Algae are the main producers of the aquatic ecosystem. Aside from being the primary source of food and energy for aquatic animals, they are also used by man as food, sources of agar, as antibiotics, and fertilizers. They are known to be rich in some important vitamins. Consequently, due to their vast ecological and economic potentials, a growing interest in them has been awakened.
Studies on marine algae have been reported in many parts of the Philippine archipelago. Most of these studies, however, have dealt on algal taxonomy and their economic uses. The taxonomic investigations include the published works of Menez (1961), Reyes (1970 & 1979), Cordero (1980), and Calumpong (1981). In Davao City and the vicinity, Medalla and Magpayo reported a total of 109 algal species in 1982.
With the rapid industrialization taking place in many cities of the country, there is a need for more than a taxonomic study of these organisms. It is essential to investigate their ecology. Industrialization can cause pollution and some other changes in the environment. Intertidal zones where algae thrive, are never immune to the unfavorable effects of industrialization. Thus, it is of outmost importance, especially to conversion programs, that distribution and abundance of algae in any one area be studied and the physico-chemical factors affecting them to be investigated.
Algae inhabit either the littoral or the sublittoral zones. Most of the macrobentic forms grow in shallow waters, as in the intertidal area (Asis, 1971). Like other organisms, their occurence is influenced by ecological and geographical factors. These autotrops are all dependent for normal growth and reproduction on such environmental factors as favorable temperature and light; sufficient supply of oxygen, carbon dioxide, and essential nutrients; optimum salinity; type of substratum, movement of water; nature of coast tidal rise, among others (Champman, 1941). Tiin, et. al. (1980) showed that types of substratum, rainfall and exploitation of the area influence algal occurence and variation.
In this study, there is an attempt to determine the biomass and species diversity of the intertidal macrobentic algae at Ilang, Tibungco, Davao City. Odun (1971) claimed that species diversity of a community tends to be low in harsh and physically controlled ecosystems. In many environmental studies, a reduction of species diversity is usually interpreted as evidence of pollution.
In the vicinity of Ilang beach, one finds the Davao Union Cement Factory, TEFASCO and MINTERBRO Shipping Companies. These establishments may have caused some changes in their immediate environment which could have some deleterious effects on the algal communities of the intertidal zone of the said beach. Specifically, the objectives of this study are to:
1. determine the species diversity of the bethic intertidal algae at Ilang;
2. measure the algal biomass of the community at Ilang beach;
3. measure some physico-chemical parameters that may have influenced the biomass and species diversity of the intertidal macrobentic algae.
Methodology
The study area (Fig. 1) is located along the coastal water of Ilang, Tibungco which is about 16 km north of Davao City. The area was divided into three sampling stations at about 500 meters intervals. The three stations did not vary mush in their substrata. Station 1 was located near the area where the Ilang River joins the sea. About 100 meters from its spray zone is reclaimed by the cement factory and used as its storage of raw materials. Station 2 was located north of Station 1. This station has a sandy substratum especially near the spray zone. The area was bounded by the MINTERBRO coastaway. Station 3 was located south of Station 1. The substratum was muddy. About 50 meters from the shore, sparse growth of *H. pinifolia* be observed. Like Station 2, the station was bounded by another concrete coastway.
The procedure includes sampling and analyses of the biological components, specifically algae; and measuring some physio-chemical parameters of the environment. Samplings were conducted every two weeks from September to December 1983.
Water samples were collected from each station and brought to the laboratory for the analyses of total suspended solids, salinity, and chemicals. The total suspended solids were measured by filtering one liter of the water sample with the use of a dry, previously weighed filter paper. The filter paper was then dried in the oven at 105°C and reweighted. The difference in the initial and final weights was taken as the weight of the total suspenden solids in the water.
Salinity of the water was determined by the use of salinometer. Fe, AL, Si Ca, and SO4 in the water were analyzed using the procedures outlined by Scott’s Standard Methods of Chemical Analyses (1959). Dissolved gases concentration and pH of the water were determined on the field. Determination of dissolved oxygen was done by Winkler’s methods as modified by Strichland and Parson. Carbon dioxide level in the water was measured by filling a 100 ml glass stoppered bottle with the water sample to which 10 drops of phenolpthalein was added. This was titrated with n/44 NaOH solutions until a pink color appeared. Water pH, on the other hand was determined by using a pHydrion paper made by the Micro-Essential Laboratory Inc., N.Y.
Three transects marked every 5 meters were set from the spray zone to 20 meters beyond the intertidal zone in the three sampling stations. A 50 x 50 cm. quadrat divided into 25 smaller squares, was used to determine the types or species of algae, their frequencies, coverages, and surface area. The biomass of the algal species was determined by taking the dry weight of the species as they appear in each quadrat. From this total biomass along the transect was calculated.
Species diversity of the algal community was computed using Shannon’s formal for diversity index:
[Refer to PDF file]
Mean biomass and mean species diversity index were also computed for each species and community respectively.
Results and Discussion
Tables 1 and 2 in the Appendix show the biomass and species diversity, respectively, of the macrobenthic algae found in the three sampling stations from September to December 1983. The intertidal community gave *low* diversity index and *low* algal biomass.
In Station 1, no algal species could be collected in the month of September. From October to December, *Enteromorpha* and *Padina* species could be found in some of the 15 quadrats established along the transect of 130 meter. This station got the lowest mean biomass and diversity index.
In Station 2, *Enteromorpha sp.* was found throughout the 4-month period. But in October, 5 other species were recovered together with it.
It can be seen from the tables that only *Enteromorpha* and *Padina* were common to all the three stations. *Dictyota cervicornis*, *Halimeda macrolaba*, and *Amphiroa fragilisima* were found only in Station 2; while *Acantophora spicefera*, *Hypnea valentii*, and *Jania* sp. could be collected only from Station 3.
It was mentioned in an earlier section of this text that algal distribution is limited by the phsico-chemical factors operating in their environment. Salinity is one such factor that can directly or indirectly influence the growth and development of marine organisms including the algae. Salinity of marine habitats where abundant growth of algae can be observed usually ranges from 33% to 40% (Mc Connaughey, 1978).
The average salinity of the intertidal water at Ilang ranged from 24 to 27 o/oo. This low salinity could have, then limited the variation and the abundance of macrobentic algae in the area. The low salinity of the water can be attributed to dilution caused by the Ilang River which has its outlet in Station 1. Menez (1961) noted that in places where rivers have their outlets, salinity is low or diminished. Only very few species of algae can tolerate low salinitiesm and *Enteromorpha* which was present in all the three stations, is one of the few (Reyes, 1970).
On the other hand, Table 3 shows the high values of total suspended solids (insoluble suspended solids can either reflect or absorb a great amount of light, hence, making the latter unavailable to the benthic dwellers) in the water. This indicates that the water was turbid. Turbidity of water in any environment limits the penetration of light. Fell (1975) claims that the amount of total suspended insoluble matter in the ocean depends on the distance from the influence of rivers.
In the Ilang beach, suspended and dissolved matter like clay, silt, inorganic and organic substances, etc. are carried by the river flow and dumped into the ocean. The highest TSS values were obtained from Station 1 where, as pointed out before, the river outlet was. This station also got the lowest biomass and diversity index. Dusts coming from the cement factory and ultimately finding their way into the ocean, definitely contributed also the amount of solids in the water.
Reyes (1970) observed that lights affects the distribution of algae. Thus, in water environments where light penetration is greatly reduced by high levels of suspended solids, algae are scarce. This is, of course, because the photosynthetic activity of the said organisms is impended by the insufficient amount of light reaching them.
Another major factor that could have considerably reduced the abundance and kinds of algae at the intertidal area of the Ilang beach was the substratum. It was generally sandy-muddy. Growth of algae, according to Velasquez (1971), depends to a great extent on the type of substratum where they have to firmly attach their hold facts to prevent them from being carried away by water currents and waves. The same observation was also made by McConnaughey (1970).
The sandy-muddy substratum at Ilang beach may be attributed to a number of factors. Firstly, the area is a reclaimed one. Soil dumped into the sea during the reclamation process could have brought about the corresponding changes in the substratum. Secondly, concrete coastways have been constructed at the TEFASCO and MINTERBRO wharves. These coast ways have been reduced tidal action resulting to the accumulation of mud and silt which eventually settled down and formed muddy layers at the bottom. Consequently, algal spores have a difficulty is establishing themselves in the area.
Tables 4 and 5 present the levels of dissolved gases in the water. No clear relationship can be established between dissolved oxygen concentration and diversity or biomass of algae. Except for September, D.O. level did not go beyond the standard minimum level of 5 ppm. On the other hand, the highest level of Carbon Dioxide was 14.25 ppm. Even this value is lower than the standard minimum concentration of 20 ppm. Considering that CO2 is an essential raw material for photosynthesis, insufficient supply of it will certainly reduce the survival potential of the algae.
Meanwhile, chemicals analyses of water samples from the study area indicated quite concentrations of insoluble substances, namely, FE2O3, Al2O3, and Sio2 (Table 6). These compounds, along with CaO and SO4, are some of the chemical components of typical cement dust (Sell, 1981). The highest levels were found in Station 2. This may be due to the fact that Station 2 is adjacent to Station 1 where the river unloads itself into the sea. Some dusts and waste materials could have been collected by the river from somewhere upstream. The presence of the coast ways can also be considered as another reason why the chemicals failed to be dispersed properly.
Sell mentioned in her book that when insoluble substances accumulate in the water, they became particulates which can be toxic to plants. Dusts from cement manufacturing processes, likewise, cause alkalinity in the wate systems. The mean pH of 8.5 in all the three stations seem to conform with the above finding of previous studies. Algae thrive only within a certain pH range. So if the water becomes alkaline they will not be able to grow and develop normally.
One or more observation made during some of the sampling periods, was the presence of films of oils floating off the waters in the three stations. Ships docking at the TEFASCO and MINTERBRO areas could be the possible source of the oils. Such oil slakes can further block the sunlight and may even interfere in the natural aeration process of the water. Either way, they are detrimental to the metabolic activities of the algae and the other organisms.
Conclusion
This present study has revealed that the algae community at the intertidal zone of Lanang Beach has a species diversity of less than 1 and a low biomass as well. These condition seem to indicate a sub-optimal environment which does not favor algal growth. Human activities could have contributed to making that sub-optimal environment at Lanang Beach.
Table 1
BIOMASS OF THE MACROBENTHIC ALGAE COLLECTED FROM THE 3 STATIONS FROM SEPTEMBER TO DECEMBER 1983
[Refer to the PDF file]
Table 2
SPECIES DIVERSITY OF THE MACROBENTHIC ALGAE IN THE 3 STATIONS DURING THE FOUR MONTHS SAMPLING
[Refer to the PDF file]
Table 3
TSS VALUES IN THE 3 STATIONS DURING THE FOUR SAMPLING MONTHS AND THEIR AVERAGE (mg/liter)
[Refer to the PDF file]
Table 4
D.O. VALUES IN THE 3 STATIONS DURING THE FOUR SAMPLING MONTHS (ppm.)
[Refer to the PDF file]
Table 5
DISSOLVED CO2 IN THE WATER OF ILANG FOR THE FOUR SAMPLING MONTHS (ppm.)
[Refer to the PDF file]
Table 6
AVERAGE LEVELS OF THE DIFFERENT CHEMICALS PRESENT IN THE SEAWATER FROM THE 3 STATIONS OF ILANG BEACH (ppm.)
[Refer to the PDF file]