Montipora australiensis (Bernard, 1897) is an encrusting scleractinian coral that exists in a range of morphologies and colours (Veron, 1993). This species is commonly found in tropicalreef environments with high wave energies at depths ranging from 2m to 30m (Veron J.E.N.,2016).M. australiensis has a broad distribution throughout the Indo-Pacific yet it is rare in this range (DeVantier,2008).This organism has an obligate, endosymbiotic relationship with zooxanthellae, gaining energy and nutrients from this relationship (van Oppen etal., 2004).Furthermore, M. australiensis is a hermaphroditic organism capable of sexual reproduction via broadcast spawning and asexual reproduction via fragmentation (Brusca et al.,2016).The IUCN Red List considers M.australiensis to be a vulnerable species. Specifically, the survival of this coral is threatened by habitat degradation, bleaching, sedimentation and pollution (DeVantier,2008).

Montipora australiensis is typically found as a growing, encrusting colony of coral polyps (DeVantier,2008).This species has a porous coenosteum and corallite walls, often causing thecoral to grow into elaborate structures as seen in Figures 1 and 2 (Veron, 1993). Montiporan corals possess the smallest corallites of all the coral families. Specifically, M.australiensis has corallites 0.5mm to 3mm in diameter (Veron J.E.N.,2016).M. australiensis exists in a range ofmorphologies and colours including brown, pink, green, blue, purple, yellow and grey (Veron and Stafford-Smith, 2000). Polyps of this coral are well-defined and closely arranged into a continuous colony. Additionally, M. australiensis has small tentacles which extend during night (Veron, 1993).

Montipora australiensis occurs in shallow, tropical reef environments with high wave energies. Moreover, M.australiensis can survive at a range of depths from approximately 2m to 30m(DeVantier,2008).

Like other members of order scleractinia, M. australiensis has an obligate endosymbiotic relationship with zooxanthellae. Clusters of these organisms produce pigments which give the coral its colour, as seen in Figure 3. Excess carbon dioxide is delivered to the zooxanthellae, while nitrogen and carbon is exchanged and received by the coral. Where some corals acquire zooxanthellae from the environment, transmission of zooxanthellae in M. australiensis occurs from parents to the eggs (van Oppen et al.,2004). M. australiensis is integral in reef formation and provides protection against predators and the environment for numerous organisms. Additionally, some organisms rely upon M.australiensis as a food source (DeVantier, 2008).

Reproduction:

Montipora australiensis has a range of reproductive strategies and is capable of both asexual and sexual reproduction. This species of scleractinian corals is hermaphroditic, with individual polyps possessing male and female gametes.Sexual reproduction in M. australiensis is achieved through synchronised broadcast spawning (Brusca et al.,2016).Specifically, individual polyps produce male and female gametes into the water column in buoyant bundles which rise to the surface, reducing the possibility of self-fertilisation(as seen in Figure 4). The synchronous release of M. australiensis gametes coincides with the spring tide. This ensures maximum fertilisation for the species (Maier, 2010).

Alternatively, M. australiensis is capable of asexual reproduction, most commonly through fragmentation. In this instance fragments of the coral are detached by mechanical forces or strong wave action and sink to the ocean floor. If the pieces land in suitable conditions and can adhere to the substrate, new colonies may form (Brusca et al.,2016).

Feeding and Nutrition:

M. australiensis utilises two methods to obtain nutrients necessaryfor survival. Montiporans are opportunistic carnivores, using their tentaclesto capture prey when they come into contact with the coral. M. australiensis also makes use of cnidaeto capture and immobilise their prey. Cilia are then used to transport the preyinto the coelenteron via the pharynx, allowing extracellular digestion to occur(Brusca et al.,2016).

Alternatively,M. australiensis has an endosymbiotic relationship with photosynthetic zooxanthellae. These endosymbionts are directly transmitted to the eggs of M.australiensis, meaning that the organism does not need to obtain zooxanthellae from the environment. Scleractinian corals can receive approximately half of their required energy through this symbiosis (van Oppen etal., 2004).

Movement:

Despite M.australiensis being a sessile organism, this species possesses a pelagic form during its reproductive cycle. Following broadcast spawning and external fertilisation in the water column, the combined gametes form a motile planula larva.The larvae use cilia in combination with chemosensory, magneto-sensory, and thermo-sensory structures to find an ideal location to settle and metamorphose (Brusca et al., 2016).

Respiration:

M. australiensis lacks discrete respiratory organs. Therefore,respiration occurs via diffusion through the body wall and tentacles.Specifically, montiporan corals utilise cilia to move fluid over the epidermisand gastrodermis (Brusca et al.,2016).

Project

Asexual reproduction and growth in Montipora australiensis polyps followingfragmentation.

Introduction:

Increased severity of weather events, such as storms and cyclones, are potentially damaging to coral populations such as Montipora australiensis. As a result of these events, the amount of fragmentation in coral reefs may also increase. It is established that colonial corals are able to regrow after a fragmentation event however, species specific investigation into M. australiensis’ rate of growth and reproduction has not been performed. It is therefore important to investigate the rate of corallite formation and polyp growth in the fragmented segments.

Method:

M. australiensis was manually fragmented using a hammer and chisel. The newly exposed surfaces were then monitored over a five-week period and the growth of new M. australiensis corallites and polyps was observed.

Discussion:

Over an observation period of five weeks M.australiensis displayed significant corallite formation and polyp growth.Specifically, Image B displays the initial formation of a new corallite on the newly exposed surface of the coral after three weeks (as seen in Figure 5). It must be noted that this structure is absent of flesh and is isolated in comparison with the surface with existing polyps. Moreover, Image C illustrates the condition of the coral fragment after five weeks of observation (as seen in Figure 5). At this stage of observation, the fragment has multiple corallites present that are distinctly formed. In addition, the corallites appear to be covered in a layer of flesh. It must be noted that this layer is conspicuously thinner and browner than the existing layer of polyps. The process of growth of new corallites in M. australiensis appears to be by extracellular budding, wherein separate polyps with individual corallites appear in the horizontal sheets of tissue called the coenosarc.

It must be noted that the rate and survivability of the coral post fragmentation is dependent on the conditions that it settles in. In this investigation, the fragment was kept in an aquarium setting ideal for growth and survival. Further studies into the rate of corallite formation in M. australiensis should be conducted in a natural setting over an extended period of time.

As shown in Figure 6, scleractinian coral polyps are tubular structures composed of two embryonic germ layers, the endoderm and ectoderm. These layers are separated by ectodermally-derived mesoglea. Additionally, polyps contain an inner gut sac,called a coelenteron, which is lined with gastrodermis (Brusca et al.,2016).Polyps are fundamentally radially symmetrical, organised around the oral-aboralaxis. The aboral end forms a pedal disc which is used to attach to the substrata.Polyps utilise a calcium carbonate skeleton composed of the calyx (base) and theca (side walls). The theca serves as the attachment point for the soft portions of the coral, such as the mouth and tentacles. Adhesive and stinging cells called cnidae lie on the tentacles surrounding the mouth and allow for predation and feeding. Digestive filaments line the coelenteron to aid in the digestion of captured food (Veron andStafford-Smith, 2000). Additionally, the gonads are protected and located within the gastrovascular cavity. Coral polyps can withdraw using retractor muscles, into a skeletal structure called the corallite. In M. australiensis, each corallite contains a single polyp, which sits within a series of horizontal sheets termed the coenosarc. This structure provides continuous connection of polyps thus forming a colony. Moreover, the coenosarc allows for the transmission of nutrients and water circulation (Brusca et al.,2016).

Montipora australiensis has a widespread biogeographic distribution yet is rare throughout its range. The IUCN red list specifies that M. australiensis is found in the central Indo-Pacific, the east China Sea, the oceanic west Pacific, Indo-West Pacific, and the southwest and northern Indian Ocean (DeVantier, 2008).

Specifically, as stated by the IUCN, M.australiensis is found in the waters surrounding the following countries (as shown in Figure 7): American Samoa, Australia, Chile, Comoros,Cook Islands, Fiji, French Polynesia, Indonesia, Japan, Kiribati, Madagascar,Malaysia, Mauritius, Mozambique, New Caledonia, Niue, Papua New Guinea,Philippines, Samoa, Seychelles, Singapore, Solomon Islands, Taiwan, Thailand, Tonga,Tuvalu, Vanuatu, Wallis and Futuna (DeVantier, 2008).

Phylum Cnidaria:

Cnidarians are diploblastic, radially or biradially symmetrical metazoans organised around an oral-aboral axis. At the level of tissue organisation, the cnidarians are diploblastic, possessing an incomplete, endodermally-derived gastrovascular cavity surrounded by an ectodermally-derived middle layer of mesenchyme. Cnidarians are defined by the presence of stinging cells called cnidocytes. These adhesive or stinging structures permit predation with the most common form being a nematocyst. Cnidarians possess true muscles formed by myoepithelial cells, a nervous system composed of a simple nerve net and a skeleton. Organisms in this phylum lack a central nervous system, cephalisation, and discrete respiratory,circulatory and excretory structures. Cnidarians exhibit alternation of motile medusoid and sedentary polypoid life stages. During sexual reproduction, a motile, ciliated planula larva is typically produced (Brusca et al.,2016).

Class Anthozoa:

ClassAnthozoa is the most diverse cnidarian class, containing over 6000 species (Veron, 1993). Organisms within Anthozoa are exclusively marine and exist as either solitary or colonial animals. This class is defined by its lack of a medusoid stage, meaning that all species exist exclusively in thepolypoid form. Anthozoans possess epidermal and gastrodermal cnidae in the form of spirocysts, ptychocysts and nematocysts. The majority of anthozoans are opportunistic feeders, utilising retractable tentacles to catch prey when they sense contact. The tentacles in these organisms contain extensions of the coelenteron,which is divided by longitudinal mesenterial filaments and surrounded by thick mesenchyme. Moreover, a stomodeal pharynx contains ciliated grooves (siphonoglyphs)that connect the mouth to the coelenteron. As anthozoans lack respiratory and excretory structures, gas exchange and excretions are achieved via diffusion. Polyps may be gonochoristic or hermaphroditic and are capable of both asexual and sexual reproduction. Gametes produced in sexual reproduction arise from the gastrodermis (Brusca et al.,2016).

Subclass Hexacorallia:

Hexocorallia is composed of solitary or colonial anemones and stony corals. Animals in hexacorallia exist either naked, with a chitinous cuticle, or with a calcareous skeleton. Internal mesenteries are paired, possessing longitudinal retractor muscles and occur in multiples of six. Additionally, mesenterial filaments are usually trilobed andciliated, bearing cnidocytes and gland cells. Cnidae in hexacorallia are diverse and endodermal zooxanthellae are profuse (Brusca et al.,2016).

Order Scleractinia:

Scleractinia is the largest anthozoan taxon containing 3600 species and is known as the stony corals. These organisms are primarily colonial but exist in a solitary form and produce an exoskeleton composed of calcium carbonate. Morphologies in Scleractinia range from small and delicate to large, calcareous skeletons. The polyp morphologies of scleractinia are nearly identical to order actiniaria. However, scleractinian corals lack siphonoglyphs and mesenterial filaments containing ciliated lobes. Scleractinian corals have a mutualistic relationship with zooxanthellae,whereby they exchange nutrients. Specifically, excess carbon dioxide is delivered to the zooxanthellae, while nitrogen and carbon is exchanged and received by the coral (Brusca et al.,2016).It is believed that order scleractinia originated 240 to 288 million years ago (Medina et al.,2006).

Family Acroporidae:

Family Acroporidae are commonly referred to as staghorn corals and are defined by the presence of a corallite at the tip of each coral branch. These organisms exist in a range of morphologies and colours and are central to reef structure and building. All members of acroporidae are hermaphroditic and utilise synchronised broadcast spawning. Additionally, these organisms are capable of asexual reproduction via fragmentations (Brusca et al.,2016).

Genus Montipora:

Montiporan corals display numerous different morphologies and colours. Some colonies of Montipora may even express more than one growth morphology (Veron, 1993). Montiporan corals are known to have the smallest corallites of any family and lack columellae. Moreover, these organisms possess porous corallites and coenosteum, resulting in intricate morphologies (Veron J.E.N.,2016).Polyps in montipora corals are only extended at night. Genetic investigations have revealed that the genus montipora is almost indistinguishable from Anacropora,with Montipora having evolved relatively recently in comparison (Veron, 1993).

Species M. australiensis:

Threats:

Montipora australiensis is exposed to many biotic and abiotic threats and is consequently categorised as vulnerable by the IUCN. Due to its rarity, M. australiensis does not have species specific population data available. Despite this, the conspicuous decline of overall coral reef habitat is used as a representation for the decline of M. australiensis populations (DeVantier,2008).

The most dominant threat to coral populations is increased temperature extremes due to global climate change. These events initiate bleaching, increased severity of El Niño and La Niña and cyclone events, intensification of disease susceptibility and acidification of the ocean. Species within the genus Montipora are particularly threatened by bleaching (DeVantier,2008).Continued temperature rises in the oceans have caused bleaching events to become increasingly frequent and severe, leading to amplified coral mortality and overall population decrease. Additionally, cooling temperatures that result from El Niño have been reported to cause coral bleaching. During periods of cooler oceanic temperatures,the photosynthetic efficiency and number of symbiotic dinoflagellates decrease,causing an increase in M. australiensis mortality(Saxby et al.,2003).

Crown-of-thorns starfish (Acanthaster planci), are a significant threat to M. australiensis,as they have been observed to preferentially predate upon reef-building corals such as the members of the Montipora genus. A.planci inhabits similar habitats to M.australiensis and is commonly found throughout the Pacific and Indian Oceans. Increased overall populations of A.planci have led to the complete removal of large areas of coral reef habitat.This trend has become a major threat to the survival of species such as M. australiensis as it reduces abundance and overall surface coverage of living coral, decreases species richness and diversity, and eliminates viable habitat (DeVantier,2008).

M. australiensis populations are also affected by localised threats including fisheries, urbanisation, alterations of native populations and introduction of invasive species. Moreover, pollution,sedimentation and fresh-water runoff resulting from agricultural practices and urbanisation further affect the survival of M.australiensis (DeVantier, 2008).

Conservation:

To ensure the conservation of M.australiensis, species specific research into abundance, population trends and ecology must be undertaken. To facilitate this, the establishment of marine conservation areas is recommended. Additionally, the harvesting of these corals outside the proposed conservation area by fisheries must also be monitored to avoid population depletion. Preservation of gametes and artificial propagation are also important techniques in ensuring the continuation of this species.Furthermore, it is necessary that significant measures be undertaken to halt climate change and reduce pollution affecting the oceans (DeVantier,2008).

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