Observation on abundance of diatom has been conducted in Gumilamo- ABSTRAKStudi kelimpahan mikroalga diatom telah dilakukan di perairan pulau Gumilamo dan Magaliho, Halmahera Utara. Penelitian ini bertujuan mengidentifikasi dan menganalisa fluktuasi harian kelimpahan diatom serta menganalisa indeks biologi plankton di di perairan pulau Gumilamo dan Magaliho . Pengambilan sampel dilakukan pada bulan Juni 2011 di tiga stasiun yang mewakili perairan selat, hutan bakau dan perairan dekat muara. Plankton dikoleksi menggunakan plankton net no. 25. Pengambilan sampel dilakukan selama 24 jam dengan interval enam jam. Identifikasi dan penghitungan sel menggunakan mikroskop dengan perbesaran 400 x. Hasil studi ditemukan tujuh genera diatom yaitu:(11 sel/L). Pada stasiun ke I dan ke II menunjukkan kelimpahan maksimum terjadi pada pukul 06:00, dan kelimpahan minimum terjadi pada pukul 18:00. Di stasiun ke 3 kelimpahan maksimum terjadi pada pukul 24:00 dan kelimpahan minimum terjadi pada pukul 12:00. Tujuh diatom tersebut memiliki fluktuasi harian yang berbeda pada waktu dan stasiun yang berbeda. Daya dukung indeks keragaman yang bernilai sedang, keseragaman rendah, dan tidak terjadi dominasi sehingga perairan GumilamoMagaliho dapat dikembangkan untuk budidaya perikanan.Kata kunci: diatom, kelimpahan diatom

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The research aims to describe the student’s mistakes in doing mathematics problem observed on kind of gender. The data is taken based on the last odd semester evaluation academic year 2017/ 2018. Based on this data, gets the result as follows: 1) The male student’s can not draw the pattern yet, can not count the area yet, don’t know the formula of the equation of the line and low at the ability of counting. 2) The female student’s can draw the pattern, can not determine the area, and low in understanding the concept of looking for the ability of counting.

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Observation on abundance of diatom has been conducted in Gumilamo-Magaliho waters, North Halmahera. The aims of this study were to identify and analyze daily fluctuations of diatom abundance also analyze the biological indices in the plankton in that waters and . Sampling was conducted at three stations representing the strait, mangrove areas and estuary. Plankton were collected using a plankton net no.25. Sampling was carried out for 24 hours with six hour interval. Identification and counting of cells using a microscope with 400x magnification. The results showed that seven genera of diatoms were found: Chaetoceros sp. with the highest of cells abundance (5.061 cells/L), successively followed by Nitzschia sp. (611 cells/L), Thalassionema sp. (569 cells/L), Skeletonema sp. (446 cells/L), Coscinodiscus sp. (176 cells/L), Navicula sp. (40 cells/L) and Amphora sp. (11 cells/L). At station I and II showed that the maximum abundance occurred at 6 am, and the minimum abundance occurred at 6 pm. At station III the maximum abundance occurred at midnight and a minimum abundance occurred at noon. Diatoms showed different daily fluctuations at different time and stations. The supporting diversity index value of medium, low uniformity, and no dominance factor causing the Gumilamo-Magaliho waters can be developed for aquaculture.Keywords: diatom, diatom abundance