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.