Catastrophe and the life span of coral reefs

A strong earthquake in the western Caribbean in 2009 had a catastrophic impact on uncemented, unconsolidated coral reefs in the central sector of the shelf lagoon of the Belizean barrier reef. In a set of 21 reef sites that had been observed prior to the earthquake, the benthic assemblages of 10 were eradicated, and one was partially damaged, by avalanching of their slopes. Ecological dynamics that had played out over the previous 23 years, including the mass mortalities of two sequentially dominant coral species and a large increase in the cover of an encrusting sponge, were instantaneously rendered moot in the areas of catastrophic reef-slope failure. Because these prior dynamics also determined the benthic composition and resilience of adjacent sections of reef that remained intact, the history of disturbance prior to the earthquake will strongly influence decadal-scale recovery in the failed areas. Geological analysis of the reef framework yielded a minimum return time of 2000-4000 years for this type of high-amplitude event. Anthropogenic degradation of ecosystems must be viewed against the backdrop of long-period, natural catastrophes, such as the impact of strong earthquakes on uncemented, lagoonal reefs.     

CO2 enrichment inhibits shoot nitrate assimilation in C3 but not C4 plants and slows growth under nitrate in C3 plants

The CO2 concentration in Earth's atmosphere may double during this century. Plant responses to such an increase depend strongly on their nitrogen status, but the reasons have been uncertain. Here, we assessed shoot nitrate assimilation into amino acids via the shift in shoot CO2 and O2 fluxes when plants received nitrate instead of ammonium as a nitrogen source (deltaAQ). Shoot nitrate assimilation became negligible with increasing CO2 in a taxonomically diverse group of eight C3 plant species, was relatively insensitive to CO2 in three C4 species, and showed an intermediate sensitivity in two C3-C4 intermediate species. We then examined the influence of CO2 level and ammonium vs. nitrate nutrition on growth, assessed in terms of changes in fresh mass, of several C3 species and a Crassulacean acid metabolism (CAM) species. Elevated CO2 (720 micromol CO2/mol of all gases present) stimulated growth or had no effect in the five C3 species tested when they received ammonium as a nitrogen source but inhibited growth or had no effect if they received nitrate. Under nitrate, two C3 species grew faster at sub-ambient (approximately 310 micromol/mol) than elevated CO2. A CAM species grew faster at ambient than elevated or sub-ambient CO2 under either ammonium or nitrate nutrition. This study establishes that CO2 enrichment inhibits shoot nitrate assimilation in a wide variety of C3 plants and that this phenomenon can have a profound effect on their growth. This indicates that shoot nitrate assimilation provides an important contribution to the nitrate assimilation of an entire C3 plant. Thus, rising CO2 and its effects on shoot nitrate assimilation may influence the distribution of C3 plant species.     

Geologic processes influence the effects of mining on aquatic ecosystems

Geologic processes strongly influence water and sediment quality in aquatic ecosystems but rarely are geologic principles incorporated into routine biomonitoring studies. We test if elevated concentrations of metals in water and sediment are restricted to streams downstream of mines or areas that may discharge mine wastes. We surveyed 198 catchments classified as "historically mined" or "unmined," and based on mineral-deposit criteria, to determine whether water and sediment quality were influenced by naturally occurring mineralized rock, by historical mining, or by a combination of both. By accounting for different geologic sources of metals to the environment, we were able to distinguish aquatic ecosystems limited by metals derived from natural processes from those due to mining. Elevated concentrations of metals in water and sediment were not restricted to mined catchments; depauperate aquatic communities were found in unmined catchments. The type and intensity of hydrothermal alteration and the mineral deposit type were important determinants of water and sediment quality as well as the aquatic community in both mined and unmined catchments. This study distinguished the effects of different rock types and geologic sources of metals on ecosystems by incorporating basic geologic processes into reference and baseline site selection, resulting in a refined assessment. Our results indicate that biomonitoring studies should account for natural sources of metals in some geologic environments as contributors to the effect of mines on aquatic ecosystems, recognizing that in mining-impacted drainages there may have been high pre-mining background metal concentrations.     

Suppressing antagonistic bioengineering feedbacks doubles restoration success

In a seagrass restoration project, we explored the potential for enhancing the restoration process by excluding antagonistic engineering interactions (i.e., biomechanical warfare) between two ecosystem engineers: the bioturbating lugworm Arenicola marina and the sediment-stabilizing seagrass Zostera noltii Hornem. Applying a shell layer underneath half of our seagrass transplants successfully reduced adult lugworm density by over 80% and reduced lugworm-induced microtopography (a proxy for lugworm disturbance) at the wave-sheltered site. At the wave-exposed site adult lugworm densities and microtopography were already lower than at the sheltered site but were further reduced in the shell-treated units. Excluding lugworms and their bioengineering effects corresponded well with a strongly enhanced seagrass growth at the wave-sheltered site, which was absent at the exposed site. Enhanced seagrass growth in the present study was fully assigned to the removal of lugworms' negative engineering effects and not to any (indirect) evolving effects such as an altered biogeochemistry or sediment-stabilizing effects by the shell layer. The context-dependency implies that seagrass establishment at the exposed site is not constrained by negative ecosystem-engineering interactions only, but also by overriding physical stresses causing poor growth conditions. Present findings underline that, in addition to recent emphasis on considering positive (facilitating) interactions in ecological theory and practice, it is equally important to consider negative engineering interactions between ecosystem-engineering species. Removal of such negative interactions between ecosystem-engineering species can give a head start to the target species at the initial establishment phase, when positive engineering feedbacks by the target species on itself are still lacking. Though our study was carried out in a marine environment with variable levels of wave disturbance, similar principles may be expected to apply to other ecosystems that are inhabited by ecosystem engineers.     

Sequestered defensive toxins in tetrapod vertebrates: principles, patterns, and prospects for future studies

Chemical defenses are widespread among animals, and the compounds involved may be either synthesized from nontoxic precursors or sequestered from an environmental source. Defensive sequestration has been studied extensively among invertebrates, but relatively few examples have been documented among vertebrates. Nonetheless, the number of described cases of defensive sequestration in tetrapod vertebrates has increased recently and includes diverse lineages of amphibians and reptiles (including birds). The best-known examples involve poison frogs, but other examples include natricine snakes that sequester toxins from amphibians and two genera of insectivorous birds. Commonalities among these diverse taxa include the combination of consuming toxic prey and exhibiting some form of passive defense, such as aposematism, mimicry, or presumptive death-feigning. Some species exhibit passive sequestration, in which dietary toxins simply require an extended period of time to clear from the tissues, whereas other taxa exhibit morphological or physiological specializations that enhance the uptake, storage, and/or delivery of exogenous toxins. It remains uncertain whether any sequestered toxins of tetrapods bioaccumulate across multiple trophic levels, but multitrophic accumulation seems especially likely in cases involving consumption of phytophagous or mycophagous invertebrates and perhaps consumption of poison frogs by snakes. We predict that additional examples of defensive toxin sequestration in amphibians and reptiles will be revealed by collaborations between field biologists and natural product chemists. Candidates for future investigation include specialized predators on mites, social insects, slugs, and toxic amphibians. Comprehensive studies of the ecological, evolutionary, behavioral, and regulatory aspects of sequestration will require teams of ecologists, systematists, ethologists, physiologists, molecular biologists, and chemists. The widespread occurrence of sequestered defenses has important implications for the ecology, evolution, and conservation of amphibians and reptiles.     

Human perspectives and conservation of grizzly bears in Banff National Park, Canada

Some conservation initiatives provoke intense conflict among stakeholders. The need for action, the nature of the conservation measures, and the effects of these measures on human interests may be disputed. Tools are needed to depolarize such situations, foster understanding of the perspectives of people involved, and find common ground. We used Q methodology to explore stakeholders' perspectives on conservation and management of grizzly bears (Ursus arctos horribilis) in Banff National Park and the Bow River watershed of Alberta, Canada. Twenty-nine stakeholders participated in the study, including local residents, scientists, agency employees, and representatives of nongovernmental conservation organizations and other interest groups. Participants rank ordered a set of statements to express their opinions on the problems of grizzly bear management (I-IV) and a second set of statements on possible solutions to the problems (A-C). Factor analysis revealed that participants held 4 distinct views of the problems: individuals associated with factor I emphasized deficiencies in goals and plans; those associated with factor II believed that problems had been exaggerated; those associated with factor III blamed institutional flaws such as disjointed management and inadequate resources; and individuals associated with factor IV blamed politicized decision making. There were 3 distinct views about the best solutions to the problems: individuals associated with factor A called for increased conservation efforts; those associated with factor B wanted reforms in decision-making processes; and individuals associated with factor C supported active landscape management. We connected people's definitions of the problem with their preferred solutions to form 5 overall problem narratives espoused by groups in the study: the problem is deficient goals and plans, the solution is to prioritize conservation efforts (planning-oriented conservation advocates); the problem is flawed institutions, the solution is to prioritize conservation efforts (institutionally-oriented conservation advocates); the problems have been exaggerated, but there is a need to improve decision-making processes (optimistic decision-process reformers); the problems have been exaggerated, but managers should more actively manage the landscape (optimistic landscape managers); and the problem is politicized decision making, solutions vary (democratizers). Although these 5 groups differed on many issues, they agreed that the population of grizzly bears is vulnerable to extirpation, human use of the area should be designed around ecological constraints, and more inclusive decision-making processes are needed. We used our results to inform a series of workshops in which stakeholders developed and agreed on new management strategies that were implemented by Parks Canada. Our research demonstrates the usefulness of Q method to illuminate people's perspectives and identify common ground in settings where conservation is contested.     

Bioluminescence in the high Arctic during the polar night

This study examines the composition and activity of the planktonic community during the polar night in the high Arctic Kongsfjord, Svalbard. Our results are the first published evidence of bioluminescence among zooplankton during the Arctic polar night. The observations were collected by a bathyphotometer detecting bioluminescence, integrated into an autonomous underwater vehicle, to determine the concentration and intensity of bioluminescent flashes as a function of time of day and depth. To further understand community dynamics and composition, plankton nets were used to collect organisms passing through the bathyphotometer along with traditional vertical net tows. Additionally, using a moored bathyphotometer closed to the sampling site, the bioluminescence potential itself was shown not to have a diurnal or circadian rhythm. Rather, our results provide evidence for a diel vertical migration of bioluminescent zooplankton that does not correspond to any externally detectable changes in illumination.     

Mobilization of arsenic and other trace elements of health concern in groundwater from the Salí River Basin, Tucumán Province, Argentina

The Salí River Basin in north-west Argentina (7,000 km²) is composed of a sequence of Tertiary and Quaternary loess deposits, which have been substantially reworked by fluvial and aeolian processes. As with other areas of the Chaco-Pampean Plain, groundwater in the basin suffers a range of chemical quality problems, including arsenic (concentrations in the range of 12.2–1,660 μg L⁻¹), fluoride (50–8,740 μg L⁻¹), boron (34.0–9,550 μg L⁻¹), vanadium (30.7–300 μg L⁻¹) and uranium (0.03–125 μg L⁻¹). Shallow groundwater (depths up to 15 m) has particularly high concentrations of these elements. Exceedances above WHO (2011) guideline values are 100% for As, 35% for B, 21% for U and 17% for F. Concentrations in deep (>200 m) and artesian groundwater in the basin are also often high, though less extreme than at shallow depths. The waters are oxidizing, with often high bicarbonate concentrations (50.0–1,260 mg L⁻¹) and pH (6.28–9.24). The ultimate sources of these trace elements are the volcanic components of the loess deposits, although sorption reactions involving secondary Al and Fe oxides also regulate the distribution and mobility of trace elements in the aquifers. In addition, concentrations of chromium lie in range of 79.4–232 μg L⁻¹ in shallow groundwater, 129–250 μg L⁻¹ in deep groundwater and 110–218 μg L⁻¹ in artesian groundwater. All exceed the WHO guideline value of 50 μg L⁻¹. Their origin is likely to be predominantly geogenic, present as chromate in the ambient oxic and alkaline aquifer conditions.     

Influence of residency and social odors in interactions between competing native and alien rodents

Residency status of individuals in populations may be an important determinant of the outcomes of interspecific competition between native and introduced species. We examined direct behavioral interactions between two similarly sized rodents, the alien Rattus rattus and native Rattus fuscipes when they were respective residents and intruders in a small enclosure. Resident individuals were dominant in their behaviors toward intruders irrespective of the species that was resident. In contrast, interactive behaviors between conspecifics were often neutral or amicable, supporting suggestions that R. rattus and R. fuscipes are social animals. We then tested whether rodent species use heterospecific odors to avoid aggressive competitive interactions and partition space in the field. Neither R. fuscipes nor R. rattus responded to traps scented with the odors of male or female heterospecifics. If R. fuscipes does not recognize the odor of introduced R. rattus, then odors will not be cues to the presence or territorial space of competing heterospecifics. Rather, findings from both enclosure and field trials suggest that direct aggressive interactions between individual R. rattus and R. fuscipes probably facilitate segregation of space between these two species in wild populations, where resident animals may typically be the winners and exclude heterospecific intruders. These findings have implications for the invasion success of introduced rodents such as R. rattus into intact forests, where native populations may have competitive advantage because of their residency status.     

Development of a new standardised method for sustainable monitoring of the vulnerable pink sea fan Eunicella verrucosa

The aim of this survey was to test a standardised method to follow the demographic evolution of a dense aggregative ‘forest’ population of the temperate gorgonian Eunicella verrucosa (Octocorallia, Gorgoniidae) using in situ photographic recordings. Distribution, density, growth and demographic evolution of the colonies was compared along two parallel transects. Computer treatment allowed the estimation of the total branch fan surface area, and the individual growth of tagged colonies was determined by measuring the increase in this surface area, using consecutive photographs taken at two-year intervals. To integrate the potential bias of branch overlapping, we proposed a correction factor between the in situ photographic surface area and the surface area of the gorgonian calculated from ex situ photographic surface area with all branches deployed. The surface-frequency distribution of colonies was converted to estimated-age-frequency distribution using an estimated growth curve based on the net growth rate. The technique used revealed significant differences in population structure and the dynamics of gorgonian colonies, as the two transects appeared to be influenced by different environmental conditions. The recruitment also seemed to vary according to year and transect, resulting in different densities. Our work showed clear results in characterising the variations of gorgonian demographic evolution at a small spatial scale; thus, it is assumed that this method could be a sustainable tool for coastal environmental managers.