Effect of light diffusion on the growth rate and respiration of Montipora digitata an

For anyone who is interested, this is the baseline study for some montipora digitata research I'm and doing. This section just got finish and the write up is a little rough still, but it gets the idea across. I know some of the science is bad (no replicates basically), but again it was a baseline to test methods so that we can have the process fine tuned for the full scale run. The next leg of research will have lots of replicates and a much higher focus on respiration as well as using the buoyant weight technique to measure growth. The graphs probably won't work so if anyone wants I can post them seperately as a picture I think.

Effect of light diffusion on the growth rate and respiration of Montipora digitata and Pachyclavularia sp.​

Abstract
Zoothanthellae algae inside of some coral tissues require specific levels of light for optimal photosynthesis and growth (Smith et al., 2005). Variances in the light levels can alter the zoothanthellae's ability to photosynthesize, thus impairing coral that the algae shares a symbiotic relationship with. The coral species Montipora digitata and Pachyclavularia sp. were placed in a 35 liter aquarium. Light from a 120 watt LED fixture was diffused threw screen to treat corals with decreasing amounts of light. The coral growth rate and mass increase was recorded from August 29 to November 2, 2012. It was found that Montipora digitata grew fastest vertically in the high light treatment, but Pachyclavularia sp. grew slowest in the high light treatment. The Montipora digitata fragments consumed more O2 as light intensity decreased. Light intensity did effect coral growth and respiration, however growth rates between the species and light treatments suggest photoinhibition may have influenced Pachyclavularia sp. growth.

Introduction
Coral reefs are diverse ecosystems that are important both environmentally and economically (Connell, 1978). Coral species grow at various depths along reefs and reef shelves, and light can be one factor that plays a role in their distribution (Connell, 1978). Single species of corals, such as in Madracis spp, are known to vary in depth and morphology to meet the light required at changing depths(Vermeij and Bak, 2002). Light availability affects the amount of daily photosynthesis the zoothanthellae algae can undergo. Changing levels of algal photosynthesis can alter the supply of algal waste supplied to the coral for nutrition, potentially causing stress or mortality if the light is below a corals minimum light threshold (Anthony and Hoegh-Guldberg, 2003). Increased photosynthesis allows for more calcification as more nutrition is supplied to the coral for use in respiration and calcification (Al-Horani et al., 2002). Zoothanthellae algae can also be exposed to excess light and experience photoinhibition, reducing the algae's photosynthetic productivity (Smith et al., 2005). If the algae's metabolic rate cannot consume coral waste at elevated production rates, there is a reduction in electron transport compounds and the ability to produce photosynthesis (Smith et al., 2005).
The stony coral Montipora digitata and soft coral Pachyclavularia sp. both require light for algal photosynthesis. To understand more about how the algal zoothanthellae in coral utilize different levels of light energy, laboratory experiments must be conducted with controlled and measured light levels. The purpose of this experiment is to determine the effect of light diffusion on the growth rate and O2 consumption of Montipora digitata and Pachyclavularia sp. in a closed circulation system.

Materials and Methods
The coral fragments used in the experiment were collected from pre-cut fragments in a closed circulation aquarium. Three fragments each of two species were collected, Montipora digitata and Pachyclavularia sp. Fragments were picked based on visible health and by which were most similar in starting size. One fragment of each species was used for each light treatment, totaling 3 Montipora digitata and 3 Pachyclavularia sp. fragments. These fragments were acclimated for one hour before being transferred into the experimental aquarium at Savannah State University.
The experimental aquarium was 38 liters with approximately 35 liters of sea water in it. Filtration was achieved by use of a under-gravel filter covered in crushed oyster shell and an Oceanic air powered protein skimmer. The under-gravel filter efficiency was increased by using an Aqua Medic circulation pump. After the first week, a hang-on filter was added with activated carbon grains to reduce dissolved organic material. The aquarium operated for three months prior to coral introduction to insure high water quality and bacterial colonization of the substrate.
A 120 watt light emitting diode fixture was placed 5 cm above the tank on brick supports to provide light to the coral. The LED used 55 emitters consisting of half 10000 K white emitters and half 455 nm actinic emitters and all running at approximately 2 watts. Both colors of LED emitters were ran 12 hours a day. To diffuse the light, a black plastic screen was used in a singe layer over the middle third of the aquarium and two layers over the right third of the aquarium. The left part of the aquarium was left unobstructed.
Once introduced, coral fragments were allowed two weeks for full acclimation. To measure growth, a small ruler was used to measure the base width and height of each Monitpora digitata every other day in millimeters. The Pachyclavularia sp. were measured twice on each fragment in a cross section, marking the longest extension of coral mat in each direction. For all samples, measurements were taken across marked lines on the fragment plate to insure they were taken from the same location each time. Growth rate was calculated as the surface area of an ellipsoid with two lengths using the calculation:

SA= π * (W1/2)*(W2/2)​

where W1 and W2 are the width measurements of each cross section.
Light measurements were taken using a LI-COR photosynthetic active radiation (PAR) meter to measure the level of photons present betweens 400 nm and 700 nm. Three readings from each level of light diffusion were taken at the beginning, middle, and end of the experiment. A spectroradiometer was also used to determine the total light spectrum present and used to make a spectral graph of the LED's.
Biological oxygen demand was measured after the growth measurements were completed. It was conducted for light and dark treatments using 300 ml B.O.D. bottles and analyzed using the Winkler method for measuring dissolved oxygen. Montipora digitata fragments were carefully removed from their mounted plates and reattached to 1 cm wide clay fragment disk. These disk were capable of fitting into the bottle neck. The newly transplanted corals were allowed to sit for a week to recover from transplanting and to insure the clay disk's were did not contain any air pockets. The bottle were filled with tank water and submerged onto the rack next to each fragment. One fragment was placed in each bottle and then allowed to sit for 12 hr treatments. The bottle was then removed from the tank and labeled. The coral were quickly removed using thin aluminum tweezers and immediately poisoned to preserve the O2 and in preparation for colorimetric titration. Dissolved oxygen was calculated using:

DO = TF - TI​

where TF is the final volume of titrant and TI is the starting volume of titrant.
Results
The Montipora digitata fragments under high light grew at 0.23±0.38 mm d-1 vertically and 0.13±0.28 mm d-1 of base growth. The high light treatment grew faster vertically than the other treatments, but had the slowest base growth. The other treatments showed decreasing vertical growth rate with the medium treatment growing at 0.05±0.45 mm d-1 and the low light treatment growing at -0.02±0.44 mm d-1. The base growth varied with medium light treatment growing the fastest at 0.30±0.61 mm d-1 and the high light treatment growing the slowest at 0.13±0.28 mm d-1.
Biological oxygen demand showed that the high light treatment consumed the least total O2, 0.11 mg L-1 hr-1. The low light treatment consumed the most O2 at 0.17 mg L-1 hr-1 and the medium light treatment consumed 0.25 mg L-1 hr-1. The respiration rates were 0.10 mg L-1 hr-1 for high light, 0.13 mg L-1 hr-1 for medium light, and 0.14 mg L-1 hr-1 for low light.
The Pachyclavularia sp. showed an opposite growth trend from the Montipora digitata as the low light treatment grew the fastest at 12.7±34.4 mm2 d-1. The high light treatment grew at 1.25±14.6 which was the slowest growth rate.
Table 1. Average vertical growth rates and base growth rates over the entire experimental period. Net primary production and gross primary production were calculated from oxygen consumption rates.

The Montipora digitata fragments grew vertically faster under higher light intensities. This was expected as Montipora digitata grow in shallower habitats on natural reef's and are often exposed to high light levels. The low light fragment growth rate was altered by horizontal growth from the top of the coral branch. This was likely the reason for little vertical growth. The base growth was sporadic with medium light having the fastest growth rate. It is uncertain why this happened, but is likely do to how the fragment was attached. It was observed that excess glue around the base inhibited growth over the glue surface. This could have influenced the ability for the base to expand in all directions.
The Pachyclavularia sp. demonstrated growth in an opposite trend and had the fastest growth in low light and the slowest in high light. This was the expected trend for this species as it has a wider range of habitation in reefs, but generally is not find exposed to very high light levels. The surface area calculation for this species represents equal growth around the coral perimeter, but growth was not equal in all directions. A major influence on the width measurements was the ability for Pachyclavularia sp. and other soft corals to expand and contract via water intake into the polyps and coral mat. This caused observable variations in width measurements. The low light fragment grew upward instead of outward due to its shape and growth inhibition from glue at the base. This fragment was removed and reattached to create horizontal growth similar to other treatments causing the initial set of measurements unusable.
The biological oxygen demand showed an increasing O2 consumption as the light level decreased. The respiration rates measured in the dark bottles was less than the O2 consumption in the light bottle on every treatment. This was unexpected and it is uncertain why light treatments consumed more total O2, suggesting a negative net primary production. It is possible that the fragments in the dark bottles were stressed from transfer into the bottle and loss of light, resulting in slower respiration rates(Golden reference here). The total O2 consumption in the light bottle treatments follow expected trend of high O2 consumption with lower light levels as compared to other studies (Ulstrup et al, 2011). The respiration rates were similar between all of the fragments and the variation that occurred was likely due to differences in the total biomass of each coral. The low light fragment was observably larger than the medium or high light fragment.
The follow up to this study will be carried out using only Montipora digitata fragments. A minimum of five fragments per treatment should be used to ensure more accurate results. Further analysis of zoothanthellae algae characteristics will be conducted by algal cell counts within tissue sample of fragments and biological oxygen demand test's will be conducted in purpose built acrylic tanks using dissolved oxygen probes.

Literature Cited
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Al-Horani, F.A., Al-Moghrabi, S.M., and de Beer, D. 2002. The mechanism of do calcification and its relation to photosynthesis and respiration in the scleractinian coral Galaxea fascicularis. Marine Biology 142:419–426

Anthony, K., and Hoegh-Guldberg, O.. 2003. Variation in coral photosynthesis, respiration and growth characteristics in contrasting light microhabitats: an analogue to plants in forest gaps and understory's?. Functional Ecology 17(2):246-259.

Connell, J. 1978. Diversity in tropical rain forests and coral reefs. Science, News Series 199(4335):1302-1310.

Davies, S. 1989. Short-term growth measurements of corals using an accurate buoyant weighing technique. Marine Biology 101(3):389-395.

Marunbini, F., Barnett H., Langdon C., and Atkinson M.J. 2001. Dependence of calcification on light and carbonate ion concentration for the hermatypic coral Porites compressa. Marine Ecology Progress Series 220:153-162.

Smith, D et al. 2005. Is photoinhibition of zooxanthellae photosynthesis the primary cause of thermal bleaching in corals? Global Change Biology 11:1-11.

Vermeij, M., and Bak, R.. 2002. How are coral populations structured by light? Marine light regimes and the distribution of Madracis. Marine Ecology Progress Series 233:105-116.

Ulstrup, K. et al. 2011. Variation in photosynthesis and respiration in geographically distinct populations of two reef-building coral species. Aquatic Biology 12:241- 248.

 

Heres the graphs and the tables won't play so I'm not including those because their a huge pain to retype.

Figure 1. High light (HL), middle light (ML), and low light (LL) treatments represent average vertical growth per day. The negative value of LL was due to a horizontal growth pattern, thus vertical growth was skewed.
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Figure 2. Average growth rates of Montipora digitata measured as a single cross section width.
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Figure 3. Average growth rate of Pachyclavularia sp. measured as the surface area of an ellipiod cross section. Averages represent the entire experimental period.
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Figure 4. Average PAR values measured at each treatment on 3 days throughout the experiment.
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Figure 5. The biological oxygen demand for high light (1), medium light (2), and low light (3) over a 12 hour period. Respiration is the O2 consumed in dark bottles and respiration+primary production is the O2 consumed in the light bottles.
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Thanks for putting this up. If you can, try to update it when you start getting the main project rolling.

 

Excellent work. Thanks for sharing. We need more of these experiments!

 

For some reason this paper now come up on Google Scholar. Just for anyone whom finds it through Google Scholar, THIS IS NOT A PEER REVIEWED ARTICLE, so don't site it as one.