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Cladiella cf. Ramosa OTU 5293

Jenna Lindberg 2016


Cladiella cf. Ramosa OTU 5293 is a species of Alcyonacean from the genus Cladiella, more commonly known as colt coral. Cladiella cf. Ramosa is a fleshy, sessile, colonial coelenterate (Rao & Kamla Devi., 2003). Alcyonacea are recognised for their thick coenosarc and the eightfold symmetry of their polyps, a distinguishing characteristic of their subclass Octocorallia. Unlike hard corals, Alcyonacea do not readily produce calcium carbonate and therefore do not produce a rigid skeleton (Ruppert 2004). To maintain structure Alcyonacea harbour minute, spiny calcareous spicules within their coenenchyme, known as sclerites (Rao & Kamla Devi., 2003). Sclerites are more or less systematically arranged at the base of each tentacle, between the body wall, between septa and in the anthosteler region (Rao & Kamla Devi., 2003). They are imperative to the identification process of the genus and species of any Alcyonacea. Cladiella are widespread, ranging from Africa and the red sea in the west, to the western pacific islands in the east (Fabricius & Alderslade, 2001). The presence of zooxanthellae in the polyps provides the specimen with the ability to photosynthesize its energy. Cladiella also capture food particles and absorb organic matter from the water column (Fabricius & Alderslade, 2001). 

The Cladiella cf. Ramosa OTU 5293 specimen was collected from the University of Queensland’s aquarium. To identify the species and genus, samples of the sclerites were examined with the help of Dr Merrick Ekins, collection manager of Sessile Marine Invertebrates at the Queensland Museum.  With the use of a Scanning Electron Microscope (SEM) we examined the sclerites of my specimen and found that the species was not previously characterised, however was close to the sclerite morphology of Cladiella Ramosa. The sclerites in the tissue at the base of the specimen had a slight dumbbell shape, a defining characteristic of the Cladiella genus.

Figure 1

Physical Description

The specimen is fixed by a main basal attachment to a piece of hard substrata. The growth pattern follows a tree like structure with erect and branching projections. The polyp bearing portion of the specimen is predominantly on the branches, while the base of the Alcyonacea is sterile with no polyps. The polyps are monomorphic autozooids, each bearing eight tentacles pinnately branched around the upper end of the pharynx (Fabricius & Alderslade, 2001). The tentacle bearing region, known as the anthocodia, retracts back into the gastrovascular cavity when disturbed. The Alcyonacea is a brownish-purple colour when polyps are fully extended (see figure 1). The polyps are darker in colouration than the main coenenchymal mass and branching arms, indicating higher concentrations of zooxanthellae in the polyps (Ruppert 2004). The length and size of the animal change depending on its state, extended (15-20cm) or retracted (5cm). Overall, while in its extracted state the Cladiella specimen shows no uniform shape with polyp population was most dense at the tips of the branched arms.
Figure 2


Morphofunctional Ecology

Cladiella are an entirely marine, phototrophic octocoral, which inhabit coastal waters on crests and rocky coasts, where the habitat is readily exposed to waves (Fabricius & Alderslade, 2001). Alycoean diversity is generally low on reef flats, inversely related to stony coral coverage (Dinesen, 1983). Cladiella can be found as individuals or clones of a small number of evenly sized colonies (Fabricius & Alderslade, 2001). Due to the phototrophic nature of Cladiella they are more common in shallow waters and are widespread in the tropical Indo-Pacific (Fabricius & Alderslade, 2001). 

Taxonomic inventories of octocorals allow for a detailed account of the distribution ranges for many of the Indo-Pacific shallow water genera of Alcyonacea. Although abundant surveys have been taken for octocorals and Alcyonacea, areas like the ‘Coral Triangle’ of the western Pacific Ocean, Papua New Guinea and the Philippines lack efficient surveying (Fabricius et al. 2007).  The species richness of Alcyonacea is dependent on three factors; the biogeographic location and colonization history of a region, environmental conditions and disturbance history (Fabricius et al. 2007). High water temperatures, storms with high wave energy, reduced water clarity and sedimentation all constitute as disturbances which contribute to the species richness of this taxon. The speed and efficiency of recolonization will determine whether the taxon can re-establish itself (Fabricius et al. 2007). If propagules from surviving colonies are available, fast colonies will continually re-establish. However, to re-establish the abundance of slow-colonizing or slow-growing taxa could take decades (Fabricius et al. 2007).

Algal Endosymbionts

​Over half of the warm shallow-water Indo-Pacific octocorals are phototrophic and are somewhat depend on light for carbon gain (Fabricius et al. 2007). The tissues of these taxa contain the endosymbiotic dinoflagellate algae zooxanthellae, which amply supplies the colonies with energy (Fabricius et al. 2007). Zooxanthellae is a term given to any dinoflagellate that partakes in symbiosis with an organism (NOAA, 2016). The algae is brown-yellow in colour and inhabits the epidermis and gastrodermis of cnidarians, often in very high concentrations. High concentrations enhances the exchange of nutrients between the dinoflagellates and their host (NOAA, 2016). The symbiotic relationship is dependent on the coral polyps undergoing cellular respiration, producing carbon dioxide and water as a by-product (NOAA, 2016). The zooxanthellae photosynthesize using these by-products, creating sugars, lipids and oxygen. The sugar, lipids and oxygen are then used by the coral polyps for growth and cellular respiration (NOAA, 2016). The cycle is efficient at recycling and the reason why corals are able to thrive in nutrient poor waters. 

As the second most abundant macro-invertebrates on many Indo-Pacific and Caribbean coral reefs (Van Oppen et al.  2005), octocorals contribute substantially to the structural complexity and biodiversity of reefs. Unlike scleractinians which rely heavily on their symbiotic relationship with dinoflagellates, the trophic contribution of zooxanthellae is much lower for octocorals reefs (Van Oppen et al.  2005). However, as mentioned earlier in the text, half of the warm, shallow-water Genera of octocorillia such as Cladiella possess a phototrophic lifestyle. This is evident in C. Ramosa cf. OTU 5293 where the concentration of zooxanthellae is highest in the polyps, specifically in the gastrodermal cells and in the gastro vascular cavity. 

Throughout the evolution of octocorals there has been an abundant loss and gain of endosymbiosis. On an evolutionary timescale, it appears that the ability to switch between mixotrophy and heterotrophy is much easier for octocorals than that of scleractinian corals (Van Oppen et al.  2005). The low reliance on photosynthetic carbon gain also coincides with this ability. The algal endosymbiosis and loss/gain of zooxanthellae is a likely indicator of smaller ecological changes within the octocoral community compared with scleractinians (Van Oppen et al.  2005)

Figure 3

Life History and Behaviour


Cladiella are a gonochoric, oviparous species of octocoral which undergo both sexual and asexual reproduction (Fabricius & Alderslade, 2001).  Three types of reproduction occur in octocorals; broadcast spawning, internal brooding of larvae and external brooding of larvae (Fabricius & Alderslade, 2001). Cladiella belong to the family Alcyoniidae, which are commonly broadcast spawners, releasing large quantities of eggs into the water column where fertilization occurs. 

The type of reproduction a species undergoes can also be dependent on the adult body size of the organism (McFadden, et al, 2001). Individuals with a large body size would obtain greater reproductive success by producing large quantities of planktonic offspring (McFadden, et al, 2001). However, this particular reproductive strategy fails smaller individuals, which are unable to produce enough embryos to counter the high mortality rates of larvae (McFadden, et al, 2001). The only method by which the relative fitness of a purely sexual population could be equal or surpass that of a population which undergoes fission, is if the total amount of energy allocated to reproduction was increased (McFadden, et al, 2001). This could only be achieved at the expense of colony growth and maintenance, shifting the population size distribution toward smaller colonies with lower reproductive output and higher mortality rates (McFadden, et al, 2001).  

Soft corals can reproduce asexually through runner formation, fission, colony fragmentation or budding (Ruppert 2004). Fission is generally the most used form of asexual reproduction among the reef. However in rough weather, which can devastate reefs and shatter colonies, fragmentation becomes an increasingly important method of reproduction. Fragmentation allows reefs in these situations to rapidly repopulate (McFadden, 1991). The sexual reproduction of soft corals is not as successful as asexual reproduction methods, however it provides the species with genetic diversity (McFadden, 1991). The sexually produced planula larva also provides the primary method of dispersal and colonization of these sessile cnidarians (McFadden, 1991).

Chemical Defense

The ability of soft bodied, sessile, alycoeans to survive and thrive in highly competitive and hostile environments is attributed to the occurrence of secondary metabolics in their tissues (Changyun et al., 2008). The chemical defence roles of the secondary metabolites of octocoral include antifeeding, cytotoxicity, reproduction, antifouling and allelopathy (Changyun et al., 2008).  Diterpenoids, sesquiterpenoids and sterols are the main compound classes accounting for the antifeeding and allelopathy activity of soft corals (Changyun et al., 2008). The allelopathic and antifouling complexes from corals show that the secondary metabolites excreted by corals including diterpenoids and sterols are able to inhibit the growth of surrounding organisms (Changyun et al., 2008) Therefore, not only are these chemical defences vital for protection against predation, the allelopathic substances are imperative to the survival and reproduction of soft corals in a competitive environment (Changyun et al., 2008). 

The production of defensive chemicals to combat predation is common in most octocorals (Epifaneo, Martins, Villaca, & Gabriel, 2016) which provide a prolific source of biologically active and structurally unique chemical compounds (Epifaneo, Martins, Villaca, & Gabriel, 2016). Soft corals experience low predation rates even while inhabiting environments characterized by high levels of predation and nutrient scarcity (Epifaneo, Martins, Villaca, & Gabriel, 2016). Majority of these bioactive molecules fall into the terpene class of compounds (Coll, La Barre, Sammarco, Williams, & Bakus, 1982). Terpenes occur throughout the colony however are concentrated in the epidermis and gonads of the octocoral (Webb, 2016). The toxicity of these terpenoids reduce the palatability of soft corals and are responsible for deterring predation (Fabricius & Alderslade 2001). Soft corals are also capable of producing anti-foulants to prevent the growth of algae or fungi on the colonies (Fabricius & Alderslade 2001). 

Other genera of Alcyoniidae corals (Sinularia and Sarcophyton) possess the ability to release allelopathic substances into the water column, inhibiting neighbouring organisms from competing for space (Fabricius & Alderslade 2001). However, it was found that corals were more likely to neutrally interact with neighbouring hard corals than other soft corals (Griffith, 1997). Allelopathy and simple overgrowth were the major aggressive mechanisms of alcyoniids. Instead, soft corals were observed to only overgrow neighbouring hard coral and release allelochemicals when the neighboring organism was another soft coral (Griffith, 1997).

The chemical constituents of the genes Cladiella has indicated a large supply of cytotoxic eunicellin-based sesquiterpenes and diterpenes (Radhika 2006). The group is home to cladiellin, acetoxycladiellin, cladioxazole and cladidiol (Radhika 2006) but overall, fifty-five complementary metabolites have been isolated from the various Cladiella species.

Anatomy and Physiology

Cellular Organisation and Function

Alcyonaria (Octocorillia) are exclusively poploid cnidarians with an invaginated mouth to form a tubular pharynx and gastrovascular cavity (Rao & Kamla Devi., 2003). This cavity is partitioned by the thin, non-calcareous septa known as mesenteries (Rao & Kamla Devi., 2003). They are branched, colonial, octomerous Anthozoans with pinnate tentacles (Stachowitsch, 1993).  As cnidarians, they are comprised of three distinct tissue layers; the epidermis, the gastrodermis and the mesoglea (Ruppert 2004). The cnidarian body plan follows radial symmetry around the oral aboral axis. This radial symmetry extents from the mouth to the base of the gut, providing Anthozoans with differentiated parts (tentacles) duplicated in each radius and distributed 360 degrees (Ruppert 2004). This is essential for sessile Anthozoans, who are able to face their tentacles (which house the sensory organs of the animal) in every direction, ideal for suspension feeding (Ruppert 2004). The epidermis and gastrodermis both house the phylum specific cell type, cnidocyte. Cnidocytes play a significant role as a combined sensory effector cell and house stinging cells called nematocysts. However, Alcyonaria lack stinging nematocysts and instead defend themselves using toxic compounds (Shepherd & Edgar, n.d.).

The colonial Alcyonaria are diverse in size and shape, but uniformly share octamerous polyps. The Cladiella genus are monomorphic with autozooid polyps (Fabricius & Alderslade 2001). These small retractile polyps (0.5mm-2cm in diameter) have eight pinnate tentacles which sit atop a cylindrical elongated column arising from an aboral pedal disc (Ruppert 2004). Opposite of the siphonoglyph (a ciliated groove at the end of the mouth) sits two septa with long, densely ciliated septal filaments called asulcal septa. These asulcal septa are responsible for orally directed water flow (Ruppert 2004). In conjunction with the aboral flow produced via the siphonoglyph, colony wide circulation of nutrients and gasses is achieved (Ruppert 2004). 

Figure 4
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Unlike Scleractinia, Alcyonaceans do not readily produce calcium carbonate and therefore lack a rigid skeleton (Ruppert 2004). Though they are fleshy and soft, they still do contain some skeletal elements to maintain structure. Alcyonacea harbour minute, spiny calcareous spicules within their coenenchyme, known as sclerites (see figure 7 & 10). These sclerites are arranged at the base of each tentacle, between the body wall, between septa and in the anthosteler region (Rao & Kamla Devi., 2003). They are imperative to the identification process of the genus and species of any Alcyonacea.  

To obtain samples of the sclerites a small section was taken from the tip of the Alcyonacean branch and the base of its stalk. Each sample was then put into a small tube with common bleach. The material was left to dissolve for 20 minutes before being rinsed again with bleach and spun through a manual centrifuge. This process was repeated for each sample till majority of the tissue was dissolved or gone, leaving only the sclerites. Once the material was ready the samples were then put onto separate microscope slides and examined. Once the wet samples were examined the slides were dried out till only the sclerites remained. Dr Merrick Ekins and I then examined the dried samples using the Queensland Museums Scanning Electron Microscope (SEM).    
The sclerites examined from the base of the Alcyonacean showed a dumbbell like shape, immediately indicating that this specimen belonged to the Cladiella genus. The sclerites closer to the polyp region however showed more smoothed oval and figure eight shaped sclerites, which was also common in Cladiella (Fabricius & Alderslade 2001). The sclerites were generally 20.6um in width and 50.9um in length (see figure 4)

Figure 9
Figure 10
Figure 11
Figure 12

Biogeographic Distribution

Cladiella are found throughout the Indo-pacific, a biogeographic region comprising the tropical waters of the Indian Ocean, the western and central Pacific Ocean and the seas which connect the two in the general area of Indonesia (Fabricius & Alderslade 2001). Australia’s distribution of Cladiella are predominant on the Great Barrier Reef of Queensland, however some species also inhabit the northern parts of Western Australia’s coast (see figure 11). They generally range from a depth of 5-18 meters (Malyutin, 1992), as the requirement of sunlight restricts them to shallower waters.  Octocorals generally inhabit fringing reefs, platform reefs and Atolls (Malyutin, 1992). Octocorals found on Fringing reefs are generally concentrated in the lower horizons of the reef slopes and sloping platforms, with spread apart colonies. Platform reefs lack steep reef slopes, with only a slight incline toward the open sea. Octocorals in these environments are generally found at depths of 4-6m (Malyutin, 1992). When a definite reef slope is present, octocorals tend to concentrate on the lower horizons. This could be related to the tendency of dissolved and suspended organic matter and minerals to be directed down the reef profile (Malyutin, 1992). Reef environments which lack a definite reef slope and experience a uniform distribution of nutrients along the reef profile generally have an evenly spread distribution of octocorals (Malyutin, 1992). The Cladiella cf. Ramosa OTU 5293 specimen was collected from the University of Queensland's aquarium, however it was thought to be originally collected from North Stradbroke Island's Amity point.
Figure 13
Figure 14

Evolution and Systematics

The phylogeny of Alcyonacea, as mentioned above, is reliant on the analysis of the skeletal elements distributed through the animal’s tissue. The genus Cladiella possess a definitive dumbbell shaped sclerite which has two more or less spherical, warty heads and a distinct waist that is longer than in the double spear sclerite (Rao & Kamla Devi., 2003). However, when defining species the location and morphology must also be taken into consideration (Rao & Kamla Devi., 2003). The eightfold symmetry of the specimen’s polyps immediately classifies this coral into the subclass Octocorallia from the class Anthozoa (Fabricius et al. 2007). The thick coenosarc and lack of a rigid skeletal structure suggests that this specimen belongs to the order of Alcyonacea, known as the true soft corals (Rao & Kamla Devi., 2003). 

My species was identified with the help of Dr Merrick Ekins by first analysing the sclerites of the individual and assessing the location it was collected from. We then read through taxonomic records of the Cladiella genus whilst listing off Australian species. Through the process of elimination we were able to conclude that the specimen was closely matched to Cladiella Ramosa described by Andree Trixie-Durivault, from the waters of New Caledonia. However, this species was not an exact match and it was concluded that this species was new, however closely related to Cladiella Ramosa. 

Conservation and Threats

There are no known threats or conservation issues regarding the Cladiella genus in research. However, the threat status of this species is yet to be evaluated by the International Union for Conservation of Nature (IUCN), so the species remains unlisted. However, like many coral species that have resident zooxanthellae, soft corals are also susceptible to the effects of increasing global temperature (Goulet, LaJeunesse, & Fabricius, 2008).

Colonies of alcyoncean found on the Great Barrier Reef during the 1998 bleaching event possessed symbiont types that were genetically indistinguishable from those in non-bleached corals (Goulet, LaJeunesse, & Fabricius, 2008). This data suggests that there are factors other than resident endosymbionts which are important in determining the susceptibility of soft corals to bleaching (Goulet, LaJeunesse, & Fabricius, 2008). These include parameters such as host identity and colony acclimatization. 

Bleaching among alcyonaceans can vary between species, however it was found that the family Alcyoniidae were moderately susceptible to bleaching (Goulet, LaJeunesse, & Fabricius, 2008). The differential tolerance to stress among cnidarian species, regardless of which Symbiodinium they host, could potentially explain the differences found in soft coral bleaching (Goulet, LaJeunesse, & Fabricius, 2008). 
On the rock in which my specimen was attached, a smaller soft coral individual believed to be the same species was present. However, this individual has experienced bleaching. A comparison between the concentrations of zooxanthellae in the longitudinal cross sections of branches were compared. As expected, the bleached coral had an extremely low number of zooxanthellae present.

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