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We summarize some of the past year's most important findings within climate change-related research. New research has improved our understanding about the remaining options to achieve the Paris Agreement goals, through overcoming political barriers to carbon pricing, taking into account non-CO2 factors, a well-designed implementation of demand-side and nature-based solutions, resilience building of ecosystems and the recognition that climate change mitigation costs can be justified by benefits to the health of humans and nature alone. We consider new insights about what to expect if we fail to include a new dimension of fire extremes and the prospect of cascading climate tipping elements.
A synthesis is made of 10 topics within climate research, where there have been significant advances since January 2020. The insights are based on input from an international open call with broad disciplinary scope. Findings include: (1) the options to still keep global warming below 1.5 °C; (2) the impact of non-CO2 factors in global warming; (3) a new dimension of fire extremes forced by climate change; (4) the increasing pressure on interconnected climate tipping elements; (5) the dimensions of climate justice; (6) political challenges impeding the effectiveness of carbon pricing; (7) demand-side solutions as vehicles of climate mitigation; (8) the potentials and caveats of nature-based solutions; (9) how building resilience of marine ecosystems is possible; and (10) that the costs of climate change mitigation policies can be more than justified by the benefits to the health of humans and nature.
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How do we limit global warming to 1.5 °C and why is it crucial? See highlights of latest climate science.
The COVID-19 pandemic is a global challenge for humanity, in which a large number of resources are invested to develop effective vaccines and treatments. At the same time, governments try to manage the spread of the disease while alleviating the strong impact derived from the slowdown in economic activity. Governments were forced to impose strict lockdown measures to tackle the pandemic. This significantly changed people’s mobility and habits, subsequently impacting the economy. In this context, the availability of tools to effectively monitor and quantify mobility was key for public institutions to decide which policies to implement and for how long. Telefonica has promoted different initiatives to offer governments mobility insights throughout many of the countries where it operates in Europe and Latin America. Mobility indicators with high spatial granularity and frequency of updates were successfully deployed in different formats. However, Telefonica faced many challenges (not only technical) to put these tools into service in a short timing: from reducing latency in insights to ensuring the security and privacy of information. In this article, we provide details on how Telefonica engaged with governments and other stakeholders in different countries as a response to the pandemic. We also cover the challenges faced and the shared learnings from Telefonica’s experience in those countries.
Posidonia oceanica, the dominant seagrass species in the Mediterranean, appears to be experiencing widespread loss. Efforts to conserve Posidonia oceanica are increasing, as reflected in the increase in the number of marine protected areas in the Mediterranean. However, the effectiveness of these measures to conserve seagrass meadows is unknown. In this study, the present status of the Posidonia oceanica meadows in the Cabrera National Park (Mediterranean), the only marine national park in Spain, was assessed, and the effectiveness of the conservation measures adopted was tested. This was done by reconstruction of past and present growth, quantification of the demographic status of the established meadows, and quantification of patch formation and growth rates in areas where recolonization is occurring. The meadows extended from 1–43 m deep at Santa Maria bay and from 1–33 m at Es Port. Leaf production rate of the stands examined ranged between 6.5 and 7.8 leaves shoot−1 yr−1, with higher rates in Santa Maria than in Es Port. Vertical rhizomes elongated at rates ranging from 5.39–10.12 mm yr−1, annual vertical growth in Santa Maria stands being larger than that in the stands developing at Es Port. Horizontal rhizomes elongated slowly (from 2.6–6.1 cm yr−1), and branching was sparse (<0.25 branches yr−1 axis−1), with maximum elongation and branching rates in areas where patches were actively colonizing. Flowering was a rare event in all the stands (<0.015 flowers shoot−1 yr−1). Patch formation and patch growth rates in active colonizing areas were slow, but they increased after implementation of mooring regulations in the Park. Similarly, the leaf production tended to increase, and vertical rhizome growth to decrease, in both bays following the onset of regulation measures. However, the decrease in vertical growth detected was greater at Santa Maria, where access is prohibited to visitors, than at Es Port, where boats are allowed to moor, attached to permanent weights. Shoot mortality rate was generally low (mean 0.10 ± 0.02 ln units yr−1) but exceeded the recruitment rate (<0.009 and 0.17 ln units yr−1) in 55% of the meadows examined, indicative of negative net population growth rates. Regulation of mooring activities has improved the status of the P. oceanica meadows at Cabrera National Park. The demographic analysis, however, indicated that while P. oceanica meadows at Santa Maria are in good shape, those at Es Port seem to be compromised. The observed differences in meadow status reflect the large differences in circulation inside the bays (water residence time at Santa Maria = 4 days, water residence time at Es Port = 11 days) and the anthropogenic pressure both bays support.
Seagrasses cover about 0.1–0.2% of the global ocean, and develop highly productive ecosystems which fulfil a key role in the coastal ecosystem. Widespread seagrass loss results from direct human impacts, including mechanical damage (by dredging, fishing, and anchoring), eutrophication, aquaculture, siltation, effects of coastal constructions, and food web alterations; and indirect human impacts, including negative effects of climate change (erosion by rising sea level, increased storms, increased ultraviolet irradiance), as well as from natural causes, such as cyclones and floods. The present review summarizes such threats and trends and considers likely changes to the 2025 time horizon. Present losses are expected to accelerate, particularly in South-east Asia and the Caribbean, as human pressure on the coastal zone grows. Positive human effects include increased legislation to protect seagrass, increased protection of coastal ecosystems, and enhanced efforts to monitor and restore the marine ecosystem. However, these positive effects are unlikely to balance the negative impacts, which are expected to be particularly prominent in developing tropical regions, where the capacity to implement conservation policies is limited. Uncertainties as to the present loss rate, derived from the paucity of coherent monitoring programmes, and the present inability to formulate reliable predictions as to the future rate of loss, represent a major barrier to the formulation of global conservation policies. Three key actions are needed to ensure the effective conservation of seagrass ecosystems: (1) the development of a coherent worldwide monitoring network, (2) the development of quantitative models predicting the responses of seagrasses to disturbance, and (3) the education of the public on the functions of seagrass meadows and the impacts of human activity.
The rapidly expanding scientific knowledge on seagrasses has led to a growing awareness that seagrasses are a valuable coastal resource. Where seagrasses abound, humans benefit directly and indirectly from the presence of this marine vegetation. At the same time, it has also become evident that seagrasses are a vulnerable resource, easily lost in coastal areas facing environmental changes. Declines of seagrasses are reported world-wide, and in many cases anthropogenic factors are suspected to be responsible for these declines. In this chapter the relations between seagrasses and humans are addressed. Particular attention will be given to the various stresses on seagrasses resulting from human activities. Knowledge of the processes that lead to seagrass decline is obviously the key to remedial measures targeting the re-establishment or protection of seagrass systems.
The value of seagrasses to humans
The value of seagrasses, as perceived by humans, changes in time and place. In the past, seagrasses have been valued because the plants yielded material for various practical purposes. This direct use of seagrasses has a long history that continues, although on a very modest scale, until today. Seventeenth and eighteenth century Spanish colonial documents indicate that the seeds of Zostera marina were a major food resource of the Seri Indians living along the Gulf of California. The Seri harvested the carbohydrate-rich seeds to obtain flour that was used in different dishes (Felger et al., 1980). In the north-west Pacific, roots and leaf bases of eelgrass were eaten (Turner & Bell, 1973).
In the previous chapter we discussed the ways seagrasses obtained carbon, nitrogen and phosphorus from the environment, elements that are vital for their structure and functioning. As tissues die, these elements are again lost from the plants, although resorption processes may somewhat mitigate the loss rates. The plants thus have a direct influence on the dynamics of chemical elements in their environment. Uptake by, and loss of, elements from the living plants are only two aspects of the fluxes of matter in seagrass systems. In this chapter we will focus on the various processes determining these fluxes, with particular attention to those relevant to the dynamics of carbon, nitrogen and phosphorus. A variety of processes, biological, physical and chemical, plays a role in shaping the dynamics of these elements, but they share one feature in common: directly or indirectly they are influenced or even determined by the presence of the key species in the system, the seagrasses. Primary production and mineralization are two major processes driving the carbon and nutrient dynamics within the seagrass system, these processes coinciding with fixation and release of inorganic compounds, respectively. Inorganic nitrogen- and phosphorus-containing compounds released during mineralization can be captured again for the production of plant biomass. Although much of the plant biomass dies without being eaten by herbivores and is directly processed by the decomposer community, some of it is consumed by herbivores.
The few members of the angiosperm flora that have succeeded in adapting to submersed life in the sea share a common architecture, all species being clonal, rhizomatous plants. This clonal nature has been interpreted as a necessary adaptation for angiosperm growth in the high-energy marine environment (Sculthorpe, 1967). A consequence of the clonal nature of the seagrasses is that they display a highly ordered growth programme (Tomlinson, 1974), developed through the regular addition of the basic set of modules. Thus, a general understanding of the design of seagrasses will provide insight into their growth patterns (Patriquin, 1973, 1975; Tomlinson, 1974; Sand-Jensen, 1975; Duarte & Sand-Jensen, 1990; Duarte et al., 1994). Although the repertoire of architecture and associated growth programmes that seagrasses display is certainly narrow, they contain sufficient plasticity to yield order-of-magnitude variability in the clonal growth between individual shoots of seagrass species (Marbà & Duarte, 1998), as well as in their reproduction and dispersal. Even within a species, the plasticity of its growth programme and architecture allows the plants to cope with stress and heterogeneity in the environment, as has been extensively documented for land plants. This plasticity is also a central trait in the ecology of seagrasses.
In this chapter we provide a description of the basic architecture of seagrasses, the growth patterns resulting from their design, and their plasticity in growth characteristics to cope with stress and resource heterogeneity.
The meadows formed by seagrasses have characteristics that make them a suitable habitat for many species of animals. The high primary productivity of the seagrasses, augmented with that of epiphytic and benthic algae, ensures an abundant supply of organic matter that can be used as the basic energy source for more or less complicated food webs. Moreover, the three-dimensional structure of the vegetation, with its network of roots and rhizomes and often dense leaf canopy, offers hiding places that protect against predation, and also provides substrate for attachment. The vegetation structure, furthermore, confers physical and chemical qualities to the environment that may attract fauna: currents within the canopy are reduced, the sediment is stabilized and often fine grained, and irradiance conditions are modified. In this chapter we will first take a closer look at the general abundance and species richness of the fauna associated with seagrass meadows, before turning to the faunal groups that have received major attention, i.e. fishes, crustaceans and molluscs. The association of sea cows and turtles with seagrass beds will also be discussed. The significance of seagrass meadows as a habitat and foraging area is a recurrent theme in these sections. In the final part of the chapter, the ways in which the fauna affect the functioning of the seagrasses will be addressed.
Abundance and diversity
The fauna of seagrass meadows are heterogeneous assemblages of animals belonging to a variety of taxa, with many different ecological characteristics.
Seagrasses comprise <0.02% of the angiosperm flora, representing a surprisingly small number of species (about 50, Table 1.1) compared with any other group of marine organisms. The limited species membership of the seagrass flora has directed some (still limited) efforts to the study of their origin and their evolution in an attempt to account for this phenomenon. A second path of research has tried to find clues for the paucity of species by studying the stress factors constraining angiosperm life in the sea. This second approach has driven much effort towards the analysis of seagrass distribution and the definition of the habitat requirements of seagrasses. The attention these issues have received extends beyond scholarly concerns, for seagrasses are, despite their limited diversity, important contributors to coastal marine ecosystems, both locally and at the global scale. In this chapter we shall provide an overview of the origin, evolution and present diversity of extant seagrasses, and describe their present distribution and the basic requirements that delimit their possible habitats. The definition of how seagrass distribution is regulated leads, in turn, to the assessment of their global extent and, from this, to the evaluation of the role seagrasses play on the global ocean ecosystem.
The seagrass flora
Seagrasses are generally assigned to two families, Potamogetonaceae and Hydrocharitaceae, encompassing 12 genera of angiosperms containing about 50 species (Table 1.1).
Seagrasses occur in coastal zones throughout the world, in the part of the marine habitat that is most heavily influenced by humans. Decisions about coastal management therefore often involve seagrasses, but despite a growing awareness of the importance of these plants, a full appreciation of their role in coastal ecosystems has yet to be reached. This book provides an entry point for those wishing to learn about their ecology, and gives a broad overview of the state of knowledge, including progress in research and research foci, complemented by extensive literature references to guide the reader to more detailed studies. It will be valuable to students of marine biology wishing to specialize in this area and also to established researchers wanting to enter the field. In addition, it will provide an excellent reference for those involved in the management and conservation of coastal areas that harbour seagrasses.
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).
The equilibrium maintaining seagrass meadows is, however, often upset, leading to a regression of seagrass meadows, whereby large meadows can be totally lost over a few years (see Chapter 7). In fact, seagrass decline is now a common phenomenon throughout the world (Short & Wyllie-Echeverria, 1996), to the point that the law in various countries now protects seagrass meadows. However, effective protection of seagrass meadows requires an understanding of the regulation of seagrass losses and gains. This is currently the bottleneck to the development of reliable forecasts on the future status of seagrass meadows. Examination of the dynamics of genetic individuals (genets) and patches within the meadow requires knowledge of the life cycles of seagrasses. Seagrass life cycles are similar to those of clonal herbs on land, except that they are entirely confined to the marine realm. However, dispersal processes are remarkably different in the underwater marine environment compared with land.
As outlined in the first chapter, seagrasses are the only angiosperms that are adapted to a marine submerged existence. Basic requirements for growth are similar for terrestrial angiosperms and seagrasses alike. Life in the marine realm, however, implies exposure to environmental conditions that are considerably different in many respects from those in terrestrial habitats, imposing constraints on the availability of some resources, or calling for specific adaptations to acquire others. In this chapter we will focus on environmental resources imperative for growth in seagrasses, i.e. light, inorganic carbon and nutrients, and on the plant properties relevant to their acquisition and use.
Photosynthesis provides plants with chemically fixed energy and with carbon skeletons for the variety of biosynthetic processes associated with plant growth and functioning. The penetration of light through natural waters, however, is at least three orders of magnitude less than through air. Light intensity thus rapidly decreases with water depth, and even in clear ocean water virtually no photosynthetically active radiation (PAR; wavelength 350 or 400 to 700 nm) can penetrate beyond a depth of 200 m. Apart from absorption by pure water, particulate and soluble substances also each contribute to the total attenuation of light in the water column. The intensity of absorption varies with the wavelength; the absorption of pure water, for instance, begins to rise as wavelength increases above 550 nm (Fig. 4.1; Kirk, 1983).