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You are here:   OldClasses > 2012 > Fungia fungites | Ben Murphy

 

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Fungia fungites (Linnaeus, 1758)                                                

Common Mushroom Coral

Ben Murphy (2012)

 

 

 

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Summary


Physical Description


Ecology


Life History & Behaviour


Anatomy & Physiology


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Life History & Behaviour

Jump to: Feeding , Reproduction, Development, Movement, Respiration, Excretion, Response to Disturbance, Experiment, Additional Observations.

Feeding

F.fungites, as with other Scleractinian corals, obtain a large proportion of their energy requirements through the photosynthesis of zooxanthellae (Battey and Patton 1984 & Muscatine 1990). The zooxanthellae provide the coral with carbohydrates and oxygen, carbohydrates can then be broken down by metabolism to yield energy. Photosynthesis byproducts provide a source of energy during the day while the zooxanthellae can photosynthesis. At night this source of energy ceases. At night, F.fungites extends its tentacles and feeds on plankton (Erhardt & Knop, 2005).

Unusually for scleractinians, Fungiids are capable of feeding on large prey items. Hoeksema & Waheed (2012) observed fungiia corals, including F.fungites feeding on salps in northwest Borneo. I have also witnessed a heliofungi coral eating a crinoid. I predict that fungiia corals are able to eat many large prey items. Further study into how much energy these corals obtain from this feeding mechanism would be very interesting.



Reproduction

Sexual Reproduction

F.fungites are dioecious (male and female sexes are separate), reproducing sexually by the release of gametes during synchronous mas spawning events (Gilmour, 2002). Fertilization occurs in the water column and the zygote develops in the plankton as per standard coral development.

Asexual Reproduction

Asexual reproduction occurs via budding after polyp injury (Gilmour, 2002a). Injury is often due to sedimentation but can also occur due to damage from wave action. Where the polyp is injured, the tissue retreats into the spaces between the septae  of the polyps hard skeleton (Gilmour, 2002a). After approximately 6 months buds emerge from the dead parent polyp (Gilmour, 2002b). The maximum number of buds per polyp is 932 (Gilmour, 2002b), hence in habitats with high incidences of injury, reproduction via asexual budding can be high. The asexual buds are small, with most being less than 5mm in diameter (Gilmour, 2002b). The number of buds produced per poly is proportional to size, with larger polyps producing larger numbers of buds (Gilmour, 2002b). The buds grow as the sexual larvae do, attached to the substrate via a stalk, but they detach at a much smaller size (~2.5cm) (Gilmour, 2002a).



Development

Once the planktonic larval stage is complete, the larvae settle onto a suitable substrate and attach via a stalk (Gilmour, 2002a). The corals then grow attached to the substrate until they reach a suitable size (~6.5cm in diameter (Gilmour, 2002a) where they detach and become free-living sexual polyps (Gilmour, 2004).  The corals detach by the dissolution of the skeleton across the plane at which the polyp and the stalk join (Yamashiro & Yamazato, 1995). 



Movement

Funiid corals can move via external abiotic and biotic means and by autonomous  locomotion (Chadwick-Furman & Loya, 1992). Polyps may be moved by direct wave or current action or indirectly via the wave or current moving sediment underneath the polyp (Chadwick-Furman & Loya, 1992). Both of these process result in coral movements which can be over large distances but occur over short time frames. Polyps can be moved by the movements and actions of other organisms such as sipunculans and foraging fish and crustaceans (Chadwick-Furman & Loya, 1992).

Multiple methods of autonomous locomotion have been discovered for the Funiidcorals. Fungids are capable of actively moving over short distances (<10 cm day), although the rate depends on the species (Chadwick‐Furman & Loya, 1992). There have been no studies describing the exact  method that F.fungites uses to autonomously move. I expect that F.fungites will have a mechanism of autonomous locomotion and that it will be similar to that described for other species within the fungiids. Examples of types of movement are: controlled constriction and relaxation of distended tissue, the use of long, continuously-expanded tentacles as ship-sail to facilitate transport by currents and secretion of a mucous float to increase buoyancy during locomotion (Chadwick-Furman & Loya, 1992).
 
Regardless of the mechanism of autonomous movement, migratory rate significantly decreases with the size of the polyp, with smaller individuals moving much faster and further than large individuals (Chadwick-Furman & Loya, 1992). Corals move faster on sand substrates when compared to reef rock (Chadwick-Furman & Loya, 1992).

Fungiid corals need a method to right themselves in the event of inversion by wave action or biological disturbance. The method that F.fungites uses to right itself after inversion has been documented, although it has been in the closely related fungid,  Fungiia scutaria .It is highly likely that they use similar methods due to their close phylogenetic relationship (reference) and it has been demonstrated that both have similar ranges of movement (Chadwick-Furman & Loya, 1992). F.scutaria rights itself passively by the use of wave action through the hydraulic response of their skeleton (Jokiel & Cowdin, 1976). Because  the center of a F.scutaria polyp is raised, when overturned it does not lie flat on the bottom. This allows low velocity waves to get underneath the polyp and overturn it. This process works relatively well, to the extent that water motion rights skeletons at velocities lower than needed to disturb upright polyps (Jokiel & Cowdin, 1976).


Respiration

Corals respire by directly diffusing oxygen from the surrounding water into the epidermal cells (Ruppert et al, 2004). Water is circulated over the body surface via the ciliated epithelial cells, this facilitates the diffusive gas exchange (Ruppert et al, 2004).
 
Excretion
Cnidarians excrete waste in the form of ammonia (Ruppert et al, 2004). This waste product readily dissolves in water, hence it moves across the body wall of the coral without any energy expenditure and is dispersed by water currents (Ruppert et al, 2004).

Response to Disurbance
 
Because Funiidcorals live on the benthos of inshore reefs, they have to deal with high rates of sedimentation (Gilmour, 2002b).  The accumulation of sediment on corals eventually leads to necrosis of the tissues due to the physical damage that the sediment exerts on the coral and the anoxic conditions that may arise between the sediment and coral tissue (Gilmour, 2002b). Fungiid species have developed active mechanisms to get rid of this sediment. The most common mechanisms are cilliary and tentacular action, mucous production and tissue expansion (Gilmour, 2002b).   

                                                              


Cilliary action appeared to be the primary response of F.fungites to an artificial sediment load that I applied to the coral. I believe this due to the spiral nature in which sediment was moved along the surface of the coral when viewed under a microscope at 4X magnification.

                                                              

Experiment: The Capacity of Different Sized Fungia fungites in Removing Sediment over Short Time Scales

Introduction

The inshore reef areas that F.fungites inhabit are prone to very high sedimentation rates (Gilmour, 2002b). The Funiidcorals have developed mechanisms to remove this sediment from their dorsal surface. Without active removal the corals would undergo tissue damage directly from the sediment and from the anoxic conditions created by burial (Gilmour, 2002b). Recently, the Gladstone Port Corporation has been granted the approval to dredge a maximum of 46 million cubic meters of sediment from the Gladstone harbor (Gladstone Ports Corporation, 2012). There are fears that his dredging activity will increase sediment load on nearby reefs, such as Heron Island. It is unknown how this will affect solitary corals on Heron Island. This study aimed to determine how different sized F.fungites polyps dealt with sediment loads over short time periods. Short time periods were chosen as it is thought that dredging plumes were unlikely to be continuous at Heron Island and would rather be periodic depending on environmental conditions. Work by Gilmour (2002,b) on the long term effect of sedimentation found that large polyps survived under sediment loads much better than the small polyps. Therefore this experimentation was done under the hypothesis that large corals would be able to quickly remove sediment loads due to their larger surface area and larger energy stores, while small individuals would struggle in removing sediment due to their smaller surface areas and hence less cilia.  

Methods

Four F.fungites polyps were collected from the Heron Island reef flat. Two large and two small polyps were collected.  They were left in aquaria for several hours before experimentation. Two unfiltered tanks were set up adjacent to each other in a temperature controlled room. Egg-crate was placed in the aquaria so that the corals could be raised from the substrate, enabling sediment to fall off onto the bottom of the tank. Two corals were placed in each tank, one of each size class.  Sediment load was calculated for each coral by multiplying  the surface area by two to obtain a 2mm coverage. Sediment was applied via pipette and photos were taken of each coral at 2.5minute intervals for one hour.

Photos were analysed in Adobe Photoshop CS6 by overlaying a standardized grid over the photo. The number of squares that the coral occupied  were counted, only squares which were 95% occupied by the coral were counted. The number of both sediment covered and uncovered squares were counted. Squares covered with greater than 50% sediment were considered covered. Percentage coverage were then calculated. Analysis of the sediment percentage coverage were stopped after  corals reached below 10% coverage or the coral stopped removing sediment. Defined by a 10 minute interval where the coral did not lose 10% coverage. An ANOVA statistical analysis was then undertaken to determine if size had an effect on sediment removal rate.

Results

Size conveyed no significant difference in sediment removal rate (p=0.0571, df=1).  Although it should be noted how close this value is to the cut-off point of p=0.005. There were definite trends in the data, with the smaller corals reaching 25% coverage quicker than the larger corals giving them faster rates of removal contrary to what was predicted (Table, 1, Figure 1).

                                                
          
  
                                                 
                     

Discussion

Although the result was not statistically significant, it came incredibly close to the p value cut off. With the low number of replicates and hence low power of the experiment it is predicted that replication of the experiment with a large sample size would provide a significant and highly useful result. Nevertheless the trends in the data clearly point to the smaller corals removing sediment at faster rates than the larger corals. This is the opposite to what was hypothesized and to what has been demonstrated by Gilmour (2002b) previously over longer time scales. It is likely that the confounding result is due to the corals being able to use the energetically expensive cilliary mechanism for sediment removal due to the short time of sediment load (Stafford-Smith,1993). Whereas in Gilmour’s (2002b) study, the corals were exposed to sediment for a 20day period and would not have been able to use this response. Based on this conclusion it is plausible that small polyps have a greater cilliary removal capacity when compared to larger F.fungites. This may have implications on Heron Island and surrounding reefs as large polyps may undergo damage due to high sediment influxes while the small individuals will be able to remove the sediment with their superior cilliary mechanism. This may change the size structure of the reef populations, with unknown consequences. This information must be kept in the perspective of short term influxes of sediment associated with dredging events. Because on longer term scales, the opposite change in size structure would be predicted and large individuals would increase in abundance (Gilmour, 2002b).

Additional Observations

While experimenting, it was observed that sediment around the mouth of the corals disappeared with out being removed via cilliary action moving the sediment to the edge of the polyp. Microscope work was done to see if the corals were actively ingesting the sediment, which they were! This is visible in the video link below. This may be a new mechanism for fungids to recover from sedimentation, but further work needs to confirm this. A post-hoc experiment was conducted by adding exact amounts of sediment to several corals. The corals were left to shed the sediment. After 3 hours, the corals were taken out of their individual containers and all sediment removed from their dorsal surface. After drying at 70 degrees Celsius over night the sediments were re weighed. Unfortunately the sediments did not loose a significant amount of sediment when compared with controls with no coral in the container. Hence I was unable to confirm that the corals were ingesting sediment via a weight experiment.

   

                                                              

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Album: 2012

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