of marine protectedareas as biodiversity conservation tools. Thisreview suggests the need for: furtherinterdisciplinary research and the use oflinked models; an increase in marine protectedareas for biodiversity conservation and asresearch sites for teasing apart fishingeffects from climate effects; a temporallyresponsive approach to siting new marineprotected areas, shifting their locations ifnecessary; and large-scale ecosystem/integratedmanagement approaches to address the competinguses of the oceans and boundary-less threatssuch as global climate change and pollution.     

The potential impacts of global climate change on marine protected areas

Reviews in Fish Biology and Fisheries - The potential effects of global climate changeon marine protected areas do not appear to havebeen addressed in the literature. This paperexamines the...     

Investigating the potential impacts of climate change on a marine turtle population

Recent increases in global temperatures have affected the phenology and survival of many species of plants and animals. We investigated a case study of the effects of potential climate change on a thermally sensitive species, the loggerhead sea turtle, at a breeding location at the northerly extent of the range of regular nesting in the United States. In addition to the physical limits imposed by temperature on this ectothermic species, sea turtle primary sex ratio is determined by the temperature experienced by eggs during the middle third of incubation. We recorded sand temperatures and used historical air temperatures (ATs) at Bald Head Island, NC, to examine past and predict future sex ratios under scenarios of warming. There were no significant temporal trends in primary sex ratio evident in recent years and estimated mean annual sex ratio was 58% female. Similarly, there were no temporal trends in phenology but earlier nesting and longer nesting seasons were correlated with warmer sea surface temperature. We modelled the effects of incremental increases in mean AT of up to 7.5°C, the maximum predicted increase under modelled scenarios, which would lead to 100% female hatchling production and lethally high incubation temperatures, causing reduction in hatchling production. Populations of turtles in more southern parts of the United States are currently highly female biased and are likely to become ultra‐biased with as little as 1°C of warming and experience extreme levels of mortality if warming exceeds 3°C. The lack of a demonstrable increase in AT in North Carolina in recent decades coupled with primary sex ratios that are not highly biased means that the male offspring from North Carolina could play an increasingly important role in the future viability of the loggerhead turtle in the Western Atlantic.     

Transferring soils from high- to low-elevation forests increases nitrogen cycling rates: climate change implications

It is well recognized that photosynthesis of C3 plants is highly responsive to CO₂ concentration. However, in natural ecosystems, plants are subject to a range of feed-back effects that can interact with increased photosynthetic carbon gain in different ways so that it is not clear to what extent increased photosynthesis will translate into increased growth. To assess the probable growth response of nutrient-limited forests to increasing CO₂ concentration, we use a previously developed modelling framework and apply it under conditions where the supply of nutrients is affected by a range of different factors. Our analysis indicates that forest growth is likely to be highly stimulated by increasing CO₂ concentration in forests with high fertility, in forests with nitrogen fixing plants, in those subject to fire or where nitrogen in wood is effectively removed from the biologically active cycle either through physical removal of stems in harvesting or through continued stem growth over long time periods. Forest growth is likely to be stimulated by CO₂ concentration in both phosphorus- and sulphur-limited forests provided nutrients in heartwood of trees are removed from the active nutrient cycle. Without this removal from the cycling system, however, sulphur-limited forests should show little response to increasing CO₂. In phosphorus-limited forests without phosphorus removal, the response to increasing CO₂ depends further on the equilibration state of the large pool of unavailable secondary phosphorus. Considered over periods of centuries during which the secondary pool has equilibrated, growth of phosphorus-limited forests is likely to be only weakly stimulated by increasing CO₂ concentration. However, over shorter periods, increasing CO₂ concentration should lead to a substantial increase in productivity. In general, it can be concluded that systems that are more open with respect to nutrient gains and losses are likely to be more responsive to increasing CO₂ concentration than systems where the amount of available nutrients is less variable. In more open systems, operation at a lower internal nutrient concentration as a result of increasing atmospheric CO₂ concentration can lead to reduced nutrient losses per unit carbon gain. Our analysis shows that the effect of increasing CO₂ on forest growth can differ substantially between forests due to interactions with a range of factors that affect nutrient supply. The response of a particular forest to increasing CO₂ concentration can only be predicted if the main factors controlling nutrient supply and growth in that forest are understood and incorporated into an assessment.     

The impact of humans on the nitrogen cycle,with focus on temperate arable agriculture

The 6 billion people alive today consume about 25 million tonnes of protein nitrogen each year, a requirement that could well increase to 40–45 million tonnes by 2050. Most of them ultimately depend on the Haber-Bosch process to fix the atmospheric N₂ needed to grow at least part of their protein and, over the earth as a whole, this dependency is likely to increase. Humans now fix some 160 million tonnes of nitrogen per year, of which 98 are fixed industrially by the Haber-Bosch process (83 for use as agricultural fertilizer, 15 for industry), 22 during combustion and the rest is fixed during the cultivation of leguminous crops and fodders. These 160 million tonnes have markedly increased the burden of combined nitrogen entering rivers, lakes and shallow seas, as well as increasing the input of NH₃, N₂O, NO and NO₂ to the atmosphere. Nitrogen fertilizers give large economic gains in modern farming systems and under favourable conditions can be used very efficiently. Losses of nitrogen occur from all systems of agriculture, with organic manures being particularly difficult to use efficiently. Although nitrate leaching has received much attention as an economic loss, a cause of eutrophication and a health hazard, gaseous emissions may eventually prove to be the most serious environmentally. Scientists working on the use and fate of nitrogen fertilizers must be careful, clear headed and vigilant in looking for unexpected side effects.     

Response of nitrogen cycling to simulated climate change: differential responses along a subalpine ecotone

In situ nitrogen (N) transformations and N availability were examined over a four‐year period in two soil microclimates (xeric and mesic) under a climate‐warming treatment in a subalpine meadow/sagebrush scrub ecotone. Experimental plots that spanned the two soil microclimates were exposed to an in situ infrared (IR) climate change manipulation at the Rocky Mountain Biological Laboratory, near Crested Butte, Colorado. Although the two microclimates did not differ significantly in their rates of N transformations in the absence of heating, they differed significantly in their response to increased IR. Under a simulated warming in the sagebrush‐dominated xeric microclimate, gross N mineralization rates doubled and immobilization rates increased by up to 60% over the first 2 years of the study but declined to predisturbance rates by the fourth year. This temporal pattern of gross mineralization rates correlated with a decline in SOM. Concurrently, rates of net mineralization rates in the heated plots were 60% higher than the controls after the first year. There were no differences in gross or net nitrification rates with heating in the xeric soils. In contrast to the xeric microclimate, there were no significant effects of heating on any N transformation rates in the mesic microclimate. The differing responses in N cycling rates of the two microclimate to the increased IR is most certainly the result of differences in initial soil moisture conditions and vegetation type and cover.     

Elemental and isotopic fractionation of carbon and nitrogen by marine, planktonic copepods and implications to the marine nitrogen cycle

Particle-grazing copepods, primarily Temora longicornis andT. stylifera, and seawater with natural particles were collectedfrom the northwest Gulf of Mexico. Control and ammonium-enrichedaliquots of seawater were incubated in triplicate for 2 days,copepods added and the incubation continued for 2 days. Analyseswere made of dissolved nutrients (nitrate, ammonium and phosphate),suspended particles (chlorophyll a and phaeopigments, C, N,     

Electrons, life and the evolution of Earth's oxygen cycle

The biogeochemical cycles of H, C, N, O and S are coupled via biologically catalysed electron transfer (redox) reactions. The metabolic processes responsible for maintaining these cycles evolved over the first ca 2.3 Ga of Earth's history in prokaryotes and, through a sequence of events, led to the production of oxygen via the photobiologically catalysed oxidation of water. However, geochemical evidence suggests that there was a delay of several hundred million years before oxygen accumulated in Earth's atmosphere related to changes in the burial efficiency of organic matter and fundamental alterations in the nitrogen cycle. In the latter case, the presence of free molecular oxygen allowed ammonium to be oxidized to nitrate and subsequently denitrified. The interaction between the oxygen and nitrogen cycles in particular led to a negative feedback, in which increased production of oxygen led to decreased fixed inorganic nitrogen in the oceans. This feedback, which is supported by isotopic analyses of fixed nitrogen in sedimentary rocks from the Late Archaean, continues to the present. However, once sufficient oxygen accumulated in Earth's atmosphere to allow nitrification to out-compete denitrification, a new stable electron 'market' emerged in which oxygenic photosynthesis and aerobic respiration ultimately spread via endosymbiotic events and massive lateral gene transfer to eukaryotic host cells, allowing the evolution of complex (i.e. animal) life forms. The resulting network of electron transfers led a gas composition of Earth's atmosphere that is far from thermodynamic equilibrium (i.e. it is an emergent property), yet is relatively stable on geological time scales. The early coevolution of the C, N and O cycles, and the resulting non-equilibrium gaseous by-products can be used as a guide to search for the presence of life on terrestrial planets outside of our Solar System.     

Antarctic echinoids and climate change: a major impact on the brooding forms

Ocean acidification (OA) and the accompanying changes to carbonate concentrations are predicted to have especially negative impacts in the Southern Ocean where, as a result of colder temperatures, there will be shallowing of both the aragonite (ASH) and calcite saturation horizons (CSH). Echinoids are a dominant group of the Antarctic macrofauna which, because of their high‐Mg calcite skeleton, are particularly susceptible to changes in the ASH. Using published information on the bathymetric distributions of Antarctic echinoids, we show that the majority of heavily calcified echinoids have their lower bathymetric limit above a depth of ca. 3000 m, approximately the current depth of the CSH. Echinoids whose depth range extends below 3000 m generally have thin, weakly calcified tests and include species from the Order Holasteroida, and the Families Cidaridae and Schizasteridae. Examination of the reproductive mode of Antarctic echinoids shows that brooding, where calcification of the young occurs in the same CaCO₃ environment as the mother, is primarily found at a depth above 3000 m. The predicted shallowing of the ASH and CSH under OA conditions is likely to negatively impact growth and reproduction of heavily calcified brooders in the Family Cidaridae, which may result in changes to bathymetric ranges, local population extinction, and associated losses in macrofaunal biodiversity. As with other calcified deep sea invertebrates, echinoids may be particularly vulnerable to the impacts of increased CO₂ and OA in the Southern Ocean.     

The global nitrogen cycle in the twenty-first century

Global nitrogen fixation contributes 413 Tg of reactive nitrogen (N_r) to terrestrial and marine ecosystems annually of which anthropogenic activities are responsible for half, 210 Tg N. The majority of the transformations of anthropogenic N_r are on land (240 Tg N yr⁻¹) within soils and vegetation where reduced N_r contributes most of the input through the use of fertilizer nitrogen in agriculture. Leakages from the use of fertilizer N_r contribute to nitrate (NO₃⁻) in drainage waters from agricultural land and emissions of trace N_r compounds to the atmosphere. Emissions, mainly of ammonia (NH₃) from land together with combustion related emissions of nitrogen oxides (NO_x), contribute 100 Tg N yr⁻¹ to the atmosphere, which are transported between countries and processed within the atmosphere, generating secondary pollutants, including ozone and other photochemical oxidants and aerosols, especially ammonium nitrate (NH₄NO₃) and ammonium sulfate (NH₄)₂SO₄. Leaching and riverine transport of NO₃ contribute 40–70 Tg N yr⁻¹ to coastal waters and the open ocean, which together with the 30 Tg input to oceans from atmospheric deposition combine with marine biological nitrogen fixation (140 Tg N yr⁻¹) to double the ocean processing of N_r. Some of the marine N_r is buried in sediments, the remainder being denitrified back to the atmosphere as N₂ or N₂O. The marine processing is of a similar magnitude to that in terrestrial soils and vegetation, but has a larger fraction of natural origin. The lifetime of N_r in the atmosphere, with the exception of N₂O, is only a few weeks, while in terrestrial ecosystems, with the exception of peatlands (where it can be 10²–10³ years), the lifetime is a few decades. In the ocean, the lifetime of N_r is less well known but seems to be longer than in terrestrial ecosystems and may represent an important long-term source of N₂O that will respond very slowly to control measures on the sources of N_r from which it is produced.     

Effect of temperature on humus respiration rate and nitrogen mineralization: Implications for global climate change

Respiration and nitrogen mineralization rates of humus samples from 7 Scots pine stands located along a climatic transect across the European continent from the Pyrenees (42°40) to northern Sweden (66°08) were measured for 14 weeks under laboratory conditions at temperatures from 5 °C to 25 °C. The average Q₁₀ values for the respiration rate ranged from about 1.0 at the highest temperature to more than 5 at 10 °C to 15 °C in the northernmost samples. In samples from more northern sites, respiration rates remained approximately constant during the whole incubation period; in the southern end of the transect, rates decreased over time. Respiration rate was positively correlated with incubation temperature, soil pH and CN ratio, and negatively with soil total N. Regressions using all these variables explained approximately 71% of the total variability in the respiration rate. There was no clear relation between the nitrogen mineralization rate and incubation temperature. Below 15 °C the N-mineralization rate did not respond to increasing temperature; at higher temperatures, significant increases were found for samples from some sites. A regression model including incubation temperature, pH, N_tot and CN explained 73% of the total variability in N mineralization. The estimated increase in annual soil respiration rates due to predicted global warming at the high latitudes of the Northern Hemisphere ranged from approximately 0.07×10¹⁵ to 0.13×10¹⁵ g CO₂ at 2 °C and 4 °C temperature increase scenarios, respectively. Both values are greater than the current annual net carbon storage in northern forests, suggesting a switch of these ecosystems from net sinks to net sources of carbon with global warming.     

Potential impacts of climate change on nitrogen transformations and greenhouse gas fluxes in forests: a soil transfer study

Relatively little research has been conducted on how climate change may affect the structure and function of arid to semiarid ecosystems of the American Southwest. Along the slopes of the San Francisco Peaks of Arizona, USA, I transferred intact soil cores from a spruce‐fir to a ponderosa pine forest 730 m lower in elevation to assess the potential impacts of climate change on soil N cycling and trace gas fluxes. The low‐elevation site has a mean annual soil temperature about 2.5°C higher than the high‐elevation site. Net rates of N transformations and trace gas fluxes were measured in high‐elevation soil cores incubated in situ and soil cores transferred to the low‐elevation site. Over a 13‐month period, volumetric soil water content was similar in transferred soil cores relative to soil cores incubated in situ. Net N mineralization and nitrification increased over 80% in transferred soil cores compared with in situ soil cores. Soil transfer significantly increased net CO₂ efflux (120%) and net CH₄ consumption (90%) relative to fluxes of these gases from soil cores incubated in situ. Soil net N₂O fluxes were relatively low and were not generally altered by soil transfer. Although the soil microbial biomass as a whole decreased in transferred soil cores compared with in situ soil cores after the incubation period, active bacterial biomass increased. Transferring soil cores from the low‐elevation to the high‐elevation site (i.e. simulated global cooling) commonly, but not consistently, resulted in the opposite effects on soil pools and processes. In general, soil containment (root trenching) did not significantly affect soil measurements. My results suggest that small increases in mean annual temperature can have large impacts on soil N cycling, soil–atmosphere trace gas exchanges, and soil microbial communities even in ecosystems where water availability is a major limiting resource.     

The potential impacts of climate change on inshore squid: biology, ecology and fisheries

Squid are important components of many marine ecosystems from the poles to the equator, serving as both important predators and prey. Novel aspects of their growth and reproduction mean that they are likely to play an important role in the changing oceans due to climate change. Virtually every facet of squid life-history examined thus far has revealed an incredible capacity in this group for life-history plasticity. The extremely fast growth rates of individuals and rapid rates of turnover at the population level mean that squid can respond quickly to environmental or ecosystem change. Their ‘life-in-the-fast-lane’ life-style allows them to rapidly exploit ‘vacuums’ created in the ecosystem when predators or competitors are removed. In this way, they function as ‘weeds of the sea’. Elevated temperatures accelerate the life-histories of squid, increasing their growth rates and shortening their life-spans. At first glance, it would be logical to suggest that rising water temperatures associated with climate change (if food supply remains adequate) would be beneficial to inshore squid populations and fisheries—growth rates would increase, life spans would shorten and population turnover would accelerate. However, the response of inshore squid populations to climate change is likely to be extremely complex. The size of hatchlings emerging from the eggs becomes smaller as temperatures increase and hatchling size may have a critical influence on the size-at-age that may be achieved as adults and subsequently, population structure. The influence of higher temperatures on the egg and adult stages may thus be opposing forces on the life-history. The process of climate change will likely result in squids that hatch out smaller and earlier, undergo faster growth over shorter life-spans and mature younger and at a smaller size. Individual squid will require more food per unit body size, require more oxygen for faster metabolisms and have a reduced capacity to cope without food. It is therefore likely that biological, physiological and behavioural changes in squid due to climate change will have far reaching effects.     

An assessment of nitrogen fixation as a source of nitrogen to the North Atlantic Ocean

The role of nitrogen fixation in the nitrogen cycle of the North Atlantic basin was re-evaluated because recent estimates had indicated a far higher rate than previous reports. Examination of the available data on nitrogen fixation rates and abundance ofTrichodesmium, the major nitrogen fixing organism, leads to the conclusion that rates might be as high as 1.09 × 10¹² mol N yr^–1. Several geochemical arguments are reviewed that each require a large nitrogen source that is consistent with nitrogen fixation, but the current data, although limited, do not support a sufficiently high rate. However, recent measurements of the fixation rates per colony are higher than the historical average, suggesting that improved methodology may require a re-evaluation through further measurements. The paucity of temporally resolved data on both rates and abundance for the major areal extent of the tropical Atlantic, where aeolian inputs of iron may foster high fixation rates, represents another major gap.     

Landscape,regional and global estimates of nitrogen flux from land to sea: Errors and uncertainties

Regional to global scale modelling of N fluxfrom land to ocean has progressed to datethrough the development of simple empiricalmodels representing bulk N flux rates fromlarge watersheds, regions, or continents on thebasis of a limited selection of modelparameters. Watershed scale N flux modellinghas developed a range of physically-basedapproaches ranging from models where N fluxrates are predicted through a physicalrepresentation of the processes involved,through to catchment scale models which providea simplified representation of true systemsbehaviour. Generally, these watershed scalemodels describe within their structure thedominant process controls on N flux at thecatchment or watershed scale, and take intoaccount variations in the extent to which theseprocesses control N flux rates as a function oflandscape sensitivity to N cycling and export. This paper addresses the nature of the errorsand uncertainties inherent in existing regionalto global scale models, and the nature of errorpropagation associated with upscaling fromsmall catchment to regional scale through asuite of spatial aggregation and conceptuallumping experiments conducted on a validatedwatershed scale model, the export coefficientmodel. Results from the analysis support thefindings of other researchers developingmacroscale models in allied research fields. Conclusions from the study confirm thatreliable and accurate regional scale N fluxmodelling needs to take account of theheterogeneity of landscapes and the impact thatthis has on N cycling processes withinhomogenous landscape units.     

Footprints of climate change in the Arctic marine ecosystem

In this article, we review evidence of how climate change has already resulted in clearly discernable changes in marine Arctic ecosystems. After defining the term ‘footprint’ and evaluating the availability of reliable baseline information we review the published literature to synthesize the footprints of climate change impacts in marine Arctic ecosystems reported as of mid‐2009. We found a total of 51 reports of documented changes in Arctic marine biota in response to climate change. Among the responses evaluated were range shifts and changes in abundance, growth/condition, behaviour/phenology and community/regime shifts. Most reports concerned marine mammals, particularly polar bears, and fish. The number of well‐documented changes in planktonic and benthic systems was surprisingly low. Evident losses of endemic species in the Arctic Ocean, and in ice algae production and associated community remained difficult to evaluate due to the lack of quantitative reports of its abundance and distribution. Very few footprints of climate change were reported in the literature from regions such as the wide Siberian shelf and the central Arctic Ocean due to the limited research effort made in these ecosystems. Despite the alarming nature of warming and its strong potential effects in the Arctic Ocean the research effort evaluating the impacts of climate change in this region is rather limited.