Corals are Wonders of Nature

Corals are the most amazing wonders of the nature. They come in variety of shapes and sizes and they are the flowers and rain-forest of the sea. And people always ask if corals are animals or plants. More amazingly they are quite both if you consider algae as plant, but infact they are animal. The algae that gives the coral its colors and provides food for the animal coral, is called a zooxanthellae. The zooxanthellae gains protection and nutrients in return. this relationship is an example of symbiosis.
Corals generally feed at night using their tentacles to capture food. Their bodies are connected so they share their food.

Corals may be both female, male or both and they can reproduce sexually or asexually. Asexual reproduction often occurs involuntarily where several parts of a fractured colony can form new colonies. Corals reproduce sexually once or twice a year, in mass spawning events. Below are some examples of corals.



Platygyra lamellina



Stylophora pistillata



Acropora humilis



Acropora gemmifera



Plerogyra sinousa

CNIDARiANS - Anthozoans

A leather sea anemone (Photo: Simeon Daple.)

ANTHOZOA

Anthozoans are exclusively marine, polypoid cnidarians. They include the familiar sea anemones, and other anemone-like groups with skeletons (such as the "stony" scleractinian corals) and without skeletons (such as tube anemones), as well as sea pens, sea fans, blue coral, and black coral. Anthozoans occur from the intertidal zone to the depths of the trenches (to 6000 m). In excess of 6000 species currently exist (Hyman 1940), comprising about two-thirds of extant cnidarian species (Dunn 1982); some anthozoans, such as the scleractinian corals, have a rich fossil history (Wells and Hill 1956).
As in all cnidarians, the body wall is composed of two cell layers—the outer ectodermis (or epidermis) and the inner gastrodermis—separated by a layer of gelatinous material known as mesoglea or mesenchyme. Tentacles bearing stinging cells surround the mouth, which is the only opening to the digestive system. A polyp is essentially a tubular sac, with the mouth and tentacles on a flattened upper surface called the oral disk. The mouth leads to a pharynx, a short tube projecting into the closed gut (the coelenteron or gastrovascular cavity). The pharynx typically has one or more ciliated grooves (siphonoglyphs) that funnel water into the coelenteron. The coelenteron is subdivided into chambers by vertical septa (or mesenteries), infoldings of the gut wall that may or may not attach to the pharynx. Below the pharynx, the free edges of the septa are thickened to form septal, or mesenterial, filaments that contain cells involved in digestion, including nematocysts. The tentacles are hollow and continuous with the coelenteron.Most anthozoan orders contain exclusively colonial species.
Anthozoans may be either solitary or colonial. In colonial species, the polyps are united by living tissue, the coenenchyme, and their gastrovascular cavities are joined by canals or tubes. Actiniarians and ceriantharians are exclusively solitary, and the octocorals and antipatharians are exclusively colonial, but the remaining orders have both types of morphologies. Solitary polyps are commonly 0.5–2 in (1–5 cm) in diameter at the oral disk, but the largest species grow to 3 ft (1 m) across. Polyps of colonial species are typically much smaller (<0.4 in (5 mm)), but the colonies themselves can be quite large.


Stichodactyla mertensii (Photo: Selma P.)

Feeding ecology and diet

Most anthozoans are suspension feeders whose diet consists of small planktonic invertebrates, phytoplankton, bacterio-plankton, or other suspended organic matter. Their methods of prey capture are generally, though not exclusively, passive. Drifting prey may be captured when it comes in contact with the extended tentacles of anthozoan polyps. Prey capture may also involve the firing of cnidae. Many scleractinians produce a slimy mucus that covers the polyp and traps floating and sinking food particles. The mucus is moved around by cilia (small hairlike projections), and eventually enters the mouth. Large sea anemones may feed on crabs, bivalves and fishes, while ptychodactarian anemones have been observed preying upon gorgonian octocorals. In 1997, colonies of the soft coral Gersemia antarctica were first reported to bend over and feed in the soft sediments of the Antarctic. Researchers proposed that this feeding strategy may be employed where suspended organic material is in low supply, as it is in the deep sea. Some anthozoans also may absorb dissolved organic matter directly from the seawater into their cells.
Another source of nutrition for many anthozoans comes from symbiotic photosynthetic algae living within cells of the gastrodermis. Like other plants, these algae produce energy-rich organic molecules through photosynthesis; between 20% and 95% of this production is transferred to the host. These symbionts are usually dinoflagellates, called "zooxanthellae"; however, green algae symbionts ("zoochlorellae") are also known. Most shallow-water, reef-building corals contain zooxanthellae, and they also may be found in tropical gorgonians, anemones, and zoanthids. The zooxanthellae are additionally thought to increase the rate at which scleractinian reef corals produce their calcium carbonate skeleton.



Reproductive biology

Anthozoans display a wide range of reproductive strategies. Asexual clones may be produced in a variety of ways. Polyps may undergo fission in either a longitudinal or transverse direction. Many sea anemones produce clones by pedal laceration, wherein pieces of the pedal disk tear off or break free and develop into new individuals. The growth of anthozoan colonies may be considered a mode of asexual reproduction. After a free-living larva settles, it metamorphoses into a polyp that repeatedly divides to give rise to additional polyps, all of which remain connected by living tissue. In some species, budded polyps may be released from the parent colony, and these then settle and develop a new colony. Anthozoans, particularly colonial species, also may reproduce by fragmentation. For many scleractinian corals, damage caused by storms or strong wave action may produce fragments that lead to new colonies.
Anthozoans may be gonochoristic (having separate sexes) or hermaphroditic. In colonial species, gonochoristic colonies are composed entirely of male or female polyps, whereas hermaphroditic colonies may have both male and female polyps ("monoecious") or hermaphroditic polyps. Polyps lack well-defined gonads; rather, the gametes accumulate in the gastrodermis of some or all mesenteries. The gametes are typically shed into the gastrovascular cavity and are either released through the mouth for external fertilization ("broadcast spawners"), or eggs are retained for internal fertilization and the embryos released through the mouth at a later time ("brooders"). Brooding species may hold the embryos internally within the gastrovascular cavity or externally in a coat of mucus on the polyp's surface. Anthozoan embryos develop into ciliated planula larvae that may or may not feed, and that can stay in the water column for days to weeks. Contrary to initial assumptions, some species also can produce larvae asexually.
There Anthozoa includes Cnidaria that have no jellyfish stage. This is the largest class of cnidarians, containing over 6,000 species. A gullet extends for a short distance into the gastrovascular cavity, and septa are present, which increase the surface for digestion and absorption. Anthozoa are flower animals, including a great many beautiful and colorful organisms, e.g., the sea anemone, sea pansy, sea fan, and coral. Anthozoans are colonial or solitary organisms.

CNIDARIANS - Hydrozoans and Sea Jellies

Mastigias papua - Papuan sea jelly (Photo: Selma P.)

The Phylum Cnidaria is a large group of over 10 000 species that includes hydroids, sea wasps, hard corals, soft corals, sea fans, corallimorphs, sea anemones, sea pens, black corals and zoanthids. All Cnidarians have tentacles with stinging cells in their tips which are used to capture and subdue prey. In fact, the phylum name "Cnidarian" literally means "stinging creature." The stinging cells are called cnidocytes and contain a structure called a nematocyst. The nematocyst is a coiled thread-like stinger. When the nematocyst is called upon to fire, the thread is uncoiled, and springs straight. The harpoon-like thread punctures through the cnidocyte wall and into the prey. Most Cnidarians also have a toxin in their stinger which helps to disable the prey. The nematocyst is fired either by the tentacle touching something, or in some cases by a nerve impulse from the animal telling it to fire.

Mastigias papua -Papuan sea jelly (Photo: Selma P.)

Hydrozoans
Hydrozoans include hydrocorals; hydroids, or sea ferns and floating sea jelly. Some are solitary, meaning that they live alone, but some are colonial, meaning that they live in groups, connected together with living tissue, and share food resources.

Hydrocorals have calcareous skeletons and look like hard corals.


Millepora sp.- Fire Coral (Photo: Simeon Daple)

Sponges

An unidentified species of Sponge ( Photo: Maunoa Karo)

Sponges are aquatic animals which mostly found in marine waters, though some of them inhabit freshwater lakes. The sponges come under the phylum porifera. Their form can resemble barrels, volcanic mounds, baskets, or encrusting sheets.
The sponges do not have muscles, nerves, mouths or body organs and their bodies are delicate and filled with a soft substance known as mesohyl, resembling jellies. Being aquatic creatures, their body allows them to absorb fluids, water, oxygen and food, with ease.

An interesting thing to note about sponges is that they don't have a digestive, circulatory or nervous system. They extract the food out of the water entering their body through pores. Since sponges need some kind of a substrate, such as rocks to remain stable in the sea, they are sessile - sedentary organisms. There are more than 7000 sponge species and possibly more of them would be discovered in the future. The different forms of sponges are encrusting-sheets, mounds, tubes and upright-sheets.

Sponges primarily feed on bacteria, but in some cases microbes live inside their bodies as endosymbiont - an organism living in symbiosis with its host, and inside its body. Some sponges have also turned into carnivores, where the food availability is scarce.



Spheciospongia vagabunda commonly found in shallow waters, in seagrass beds or sand.

Mangrove roots

All Plants and animals in the world has its method of adaptation to harsh environmental conditions. The root systems of mangroves are an example. The unique structure of the rooting system helps trapping sediment carried in the incoming currents and high tides. In the extended process, the vegetation regenerates the fine deposit into peaty soil, which work much protecting the land from abrasion. The environment where the plants thrive, is a wet, waterlogged swamp, which is inundated periodically for once or two times a day, or depends on the characteristics of local tidal periods.

The swamp has the anaerobic condition limiting the oxygen intake from the root. For this reason, the plants have physically developed their roots exposed to the air. Modified differently from other terrestrial vegetation, mangroves developed the aerating component. The above-ground part of the root system will enable the plants to allow the gas exchange process.



Xylocarpus roots



Xylocarpus roots




Rizophora stylosa roots



Xylocarpus roots



Nypa Fruticans roots

Mangrove seedlings establish soon after ripe fruits drop and drift away into a suitable environment, the closest fine sediment substrate they may get. The embryo often has developed since it is still attached to the parent plant. Sometimes even when tide doesn’t occur, the fruit just plops down into the soft mud under its parent plant and erects its first anchoring roots.

Seed of a Xylocarpus species

Besides forming the very important green belt of the island, mangroves also play the significant role as the nourishing ground and the roots has something to do with it. The intertwining root construction above the ground often keeps wave current at minimal which provides still and safe environment for larvae and juveniles of crustacean and other associated organisms to grow their early stages. Some bottom dwelling organisms such as mud crabs and worms burrow tunnels and enable oxygen circulation throughout the soil. Other bacterial organisms get advantage from rich nutrient as the consequence of decayed litters from the trees or entrapped sediment from the surrounding waters.

Ecological Degradation

It is intriguing to see the changes in the environment when there is to some extend an external disturbance to their surrounding ecological community.
The centrality of the theory of evolutions and the concept of geological time to modern biological and ecological thinking means that in the present context of accelerated extraction of forests and reef resources, the degradation and loss of natural virgin forests and reef ecosystems, scientists are collectively alarmed by the concomitant threats of biodiversity loss and species extinction. Some form of ecological degradation cannot be reversed. Example, from a rich virgin forest to grassland or desert, and corals disappear replaced by macro-algae, mostly species of Sargassum become dominant.

From hundred percent Coral cover (above) to seaweeds overgrowth (below).


From thick primary forest (above)to grassland (below).

Beauty of Papua New Guinea

Papua New Guinea is actually a paradise. Home to millions of named and unnamed creatures that are abundant from the Low lands to the Highlands. From the pristine coral reefs to thick foggy forest. Truly Papua New Guinea is a world of its own.



Turbinaria sp. Bootless Bay.

One of many Natural fresh water (Ph. Gilton Alimaka in Kimbe)

sarcophyton sp. the soft coral species photo was taken by the author at Bootless Bay, Central Province. Bootless Bay offers the best dive sites in Papua New Guinea.

Orchid show at the National Parliment (Ph. Selma P.)

Leptoria Phrygia, common in PNG coral reefs