French fishing vessel Alf during a storm in the Irish Sea. Photo: UK Royal Navy/MOD (CC 2.0)
Closing the high seas to fishing could increase fish catches in coastal waters by 10%, compensating for expected losses due to climate change, finds a new Nippon Foundation-Nereus Program study published in Fish and Fisheries.
The high seas are those areas of the ocean outside the jurisdiction of countries; the high seas cover nearly two thirds of the ocean's surface. These results could be seen by 2050 relative to 2000 and cooperatively managing the high seas fisheries would have similar effects.
"The oceans are interconnected. Many important fish stocks live in both the high seas and coastal waters," says co-author William Cheung, Nippon Foundation-Nereus Program Director of Science. "Although the high seas may seem far from the coast, effective management of high seas fisheries could benefit coastal waters in terms of productivity and thus help reduce climate change impacts."
The study used a computer model to project catches of 30 important fish stocks that occur in both the high seas and coastal waters under two CO2 emission scenarios and three high seas management scenarios.
Strengthening high seas governance would also increase the resilience of coastal countries to climate change, especially in tropical countries where there is a high dependence on fisheries for food and livelihood. Under a "business-as-usual" CO2 emissions scenario, disproportionate impacts of climate change on countries in the South Pacific, Indo-Pacific, West African coast and west coast of central America include decreases of over 30% of fish stocks due partly to migration of fish towards cooler waters.
"The scenarios of closing the high seas may greatly reduce the issue of inequity of benefits and impacts among different countries under climate change," says co-author Vicky Lam, Nippon Foundation-Nereus Program Fellow at UBC.
The authors note that impacts felt in tropical countries will still be high though, even under best-case scenarios. Adaptation measures, such as diversifying employment opportunities or fishing a different type of fish, would need to be introduced.
But would it be possible to close the high seas to fishing?
"We recognize that it is a big challenge," says Cheung. "Our study suggests that both the effective management of the high seas or its closure are effective in helping coastal waters to reduce climate change impacts. Thus, it may be on a spectrum within these scenarios that would be possible."
"The findings of this paper suggest that the high seas can serve as a fish bank of the world by providing the insurance needed to make the whole global ocean more resilient," says Rashid Sumaila, OceanCanada Director and co-author of the paper. "By closing it to fishing or seriously increasing the effectiveness of its management, the high seas can help us mitigate and adapt to the effects of climate change on marine ecosystems."
Underwater soundscape may offer clues to coral health and aid reef conservation.
MIT-WHOI Joint Program Student Max Kaplan scuba diving over a coral reef in the Virgin Islands. (Photo by T. Aran Mooney, Woods Hole Oceanographic Institution)
A new study from the Woods Hole Oceanographic Institution (WHOI) will help researchers understand the ways that marine animal larvae use sound as a cue to settle on coral reefs. The study, published on August 23rd in the online journal Scientific Reports, has determined that sounds created by adult fish and invertebrates may not travel far enough for larvae --which hatch in open ocean--to hear them, meaning that the larvae might rely on other means to home in on a reef system.
"To keep a reef healthy, you need a constant supply of new larvae to repopulate animals that die off," said Max Kaplan, the lead author of the paper and a graduate student in the MIT/WHOI Joint Program in Oceanography. "How larvae find reefs has been a big question, though. We think sound may play a role in attracting them, but exactly how far away they can sense those sounds has not yet been accurately measured."
To address that problem, Kaplan and his PhD adviser, WHOI Associate Scientist Aran Mooney, a co-author on the paper, traveled to the Hawaiian island of Maui to make painstaking acoustic measurements of a healthy reef system. The pair focused their efforts on recording two different components of sound--pressure waves (the element of sound that pushes on a human eardrum), and particle motion (the physical vibration of the water column as a sound wave travels through it). The latter, Kaplan explained, is how the majority of fish and marine species detect sound, yet no previous studies have focused on recording it.
"Think of it like being at a loud concert--if you're standing next to a huge speaker, you effectively feel the sound as it vibrates your skin," Kaplan said. "Fish and invertebrates sense sound in a similar way." Species like squid, octopus, and shrimp, for example, can detect vibrations through nerves embedded in their flesh. Similarly, adult fish sense them through the motion of tiny bone-like structures called otoliths inside their skulls.
Although researchers in the past have detected reef sounds from many kilometers away, Kaplan says that most of those studies rely on a hydrophone, an underwater microphone, which can only detect pressure waves. In their Maui study, however, the researchers recorded particle motion as well, using a sensitive accelerometer alongside a hydrophone. The data the accelerometer provides is directly relevant to how marine organisms sense sound, said Mooney.
"Particle motion is really the relevant cue for marine animals," Mooney said. "When we're measuring pressure, we're measuring the wrong thing--it only gives a ballpark sense of what marine species hear. We think studying particle motion is a big step to figuring out how larvae find their way to a reef."
Using an accelerometer to measure that motion, however, comes with a few challenges, said David Mann, President of Loggerhead Instruments, which designs small accelerometers for marine research. "To sense particle motion, an accelerometer has to be able to move along with the water as the sound passes by. It can't be mounted rigidly on frame or on the bottom, but it also can't be allowed to drift loosely with the currents. It's a lot harder to use than a hydrophone."
Kaplan worked with Canadian company GeoSpectrum Technologies to fine-tune existing accelerometers for use in the study, then deployed them at multiple sites around the reef. Over three days, he and Mooney measured sound levels at dawn and mid-morning, placing the sensors at distances ranging from zero to 1500 meters away from the reef itself.
In doing so, the pair found that particle motion was much lower than expected, dropping rapidly below levels that most marine species can sense--even just a few meters away from the reef.
"It's possible that larvae are still able to use chemical signals from other animals to locate the reef, or maybe can read the currents to move towards shore," Kaplan said, "but based on this data, it seems unlikely that they'd be able to use sound to find the reef. That was a surprise to us."
Once larvae do locate a reef, Kaplan thinks sound may play an important role in finding a suitable location to settle down. Many species living on reef systems are extremely localized, he notes. For example, some damselfish species live their entire adult lives within one square meter, so finding the best possible location is key to their survival. "In cases like that, sensing sound on order of meters would make a big difference," Kaplan said. "If you hear sounds of your species instead of predators, you might be more inclined to settle in a specific spot."
The researchers's findings might also be useful for reef conservation efforts. Past studies have shown that larvae are attracted to reef sounds when played through an underwater loudspeaker, so Kaplan thinks that playing back recorded biological sounds at high volumes could be used to steer larvae to damaged reef areas.
"You'd have to boost sound levels by quite a bit to get the response you want, but it could be one solution," said Kaplan. "If we can figure out the hearing threshold of each species' ability to sense particle motion, we might be able to amplify that motion to make it audible to them at a distance."
Kaplan notes that the Maui study only covers one shallow reef, so further study is needed to gain a full understanding of how sound propagates from other types of reef systems. "Recording particle motion in the field hasn't really been done before," said Kaplan, "but now that we've worked out these methods, we can start to expand our work."
International team of researchers led by GEOMAR finds increased larvae mortality.
Increasing ocean acidification could double the mortality of newly-hatched cod larvae. This would put populations of this economically important fish species more and more under pressure if exploitation remains unchanged. For the first time ever, members of the German research network BIOACID have quantified mortality rates of cod in the western Baltic Sea and the Barents Sea under more acidified conditions which the fish may experience towards the end of the century. They integrated their results of two several-weeks long experiments in model calculations on stock dynamics. The various model scenarios showed that the recruitment could decrease to levels of one quarter to one twelfth of the recruitment of the last decades - a strong call for action for fisheries management.
As one of the most important commercial species in the North Atlantic, Atlantic cod (Gadus morhua) has been under intense fishing pressure for decades, causing stocks to shrink or crash. In the online journal PLOS ONE, an international team of marine researchers draws attention to another important stressor triggered by climate change: ocean acidification. When additional carbon dioxide (CO2) from the atmosphere dissolves in the ocean, the water gets more acidified - with negative consequences for the behaviour, growth and development of fish larvae.
In two independent experiments, scientists found that the mortality of cod larvae in the critical phase between hatching and the development of the gills was twice as high at elevated carbon dioxide concentrations than at current conditions. The experiments were conducted in Sweden and Norway as part of the German research network BIOACID (Biological Impacts of Ocean Acidification) and the EU BONUS project BIO-C3 („Biodiversity Changes - Causes, Consequences and Management Implications").
For the first experiment, fertilized eggs and larvae of cod caught in the Öresund were kept in the lab of the Sven Lovén Centre at the University of Gothenburg (Sweden) for six weeks. Some were held in seawater at ambient carbon dioxide concentrations, others were exposed to CO2-conditions that are projected to occur by 2100. Temperature, light and food densities remained at natural conditions. The second experiment was conducted with cod offspring from the Barents Sea in the Centre for Marine Aquaculture Tromsø, NOFIMA (Norway).
"Even though the experiments were conducted in two consecutive years at different research stations under different conditions in relation for example to food or tank sizes and with two different stocks, their results are surprisingly similar", explains first author Martina Stiasny, PhD student in the research unit Evolutionary Ecology of Marine Fishes at GEOMAR and in the unit for Environmental, Resource and Ecological Economics at Kiel University. "The daily mortality rate for cod from the Öresund under current conditions was nine per cent compared to 20 per cent under increased CO2 concentrations. For the Barents Sea stock, we found mortality rates of seven and 13 per cent respectively."
The scientists integrated these increased mortality rates into model calculations, which were based on the stock data of the International Council of the Exploration of the Sea (ICES), to calculate the number of cod that will enter the fished population. According to the scenarios, ocean acidification could potentially decrease recruitment to levels one quarter to one twelfth of today's numbers.
"Our results show for the first time, how ocean acidification can add up to the fishing pressure on stocks of a commercially important fish species", Dr. Catriona Clemmesen, head of the GEOMAR working group Larval Fish Ecology, points out. "The repercussions of the anthropogenic climate change need to be included into stock projections and considered in the management of fish stocks. Only this will enable us to define realistic limits for fishing pressure and to avoid overfishing and depletion of fish stocks". To retain the stocks, fisheries ought to adjust to climate change, advises first author Martina Stiasny. "Ocean acidification cannot be completely avoided anymore. But the bigger the stocks are and the more responsibly and sustainably fishing activities are, the bigger the recruitment will remain. This will in the long run not only allow for larger fisheries, but also helps stocks to better adapt to climate change and other anthropogenic influences."
Researchers used state-of-the-art computer model developed by UM Associate Professor Claire Paris.
An international team of scientists used a state-of-the-art computer model, a high-powered supercomputer, and five billion 'virtual' coral larvae to test Charles Darwin's 1880 hypothesis that marine species cannot cross the Eastern Pacific's "impassable" marine barrier. The team, which included University of Miami (UM) Rosenstiel School of Marine and Atmospheric Science Associate Professor Claire Paris, found that Darwin's theory still hold true today even under extreme El Niño conditions known to speed up ocean currents.
To trace the journey of coral larvae transported by ocean currents in the Eastern Pacific Barrier, a 4,000-mile stretch of ocean that separates the central from the eastern Pacific Ocean, researchers from University of Bristol and Penn State University used Paris' biophysical model on Bristol University's BlueCrystal supercomputer to simulate five billion model 'larvae' from 636 remote reefs traveling on ocean currents over a 14-and-a-half year period.
"This work wouldn't have been possible until recently because of the computer power, the climate data, and the probabilistic biophysical model necessary to find some robust modeling results," said Paris, a coauthor of the study. Paris' open-source software, called the Connectivity Modeling System, simulates the movement of larvae in the ocean by currents and incorporates aspects of their biology, such as development and death.
The simulations showed that even in extreme environmental events such as the 1997-1998 El Niño that speed ocean currents, coral larvae could not survive long enough to make the trip from coral reefs in the western and central Pacific to help corals in the east recover from recent environmental damage. The findings have also been confirmed by genetic analysis.
"Whether coral reefs can survive the pressure of climate change as well as local stresses will depend to a large extent on the ability of coral to reproduce and disperse; to replenish damaged populations, migrate from deteriorating conditions and colonize new frontiers," said Sally Wood, a coral reef researcher at the University of Bristol and lead author of the paper. "So it's important to map where coral are able to get to."
The results indicate that vulnerable coral populations in the eastern tropical Pacific have been completely isolated from the rest of the Pacific Ocean for at least the past two decades. The findings provide important information to conservation efforts for the economically and environmentally important coral reefs in the eastern Pacific Ocean.
"While genetic data can tell us the degree to which coral reefs are related, the model reveals the processes by which larval connectivity or barrier to their dispersal happens. This is important for effective conservation measures." said Paris.
Reefs provide habitats for one of the most diverse ecosystems in the world and they are extremely economically important for fisheries, coastal protection, tourism, the aquarium trade, and as sources for new pharmaceuticals. The reefs in the eastern Pacific that we study are particularly important because they survive in inhospitable conditions, and understanding how they do this could be critical when designing strategies for reef conservation as climates continue to change.
The team found that even during the record-breaking El Niño of 1998, coral larvae could not survive long enough to make the trip from reefs in the central Pacific to those in the east. These findings support the opinion of Charles Darwin, who considered this intimidating expanse of open ocean 'impassable' and counter recent arguments that the 'East Pacific Barrier' must be breachable since the same coral species are found on both sides.
Large carnivores play important roles in ecosystems by regulating populations of herbivores and other animals. Understanding how human activities affect the role of predators, particularly within human-modified systems such as agricultural landscapes, is, therefore, important. This study investigated how predator and prey populations were distributed in Transylvania, Romania, and assessed them in relation to human activities. The research highlights how relationships between large carnivores and people need to be considered as part of biodiversity conservation efforts, especially considering the successful recovery of several large carnivore populations within the EU.
Top predators are a key component of ecosystem function. Large predators such as the brown bear (Ursus actus) or grey wolf (Canis lupus) can control populations of deer and other herbivores by killing prey or changing herd behaviour. Fear of predators can cause herbivore herds to move more frequently or in smaller groups, for example, which can lead to changes in grazing patterns. Top predators may also affect the abundance of foxes and other small carnivores through competition for food and by direct killing. Human-dominated landscapes, such as agricultural land, can support top predators. Understanding the influence of humans on these predators (and their prey) has an important role to play in efforts to conserve and manage biodiversity.
In parts of Europe large carnivores are making a comeback and the reintroduction of mammal species can also be a part of conservation efforts such as ecosystem restoration or rewilding initiatives, such as Rewilding Europe. This study explored the relationship between humans and large carnivores in the foothills of the Carpathian Mountains in Transylvania, Romania, a traditional farming region that includes large areas of pasture and arable land as well as high forest cover and populations of large mammals.
To monitor the numbers of mammal species the researchers used camera traps in 138 locations, selected in relation to forest cover and within state-managed hunting grounds. Records of bear and wolf numbers were also used from the 35 hunting grounds within the study area. To explore the interactions between different groups of species and their habitats, the relative abundance of carnivores was then modelled in relation to surrounding land-use type, relative abundance of humans, prey (roe and red deer, Capreolus capreolus and Cervus elaphus), smaller predators such as red foxes (Vulpes vulpes) and large dogs used to guard livestock.
Between May and August 2013 (with individual cameras operating for between 20 and 29 days), the camera traps recorded 2 197 occurrences of roe deer, 388 of red foxes, 275 of humans, 120 of dogs, 94 of red deer, 76 of bears and 2 of wolves. As wolf and bear observations were limited, additional information on their numbers was obtained from the 35 hunting grounds and added to the analysis. Humans and top predators (dogs, wolves and bears) had a stronger influence on the occurrence of other species than did the surrounding land use. As expected, the presence of humans limited all other species apart from dogs. Wolves limited the presence of red deer and this effect was three times stronger than the positive effect of the availability of pasture. Bears limited the presence of roe deer and the surrounding land use was also a key determinant for bears, which were found in areas of higher forest and lower pasture cover.
The research shows that top predators can maintain their important role as limiters of herbivore populations in agricultural landscapes. However, as human activities limited the presence of all other mammal species in this study, humans may have a stronger influence on ecosystem processes and species densities than other top predators. For example, human effects on red deer densities were 4.6 times greater than the effect of wolves. As well as direct killing of predators and deer through hunting, humans can alter habitats and densities of wild species, e.g. by using land for agriculture
The researchers point out that humans do not fulfil the same ecological role as bears and wolves in controlling herbivore populations. Suppression of bear and wolf numbers could, therefore, lead to increases in herbivores with knock-on effects on ecosystems, such as overgrazing and a reduction in tree regeneration. Species protection and management programmes cannot protect their target species or ecosystems without also accounting for human effects at all levels of the food pyramid. The researchers therefore recommend that human activity be considered an influential part of the ecological system, rather than being dealt with in separate analyses. This may be particularly important in areas of Europe which are seeing the return of native wildlife, including the wolf and bear, due to the success of conservation efforts such as the Habitats Directive.
Governance of biodiversity is closely linked to social and economic processes and human behaviour, appreciation of which can enhance conservation outcomes. This study reviewed findings on the social aspects of Natura 2000, identifying research gaps and recommendations for improving the network’s implementation across the EU. The researchers say limited stakeholder participation, negative perceptions of the network and a lack of consideration of the local context hinder the network’s effectiveness. They recommend increasing public awareness and compensating private landowners.
Traditionally, an interdisciplinary approach to conservation issues has been limited, as has collaboration between social and natural scientists. This is gradually changing as scientists are recognising the importance and ubiquity of human–environment interactions. The global watercrisis, for example, threatens both human societies and freshwater biodiversity. Similarly,climate change poses serious challenges to society and the environment.
With this in mind, successful conservation initiatives should consider human behaviour and social processes, as they ultimately influence biodiversity. Sustainable conservation initiatives should not only be based on the requirements of species and habitats but also consider economic, social and cultural factors. This is demonstrated by this study, which reviews social-science research with regard to a major conservation initiative: Natura 2000, the world’s largest coordinated network of protected areas. Although social, economic and policy research on the network is, to date, scarcer than ecological research, there is a sizeable body of research focusing on these aspects of Natura 2000. This paper is the first to comprehensively review these studies. The researchers focused on peer-reviewed literature published between 1998 and 2014, gathering a total of 149 publications.
One of the issues important to Natura 2000 that was identified by the review was public participation. Although the researchers identified a trend towards more inclusive approaches, stakeholder involvement was overall small scale and of low quality. Similarly, the findings revealed the importance of public perception of the establishment, operation and monitoring of the network: although the network was generally perceived as a useful approach for conservation, the review identified some negative perceptions of it, especially as a barrier to economic development.
Several studies also discussed a lack of flexibility in regulations, leading to decisions being made based on strict rules and not always being appropriate to the local context. As a result, the researchers recommended better transfer of knowledge from the EU to the local level (e.g. stronger links between EU policy and national, regional and local authorities), more qualified staff (e.g. to facilitate stakeholder participation) and enhanced funding.
In addition to identifying the complexities of the social aspects of Natura 2000, the authors also discuss knowledge gaps. In particular, they say more research is needed to evaluate the effects of participation on conservation (e.g. the extent to which it actually affects biodiversity and improves ecological, as well as social, outcomes). They also recommend efforts to increase awareness and acceptance of the network, such as educational and information initiatives.
Finally, the authors report that very few studies looked at the costs and benefits of the network, and they could not identify any comprehensive economic analyses. They — therefore — recommend research to quantify the benefits of the network and to develop indicators of its effectiveness, which they say are ‘urgently needed’ to evaluate Natura 2000. This could facilitate the design of compensation — such as reimbursement to owners of private land to cover the costs of complying with Natura 2000, such as changing the way they farm the land — which is, the authors suggest, one potential solution to improving the public perception of the network.
Overall, although Natura 2000 has been shown to be a successful conservation initiative, this review suggests there are some shortcomings. Although issues vary across EU Member States, there are some common challenges: limited public participation, negative public perceptions, inflexible regulations and authorities, low capacity of local authorities and insufficient consideration of the local context. The authors suggest social-science research could benefit implementation by highlighting the areas that need improvement and thus contributing to an ongoing ‘fitness check’ of the network.
It is important to note that this review only includes peer-reviewed scientific articles published in English and, therefore, could omit issues covered in other languages or in the grey literature. However, this review does present a reliable overview of knowledge and provides useful recommendations for improving the Natura 2000 network’s effectiveness, which could be used alongside existing local recommendations and guidelines.
Cape May National Wildlife Refuge is significant for a lot, but we cant talk about it without mentioning its importance to shorebirds. The refuge’s five-mile stretch along the Delaware Bay is a major resting and feeding area for migrating shorebirds and wading birds each spring. The Delaware Bay shoreline is a major shorebird staging area in North America second only to the Copper River Delta in Alaska! Each year hundreds of thousands of shorebirds stop to rest and feed during their spring migration from Central and South America to their Arctic breeding grounds. The arrival at Cape May of more than twenty shorebird species-primarily red knots, ruddy turnstones, sanderlings and semipalmated sandpipers-coincides with the horseshoe crab spawning season which occurs in May/early June. The crab eggs provide an abundant food supply, which these long-distance flyers use to replenish their energy reserves before moving on. In May, virtually the entire North American red knot population gathers along Delaware Bay beaches! LWCF has conserved 5486 acres of this Delaware Bay hot spot. Credit: USFWS
Batches of sand from a beach on the Delaware Bay are yielding insights into the powerful impact of temperature rise and evaporation along the shore that are in turn challenging long-held assumptions about what causes beach salinity to fluctuate in coastal zones that support a rich network of sea creatures and plants.
The findings have implications for the migration and survival of invertebrates such as mussels and crabs as global warming drives temperatures higher.
A first major study of the effects of evaporation on the flow of subsurface water and salinity, or salt content, in the beach intertidal zone - the section of the beach between the low and high tide marks - is being published today in Scientific Reports, an online affiliate of Nature.
The study, by New Jersey Institute of Technology's Center for Natural Resources Development (CNRDP) and led by two environmental engineers and a coastal geologist, shows that sediments from some sections of Slaughter Beach in Delaware have salt concentrations four times as high as the ocean water that washes over them. The finding came as a surprise.
The nearshore seawater the team measured had salt concentrations of 25 grams per liter (g/L), leading the researchers to expect that the subsurface water in areas of the beach it infiltrated would have similar or even lower levels as seawater mixes with inland groundwater in this zone. However, they discovered that the average salinity in the upper intertidal zone - the high tide line - was 60 g/L, with some values reaching as high as 100.
"These elevated levels can only be caused by evaporation, as there is no other mechanism for increasing the salt in pore water - the water trapped between the grains of sediment," said Xiaolong Geng, a postdoctoral fellow at NJIT and the principal author of the study, noting that the rates of evaporation - and salinity - are thus mainly determined by temperature and relative humidity, while tide and wave flows dilute a beach's salt content.
"Previous studies have identified seawater as the primary source of salinity in coastal aquifer systems, thereby concluding that seawater infiltration always increases pore-water salinity by seawater-groundwater mixing dynamics," said Michel Boufadel, director of the CNRDP, who is also an author of the study. "Based on what we learned, we think this finding should alter the way water management in coastal areas is conducted."
The team analyzed nearly 400 sediment samples collected during the sequential phases of a complete tidal cycle, from day to night, on seven discontinuous days.
The intertidal, or littoral, zone, is a dynamic habitat, washed by seawater at high tide and uncovered at low tide, that is favored by crabs, mussels and sea anemones, the birds and sea mammals that feed on them, and plants such as kelp. Many of these animals burrow in the beach to find food and to seek protection from predators and the action of waves, and are in near constant contact with pore water.
The researchers have developed models that show that increases in temperature associated with global warming will not only make inland locations more salty, but would also create drastically different pattern of pore water salinity that will have implications for animals and plants in the intertidal zone.
"Evaporation is an important driver of underground water flow and salinity gradients, and animals such as mussels and crabs are affected by changes in salinity. If the concentrations are too high or too low, they will move away," noted Geng.
Nancy Jackson, a professor of coastal geomorphology in the Department of Chemistry and Environmental Science and the study's third author, collected the beach samples from Slaughter Beach and provided interpretations of pore water dynamics.
The Almaco jack is a large predator fish, pictured here in the Caribbean. Credit: Abel Valdivia.
Coral reefs wouldn't be the same without their beautiful fish. A diversity of colorful, beautifully patterned species lives in tandem with coral reefs around the world, having adapted their appearance, body structure and lifestyle to take refuge in the folds of spiny, spongy, slippery reefs.
Recent studies suggest that coral reefs, however, are just as dependent on these fish for key nutrients that help coral grow. When fish urinate, they release phosphorus into the water. This phosphorus, along with nitrogen excreted as ammonium through the gills of fish, is crucial to the survival and growth of coral reefs.
A new study appearing Aug. 16 in Nature Communications takes this a step further, finding that in coral reefs where fishing occurs, nearly half of these key nutrients are absent from the ecosystem. The main reason? Fewer large-bodied and predator fish to pee nutrients into the water, the study found.
"Part of the reason coral reefs work is because animals play a big role in moving nutrients around," said lead author Jacob Allgeier, a postdoctoral researcher at the University of Washington's School of Aquatic and Fishery Sciences.
"Fish hold a large proportion, if not most of the nutrients in a coral reef in their tissue, and they're also in charge of recycling them. If you take the big fish out, you're removing all of those nutrients from the ecosystem."
Paper co-authors Abel Valdivia at the Center for Biological Diversity in San Francisco and Courtney Cox at Smithsonian Marine Station at Fort Pierce, Florida, surveyed 143 fish species at 110 sites across 43 Caribbean coral reefs that varied in the amount of fishing pressure sustained -- ranging from marine preserves that banned all fishing to heavily fished reefs where large predator fish are almost gone.
The researchers found that reefs with more large, predator fish had healthy levels of nutrients, while reefs depleted of large fish had nearly 50 percent fewer nutrients, including phosphorous and nitrogen, essential to their survival.
"This study is useful to understand alternative ways fishing is affecting coral reef ecosystems," Allgeier said.
The researchers determined that, despite the substantial reduction in fish-mediated nutrients, fishing didn't substantially reduce the number of fish species present. Instead, the large reductions in fish pee were driven by the reduction of large-bodied fish and predator fish such as grouper, snapper or barracuda that occurs through selective fishing practices.
"Simply stated, fish biomass in coral reefs is being reduced by fishing pressure. If biomass is shrinking, there are fewer fish to pee," Allgeier said.
The Nassau grouper, pictured center with stripes, is one of the larger fish that lives around coral reefs. Credit: Craig Layman.
Phosphorus in fish pee and nitrogen excreted through their gills are important nutrients for coral reefs to grow. In many reef communities, fish will take shelter in and around coral during the day -- peeing out valuable nutrients -- then forage for prey in and around the reef by night.
A Science paper in the 1980s showed that coral reefs where fish were present grew at more than double the speed of reefs where fish were absent. It was this study, undertaken by now emeritus research professor Judith Meyer at the University of Georgia, that inspired Allgeier to figure out why fish help coral reefs grow.
Coral reefs are the very definition of a delicate ecosystem. They are highly productive in terms of the biodiversity they support, but there aren't a lot of nutrients to spare. Reefs operate on what scientists call a "tight" nutrient cycle, meaning there must be an efficient transfer of nutrients for coral to grow. This cycle is largely controlled by fish, which hold nutrients in their tissue and then excrete them through their gills and urine.
Allgeier spent four years measuring the amount of nutrients in fish pee and fish tissue to eventually build a massive dataset that tracks fish size and nutrient output and the amount they store in their tissue.
As a graduate student, Allgeier's kitchen on Abaco Island in the Bahamas became his lab, and he caught hundreds of live fish, put them in plastic bags for half an hour, then measured the nutrients in the water before and after. He found that nitrogen output varied consistently with body size among all fish, and that carnivorous fish would pee more phosphorus than smaller herbivores.
Now, with these data serving as the basis for their models, Allgeier and collaborators can estimate the total amount of nutrient output from fish by knowing the species and body size of fish in a coral reef community.
"It's remarkable how robust the models are just from knowing fish size and species," he added.
Coral reefs continue to decline in the Caribbean and worldwide, but curbing fishing practices that target large predator fish could help reefs recover, Allgeier said.
The researchers expect this relationship between fish and coral exists in other reefs around the world. Allgeier is currently working with researchers at the University of California, Santa Barbara, to collect data next on fish pee in tropical Pacific Ocean reefs, essentially building upon the data collection Allgeier did as a graduate student.
Hardened shorelines reduce species diversity and abundance.
Shoreline hardening, defined as the installation of structures to prevent erosion or provide flood protection, is a common practice worldwide. Over 22,000 kilometers of shoreline have been hardened in the United States alone, and many major coastal cities, such as Hong Kong and Sydney, have 50% or more of their shorelines protected by artificial structures. With growing urban populations and rising seas, these trends are expected to continue. However, despite a growing chorus of conservation practitioners advocating for more nature-based approaches to coastal protection, the science on shoreline hardening's effects has failed to keep pace.
To address this shortcoming, a team of marine ecologists led by Rachel K. Gittman of Northeastern University conducted a meta-analysis of 54 existing studies on shoreline hardening. The results, described in the journal BioScience, highlight stark ecological effects of shoreline hardening and of seawalls in particular. "Biodiversity was 23% lower along shorelines with seawalls when compared with that of natural shorelines," observed the authors. Moreover, Gittman and her colleagues noted that overall organism abundance was 45% lower in seawalled areas.
The authors describe the possible mechanisms underlying this phenomenon, including the loss of shoreline habitat: "Because they are typically placed in the high intertidal zone, installation of a seawall and to a lesser extent, a riprap revetment, can sever the connection between upland and intertidal habitat, reflect wave energy and alter sediment transport, and potentially increase the depth of the intertidal and nearshore subtidal zones."
Despite this, one potentially encouraging finding was that biological diversity and the abundance of organisms were not demonstrably altered by other forms of shoreline hardening, such as riprap and breakwaters. The authors report that "some shore-protection structures may serve as surrogate habitats for native epibiota where natural hard substrates, such as oyster reefs and mussel beds, have been lost to overharvest, erosion, and poor water quality." However, Gittman and her colleagues caution that such structures may enable invasive species or have other unintended consequences: "In general, additional studies examining the ecological effects of riprap revetments and breakwaters are needed to inform future decisions on the consequences of selecting these types of structures."
Greenland sharks live for hundreds of years. Credit: Julius Nielsen.
While the more than 5 meter long Greenland shark is one of the world's largest sharks, it is also one of the least understood animals on our planet. The Greenland shark's general biology and way of life have been a mystery to biologists for many years. However, marine biologists at the University of Copenhagen have now deployed an epoch-making method to unveil one of the greatest of the mysteries surrounding this enigmatic shark - and have come to an amazing revelation: with a life expectancy of at least 272 years, the Greenland shark has the longest life expectancy of all vertebrate animals known to science.
More than 50 years ago, Danish fishery biologist Paul Marinus Hansen reported that Greenland sharks only grow a few centimeters over several years. Since then, researchers around the world could only speculate upon the lifespan of Greenland sharks. The question remained unanswered because the age of Greenland sharks cannot be determined using the traditional methods to determine the age of fish.
Carbon-14 dating of shark eye lenses
An international team of researchers, led by marine biologists at the University of Copenhagen's Department of Biology, has revealed one of the enigmatic shark's many secrets. Through carbon-14 dating, they have found a method to estimate the lifespan of Greenland sharks. Their dramatic results have now been published in the distinguished American scientific journal, Science. The sharks' eyes have hidden the main clue to their life expectancy all along.
The article's main author is PhD student Julius Nielsen of the University of Copenhagen's Department of Biology. He performed the study in close cooperation with the Greenland Institute of Natural Resources, Arctic University of Norway and Aarhus University.
"Our lifespan study is based on the carbon-14 dating of Greenland shark eye lenses. As with other vertebrates, the lenses consist of a unique type of metabolically inactive tissue. Because the center of the lens does not change from the time of a shark's birth, it allows the tissue's chemical composition to reveal a shark's age. We use well-established radiocarbon methods, but combine them in a new way. This approach, along with the extraordinary ages for these sharks makes this study highly unusual," according to Julius Nielsen.
Archaeological methods used to produce revolutionary results
The unique aspect of eye lenses has previously been used to discover the age of whales, but it is the first time that the carbon-14 dating of eye lenses has been used to estimate the life expectancy of fish.
Carbon-14 dating is primarily heard about in relation to archaeological dating. However, due to the incredible life-expectancy of Greenland sharks, it can also be used with them as well.
The study also marks an important milestone for the establishment of sustainable management plans for Greenland sharks. Julius Nielsen continues:
"Greenland sharks are among the largest carnivorous sharks on the planet, and their role as an apex predator in the Arctic ecosystem is totally overlooked. By the thousands, they accidentally end up as by-catch across the North Atlantic and I hope that our studies can help to bring a greater focus on the Greenland shark in the future."
Interdisciplinary collaboration Aarhus University researchers were responsible for the carbon-14 analyses, and the study is a good example of the synergistic effect that occurs when different research fields collaborate and make use of each other's competencies. The analyses based on these results are anchored in the complex interactions between atmospheric physics and fish biology. According to Jesper Olsen, of Aarhus University:
"This study of the Greenland shark's lifespan has been made possible due to the close cooperation between University of Copenhagen and Greenland Institute of Natural Resources biologists, with their knowledge of sharks, and Aarhus University researchers, with their carbon-14 dating expertise. While measuring the carbon-14 was unproblematic, the model used to date the longest and oldest of the Greenland sharks was challenging."
The Greenland shark lifespan study is part of a PhD project addressing the Greenland shark's general biology and runs for a period of 3 years. As such, the project also examined other aspects of Greenland shark's biology. The collection of Greenland shark specimens used in the study has been conducted over a number of years mainly from accidental by-catch during the Greenland Institute of Natural Resources annual fish survey but also from UiT Norway's Arctic University, DTU Aqua and University of Copenhagen research vessels. The international team of researchers behind the article in Science also includes researchers from National Aquarium Denmark/ Den Blå Planet, Oxford University (UK), Indiana University South Bend (US), and the Virginia Institute of Marine Science (US).
