HOW CANCER CELLS SPREAD TO THE BRAIN AND THRIVE

Holding On and Hiding Out: How Cancer Cells Spread to the Brain and Thrive

 

This image shows a breast cancer cell (green) clinging to a blood capillary (purple) in the brain.

Metastasis, the process that allows some cancer cells to break off from their tumor of origin and take root in a different tissue, is the most common reason people die from cancer. Yet most tumor cells die before they reach their next destination, especially if that destination is the brain. In people with lung cancer, for example, occasional tumor cells may enter the bloodstream and infiltrate the brain, but very few survive long enough to seed new tumors.

Now a team of Memorial Sloan Kettering scientists has looked into why most circulating tumor cells die upon reaching the brain and why, in exceptional cases, other cells don’t. Their latest study, published today in the journal Cell, identifies genes and proteins that control the survival of metastatic breast and lung cancer cells in the brain.

These survival factors might one day be targeted with drugs to further diminish people’s risk of metastasis. According to the study’s senior author, Sloan Kettering Institute Director Joan Massagué, a single mechanism is likely to enable cancer cells to colonize various organs, including the brain, in a number of disease types.

An Understudied Disease Type

Metastatic brain tumors occur in several types of cancer — including breast, lung, and colorectal cancer, among others — and are estimated to be about ten times more common than primary brain cancers. Until now, little research has been done into how metastatic brain tumors develop.

Dr. Massagué and his coworkers began to tackle this problem four years ago and have since learned that the brain is better protected than most organs against colonization by circulating tumor cells. To seed in the brain, a cancer cell must dislodge from its tumor of origin, enter the bloodstream, and cross a densely packed vasculature structure called the blood-brain barrier. Mouse experiments in which metastatic breast cancer cells were labeled and imaged over time revealed that a very small number were able to complete this journey, and of those cells that did make it to the brain, fewer than one in 1,000 survived.

“We didn’t know why so many of these cells die,” Dr. Massagué says. “What kills them? And how do occasional cells survive in this vulnerable state — sometimes hiding out in the brain for years — to eventually spawn new tumors? What keeps these rare cells alive and where do they hide?”

Dodging Death Signals

To answer these questions the researchers conducted experiments in mouse models of breast and lung cancer, two tumor types that often spread to the brain, investigating a panel of genes that have been linked to brain metastasis. Their research revealed that many cancer cells that enter the brain are killed by astrocytes — the most common type of brain cell — that secrete a protein called Fas ligand.

When cancer cells encounter this protein, they are triggered to self-destruct by the activation of an internal death program. The study also showed that the exceptional cancer cells that escape do so by producing a protein called Serpin, which acts as a sort of antidote to the death signals fired at them by nearby astrocytes.

Hugging Blood Vessels

The researchers used imaging methods to examine the behavior of these defiant metastatic cells in the brains of mice. They noticed that the surviving cells grew on top of blood capillaries — each cell sticking closely to its vessel “like a panda bear hugging a tree trunk,” Dr. Massagué says.

“This hugging is clearly essential,” he explains. “If a tumor cell detaches from its vessel, it gets killed by nearby astrocytes. By staying on, it gets nourished and protected, and may eventually start dividing to form a sheath around the vessel.”

Under the microscope, the researchers watched these sheaths grow into tiny balls, which eventually became tumors. “Once you’ve seen it, you can never forget this image,” Dr. Massagué says.

The scientists also did experiments to pinpoint the molecular basis of the cells’ behavior and showed that a protein produced by the tumor cells acts as a kind of Velcro, attaching the cells to the outer wall of a blood vessel.

Therapeutic Ideas

The findings give scientists new possibilities to understand and study the biology of metastasis, and could also lead to the development of new therapies that would work by strengthening the natural impediments to metastasis. The study identifies several mechanisms such drugs could target. Dr. Massagué is particularly interested in the ability of some tumor cells to hug blood vessels, as he suspects this behavior may be essential for the survival of metastatic cancer cells not only in the brain but also in other parts of the body where metastatic tumor growth can occur.

“Most cancer patients are actually at risk of having their tumor spread to multiple sites,” Dr. Massagué notes. For example, breast cancers can metastasize to the bones, lungs, and liver as well as to the brain. “What we may be looking at,” he adds, “is a future way to prevent metastasis to many organs simultaneously,” using drugs that make tumor cells let go of the blood vessels they cling to. 

STONEHENGE

Stonehenge Rock Source Identified

The site however raises further questions about how the stones were transported from their source to what is now the monument

Stonehenge monument in southern England

Scientists have found the exact source of Stonehenge's smaller bluestones, new research suggests.

The stones' rock composition revealed they come from a nearby outcropping, located about 1.8 miles (3 kilometers) away from the site originally proposed as the source of such rocks nearly a century ago. The discovery of the rock's origin, in turn, could help archaeologists one day unlock the mystery of how the stones got to Stonehenge.

The work "locates the exact sources of the stones, which highlight areas where archaeologists can search for evidence of the human working of the stones," said geologist and study co-author Richard Bevins of the National Museum of Wales. 

Mysterious megaliths

The Wiltshire, England, site harbors evidence of ancient occupation, with traces of pine posts raised about 10,500 years ago. The first megaliths at Stonehenge were erected 5,000 years ago, and long-lost cultures continued to add to the monument for a millennium. The creation consists of massive, 30-ton sarsen stones, as well as smaller bluestones, so named for their hue when wet or cut.

Stonhenge's purpose has long been a mystery, with some arguing it was a symbol of unity, a memorial to a sacred hunting ground or the source of a sound illusion.

But for decades, researchers agreed upon at least a few things. In 1923, geologist Herbert H. Thomas pinpointed the source of one type of the stones, known as dolerite bluestones, to a rocky outcropping known as Carn Meini on high ground in the Preseli Hills of western Wales. He became convinced the other bluestones (made from other types of igneous, or magmatic, rock) came from the nearby location of Carn Alw. That, in turn, lent credence to the theory that Stonehenge's builders transported the stones south, downhill, to the Bristol Channel, then floated them by sea to the site.

Different origins?

But a few years ago, Bevins and his colleagues found that at least some of the bluestones came from a slightly different region of the landscape, at lower elevation, called Craig Rhos y felin. If true, this would have meant builders would have to the stones uphill over the summit of the hills, then back downhill before floating them on rafts to the sea, Bevins said.

Another competing theory argues glaciers carried the bluestones to the general region of Stonehenge during the last Ice Age.

The researchers wondered about the origins of the dolerite bluestones that Thomas had identified, and took a second look at the mineral composition of the rocks. In general, when rock forms from molten magma, some minerals known as incompatible elements remain outside the crystallizing magma in residual magma, whereas others get embedded within the crystallizing magma. Past work identifying the origins of the rocks had used the presence of only a few incompatible elements, Bevins said.

In the new study, the team looked at the minerals, such as chromium, nickel, magnesium oxide and iron oxide, which are part of the crystallizing structures forming in the original magma. The researchers found that at least 55 percent of the dolerite bluestones came from a location, known as Carn Goedog, which is farther north than the location Thomas had proposed in 1923, and about 140 miles (225 km) away from Stonehenge, Bevins said.

That, in turn, made the raft-theory of transportation more unlikely, Bevins told Live Science.

Transportation mystery

The new findings raise more questions than answers about how the rocks could have made it to Stonehenge.

But pinpointing the exact location of the stones' origins could help archaeologists looking for other evidence of ancient human handiwork near the area, which could then shed light on the transportation method, Bevins said.

"For example, if we could determine with confidence that the stones had been worked by humans in Neolithic times, then the ice-transport theory would be refuted," Bevins said.

The findings were published in the February issue of the Journal of Archaeological Science.

Sunscreen for marine microbes

Most all of us are aware of the deleterious effects of too much sun exposure, specifically by ultraviolet radiation (UV). We know that UV-A and UV-B can damage our skin, resulting in a sunburn, but other organisms can also get too much sun exposure. For example, in microscopic plants known as phytoplankton, it can inhibit photosynthesis. Humans are not the only species that applies suntan lotion to prevent sunburns. Microbes all over the globe produce their own suntan lotion, called MAAs, to protect themselves from the sun’s harmful rays.

MAAs: The sunscreen for microscopic marine plants.

One strategy that phytoplankton and bacteria use to protect themselves is via the production of mycosporine-like amino acids, abbreviated MAAs, to act as a photo-protectant, much like the suntan lotion that we use to protect our skin. We use sunscreen to block UV-B (i.e. 290 – 320 nm wavelengths) and UV-A (i.e. 320-400 nm wavelengths) rays. Similarly, MAAs absorb electromagnetic radiation between these wavelengths. Although the chemical composition of MAAs is different than that of sunscreen, it offers similar protection. However, unlike man-made suntan lotions, scientists do not know the chemical composition of MAAs produced in the ocean and cannot predict the microbes’ response to varying UV radiation or environmental conditions.

The dinoflagellate Akashiwo sanguinea featured in this image is one of many phytoplankton species known to produce high concentrations of MAAs. Image taken by Françoise Morison using Flowcam® imaging.

The study site: Sub-Antarctic Zone and Polar Frontal Zone

Between January and February of 2007, aboard the RV ‘Aurora Australis’, scientists incubated phytoplankton at the sea surface for one to two days under different UV radiation treatments. Incubation experiments were conducted in marine waters to the southwest and southeast of Tasmania in the Sub-Antarctic Zone and in the Polar Frontal Zone, which are known to have high and low abundances of phytoplankton, respectively. Using phytoplankton from these sites was advantageous because it permitted scientists to see how different environmental conditions such as light, vertical mixing, and nutrient availability influenced MAA production.

Experimental set-up: Ultraviolet radiation treatments

Dr. Oubelkheir and his research crew wondered whether or not phytoplankton respond to changes in UV radiation by applying more sunscreen, meaning that they increase their MAA production. To test this question, Dr. Oubelkheir’s team phytoplankton to several treatments, consisting of natural surface irradiance, called photosynthetically active radiation (PAR), and ultraviolet radiation (UV), over an incubation period of two days. To create each treatment, they used three different materials, in which each was designed to vary the degree of UV exposure to phytoplankton. It was similar to testing UV effects on phytoplankton placed under three different kinds of sunglasses, ranging from protective to inefficient. The first material, UV-transparent Plexiglas, allowed the passage of UVA, UVB, and PAR. A more effective material to block the sun, Mylar-D, allowed the passage to UVB and PAR and an even more efficient screen, a UV opaque Plexiglas, only allowed the passage PAR. These experiments helped the scientists figure out how phytoplankton respond to UV radiation and in particular, to see if phytoplankton adapt to changing light conditions by altering MAA production. The graph below shows that the UV transparent Plexiglas (closed circles) allowed the passage of much more ultraviolet light compared to the UV opaque Plexiglas (open circles).

Fig. 2. Transmission of the UV transparent Plexiglas and UV opaque Plexiglas used for the incubation experiments between 250 and 450 nm.

In addition, scientists collected samples at different depths to measure the amount of UV radiation at each depth and the corresponding concentration of MAAs to determine its distribution in the sub-Antarctic waters and sub-tropical waters south of Tasmania.

The Findings

The researchers discovered that some species of phytoplankton naturally accumulate MAAs over time. In general, it appears that if phytoplankton are well-protected from ultraviolet radiation and only exposed to PAR – equivalent to a human using very efficient sunglasses to block out UV rays but let in natural light – MAA production is low. However, MAA production increases when the same phytoplankton are exposed to UVB radiation, and to a lesser extent by UVA radiation. Interestingly, Dr. Oubelkheir and his crew found that phytoplankton’s response to increased UV radiation can occur in as little as two days!

In addition, the phytoplankton response to ultraviolet radiation differed depending on location. Within the Sub-Antarctic Zone, incubated phytoplankton responded by producing similar amounts of MAAs across UV treatments. However, in the Polar Frontal Zone, the incubated phytoplankton responded very differently across treatments. The scientist attributed this difference to vertical mixing. In the Polar Frontal Zone, waters are deeply mixed to a depth of greater than sixty meters below the water’s surface. Here, phytoplankton are well acclimated to low UV radiation and are therefore not producing a lot of MAAs in the water column. It is only when they were brought to the surface for the two-day incubation, that they produced high concentrations of MAAs to protect themselves from UV radiation. In comparison, the stratified waters of the Sub-Antarctic Zone only have vertical mixing to a depth of about thirty meters. As such, the phytoplankton are already well acclimated to high UV radiations due to their high MAA production rates. Therefore, when the Sub-Antarctic phytoplankton were brought to the surface for the incubation experiment, MAAs production could not increase much more. The observations provide evidence that phytoplankton can adapt to increased UV by producing UV-absorbing compounds such as MAAs.

Changes in the types of phytoplankton present can also explain variability in MAA concentration. Previous research discovered that some species, like dinoflagellates, typically produce lots of MAAs, while others produce less MAAs. The present study found that a specific kind of MAA, called porphyra-334, dominated the Polar Frontal Zone, whereas palythenic acid, a different MAA, dominated north of the Sub-Antarctic Zone. The shift in the type of MAA was coincident with the presence of dinoflagellates and cyanobacteria. The figure below shows that as dinoflagellate and cyanobacteria concentrations increased, MAA concentration increased.

Fig. 10 Relationship between pMAAs (MAAs in the particulate fraction) and the chl a concentration associated with dinoflagellates-A (peridinin-containing dinoflagellates) and cyanobacteria in the SAZ-N.

 Significance

Each phytoplankton species respond differently to UV radiation. Just as some people are more sensitive to the sun than others, phytoplankton species differ in their sensitivity to UV radiation and in response seek out more or less sun protection by varying production of MAAs. The length of exposure to UV radiation, the amount of mixing, and the type of phytoplankton species present all contribute to how much MAAs get produced. The ability of phytoplankton use photo-adaptation processes has global implications regarding the primary productivity of our oceans.

Biomagnification of Natural Toxins

Ciguatoxins: Natural poisons hidden in algae

These days, it seems that eating seafood is fraught with danger. Numerous agencies provide guidelines to help us avoid pollutants like PCBs and mercury that accumulate in sea life. On top of that, natural toxins from the marine environment can also be a concern: poisons produced by some types of microorganisms can accumulate in marine life, just as pollutants do. These compounds can cause severe and sometimes fatal illnesses such as paralytic shellfish poisoning and norovirus.

One of the most common illnesses associated with eating seafood is ciguatera fish poisoning. While ciguatera is rarely fatal, it is incurable and has unpleasant symptoms that can last for days, week, or in some rare cases, years. These include nausea, headaches, and neurological symptoms such as numbness and hot/cold reversal (hot things feel icy cold, and cold things feel scorching hot!). Cooking does not lessen the risk of ciguatera, and it’s difficult to test for ciguatera-causing toxins (ciguatoxins) before consumption.

Gambierdiscus toxicus, the toxin-toting microorganism responsible for ciguatera poisioning (Source: http://www.livingoceansfoundation.org/)

What Causes Ciguatera Poisoning?

Ciguatoxins are produced by certain species of dinoflagellates(microscopic marine organisms) from the genus Gambierdiscus. These organisms live in benthic (seafloor) environments in equatorial regions. They are often found adhered to plants like algae and seaweed that would be attractive food for herbivorous and omnivorous fish.

Biotransformation and Bioaccumulation

When a fish ingests plant matter that contains Gambierdiscus, toxins from the microscopic organisms are stored in the fish’s body. Like persistent organic pollutants, these toxins are not easily excreted from the body, so they can accumulate over time as the fish continues to eat plants that contain Gambierdiscus. While accumulating in the body, these compounds can also undergo biotransformation, meaning that they are modified by biological processes. Transformed compounds are often similar in chemical structure, but can have strikingly different biological effects. 

We all know what happens next: big fish eats little fish. When large, carnivorous fish prey on small, herbivorous fish contaminated with ciguatoxins, these compounds travel up the food chain, bioaccumulating and biomagnifying in top predators. For this reason, the fish considered most likely to contain dangerously high levels of ciguatoxins are large, predatory reef fish like moray eels, groupers, and barracudas. Since the largest of these fish have lived the longest, it’s likely they will have accumulated even higher concentrations than smaller fish of the same species.

To minimize the risk of ciguatera, many countries have instated guidelines identifying high-risk fish, usually focusing on fish trophic level and size. However, our ability to actually predict which reef fish are safe and which are risky is rudimentary at best. It’s much more complicated than “big fish eats little fish”: food web dynamics in diverse reef ecosystems are poorly understood and highly variable depending on the specific region considered.

Many previous studies on ciguatera focused on the disease’s effects, measuring the toxicity of reef fish from at-risk regions. In this study, researchers focused on the causes of ciguatera by directly measuring levels of three specific ciguatoxins in fish and invertebrates of different trophic levels to determine which fish were most risky to consume and how ciguatoxins move through the reef ecosystem.

Methods

An island in the Republic of Kiribati

Researchers traveled to the Republic of Kiribati, a group of islands in the central Pacific Ocean where occurrences of ciguatera have frequently been reported. They identified two locations with a high abundance of Gambierdiscus, the toxin-toting microorganism, where toxicity due to ciguatoxins had previously been reported.

Blue-spotted grouper, known to carry ciguatoxins

The study focused mainly on the species of greatest concern – blue-spotted grouper, yellow-edged moray, and the giant moray – all large, top predator species. They also measured ciguatoxins in benthic crustaceans and herbivorous and omnivorous fish, aiming to analyze how concentrations of different ciguatoxins change with trophic level (an animal’s position in the food chain) and identify the species that are most effective at transferring toxins to top predators.

The researchers focused on three ciguatoxins called P-CTX-1, P-CTX-2, and PCTX-3, where P-CTX stands for Pacific ciguatoxin. These compounds are not the toxins initially present in dinoflagellates. Rather, they are biotransformation products that form once the toxins have been ingested by fish. Both PCTX-2 and PCT-3 are intermediate compounds that biotransform to become PCTX-1 within fish. PCTX-1, the most potent toxin of the three, does not transform any further. Scientists used an extremely sensitive analytical technique called liquid chromatography-tandem mass spectrometry (LC/MS/MS) to separate out and measure these three toxins in reef fish.

Ciguatoxins analyzed in this study

To trace the complex reef food web and determine who is eating who, researchers used a technique called nitrogen stable isotope analysis, in which they measure the amount of 15N relative to 14N in each fish species. 15N is generally known to transfer more efficiently from prey to predator, so that fish at higher trophic levels will have higher levels of15N relative to 14N. While the method isn’t flawless (some organisms scavenge, throwing off stable isotope readings, and there are other parameters that could affect 15N levels besides just trophic level) it provides some guidance when dealing with immensely complex marine food webs.

Results

In a few instances, researchers found different levels of toxins in organisms of similar trophic levels. For example, they found very low levels of P-CTX-1 in octopus and lobster, but they found no trace of any of the toxins in crab. All of these species eat at a similar level on the food chain, but they have different preferences: lobsters and octopuses are expected eat more crustaceans, while crabs may eat more clams and oysters.

Similarly, plant-eating fish that seemed to be of similar trophic level had different levels of the toxins. This data led the researchers to believe that understanding food choice – the specific type of plant a fish species prefers – is crucial in understanding how ciguatoxins transfer to upper trophic levels.

Concentrations of the three toxins measured, and their sum, in a range of species from the complex reef food web.

As expected, concentrations of ciguatoxins were generally higher in piscivorous (fish-eating) predators. Stable nitrogen analysis confirmed what researchers suspected: groupers and morays seemed to be top predators in the reef ecosystem, and concentrations of the toxins were generally highest in these species, even compared to other predators. Researchers compared trophic level to toxin concentration to determine whether they could observe biomagnification. They found that concentrations of P-CTX-1, the final biotransformation product, did indeed seem to increase from the lowest to highest trophic level, confirming that the toxin biomagnifies. The other intermediate products did not show evidence of biomagnification.

Next, the researchers set out to determine whether the biggest fish were really the most toxic. They found ciguatoxin concentration correlated well with giant moray length and weight: bigger, longer morays were more risky to consume. However, the relationship was not so straightforward in yellow-edged morays or blue groupers. Size and length of these fish did not effectively predict toxin levels. This may be due to complexities of the food web dealing with food choice, etc., that aren’t necessarily detected via stable nitrogen analysis.

Significance

Endangered Hawaiian monk seal, a top predator that could feed on tainted reef fish

Diseases like ciguatera poisoning post a risk not only to humans, but also to marine mammals like Hawaiian monk seals that prey on reef fish, many of which are endangered. A better ability to predict risk of ciguatera is crucial in regions like the Republic of Kiribati, where reef fishing provides food for local people and is an important aspect of the economy. Fish are often exported to many other nations, making ciguatera poisoning a global concern.

While this study confirmed what was already understood about ciguatoxins (they tend to be higher in top predators) it also highlighted many of the subtle complexities prevalent in this type of research: food web research is rarely clear-cut and researchers reported some unsuspected findings.

This study highlights how much more there is to learn about what makes a fish too toxic to eat. The simplified view is that “big fish eats little fish,” but real food chains are actually interconnected webs where different species have different dietary preferences and accumulation of hazardous substances can be difficult to trace. This research offers cautionary evidence avoiding larger fish is not a foolproof way to ensure safe seafood.

GREAT BARRIER REEF - AUSTRALIA

Australia permite el vertido de millones de metros cúbicos de barro en la Gran Barrera de Coral

El plan, propuesto por el ministro de medio ambiente, pretende crear el mayor puerto de carbón del mundo para dos empresas indias y un multimillonario local

 El organismo australiano encargado de supervisar la Gran Barrera de Coral ha dado este viernes 'luz verde' al vertido cerca del frágil ecosistema de tres millones de metros cúbicos de barro extraídos para crear el mayor puerto de carbón del mundo, plan que había sido propuesto en diciembre por el ministro de Medio ambiente, Greg Hunt.El vertido allana el camino a la expansión del puerto de Abbot Point para dos empresas indias y un multimillonario australiano, que tienen proyectos por valor de 16.000 millones de dólares (alrededor de 11.805 millones de euros) en la cuenca de Galilea, ubicada en la región de Queensland.Científicos y activistas ambientalistas habían pedido al organismo que rechazara la expansión del puerto argumentando que el mismo "tendrá efectos negativos en la Gran Barrera de Coral", según ha recordad la cadena de televisión australiana ABC."Los sedimentos de barro extraído podrían ahogar a los corales y los pastos marinos y exponerles a venenos y cantidades de nutrientes demasiado elevadas", sostuvieron en una carta enviada al presidente del organismo, Russell Reichert.Asimismo, Greenpeace ha advertido que el vertido supondría "una vergüenza internacional" que equivaldría "a tirar basura en el Gran Cañón del Colorado"."No tiraríamos basura en lugares Patrimonio de la Humanidad como el Gran Cañón o Ciudad del Vaticano, así que ¿por qué tirarla en la barrera de coral?", se ha preguntado.En este sentido, la Autoridad del Parque Marino de la Gran Barrera de Coral  ha sostenido que, pese a que reconoce las preocupaciones, la expansión de Abbot Point requerirá menos vertido que cualquiera de las opciones de expansión de otros puertos."Es importante destacar que el fondo del mar en la zona está compuesto por arena, limo y arcilla, y que no tiene corales ni pastos marinos", ha sostenido Reichert, según ha recogido la agencia británica de noticias Reuters.El permiso amenaza la pertenencia de la Gran Barrera de Coral, la principal atracción turística del país y que genera 5.700 millones de dólares anuales (unos 4.206 millones de euros) en la lista de Patrimonio de la Humanidad de la Organización para la Cultura, la Ciencia y la Educación de Naciones Unidas (UNESCO).El año pasado, el organismo pospuso hasta junio de 2014 su decisión de incluir la Gran Barrera de Coral en su lista de patrimonio "en peligro" o de incluso eliminarla de la misma.

OCELLS AL DELTA DE L'EBRE

Récord de aves acuáticas en el Delta de l'Ebre durante este invierno

Se han contabilizado 315.343, máximo valor registrado desde el inicio de este tipo de censo (1972)

Flamencos en les Salines de la Trinitat del Delta de l'Ebre Xavi Jurio

Deltebre (Tarragona). El censo invernal de aves acuáticas en el Delta del Ebro, con 315.343 ejemplares, ha alcanzado este año el máximo del registro histórico, iniciado en 1972, y se sitúa casi un 30% por encima de la media de los últimos 10 años.
El Parque Natural del Delta de l'Ebre realizó hace unas semanas el censo invernal de aves acuáticas en una operación en la que participaron una cuarentena de personas, entre personal técnico del Parque, miembros del cuerpo de Agentes Rurales y voluntarios.
Se trata de un censo que conlleva una gran complejidad, tanto por la diversidad de especies y de hábitats (arrozales, lagunas, río, salinas, bahías, humedales) como por la gran cantidad de aves.
Globalmente, se han contabilizado 315.343 aves acuáticas, máximo valor registrado desde el inicio de este tipo de censo (1972) y que se sitúa un 29,1% por encima de la media de los efectivos invernales de estos últimos 10 años.
El grupo más destacado ha sido el de las anátidas (51% de los efectivos) , en las que sobresalen el pato real, la cerceta y el pato cuchara, con 85.576, 28.865 y 24.260 ejemplares, respectivamente.
En los casos del ánade real y el ánade friso, con 6.428 ejemplares, se han alcanzado los valores máximos de toda la serie histórica. Por su rareza en Catalunya, destaca un ejemplar de pato glacial, uno de porrón buixot, cinco de porrón chocolatero y 9 de cerceta pardilla.
Los limícolas constituyen el segundo grupo de aves acuáticas mejor representado, con 80.830 ejemplares (26% del total). Este año se ha logrado, por quinto año consecutivo, el máximo absoluto de todo el registro histórico.
Por su abundancia, destacan el correlimos variante y la avefría, con 44.991 y 14.687 ejemplares, respectivamente. Sin embargo, el correlimos menudo, una especie que en los últimos años superaba los 9.000 ejemplares, este año se ha situado por debajo de los 5.600.
De entre las especies más accidentales, sobresale un ejemplar de dorada pequeña del Pacífico, otro de andarríos y 11 de correlimos de Temminck.
Los ardeidos han presentado resultados muy contrastados según la especie considerada ya que mientras que algunos, como la garza blanca y el martinete, han alcanzado máximos históricos, otros, particularmente la garceta y la garcilla, han mostrado significativas bajadas de un 30-40% en relación con los 10 últimos años.
Otras especies pertenecientes a grupos diversos y bien representadas en este censo han sido los 17.971 flamencos -máximo registro histórico- los 3.899 capones reales y los 100 picoplano.
La cuenta invernal de aves acuáticas en el delta del Ebro se integra dentro del International Waterbird Census (IWC), el cual tiene como objetivo cuantificar anualmente el número de aves acuáticas (anátidas, limícolas, ardeidas, fochas, etc) que hibernan en más de 80 países de Europa, Asia y el norte de África.
Los datos obtenidos permiten conocer a escala global el estado de conservación de estas especies y, a escala local, evaluar la capacidad de acogida de las zonas húmedas del Delta de l'Ebre.