GROWTH OF SELECTED MANGROVE SEEDLINGS UNDER SIMULATION OF OCEAN ACIDIFICATION

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1 2016, 79 (1& 2), GROWTH OF SELECTED MANGROVE SEEDLINGS UNDER SIMULATION OF OCEAN ACIDIFICATION ROZAINAH, M.Z. 1, 2 *, TAN, X.L1 AND JENNICE, Y.S.E 1. 1 Institute of Biological Sciences, University of Malaya, Kuala Lumpur, Malaysia. 2 Institute of Ocean & Earth Sciences, University of Malaya, Kuala Lumpur, Malaysia. *Corresponding author: rozainah@um.edu.my Abstract: The increase in anthropogenic carbon dioxide emission has caused the lowering of ocean ph value. This phenomenon has also caused disturbance to oceanic and intertidal organisms. A simulation study on the effect of ocean acidification was conducted to determine its effect on the growth of selected mangrove species, Avicennia sp. and A total of 60 Rhizophora sp seedlings and 50 seedlings each for the latter two species were monitored for their growth in this simulation study. Half of the seedlings were raised in normal saltwater (ph 8.2) and the other half were in the acidic saltwater (ph 5.0). The living conditions were adjusted and modified to simulate the natural environment at coastal area. The growth of seedlings were observed and monitored for 20 weeks, where the parameters such as number of leaves, plant height, stem diameter, chlorophyll fluorescence and dry weight were measured every 3 weeks. Statistical test was conducted to seek any significance impact posed by ocean acidification on the survival and growth of these important mangrove seedlings. The results indicated that generally there was no significant difference in terms of growth rate of, and Avicennia sp. apart from a significant increasing in height of in acidic water. In general, this short term study concluded that there were no effects of ocean acidification to the growth rate of mangrove seedlings. Key words: Ocean acidification,, Avicennia sp., Brugueira sp. INTRODUCTION Ocean acidification is the decreasing of ph value of the seawater which caused mainly by the increasing of CO2 being absorbed by the ocean. The increasing of CO 2 concentration was recorded since the industrial revolution. Ocean anthropogenic CO 2 uptake is leading to a rapid decrease in the world s surface oceans ph (Henderson 2006). This process, commonly known as ocean acidification (OA) is accelerated by increasing anthropogenic released CO 2, (Duarte et al. 2013). According to Sabine et al. (2004), oceans have taken up about one-third of anthropogenic CO 2 produced in the past 200 years. OA is expected to further accelerate unless future CO 2 emissions are being tackled. One well-known effect of OA is on the shell-forming marine organisms, in which OA will lower the calcium carbonate saturation states. 157

2 However the effects of OA go more than just affecting specific marine organisms. It impacts the fundamental processes that are essential to the marine and millions of people that depend on ocean for food and livelihoods (Henderson 2006). Mangroves are known to be highly adapted to saline living conditions and able to withstand the erosion from tidal winds and waves. However there is a need and urgency to understand the ocean acidification effects on mangroves for their anthropogenic as well as non-anthropogenic importance. Studies of ocean acidification on marine organisms such as calcifying living and coral reefs has been done, but there is still lacking of studies on mangroves for this phenomenon (Anthony et al. 2011, Hoegh-Guldberg et al. 2007, Orr et al. 2005). This paper attempts to evaluate the situation on how ocean acidification will affect the growth of the mangrove species MATERIALS AND METHODS The study was conducted in a glasshouse at the Institute of Biological Sciences, University of Malaya, Kuala Lumpur, where two big tanks inside the glasshouse were filled with tap water. The same amount of Instant Ocean Aquarium Sea Salt Mixture was added into the tanks respectively for saltwater preparation. Sea salt was allowed to dissolve in the tank water, and the salinity was measured by using ATAGO Master Refractometer (Japan). The salinity for both tanks was set at 30 ppt as artificial seawater (Ye et al. 2003), and was maintained throughout the experiment. To simulate ocean acidification, 1M Sulphuric acid (H2SO4) was prepared in laboratory following the standard method. Firstly, a 1000ml PSL-BS 1792 volumetric flask (England) was half-filled with distilled water. Then, it was slowly added with 55.6ml of H 2SO 4 reagent. Finally it was being top off with more water until the flask was filled with 1l of solution. The volume of H 2SO 4 needed was determined by the calculation as follow: The concentrated H 2SO 4 used was at 18.0 Molarity. In other words, there are 18 moles of H 2SO 4 in each litter of the solution. That means 1ml of H 2SO 4 contains moles of H 2SO 4. Therefore, we need 55.6 ml of H2SO4 reagent to make 1M of H 2SO 4 solution. The solution was mixed well by shaking. The acid solution was added into one of the tank of saltwater drops by drops until the ph 5.0 was obtained. The other tank was left as it is and was read as ph 8.2. A total of 60 seedlings of 50 seedlings Avicennia sp. and 50 seedlings of were divided and arranged equally in both tanks. Growth parameters i.e. height, number of leaves, diameter of first node and dry weight were measured every 3 weeks for 20 weeks. The photosynthetic performance was also tested by using Handy Pea Chlorophyll fluorimeter analyser (Hansatech). The equipment can measure the efficiency of the light use for photochemistry to indicate the maximum efficiency of Photosystem II of the seedlings. ANOVA was carried out to test the equality of these three mangroves population means by analysing sample variances. Each mangrove sample is assumed independent of the other sample and population variances are equal. 158

3 RESULTS AND DISCUSSION At the end of the experiment, the survival rate of under normal ph remains 100% but reduced ph caused 12% mortality, and this difference is significant at p<0.05. While in Avicennia sp., both treatments resulted in 12-20% mortality. The survival rate of on the other hand was recorded at 100% till the end of the experiment. This probably due to the reason that the seedlings quality were good and they were able to withstand and adapt to the living environment in glasshouse that was simulated as tidal area where mangroves naturally grow. The glasshouse were equipped with fan to simulate tidal wind, pump as simulation of tidal waves and watering system twice a day to ensure the growth of mangrove seedlings. Table 1. Growth rates for both mangrove species under different ph. Species ph Height (cm/week ) Avicenn ia sp. Bruguie ra sp. Rhizoph ora sp. 5.0 y=2.13x y=1.51x y=0.76x * 8.2 y=0.59x * 5.0 y=2.09x y=2.34x (* denotes significant at 0.05) Number of leaves (number/w eek) y=1.00x+6.43 y=0.63x+7.88 y= 0.55x y= 0.41x y= 0.69x y=0.66x Diameter (cm/week) y=0.34x y=0.22x y=0.39x y=0.39x y=0.232x y=0.277x Biomass (g/week) y=0.23x+0.95 y=0.20x+1.23 y=0.14x+5.11 y=0.13x+5.16 y =1.02x + 43 y=1.34x Final Chlorop hyll fluoresc ence The growth results are shown in Table 1. Both treatments were able to show steady and positive growth rates towards the end of experiment. From the t- test conducted, the results also showed no significant difference between acidic and normal saltwater in their leaves growth rate. The reduced ph only gave impact on where reduced ph was significantly better than normal ph in terms of height increment (Table 1). Study from Gudadari and Nayak (2014) showed that the plant height and its diameter are inter-related where the increase in one factor will leads to the increase of another. However, the reduced ph did not influence Avicennia sp. and at all. However, the results shown some variations in terms of growth rates between normal and reduced ph. 159

4 The species studied were also tested for their healthiness under ph stress via measurement of their chlorophyll fluorescence. A very healthy sample will read as Our current study showed that the t-test for showed there was no significant difference of the chlorophyll fluorescence of this mangrove species in normal ph (0.8325) and reduced ph (0.8327). However, chlorophyll fluorescence of Avicennia sp. showed a significant difference in normal ph (08) and reduced ph (0.82). The result showed that Avicennia sp. was healthier when raised in acidic saltwater (ph 5.0). For Rhizphora sp., t-test conducted showed there was no significant difference of the chlorophyll fluorescence in normal and acidic saltwater. From calculation, the mean value of chlorophyll fluorescence of in normal saltwater differ from acidic saltwater by merely This showed the healthiness of seedlings were similar in both tanks. However, the values of chlorophyll fluorescence of, Avicennia sp. and were less than 0.85, the optimum value of chlorophyll fluorescence of a healthy plant (Hansatech Instruments 2006). This could meant that these three mangrove species were still under stress in their environment, and perhaps a longer experiment is essential to get more readings and let the mangrove seedlings to have longer time to fully adapt to a new environment. The current results indicated that mangrove can survive under reduced ph, even as low as 5 although Orr et al. (2005) estimated that the ph level of ocean will decrease to in 2050 and continuously dropped to in 2100 by doing a CO 2 doubling experiment. Farnsworth et al. (1996) proved that the growth rates of mangroves increased with the increasing of atmospheric concentration of CO 2, similarly current study shows that Avicennia sp. is healthier in reduced ph. Ocean is not the only source of acid. Mangroves also produce acid when the shed mangrove leaves which contain high tannin that can be preserved in the sediments will also cause the mangrove soil to be naturally acidic (Lacerda et al. 1995). There is also present of humic acids in the mangrove areas as a part of the contributor to the acidity of the mangrove soils (Lacerda et al. 1995). Mangroves litter which also contains pyrites (FeS2) will release sulfuric acid (H 2SO 4) when exposed to the air (Struve & Falconer 2001). Table 2 shows that all three mangrove species did not differ significantly under the influence of reduced acid or ocean acidification, as seen in the P-value where all values are above However, this study was only restricted to seedlings performances. If the experiment extended to much older specimens, there could be a different study. Even though survival rates are considered good, the growth performances may be stunted and unhealthy. The effects of ocean acidification on other organisms were well studied compared to its effects on mangrove. For example, Henderson (2006) discussed about the profound effects of ocean acidification on the process of shell-forming on marine living such as mollusks, corals and echinoderms. It will lower the calcium carbonate (CaCO 3) saturation states that slow down the formation of shell of these organisms. This is very crucial as these organisms is largely depends on the protection of their exoskeleton. Takahashi et al. (2006) also studied that the increase uptake of anthropogenic CO 2 is the main contributor major for long-term increases in dissolved inorganic carbon (DIC) and decreases in CaCO 3 saturation state. Kurihara et al. (2007) reported that after fertilization of the oyster species C.gigas that were 160

5 exposed to elevated CO 2 concentration, more than 80% of the larvae grown in high- CO 2 seawater displayed malformed shells or remained unmineralized. Table 2. Comparison between growth performance of different species under the impact of ocean acidification. Growth parameter ph Species P value Number of leaves 8.2 Avicennia sp Height 8.2 Avicennia sp Biomass 8.2 Avicennia sp Diameter 8.2 Avicennia sp Chlorophyll fluorescence 8.2 Avicennia sp On the other hand, a work by Fine & Tchernov (2007) showed two species of corals grown in highly acidified water have completely lost their skeletons. Then, they are regrown after being returned to seawater of normal ph. The study highlighted important points, where coral calcification rates can vary greatly in response to changes in ph and the organisms healthiness overall would change because of the loss of the protective skeleton. Increasing ocean acidification has not only shown the decrease coral community calcification rate, but also coral dissolution rates (Langdon et al. 2000, Yates & Halley 2006). It is therefore very important to handle the problem of ocean acidification at once since studies have shown its effects on the food web, carbon and nutrient cycling of the marine ecosystems. 161

6 CONCLUSION Generally, the reduced of ph value of saltwater does not affect the growth rates of Rhizophora sp, Avicennia sp. and in terms of number of leaves, plants height, diameter at the first stem node and biomass. This also showed the ability of mangroves to adapt to the ph changes in their living environment and ocean acidification phenomenon seems to contribute little influence on the growth of mangrove species. ACKNOWLEDGEMENTS The authors are grateful to the Institute of Biological Sciences (ISB), and the Institute of Ocean & Earth Sciences (IOES), University of Malaya for financial and technical assistance conducting the study. REFERENCES Anthony, K., Maynard, J. A., Diaz pulido, G., Mumby, P. J., Marshall, P. A., Cao, L. & Hoegh- Guldberg, O Ocean acidification and warming will lower coral reef resilience. Global Change Biology 17(5): Farnsworth, E.J., Ellison, A.M. & Gong, W.K Elevated CO2 alters anatomy, physiology, growth and reproduction of red mangrove (Rhizophora mangle L.). Oecologia 108: Fine, M. & Tchernov, D Scleractinian coral species survive and recover from decalcification. Science 315(5820): Hansatech Instruments Ltd Setup, Installation & Maintenance. Operations Manual. Harvey, H. W The Chemistry and Fertility of Sea Water. London: Cambridge University Press. Henderson, C Ocean acidification: the other CO2 problem. New Scientist 2563: Hoegh-Guldberg, O., Mumby, P., Hooten, A., Steneck, R., Greenfield, P., Gomez, E. & Caldeira, K Coral reefs under rapid climate change and ocean acidification. Science 318(5857): Kurihara, H., Kato, S. & Ishimatsu, A Effects of increased seawater pco2 on early development of the oyster Crassostrea gigas. Aquatic Biology 1(1): Lacerda, L.D., Ittekott, V. & Patchineelam, S.R Biogeochemistry of mangrove soil organic matter: A comparison between Rhizophora and Avicennia soils in South-eastern Brazil. Estuarine, Coastal and Shelf Science 40 (6):

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