Marco Lassandro Student ID Number 23531525 Rock Pool Field Trip Report Abstract The intertidal zone is a unique ambient characterised by extreme fluctuations both during the day and throughout seasons, and it is a harsh and unforgiving habitat. However, it offers also some advantages to the species inhabiting it, for instance, a constant influx of oxygen and nutrients thanks to the action of waves. Depending on the amount of exposure each gets, the intertidal zone is divided into four subdivisions: the spray zone, and the high, middle and low tide. Each of them has its peculiar challenges, and both demand high adaptability. This study compares five pools located in Woody Head, north coast NSW, and aims at analysing the relationship between rock pools location and size, water quality and marine life sustained. The test was carried in a sunny and windy day, and different instruments were used to gauge pH, dissolved oxygen, temperature and conductivity, and the latter combined with a conversion table also allowed the extraction of salinity (see Figure 7, Appendices). The study has shown that the pH tended to decrease with the augment of the distance from the ocean. At the same time, conductivity and salinity displayed a positive association with the distance from the ocean. Instead, dissolved oxygen levels did not register a fixed trend, suggesting a more complex relationship with the environment. Overall, the results indicate that both the physical and chemical characteristics of a pool, the environmental conditions and the marine life present have all an impact on water quality. 1.Introduction Woody head is a renowned campground beach proximate to Iluka. Local weather on the 12th of September 2019 was sunny and windy; having a minimum temperature of 11.10C, and maximum 23.20C; a difference of 12.2 degrees. These conditions were combined with 11.535.5kms/hr. wind gusts. August rainfall of 76.4mm was supplemented by 0.6mm earlier in September (BOM, 2019). The data were measured between 11:05 am and 12:20 pm and spring tides marked their lowest measure at 12:54 pm (0.32 meters). During spring tidal cycles there is a more considerable variation between high tides and low tides compared to neap tides (i.e. high tides are higher, low tides are lower). This signifies that the pools may be exposed to agents like sun and wind, except than in periods of high seas (Cullen M. & Reichelt-Brushett A., 2019). Five pools were selected for the test, and their distance from the ocean ranged from 10 to 50 meters. The scope of the project was to gauge the pH, conductivity and dissolved oxygen (DO) and analyse how the chemical and physical properties of the rock pools can affect these parameters. Moreover, other variables like the dimensions of the pools (length, width and depth), and temperature of the water were recorded to have a complete overview (knowing both conductivity and temperature is possible to calculate the salinity ‰ using a conversion table). Different instruments like pH meter, conductivity meter and dissolved oxygen micro- titrator kit were used to collect the data. Conditions in rock pools are far from stable and integral factors like pH, salinity, temperature and DO vary widely within pools both during the day and throughout seasons (Daniel M. J. & Boyden C.R., 1975). In fact, within rock pools, salinity can augment by 3 part per thousand (ppt), temperatures can rise to the extent of 15°C and oxygen levels can drop dramatically in just a few hours (Congleton J. L., 1980; Metaxas A. & Scheibling R.E.,1993; Jensen S. L. & Muller-Parker G., 1994). DO is a measure of the quantity of oxygen dissolved in water, i.e. the amount of oxygen available to the organisms inhabiting the system, and it is a crucial factor to determine the habitability of a determined environment. The quantity of DO is affected by several components. For instance, aquatic respiration and decomposition decrease DO concentrations and oppositely rapid aeration and photosynthesis can cause supersaturation. An insufficient level of oxygen dissolved in the water for a period of time can render the water unsuitable for many organisms due to hypoxia conditions. Just as low dissolved oxygen can cause problems, so too can high concentrations. Supersaturated water can cause gas bubble disease in fish and invertebrates; this usually occurs when the DO maintain a level of 115-120 % for a prolonged period. Similarly, also an acidic pH can impact the habitability of a rockpool for marine species. Today, the major driver of ocean acidification is anthropogenic atmospheric CO2, albeit in some coastal regions, nitrogen and sulphur are also important (Doney S. Et. Al., 2007). Salinity represents the quantity of salts dissolved in water, and its stability is essential to maintain the osmotic balance. In addition to that, salinity also covers a role in the determination of the electrical conductivity of water, being a measure of the concentration of dissolved salts within that water. Figure 1: Left: Enlarged view of Woody Head and its surroundings. Right: Location of Woody Head. Source: Google maps,2020. 2.Methods After having selected the pools, the first step was to measure their dimension (length, width and depth). Next, the pH was taken using a pH meter (Eutech Model Ecoscan pH6, resolution: 0.01 pH and accuracy: ±0.01 pH). It is important to be consistent with the time waited after that the measurements settle down, as this practice can remove a source of error. Furthermore, it must be remembered that the instrument cannot be fully submerged given that the probe is not waterproof. After that, a conductivity meter (Eutech Model Ecoscan Con6, resolution and accuracy = 0.01, 0.1, 1 µS/cm & 0.01, 0.1 mS/cm; ±1% Full Scale) was utilized to appraise both conductivity and temperature. These two measures can then be converted into salinity using a conversion table provided with the meter. The DO was computed with a dissolved oxygen micro-titrator kit following the Winkler method (see A Figure 8, Appendices), the results obtained were in mgL-1 and were later converted into a percentage (see Figure 9, Appendices). Considering the chemical properties of the elements used, it is fundamental wearing protective equipment, such as gloves and goggles. It is also of the prime importance to prepare a waste bin to collect all the waste produced to avoid dispersion on the environment. Likewise, it is important to fill the jar underwater to avoid any possible interference with oxygen in the atmosphere, which can falsify the test. B 3.Results C D E Figure 2: Raw data of rock pool observations and measurements (Clark S.,2019) 8,65 8,6 8,55 8,5 pH 8,45 8,4 8,35 8,3 8,25 8,2 8,15 10 20 30 40 50 Distance from the ocean (m) Figure 3: Graphic of the pH related to the distance from the ocean (m). 55 Conductivity (mS/cm) 54 53 52 51 50 49 10 20 30 40 50 Distance from the ocean (m) Figure 4: Graphic of the conductivity (mS/cm) related to the distance from the ocean. 140 120 DO % 100 80 60 40 20 0 0 10 20 30 40 50 60 Distance from the ocean (m) Figure 5: Scatter plot of the DO % related to the distance from the ocean. 36,5 36 Salinity ‰ 35,5 35 34,5 34 33,5 33 32,5 0 10 20 30 40 50 Distance from the ocean (m) Figure 6: Scatter plot of the salinity ‰ related to the distance from the ocean. Examining the data gathered is observable that the pH tended to decrease with the augment of the distance from the ocean, while conductivity and salinity displayed a positive association with the distance from the ocean. Instead, dissolved oxygen levels did not register a fixed trend, suggesting a more complex relationship with the environment. 4.Discussion The results indicate that both the physical and chemical characteristics of a pool, the environmental conditions and the marine life present have all an impact on water quality. The pH recorded was slightly alkaline in all cases, ranging from 8.59 to 8.3, with an overall negative trend with the augment of the distance from the ocean. Conductivity ranged from 50.9 mS/cm to 54.2 mS/cm, and even if the graphic is bit erratic, it suggests that this parameter tend to have a positive association with the distance from the ocean. The salinity measured varied from 33‰ (at 10 meters from the ocean) to 36‰ (at 40 and 50 meters from the ocean), this suggests that the salinity increases as the distance from the ocean augments. The DO % had a fluctuating trend but was acceptable in all the pools (according to the Australian and New Zealand Environment and Conservation Council (2000) it should be between 90% and 110% saturation), except than in the third pool on which it was slightly superior (122.35%). The solubility of oxygen decreases as temperature increases. This means that warmer surface water requires less dissolved oxygen to reach 100% air saturation than does deeper, colder water. Besides, dissolved oxygen decreases exponentially as salt levels increase. Oppositely, salinity would be higher on a warm day, due to the enhanced evaporation. In contrast, as temperature decreases salinity values drop and DO percentage tend to increase. Another component playing a role in these fluctuations is the volume of a pool. A pool with a larger volume is less vulnerable to brusque changes. This signifies that while salinity and dissolved oxygen would still vary depending on the climatic conditions as previously discussed, the variations are more contained than in a pool having a smaller volume. In addition to that, also the abundance of marine life covers an integral role in the variance of parameters such as pH and DO. For example, especially in small rock pools, pH can vary significantly throughout the day, even to the extent of 1.5 units (Scholnick D.A., 1994). That occurs because during the night organisms like plankton and aquatic plants produce more carbon dioxide via respiration, thus decreasing pH in the early morning (Chan M.A. Et Al., 2005). Phytoplankton affect water quality in several ways (Boyd C.E.,1982; Smith D.W., 1987) nevertheless their importance on rock pools system derives chiefly from the complex role that they cover when it comes to dissolved oxygen levels. In fact, the relative magnitudes of photosynthetic oxygen generation and total plankton respiration are two of the main drivers of DO levels (Steel J.A., 1980). At intermediate levels of phytoplankton biomass dissolved oxygen levels peaks; however, with dense algae, the net primary production (NPP) is scarce, due to the lack of sufficient nutrients and light (Goldman J.C.,1979; Javornicky J.A.,1980; Laws E.A. & Malecha S.,1981). Rock pools can present extreme conditions that are highly challenging for the organisms living in this environment. The brusque variations on vital factors like pH, dissolved oxygen levels and temperature require the ability to be highly adaptable. Hence, species which are less vulnerable to these changes are the ones which are most likely to thrive. Both sea anemones and Scleractinian corals have a symbiotic relationship with zooxanthellae, which are members of the phylum Dinoflagellata. Zooxanthellae translocate products of the photosynthesis to their host and in return receive inorganic nutrients, for instance, CO2 and NH4+. Anemones are highly pliable thanks to a tissue layer called mesoglea; in fact, its elastic property helps anemones on restoring the shape after a contraction of their bodies. This characteristic can be useful to resist to extreme conditions, such as desiccation on periods of low-tide and strong ocean currents. In contrast, corals are more sensitive to alterations of temperature, they can bleach following a spike of just 1 to 2 degrees, and if the bleaching is prolongated they can eventually die. So, they are also more prone to desiccation, and this phenomenon can be amplified if periods of extreme low tides coincide with high solar radiation (Anthony K.R.N. & Kerswell A.P., 2007). Furthermore, corals require calcium carbonate to develop their skeletons, which they produce combining calcium ions (Ca2+) with carbonate (CO32-) present in the water. However, the acidification of the water can endanger this process; indeed, a major concentration of hydrogen ions (H+) reduce the carbonate available for corals seeing that the hydrogen ions have a superior electronegativity compared to the calcium ions. This favours the production of bicarbonate ions (HCO3-), preventing corals from building their skeletons (see Figure 10, Appendices). Actually, corals can still extract carbonate from more acidic water, but this process requires more energy, which then cannot be allocated to other activities like reproduction. Oppositely, sea anemones can withstand better superior concentrations of CO2 in water; factually, their productivity can even increment with elevated concentrations of carbon dioxide (Suggett D.J. Et. Al., 2012). To summarise, adaptability is an integral quality, particularly on harsh environments such as rock pools. Thus, a significant presence of sea anemones can be ascribed to their superior versatility, a factor that can give them a crucial edge on Scleractinian corals when it comes to survive and flourish. 5.References Anthony K.R.N. & Kerswell A.P. (2007) Coral mortality following extreme low tides and high solar radiation. Marine Biology,15, 1623-1631. Australian and New Zealand Environment and Conservation Council & Agriculture and Resource Management Council of Australia and New Zealand ( 2000) Australian and New Zealand Guidelines for Fresh and Marine Water Quality, Volume 1, The guidelines, 314 pp. Boyd, C.E. (1982) Water Quality Management for Pond Fish Culture. Elsevier, Amsterdam, 318 pp. Chan M.A., Moser K., Davis J.M., Southam G., Hughes K. & Graham T. (2005) Desert potholes: Ephemeral aquatic Microsystems. Aquatic Geochemistry, 11, 279– 302. Clark S. (2019) Raw data of rock pool observations and measurements. Congleton J.L. (1980) Observations on the responses of some southern California tidepool fishes to nocturnal hypoxic stress. Comparative Biochemical and Physiology Part A: Molecular & Integrative Physiology, 66, 719–722. Cullen M. & Reichelt-Brushett A. (2019) Laboratory Manual (Twelfth edition) CHE00201. Southern Cross University,104 pp. Daniel M. J. & Boyden C.R. (1975) Diurnal variations in physico-chemicals conditions within intertidal rockpools. Field Study Journal (1975),4,161-176. Doney S.C., Mahowald N., Lima I., Feely R.A., Mackenzie F.T., Lamarque J.F. & Rasch J., (2007) The impacts of anthropogenic nitrogen and sulfur deposition on ocean acidification and the inorganic carbon system. PNAS September 11, 2007, 104(37), 14580–14585. Goldman, J.C., (1979) Outdoor algal mass cultures-II. Photosynthetic yield limitations. Water Research, 13,119-136. Google Maps (2020a) Enlarged view of Woody Head and its surroundings. Google Maps (2020b) Location of Woody Head. Javornicky, J.A., (1980) The Functioning of Freshwater Ecosystems. Cambridge University Press, 588 pp. Jensen S.L. & Muller-Parker G. (1994) Inorganic nutrient fluxes in anemone-dominated tide pools. Pacific Science, 48, 32–43. Laws, E.A. and Malecha, S. (1981) Application of a nutrient-saturated growth model to phyto- plankton management in freshwater prawn (Mucrobrachium Fosenbergii) ponds in Hawaii. Aquaculture, 24,91-101. Metaxas A. & Scheibling R.E. (1993) Community structure and organisation of tidepools. Marine Ecology Progress Series, 98, 187–198. Scholnick D.A. (1994) Seasonal variation and diurnal fluctuations in ephemeral desert pools. Hydrobiologia, 294, 111– 116. Smith D.W. (1987) Biological control of excessive phytoplankton growth and enhancement of aquacultural production. PhD Dissertation, University of California, Santa Barbara, Ca, 196 pp. Steel J.A., (1980). Phytoplankton models, Functioning of Freshwater Ecosystems. Cambridge University Press, Cambridge,220-227. Suggett D.J., Hall-Spencer J.M., Rodolfo-Metalpa R., Boatman T.G., Payton R., Pettay D.T., Johnson V.R., Warner M.E. & Lawson T. (2012) Sea anemones may thrive in a high CO2 world. Global Change Biology,18(10),3015-3025. 6.Appendices Figure 7: Conversion table to obtain salinity from conductivity. Figure 8: Instructions for the usage of the dissolved oxygen micro-titrator kit. DO% saturation = (DO in sample – DO at saturation) * 100 Figure 9: Formula for the conversion of DO to mgL-1 to percentage. CO2+H2O=> H2CO3=> H++HCO3Equation 1: Dissociation of carbon dioxide in seawater H++HCO3-=> 2H++CO32Equation 2: Dissociation of bicarbonate ions. Ca2++ CO32-=> CaCO3 Equation 3: Formation of calcium carbonate. This compound is fundamental for corals to build their skeletons. CO2+H2O=> H2CO3<<=> H++HCO3-<<=> 2H++CO32Equation 4: Modified carbonate equilibria as a consequence of a higher concentration of CO2 absorbed by the ocean. The reaction tends to shift towards left yielding more carbonic acid, causing acidification of seawater. Figure 10: Series of equations describing carbonate equilibria in seawater.