sponge Sponges (Scientific name: Porifera) are simple aquatic animals with dense, yet porous, skeletons that are highly adapted to their environments. Mostly anchored to reefs or other hard surfaces, sponges are plant-like animals that live in water and survive by drawing water through small pours of their tubelike walls and expelling it through openings at the top, in the process filtering out the plankton it feeds on. Sponges can grow to the size of barrels. [Source: Henry Genthe, Smithsonian]s
Sponges are found in virtually all aquatic habitats, although they are most common and diverse in the marine environment. They are particularly associated with coral reefs. Sponges are found in a wide variety of colors, shapes, and sizes and are often mistaken for plants. Scientists believe that their varied colorations may protect them from the sun’s harmful ultraviolet rays. For a long times they were thought to be plants. Aristotle (384-322 B.C) was the first person to recognize that maybe they were animals. Still the idea of sponges were animals was not widely accepted until about 200 years ago. [Source: NOAA]
Sponges are mostly immobile, living attached to solid surface. Instead of organs or tissues that have colonies of cells that perform specific tasks. Sponges are colonies of single cells with a porous structure. Some sponges form spectacular, bright colored masses on reefs around the world. Most sponges live in salt water but a few species live in fresh water. Sponges belong to the phylum porifera, meaning "pore-bearing animals.” These are animals with porous bodies and specific cells for extracting plankton from seawater. The approximately 8,550 living sponge species are scientifically classified in the phylum Porifera, See Separate Article on Sponge Species
Sponges also provide a home for a number of small marine plants, which live in and around their pore systems. Some sponges have symbiotic relationships with crabs and shrimp that extract food as they clean algae and parasites and tend and prune the sponges themselves. Symbiotic relationships with bacteria and algae have also been reported, in which the sponge provides its symbiont with support and protection and the symbiont provides the sponge with food. Some sponges (boring sponges) excavate the surface of corals and molluscs, sometimes causing significant degradation of reefs and death of the mollusc. The corals or molluscs are not eaten; rather, the sponge is probably seeking protection for itself by sinking into the hard structures it erodes. Even this process has some beneficial effects, however, in that it is an important part of the process by which calcium is recycled. /=\
Websites and Resources: Animal Diversity Web (ADW) animaldiversity.org; National Oceanic and Atmospheric Administration (NOAA) noaa.gov; Fishbase fishbase.se; Encyclopedia of Life eol.org; Smithsonian Oceans Portal ocean.si.edu/ocean-life-ecosystems ; Monterey Bay Aquarium montereybayaquarium.org ; MarineBio marinebio.org/oceans/creatures; Websites and Resources on Coral Reefs: Coral Reef Information System (NOAA) coris.noaa.gov ; International Coral Reef Initiative icriforum.org ; Coral Reef Alliance coral.org ; Global Coral reef Alliance globalcoral.org ; Global Coral Reef Monitoring Network gcrmn.net
Sponges, Corals and Reefs
While sponges, like corals, are immobile aquatic invertebrates, they are otherwise completely different organisms with distinct anatomy, feeding methods, and reproductive processes. The main differences are: 1) Corals are complex, many-celled organisms. Sponges are very simple creatures with no tissues. 2) All corals require saltwater to survive. While most sponges are found in the ocean, numerous species are also found in fresh water and estuaries. [Source: NOAA]
Regardless of these differences, sponges are important inhabitants of coral reef ecosystems. A diverse sponge population can affect water quality on the reef as the sponges filter water, collect bacteria, and process carbon, nitrogen, and phosphorus. In nutrient-depleted coral reefs, some sponge species are thought to make carbon biologically available by excreting a form of “sponge poop” that other organisms feed on, thereby fueling productivity throughout the ecosystem. In this way, sponges protect the reef against extreme fluctuations in nutrient density, temperature, and light, benefiting the survival of other reef organisms.
A sponge’s skeletal type adapts well to its particular habitat, allowing it to live on hard, rocky surfaces or soft sediments such as sand and mud. Some sponges even attach themselves to floating debris! Rarely are they found completely free-floating. As water filters through a sponge’s porous exterior, the sponge gains some motion, receives food and oxygen, and dispels waste. Inside the sponge, tiny hairlike structures called flagella create currents to filter bacteria out of the sponge’s cells and trap food within them. Their strong skeletal structures help sponges withstand the high volume of water that flows through them each day.
History of Sponges — the World’s Earliest Animals?
white tine sponge Sponges are among the world's oldest creatures. Along with jellyfish they first emerged between 800 million and 1 billion years ago. They are more primitive than coral, sea urchins and jellyfish in that they don't have stomachs or tentacles and are regarded as the simplest of all living animals. Sponges with a clear fossil record date back to approximately 600 million years ago during the Precambrian) period of Earth’s history.
In August 2010, Adam Maloof at Princeton University and colleagues published a study in Nature Geoscience in which they said they found remains of ancient sponges dating to about 650 million years ago, making sponges the oldest known animals by 70 million years. The prior oldest known hard-bodied animals were reef-dwelling organisms called Namacalathus, which date to approximately 550 million years ago. Disputed remains for other possible soft-bodied animals date to between 577 and 542 million years ago. [Discovery News, August 2010]
Discovery News reported: At 650 million years old, the sponges would predate the Cambrian Explosion — a huge blossoming of diversity in animal life — by 100 million years. These organisms would also predate an intense moment in our planet’s history known as “Snowball Earth,” according to paleobiologist Martin Brasier. It’s even possible that they helped cause it. However, there may be controversy to come on this finding. The Australian reports on geologists from that country pooh-poohing the find by their American rivals and saying they have better and older fossils.
A few million years after the sponges were around a glaciation extended to the equator, wiping out large swathes of life. Brasier argues that in the absence of more complex creatures that can recycle debris, like worms, the carbon in early life forms got buried in a constantly growing carbon sink, sucking carbon dioxide out of the air and causing global cooling. Sponges would have contributed to such a cooling sink, he says [New Scientist].
According to Maloof, his team found the fossils by sheer accident: They were digging around in Australia for clues about the climate of the past, and first wrote off the finds as mere mud chips. “But then we noticed these repeated shapes that we were finding everywhere — wishbones, rings, perforated slabs and anvils. By the second year, we realised we had stumbled upon some sort of organism, and we decided to analyse the fossils. No-one was expecting that we would find animals that lived before the ice age, and since animals probably did not evolve twice, we are suddenly confronted with the question of how some relative of these reef-dwelling animals survived the “snowball Earth?” [BBC News].
The analysis itself was no picnic. To perform an x-ray or CT examination of fossils, you need to be looking at a fossil that has a different density than the surrounding rock. But the sponges were essentially the same density, forcing Maloof’s team to get creative. To get around this problem, the researchers used what Maloof called a “serial grinder and imager.” One of 32 collected block samples from the formation was shaved off 50 microns at a time — about half the width of a human hair — and then photographed after each minute shaving. The images were then stacked to create complete three-dimensional models of two of the sponge fossils [Discovery News].
Comb Jellies Not Sponges the World’s Oldest Animals?
In December 2013, sponges lost their crown as the world’s oldest animals when scientists from the University of Miami announced in the journal Science that a species comb jelly known as sea walnuts and sea gooseberries represented the oldest branch of the animal family tree based on DNA research. Associated Press reported: All animals evolved from a single ancestor and scientists want to know more about how that happened. More than half a billion years ago, the first split in the tree separated one lineage from all other animals. Traditionally, scientists have thought it was sponges. [Source: Malcolm Ritter, Associated Press, December 12, 2013]
“The evidence in favor of comb jellies comes from deciphering the first complete genetic code from a member of this group. Scientists were finally able to compare the full DNA codes from all the earliest branches. The genome of a sea walnut, a plankton-eating creature native to the western Atlantic Ocean, was reported online Thursday in the journal Science by Andreas Baxevanis of the National Human Genome Research Institute with co-authors there and elsewhere. The work supports some earlier indications that comb jellies were the first to branch off.
Sorting out the early branching of the tree could help scientists learn what the ancestor of all animals was like. But despite decades of study and the traditional view favoring sponges, there is plenty of disagreement about which early branch came first. The question is "devilishly difficult" to answer, and the new paper is probably not the last word, said Antonis Rokas of Vanderbilt University, who did not participate in the new work. "The results need to be taken seriously," he said, but "I'm pretty sure there will be other studies that suggest something else."
A study published in Nature in July 2021 suggested that mesh-like structures found 890-million-year-old rocks in the "Little Dal" limestones in northwest Canada were fossils of primitive sponges. If the claim holds up the sponges would predate the earliest undisputed animals by more than 300 million years. National Geographic reported: However, most claims of extremely old fossilized life kick up controversy. The creatures that flourished in ancient seas may have looked quite different than those that swim through oceans today, and scientists disagree about how much and which types of evidence can distinguish animals from other forms of life — or geologic structures. And the Little Dal fossils are no different. "What we have is essentially something a bit like a Rorschach inkblot test, where there are some squiggles in a rock," says Jonathan Antcliffe, a paleontologist specializing in early life at the University of Lausanne, Switzerland.[Source: Maya Wei-Haas, National Geographic Science News, July 29, 2021]
Elizabeth Turner, the sole author of the study, held up a mustard yellow natural bath sponge — a modern relative to the newly proposed fossil sponge. She pointed out the network of flexible tubes that give the sponge its squish, explaining that the mesh is "identical" to the newly analyzed fossils, as well as to several younger mesh-like fossils recently identified by other scientists. "It seems almost like a no-brainer," says Turner, a field geologist at Ontario's Laurentian University. But she acknowledges that the proposed animal identity will be controversial. "It's time for it to be published and go out to the community for discussion and challenge."
The newly described fossils were tucked in the nooks and crannies of the towering Little Dal reef. The structure formed at a time when warm, shallow seas flooded a vast tract of land through what is now North America Many sponges build their skeletons out of tiny rigid structures called spicules, which are made from calcium carbonate or silica and shaped like toy Jacks. In fossils, the structures provide telltale signs of early sponges, but keratosan sponges lack these rigid skeletons. Instead, they get their squishy structure from networks of the protein spongin, which has a soft, spring-like texture that is ideal for their modern use for bathing. By studying paper-thin sections of the rocks under a microscope, Turner documented the similarities of the tubular shapes and structures in the Little Dal samples to fossils that were previously identified as keratosan sponges, as well as to modern sponges.
Sponges have cells that carry out specialized functions but they do not form true tissues or organs. They have no sense organs or nerves but they can feel water through mechanisms in their cells. They are very good at regeneration. According to Animal Diversity Web: Sponges have cellular-level organization, meaning that that their cells are specialized so that different cells perform different functions, but similar cells are not organized into tissues and bodies are a sort of loose aggregation of different kinds of cells. This is the simplest kind of cellular organization found among parazoans. [Source: Phil Myers, Animal Diversity Web (ADW) /=]
Sponges lack a nervous system and therefore have little ability to communicate or perceive the outside environment. However, synchronized spawning events may imply a degree of communication between individuals, and research shows that these events may be coordinated by phases of the moon. There is also evidence that larvae have the ability to respond to light and polarized light as an indicator for determining the final location of settlement. While not confirmed one theory is that the posterior flagelar tuft which provides locomotor capabilities may contain pigment granules used for photoresponse. In experiments fire sponges responded to various stimuli through a reaction in their oscules. For example, a reduction in hydrostatic pressure caused partial oscular closure. Fire sponges were not affected by electric stimuli or by slight changes in pH of the surrounding water. Finally, stretching the oscule for short periods resulted in contraction; however, it did not contract if stretched for longer periods of time.
Other characteristics of sponges include a system of pores (also called ostia) and canals, through which water passes. Water movement is driven by the beating of flagellae, which are located on specialized cells called choanocytes (collar cells). Sponges are either radially symmetrical (symmetrical around a central axis) or asymmetrical. They are supported by a skeleton made up of the protein collagen and spicules, which may be calcareous or siliceous, depending on the group of sponges examined. Skeletal elements, choanocytes, and other cells are imbedded in a gelatinous matrix called mesohyl or mesoglea. Sponges capture food (detritus particles, plankton, bacteria) that is brought close by water currents created by the choanocytes. Food items are taken into individual cells by phagocytosis, and digestion occurs within individual cells./=\
The shape and size of spicules are a major characteristic used for classification and identification of sponges. Calhoun Bond and Albert Harris of the University of North Carolina Bond discovered that geometrical pattern of flow and propulsion of water through the interior of sponges is very different from what the textbooks say. This flow is analogous to the flagellar pumping of water through the category of invertebrate kidneys called nephridia; in other words, water is sucked from the mesohyl space between flagellated choanocytes, instead of being pushed along past the apical ends of choanocytes, as has always been assumed. Excurrent canals really do exist, but are closed at the end from which the water is being pumped. No incurrent canals lead to these excurrent canals, however, except to the extent that indentations sometimes occur in the outer surfaces of sponges. Water is pulled inward through holes in a special kind of surface cell, and then flows through the same "mesohyl" spaces where the spicules are located, before being sucked between choanocytes into the excurrent canals. This pattern of water flow can be made visible by feeding small particles to sponges, or by feeding them fluorescent beads, or by dissolving fluorescent dyes in their water.
Merging Sponges and Sponge Forms
Most sponges are tubes, closed at one end, but they can also take other forms such as spheres or branching structures. Sponges can become quite large. Some that grow as soft staple lumps onthe ocean floor can reach a size of one meter high and two meters across. According to Animal Diversity Web: Sponges have three different types of body plans, although these morphologies do not define taxonomic groups. Asconoid sponges are shaped like a simple tube perforated by pores. The open internal part of the tube is called the spongocoel; it contains the collar cells. There is a single opening to the outside, the osculum. Syconoid sponges tend to be larger than asconoids and have a tubular body with a single osculum. The synconoid body wall is thicker and the pores that penetrate it are longer, forming a system of simple canals. These canals are lined by collar cells, the flagellae of which move water from the outside, into the spongocoel and out the osculum. [Source: Phil Myers, Animal Diversity Web (ADW) /=]
The third category of body organization is leuconoid. These are the largest and most complex sponges. These sponges are made up of masses of tissue penetrated by numerous canals. Canals lead to numerous small chambers lined with flagellated cells. Water moves through the canals, into these chambers, and out via a central canal and osculum. Sponges in the class Calcarea, considered to be the most primative group, and have asconoid, synconoid and leuconoid members. The Hexactinellida and Demospongiae groups have only leuconoid forms. /=\
The bonds between sponge cells are very loose. Individual cells can dislodge themselves and crawl around the surface of a sponge. Sometimes two sponges next to each other merge and form a single organism. If a sponge is broken apart into individual cells, in many cases these cells will reorganize themselves into a sponge. If you break apart two sponges in this way they will reorganize themselves into a single sponge.
H.V. Wilson, of the University of North Carolina at Chapel Hill, Department of Biology, discovered that sponges will re-form functional individuals by sorting-out, even after having been mechanically dissociated into random mixtures of their several differentiated cell types. This led eventually to the discovery of specific cell adhesion molecules, including the cadherins and N-CAM. Sponge cells constantly undergo active rearrangements and migrations of cells from place to place, even when not dissociated. Calhoun Bond and Albert Harris of the University of North Carolina Bond and Harris also discovered that small sponges crawl. [Source:University of North Carolina]
Feeding Sponges and Their Toxic Defenses
Sponges feed by filtering tiny particles from the water, which are directed to pores on the animal’s surface by flagella. After entering the pores the water travels through a system of canals with specialized cells that strain food particles from the water and expel the water through large vents. The canal system is supported by an internal skeletons made of spicules (bits of silica and calcium carbonate) embedded in a strong protein known as spongin. Some sponges create incredible sophisticated lattices that seem beyond the means of colonies of single cells. How the cells orient themselves to create these structures is not known.
Most sponges depend on ocean currents to carry food their way and feed on diatoms, detritus and various kinds of plankton but some species eat tiny crustaceans. Sponges play an important role in the reef community by filtering matter suspended in the water, ensuring life-supporting sunlight can reach the reef's life forms. Because they are largely immobile the are dependent on their environment to bring them food.
Most sponges contains toxins to protect them from grazing fish and mobile invertebrates. Some species of sponges produce toxins that inhibit the growth of surrounding individuals. Without toxins the sponges are vulnerable and an easy meal for many fish and other sea creatures. Sponges also defend themselves with tough layers of skin and sharp spicules. Certain marine animals take advantage of sponge toxins and use the chemicals and sponges themselves for their own purposes. Some creatures place adult sponges on their bodies, where the sponges attach and grow. [Source: Phil Myers, Animal Diversity Web (ADW) /=]
Sponge chemicals also probably play a role in competition among sponges and other organisms, as they are released by sponges to insure themselves space in the marine ecosystem. Some sponges, emit a scent that crabs may be using to chemically mask or camouflage itself from predators like eels, which have terrible eyesight but are known to hunt through smell.
Contrary to what most people think, sponges are not completely stationary. They can crawl across the sea floor. Some species move around four millimeters a day by extending a flat foot-like appendages and dragging the rest of the body behind, often leaving pieces of their skeleton on their wake. Scientists have studied sponge mobility in tanks by outlining the position of sponges and measured how far they moved.
In April 2021, researchers announced in Current Biology that deep sea sponges in the Arctic Sea creep around and leave behind pieces of their bodies.Science reported: During an Arctic expedition, scientists aboard the icebreaker Polarstern surveyed an underwater mountain ridge, using a boat-towed camera and a remote-controlled aquatic vehicle. At depths between 1000 and 580 meters, beyond the reach of sunlight, the researchers observed a thriving community of sponges. They also found snaking trails of spicules — fragments of the sponge skeleton — connected to many of the creatures. [Source: Nikk Ogasa, Science, April 26, 2021]
The researchers ruled out gravity and currents as likely sponge-moving forces because many of the animals were plopped on the uphill ends of these trails, and because the site lacked evidence of strong flows. Instead, the sponges are moving on their own, the team concludes. The scientists believe the sponges sink their spicules into the ground and pull on them to haul their bodies forward. As the animals move ahead, the embedded spicules rip off their bodies, and a trail of skeletal fragments and fleshy bits forms behind. (You can see a zig-zagging spicule trail in the image above.) Laboratory experiments had shown some sponges were capable of this behavior, but no one had found evidence in the wild.
As for why the animals are crawling around in the first place, the researchers think it's a way to scavenge for food in the nutrient-scarce polar depths. Another possibility is that the sponges move to disperse their offspring, or that they build spicule trails to provide sponge larvae with surfaces to settle on.
Sponges are oviparous (young are hatched from eggs) and iteroparous (offspring are produced in groups). Some sponges are hermaphrodites; others are dioecious (male and female reproductive organs are in separate individuals) . Many: 1) are simultaneous hermaphrodites in which individuals have sex organs of both sexes and can produce both sperm and eggs even in the same breeding season; 2) employ both sexual and asexual reproduction; and 3) engage in internal reproduction in which sperm from the male parent fertilizes an egg from the female parent. Hermaphroditic individuals generally produce female eggs and male sperm at different times. [Source: Mary McCarthy, Animal Diversity Web (ADW) /=]
Sponges do not have true reproductive organs. They s reproduce in many different ways. Many species release clouds of eggs and sperm into the water from their large central cavity. The eggs and sperm unite, forming larvae that drift into the sea until finding a place to attach themselves and metamorphose. Other ways they reproduce include larval metamorphosis, differentiation of tissue, production of gemmules (internal buds found in sponges and are involved in asexual reproduction) and budding. In asexual reproduction the gemmules are an aggregation of mesohyl cells (cells that perform various functions after forming extracellular matrixes in collagen-like gels). Typically eight to 12 eggs are in each brooded group at the beginning of the reproductive period. The production of gemmules is seasonal and varies among species.
Sexual reproduction sometimes takes place in the gel-like mesohyl. Male eggs and sperm are released into the water by a sponge and taken into the pore systems of its neighbors in the same way as food items. Spermatozoa are "captured" by collar cells, which then lose their collars and transform into specialized, amoeba-like cells that carry the spermatozoa to the eggs. [Source: Phil Myers, Animal Diversity Web (ADW) /=]
Amoebocytes (motile, amoeba-like cells that transport nutrients between cells and transform into other cell types, and enable sexual reproduction) and choanocytes (cells with flagellum) have both been observed maturing into eggs and sperm. Sperm enter the sponge through the inhalant current and then fertilize the ova. A carrier cell, an amoebocyte, effects fertilization of the ovum so that not just sperm and ova are involved. Then the carrier cell and the sperm both reach the ovum, and form a cytostome, which engulfs both the carrier cell and sperm. This zygote then goes through radial holoblastic cleavage forming cells all similar in size and shape. Then the embryo forms a free-swimming larva, which eventually develops into the new sponge. [Source: Beau McKenzie Soares, Animal Diversity Web (ADW) /=]
Many times when unfavorable conditions occur sponges will resort to asexual reproduction. Marine sponges using asexual reproduction often employ amoebocytes cells, which attach themselves around the deteriorating sponge. Later epithelial cells (cells that cover surfaces) surround the amoebocytes, and when the deteriorating sponge is all gone a new animal grows from the clump of cells. Asexual reproduction is often by means of external buds. Some species form internal buds which can survive extremely unfavorable conditions that cause the rest of the sponge to die.
Sponge development is characterized by metamorphosis and indeterminate growth (they continue growing throughout their lives. In most sponges in which developmental patterns are known, the fertilized egg develops into a blastula, which is released into the water (in some species, release takes place right after fertilization; in others, it is delayed and some development takes place within the parent). The larvae may settle directly and transform into adult sponges, or they may be planktonic for a time. Adult sponges are generally assumed to be completely sessile (fixed in one place), but a few studies have shown that adult sponges in a variety of species can crawl slowly. [Source: Animal Diversity Web (ADW)]
Fire sponges are a sessile (fixed in one place) organism in the adult stage. In the larval stage they have flagellum and can swim to an appropriate location for settlement. However, the swimming abilities are rather limited and often the settlement site is determined by water currents and turbulence in the area. In similar sponge species larvae can swim several millimeters per second. Fire sponges are known for its ability to successfully over grow other sponge species when competing for space.
According to Animal Diversity Web: Often within the class Demospongiae, sponges brood embryos and eventually release parenchymella larvae. The larvae often have a flagella tuft which it uses to swim while finding a suitable space for settlement. Larvae can respond to light to a certain extent to guide their search but that their eventual settlement is largely attributed to the water currents and conditions. Once the larvae find a suitable substrate location they will settle and metamorphose into adults. This transformation and growth period involves four basic stages: the formation of functional areas including, choanocyte chambers, mesohyl, pinacoderms, ostia and the initial stages of oscules; maturation of functional tissues, increasing complexity of skeletal structure and canal system; remodeling of mature tissue; and the general increase in size. The growth rate of a sponge is largely dependent on the environmental conditions, specifically light, food and space. [Source: Mary McCarthy, Animal Diversity Web (ADW) /=]
Sponge-Derived Drugs and Commercial Uses of Sponges
Sponges that are sold commercial having the living organism removed so that only the spicules and spongin remain. Of the thousands of species of sponge only a dozen or so have been harvested for commercial uses. Even outside of Greece sponges have traditionally been collected by divers of Greek descent. Natural sponges have largely been replaced by synthetic sponges for commercial uses. Natural sponges are still used in things like surgery because they are softer and more absorbent than synthetic varieties. Deep water sponges have uses in fiber optics.
Commercially-used sponges include the yellow sponge, sheep-wool sponge, velvet sponges, grass sponges, glove sponge, reef sponge, wire sponge and hardhead sponges from the Caribbean and Florida, and turkey cap sponge, turkey toilet sponge, zimocca sponge, honeycomb sponge and elephant-ear sponge from the Mediterranean.
Chemicals derived from sponges have been found to have beneficial pharmaceutical effects for humans, including compounds with respiratory, cardiovascular, gastrointestinal, anti-inflammatory, antitumor, and antibiotic activities and applications. Some toxins have been important to understanding nerve impulse transmission. Other sponges contain antibiotic substances and pigments with medicinal applications. /=\
Sponges from tropical reefs contain analgesic and anticancer compounds. Possible cancer fighting agents have been found in compounds found sponges first studied in Fiji. A compound from a Caribbean sponge, discodermia, is in clinical trials for a treatment for pancreatic and other cancers. Another sponge-derived compound, Contignasterol, is being studied as an asthma treatment.
The study of virus-killing chemicals in a Caribbean sponge in the 1950s led to the discovery of the AIDS-fighting drug AZT as well as Acyclovir, used to treat herpes infections. These have been called the first marine drugs. Sponges have also yielded cytarabine, a treatment for a kind of leukemia.
Image Sources: Wikimedia Commons, NOAA
Text Sources: Animal Diversity Web (ADW) animaldiversity.org; National Oceanic and Atmospheric Administration (NOAA) noaa.gov; Wikipedia, National Geographic, Live Science, BBC, Smithsonian, New York Times, Washington Post, Los Angeles Times, The New Yorker, Reuters, Associated Press, Lonely Planet Guides and various books and other publications.
Last Updated May 2023