FLUKTUASI DAN POLA SUKSESI MUSIMAN FITOPLANKTON PADA BEBERAPA JENIS PENYUSUN KOMUNITAS HUTAN MANGROVE DI REMBANG

Abstract

sekitar Rhizopora sp. dengan indeks. perataan 0,76, Sedangkan Nilai indeks keanekaragaman terendah terjadi pada bulan September sekitar Soneratia sp. dengan indeks perataan 0,01. Jumlah total individu pada bulan Mei—Oktober 2003 berkisar antara 35.703-125.888. Jumlah individu mencapai puncak fluktuasi path bulan Agustus dimana jumbh total individu mencapai 125.888 individu/m3. Dad ketiga jenis penyusun hutan mangrove Rembang, jumlah fitoplankton yang paling banyak dijumpai adalah di sekitar Rhizopora sp. Kemudian path perairan sekitar Avicennia sp. dan paling sedikit dijumpai pada perairan sekitar Soneratia sp. Hal ini terjadi dimungkinkan karena jatuhan serasah dari Rhizopora sp. paling banyak dibandingkan kedua jenis penyusun mangrove lainnya. Selain itu laju penghancuran serasah pada Rhizopora sp. paling cepat, sehingga ketersediaan unsur hara lebih banyak. Spesies yang dominan adalah Noctilluca dan Thichodesmiun, selalu dijumpai keberadaannya sepanjang penal itian. Kesimpulan yang dapat diambil dart penelitian ini adalah pada perairan sekitar Rhizopora sp mempunyai Indeks Keanekaragaman (1-1') fitoplankton tertinggi 2,246 dengan Indeks Perataan (e) 0,75 terjadi pada bulan Agustus 2003, sedangkan terendah 0,447 dengan nilai e 0,24 terjadi pada bulan September 2003. Perairan sekitar Avicenna, sp H' tertinggi 1,756 dengan nilai e 0,76 pada Agustus 2003, sedangkan I l' terendah 0,447 dengan nilai e 0,20 terjadi pada bulan juli 2003. Perairan sekitar Soneratia sp H' tertinggi 1,528 dengan nilai e 0,46 terjadi pada bulan Agustus 2003, sedangkan H' terendah 0,025 dengan nilai e 0,01 terjadi pada bulan September 2003. Kemelimpahan jenis (Di) fitoplankton ditandai dengan melimpa.hnya jenis-jenis Noctilluca dan Thchoclestnium path setiap jenis penyusun mangrove dengan Niiai Di terbesar di perairan sekitar Rhizopora sp 55,78 dan 36,82. The community of phytoplankton on time scale always he changed and has certain patterns. The most important thing in this pattern is the sufficiency of food and nutrients. Phvtoplankton will live in a place anti certain time in mangrove commutzities to move on other places. The abandoned places will he filled bv other biota in a similar status. The question of this research is whether phytoplankton has different abundance on mangrove composition types or certain fluctuation pattern either places or time The aims (ow research is to find the seasonal fluctuation of phytoplankton, to gel the diversity of phytoplanklon. Besides, this research can be used to determine phytoplankton certain fluctuation pattern in mangrove condition and to find dominant types of phytoplankton. In this study, samples of water were taken from 3 kinds ("mangrove 's species, i.e : Rhizopora sp, Avicenniu sp and Soneratia sp. There are 5 sampling point in each location: I in center , 2 in front of mangrove and 2 behind mangrove. A Conventional plankton net with 30 pm mesh size were deployed. To preserved the water sample, forinalyn 4 % concentration was added into each bottle. Samples were conducted 6 times on 6 months. Samples were sent to Ecology and 13iosystemcitics laboratory to be identified about the type of phytoplcinkton using determination and identification books. The Identified phytoplankton is analyzed with Krebs' community structure analyze which contain divemity index (I)0, abundance index (H) and average index (e). The results ("observation showed that there are 35 species phytoplankton at mangrove ibrest. The highest value diversity index (H) happens on October at Rhi:opora sp. with e = 0,76. The lowest value diversity index (HP) takes place on September at Soneratia sp. with e 001. From May up to October 2003 the total number of population is 35.703425.888 ind filers. Those population fluctuate on august ( total number is 125.888 indditers). From 3 types of vegetation of Mangrove community, the highest value of phytoplankton was found at Rhizopora .cp then in the surround of Avicennia and the smallest is in Sonerutia. It happened because mangrove fitter from Rhizopora sp. is more dominant from the two others, and becomes the fastest decomposed litter. The dominant species are Noctilluca and Thichodesmium that were found during this research. From this study, it can be concluded that Rhizopora sp have the highest diversity index of phytoplankton with H' = 2,246 and e = 0,75 on August 2003, and the lowest diversity with H' 0,447 and e 0,24 on September. Avicennia sp have the highest diversity index of phyloplankton with H' - 1,756 and e - 0,76 on August 2003, and the lowest diversity with 0,447 and e 0,2(1 on Soneratia .sp have the highest diversity index of phytoplankton with - 1,528 and e = 0,46 on August 2003, and the lowest diversity with H' 0,025 and e -, 0,01 on September. The value of abundance index (Di) was 55,78 for Noctilluca and 36.82 for Trichodesmium. Both of them were found on the type vegetation of mangrove communal ut l'asarbungi, Rein hang during this research.