9 Potential Roles of Biotic Factors in Regulating
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Jurnal Ilmu dan Teknologi Kelautan Tropis, Vol. 4, No. 1, Hlm. 9-23, Juni 2012 POTENTIAL ROLES OF BIOTIC FACTORS IN REGULATING ZOOPLANKTON COMMUNITY DYNAMICS IN JAKARTA BAY SHALLOW WATER COASTAL ECOSYSTEM Arief Rachman1 and Nurul Fitriya1 1Research Center for Oceanography Indonesian Institute of Sciences Jl. Pasir Putih I, Ancol Timur , Jakarta Utara 14430 [email protected] ABSTRACT The dynamics in zooplankton abundance were regulated by changes in water physical-chemical parameters and interaction with biotic factors. In this research we examined the relationship between zooplankton community dynamic and important biotic factors, such as predation and food availability, in Jakarta bay. Plankton samplings were done in 10 sampling stations in Jakarta bay, from July to November 2009. Zooplankton samples were collected using horizontal towing method with NORPAC plankton net (mesh size 300 µm). Salinity, water depth, water temperature, and water transparency were measured. Phytoplankton samples were also collected with the same method as zooplankton, using Kitahara plankton net (mesh size 80 µm). Zooplankton taxas were grouped into two groups, the prey and predatory zooplankton. The results showed that there were two different patterns in zooplankton groups dynamic i.e., the single and double peak. The abundance peak in most zooplankton groups, such as copepods, cirripeds, luciferids, and tunicates, were induced by the high food availability during the phytoplankton bloom in August. The high abundance of prey zooplankton groups in August was responded by the predatory zooplankton groups, resulting in high abundance of predatory zooplankton in adjacent month. The high abundance of ctenophores and chordates (fish larvae) were suggested as the main factor for the low abundance of other zooplankton in September. Physical and chemical factors were not the regulating factors due to the stability of those factors during this research period. Thus we concluded that food availability and predator-prey interaction were the main factors which regulate zooplankton community dynamics in Jakarta bay. Keywords: predator-prey interaction, zooplankton, abundance peak, food availability, phytoplankton bloom I. INTRODUCTION bioindicator for environmental changes and pollution, due to the high sensitivity In marine ecosystem, zooplankton of some species to any changes in water plays an important role as a link in marine quality. Variation or fluctuation in water food web, connecting the energy transfer quality might induce seasonal succession between primary producer and higher and fluctuation in the abundance and trophic level organisms, such as shrimps distribution of zooplankton in marine and fishes. Thus any change in ecosystem (Woodmanse, 1958; Hsiao et zooplankton community could affect the al., 2011). The physical and chemical community of the primary producer and parameters that usually limiting the higher trophic level organism (Horne and zooplankton abundance and distribution Goldman, 1994; Nybakken and Bertness, are dissolved oxygen, turbidity, 2005; Marques et al., 2008; Hsiao et al., temperature, current, salinity and pH. 2011). Zooplankton could also be used as Food availability, competition, predation ©Ikatan Sarjana Oseanologi Indonesia dan Departemen Ilmu dan Teknologi Kelautan, FPIK-IPB 9 Potential Roles of Biotic Factors in Regulating... and disease were other factors which relatively eutrophic condition during all might also limiting the abundance and seasons, especially during rainy season. distribution of zooplankton in marine This condition should creating a relatively ecosystems (Horne and Goldman, 1994; stable pattern, with low fluctuation, in Nybakken and Bertness, 2005; Escribano both phytoplankton and zooplankton et al., 2007; Hsiao et al., 2011) abundance in shallow water tropical Research on zooplankton coastal ecosystem (Wickstead, 1976; community dynamics revealed that Raymont, 1983; Nybakken and Bertness, bottom-up control by phytoplankton was 2005). an important factor that determines the Jakarta bay locates in the north of abundance and distribution of zooplankton jakarta and it is a shallow coastal waters.. in marine ecosystem. Thus zooplankton There are 13 big and small rivers flows to maxima were usually occurred right after the Jakarta Bay which makes river the occurrence of phytoplankton maxima. outflow plays a great role in transporting Predation by zooplanktivorous fish and huge amount of sediments, nutrients and carnivorous zooplankton, such as pollutants to its ecosystem. A number of ctenophores and chaetognaths, also investigations have been done in the capable on limiting the zooplankton Jakarta Bay and shows a decline in abundance and distribution in marine plankton diversity but harmful algal ecosystem (Horne and Goldman, 1994; blooming was occured more often due to Uye et al., 2000; Escribano et al., 2007; low water quality (Hadikusumah, 2008; Reaugh et al., 2007; Sullivan et al., 2007). Muchtar, 2008; Sidabutar, 2008). Predation was known as one of the major Although research on zooplankton ecological forces that regulating the community in Jakarta bay has been done abundance, biomass and composition of several times, little or no specific attention the prey organisms in coastal ecosystem. was given to the interaction between Predator might also act as top-down zooplankton community dynamic to some control to regulate the dynamics of other important biological factors, such as zooplankton groups, thus might inducing predation and food availability. Thus in the trophic cascade phenomena to happen this research, we examined the in the ecosystem (Pace et al., 1998; relationship between the changes in Vadeboncoeur et al., 2005; Rilov, 2009). zooplankton abundance to predation and Biotic factors plays great role when food availability in Jakarta bay shallow there were no apparent fluctuation on water coastal ecosystem. water physical and chemical parameters during seasonal change. In contrast with II. METHODS temperate marine ecosystem, tropical marine shallow water ecosystem has no The research was conducted in extreme changes in both water Jakarta bay (Figure 1) which was a temperature and salinity all over the year. shallow marine tropical waters, located in Waves and currents were also played a the north of Jakarta, the capital city of great role in creating well-mixed or Indonesia. The width of Jakarta bay is 22 homogenous water columns, thus miles, with maximum depth is ± 30 m. preventing strong thermocline to form in There are 13 rivers flows to Jakarta bay. the shallow water tropical ecosystem. At Those rivers are river of Citarum, Bekasi, the same time, land run-off and river Marunda, Angke, Ciliwung, Cengkareng, outflow carried huge amount of nutrients Kamal, Ancol, Karang, Cakung, lencong, which enriched the ecosystem, creating a Sunter, Pesanggrahan, and Grogol. 10 http://www.itk.fpik.ipb.ac.id/ej_itkt41 Rachman dan Fitriya Samples were taken five times at 10 exactly the same method as zooplankton stations around Pluit, Bidadari Island, sampling. Sunda Kelapa, Tanjung Priok, and Muara Both zooplankton and phyto- Gembong from July to November 2009. plankton were identified and counted in Zooplankton were taken with Plankton and Primary Productivity NORPAC plankton net (mesh 300 µm) by Laboratory, Research Center for horizontal towing method at 1 m depth. Oceanography, Indonesian Institute of The net were towed at 2 knot boat speed Sciences. Zooplankton identification and in 5 minutes. Samples were preserved in enumeration were done using fraction 250 cc plastic bottle and fixated with 4% sub-sampling, taken with 2.5 ml sample borax-neutraled formaldehyde. Salinity, pipette, placed in Bogorov disc and water depth, water transparency, and observed with LEICA MZ-6 stereo water temperature were measured in each microscope. Phytoplankton were also sampling station. Water depth and counted using fraction sub-sampling with transparency were measured with secchi 1 ml stample pipette, placed in Sedgewick disc, while salinity and water temperature Rafter Counting Cell (SRCC) and were measured with SCT. Phytoplankton observed with Nikon Diaphot inverted samples were taken with Kitahara microscope. Phytoplankton cells were not plankton net (mesh 80 µm), using the identified. Figure 1. Sampling stations in Jakarta bay during research in July to November 2009. The stations were located around Pluit, Bidadari Island, Sunda Kelapa, Tanjung Priok, and Muara Gembong. Jurnal Ilmu dan Teknologi Kelautan Tropis, Vol. 4, No. 1, Juni 2012 11 Potential Roles of Biotic Factors in Regulating... Zooplankton was identified and was not as high as the first peak (Figure grouped into 15 functional groups, then 2). Although in general the predator and further grouped into 2 major groups based prey zooplankton groups have similar on its trophic level, which are predator pattern (Figure 2), all taxa in both groups and prey. The predatory group consist of have its own pattern, which sometimes Cnidaria, Ctenophora, Chaetognatha, very different from the others (Figure 5 Polychaeta, and Chordata (fish larvae), and 6). while prey group consist of Copepoda, Different patterns were occurred Cladocera, Luciferidae, Mysidae, when the absolute abundance data was Malacostraca, Ostracoda, Cirrpedia, converted into relative abundance. The Echinodermata, Mollusca, Bryozoa, and double peak pattern was still observed in Tunicata. Zooplankton identification and predatory zooplankton group, but the grouping was done using reference