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You are here:   OldClasses > 2012 > Stylophora pistillata | Alex Coughlan

 

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Stylophora pistillata, Esper 1797

 Hood coral        
   
 (Alex Coughlan, 2012)

 

 

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Fact Sheet

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Summary


Physical Description


Ecology


Life History & Behaviour


Anatomy & Physiology


Evolution & Systematics


Biogeographic Distribution


Conservation & Threats


References & Links

Ecology

Pocilloporids which the genus Stylophora belongs is known for its high recruitment, and its success as an early successional group (Wallace, 1985). S. pistillata exhibits a broad ecological niche, occupying a range of depths from shallow intertidal reef flats less than 1m deep down to 70m (Mass et al., 2007). This species has large phenotypic variations in which it alters its branching and colour morphologies in response to the surrounding environmental conditions (see Physical Description). By reducing either the number of zooxanthellae or the photosynthetic pigments within the zooxanthellae, coral colonies exposed to high light intensities can reduce their irradiance. On the other hand, S. pistillata can alter their branching morphology by changing the branch density to control the penetration of light to its surface (Kaniewska et al., 2008). Similarly, the feeding mechanisms utilised by the S. pistillata colonies is dependent on the depth in which the colony occupies (see Life History and Behaviour for feeding mechanisms). These adaptations to the surrounding environment allow S. pistillata to be successful over a broad ecological niche.

Described by Pianka (1979), unlike most corals (which are K-selected) S. pistillata appears to be r-selected given its success in colonising unpredictable reef habitats, rapid development, great population turnover, early reproduction, small body size, short life span, density independent mortality, wide dispersal gradient and poor competitive ability. An observation made by Loya (1976) regarded the poor competitive ability of S. pistillata. While conducting experiments in deep water (20-50m depth) it was noted that S. pistillata was the first of the corals to be competitively excluded by the deep reef specialists.

 

Symbiotic Interactions

Internal associations

Like most hermatypic corals, S. pistillata is in a mutualistic symbiotic relationship with a unicellular dinoflagellate, Symbiodinium. Once thought to be a single species is now known to comprise many clades. Symbiodinium clade C (1, 8, 78 and 79) is utilised by S. pistillata (LaJeunesse et al., 2003, LaJeunesse, 2005, Sampayo et al., 2007).The dinoflagellate known as zooxanthellae lives within the coral tissue uses coral waste products such as CO2 and nutrients, to photosynthesise and in turn provide energy for the coral host. S.pistillata colonies in shallow water systems get their total energy requirements from this association alone, however colonies at depth gain up to 60% of their energy from predating on zooplankton (Falkowski etal., 1984) (see Life History and Behaviour for feeding mechanisms).

 

External associations

Due to the dense branching morphology of S. pistillata in shallow waters, a diverse range of organisms such as crustaceans, worms and small fish seek refuge in the coral branches (Edwards and Emberton, 1980, Liberman et al., 1994). Crustaceans such as Trapezia and Tetralia are considered obligate symbionts with Pocillopora species including S. pistillata. Edwards and Emberton (1980) found that most S. pistillata colonies are dominated by a single heterosexual pair of Trapezia, while up to 15 individuals were found in any single colony. Trapezia use modified dactyli to feed on bacteria and detritus within the mucous secreted by the S. pistillata (Knudsen, 1967, Castro, 1976). To find out more about Trapezia visit: Trapezia cymodoce within this website.

In combination with crustaceans and polychaetes, many small fish such as damsels (Dascyllus spp.) seek protection in the branches of S. pistillata. Different branching morphologies may be inhabited by different developmental stages of the same fish species (Fricke, 1980). While not every S. pistillata colony is inhabited by Dascyllus, it is an obligate coral dweller (Liberman et al., 1994). Liberman (1994) showed that S. pistillata  direct benefits from the association with a significant increase in coral growth and an increase in surface area and therefore number of polyps.

Image: Trapezia crab in Stylophora pistillata

Location on a coral reef

A highly abundant species, S. pistillata has a wide geographic distribution around the Indo-West Pacific (Veron, 2000) (see Biogeographic distribution for more details). S. pistillata can be found in shallow intertidal reef flats, on the reef crest and deep water reefs and caves up to 70m depth (Mass et al.,2007).

 

A BRIEF INVESTIGATION INTO THE ABUNDANCE AND PHENOTYPIC VARIATION OF S. PISTILLATA ON HERON ISLANDS REEF FLAT

Stylophora pistillata is a hermatypic coral found commonly in the Indo West Pacific region (Veron, 2000). Occupying a wide variety ofecological niches, S. pistillata lives in a range of environmental conditions including down to depths of 70m (Mass et al., 2007). S. pistillata is known to exhibit high phenotypic plasticity in relation to its colour and branching morphologies. It is known that the brown colour morphs are more abundant in shallower waters (Ford, 2012). However, observations made in the field at Heron Island identified many colonies of the pink morph occurring in shallow (<1m) depths. As a result, the question was asked, in relative terms, how abundant is the pink morph? In addition, is this abundance equal over the reef flat?

The aim of this brief study was to investigate this apparentvariation in colour morphs, identify any variation in branching morphology and determine the overall relative abundance of S.pistillata on Heron Island’s reef flat. Given the available literature it was hypothesised that;

1.      The brown colour morph would be most abundant on the reef flat,

2.      Branching morphology would consist of short, branches with a dense arrangement

3.      In response to differences in the environmental conditions on the Heron Island reef flat, S.pistillata would be more abundant on the Northern, more sheltered side.

 

Methods

Study site

Heron Island is a coral cay located in the Southern Great Barrier Reef off the Queensland coast (23° 26’ 29.75” S, 151°54’ 50.87” E). Due to the topography and positioning of the coral reef surrounding the island, there are differences in the environmental conditions on the Northern and Southern sides of the island. Approaching low tide, the Southern side is subject to quite strong currents which channel through the small patch reefs on the reef flat and continue out into the main channel. In contrast, on the Northern side there is less of this tidal current although it is still present. Evidence for this is both from personal observation, local knowledge and also observation of the size of the substratum particles (Southern side is very coarse coral rubble, while the Northern side is quite fine sand reflecting the wave and current energy). As a consequence of these contrasting environmental parameters the Northern (23° 26’ 23.52” S, 151°55’ 02.11” E) and Southern (23° 26’ 41.05” S, 151°54’ 51.52” E) sides of the island were selected as study sites (see map below).

Map of Heron Island showing the two sites (North in blue, South in orange) with the three distinct bands used to complete 2 minute timed searches to collect size, colour and branching morphology data.


Relative abundance

Two minute timed searches were conducted at low tide along three distinct bands (see map above). Five succeeding replicates along each of the three bands were completed at each site. Colonies of S. pistillata irrespective of size, were identified and counted. An accumulated total of each band and site was later compared (see Figure 1 in Results).

Size, colour and branching morphology

Following the timed searches, belt transects were conducted within the same bands. 10 colonies within each band were randomly selected and the colour, size and branching morphology was noted. Three categories were used to discriminate size; <10cm in diameter, >10cm in diameter and >20cm in diameter (see Figure 2). Likewise the colour was categorised as white, pink or brown while photos (Figure 3) were used to compare the branching morphology.

Data Analysis

Microsoft Excel was used to compare the relative abundance, variation in colour and size of S. pistillata between the two study sites. Windows Photo Gallery was used to view the coral colony branching morphology. The total counts were compared within and between the two sites to identify any trends.

 

Results

Relative abundance

There was a noticeable difference between the colony counts between the two sites. The Northern site recorded 155 colonies of S. pistillata, while at the Southern site just 66 colonies were identified in 15 transects.

Figure 1 Total accumulated colony counts over the 15 transects per site. The total count of S.pistillata colonies on the Northern side was 155, while a noticeable reduction to 66 was observed on the Southern side. Data points represent the colonies identified during two minute timed searches on the reef flat at Heron Island, blue represents the Northern site while orange represents the Southern site.

 

Colony size

The Northern site shows a more sequential trend of small to large sized colonies of S. pistillata. There is a much higher abundance (12 colonies) of larger, more mature colonies on the Northern side in comparison to the Southern side (4 colonies). The Southern side however is dominated by small to intermediate sized colonies under 20cm in diameter.

Figure 2 Total number of colonies per site in each of the three size categories; <10cm in diameter, >10cm in diameter and >20cm in diameter. The Northern site (blue) shows a more sequential trend in size with a relatively large number of colonies over 20cm in diameter. The Southernside (orange) is dominated by small to intermediate sized colonies. Data points represent the accumulated site totals for each transect (n=30).

 

Coral colour

The Northern site showed dominance of the brown colour morph (20 colonies) followed by pink (7 colonies) and white (3 colonies). In contrast, the Southern site showed more morph similarity between the brown (15)and pink (13) colonies. The white colonies were equally as low in abundance as the Northern site (2 colonies).

Figure 3 Total number of colonies found of each colour morph on the reef flat. A higher number of brown morphs were found at the Northern site. Brown and pink colour morphs were quite similar in abundance at the Southern site.

Branching morphology

Field observations showed that the branching morphology S. pistillata had little variation from the densely branched phenotypic trait. There was one exception, of the 60 coral colonies identified, one colony on the Northern side was found to be sparsely branched. While photographs were taken, later analysis of the photos showed that the small variation that did exist may be dependent on the size of the coral colony.

 

Discussion

S. pistillata is a very abundant taxa on coral reef around the Indo West Pacific region (Veron, 2000). Its high phenotypic plasticity allows S. pistillata to exist in a wide range of ecological niches. The abundance, colour and branching morphology of any given colony is a reflection of the surrounding environmental conditions. Field observations made at Heron Island raised questions regarding the variability of S. pistillata within a single reef system.

Data on overall abundance, size (reflecting coral maturity), colour morph and branching morphology highlighted some interesting trends. As expected, S. pistillata was found to be more abundant on the Northern side, with colonies appearing to be more mature (based on size) and well established given the sequential trend of the population sampled. However on the Southern side, the S. pistillata population appears to be dominated by intermediate sized colonies, shifting towards a more mature population.

Interestingly on the Southern side, the pink colour morph appears to be relatively abundant when compared to the brown colour morph. This result was unexpected and the possible cause of this is unknown given the clear dominance of the brown colour morph on the Northern side. It is possible that the perceived high colony count is due to sampling error or it could be abiotic factor relating to the recruitment of deeper water corals during the strong tidal efflux on the reef flat at low tide.

Confirming the predicted hypothesis, branching morphology was fairly conserved across the reef flat. The only natural variations in branching morphology seemed to occur in relation to the size of the colony. There was one colony of the 30 sampled on the Northern side which was an exception, the branches were found to be very sparse similar to the deep water variants. To conclude, while the findings of this study do not identify significant differences in the ecology of S. pistillata, it does highlight the degree of phenotypic variability which can occur within a single reef system.

 

Images

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(2 objects, created 5/6/2011)

Album: This is a private album that is not visible to anonymous users Great Barrier Reef Invertebrates

Summary:

Date:

Album: 2012

Album: 2011

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