DISTRIBUSI DAN KEMELIMPAHAN LAMUN (SEAGRASS) SEBAGAI RESPON TERHADAP MUSIM DI PANTAI JEPARA

NURUL KUSUMA DEWI, Dr. Tjut Sugandawaty Djohan, M.Sc.

2012 | Tesis | S2 Biologi

Tujuan penelitian ini adalah mempelajari respon komunitas lamun terhadap musim kering dan basah. Lokasi kajian adalah perairan Pantai Jepara: di Pantai Bandengan, tambak rusak, Prawean, dan Pantai Pulau Panjang. Distribusi dan kemelimpahan lamun ditentukan oleh nutrien dan cahaya. Pada musim basah, debit sungai yang tinggi meningkatkan nutrien di lokasi kajian. Pada lokasi yang dekat sungai, kekeruhan meningkat karena sedimentasi. Input nutrien dan sedimen dipengaruhi oleh kondisi watershed. Metode yang digunakan adalah kuadrat plot, ukuran 0,5 m x 0,5 m dengan bantuan garis transek, yang membagi lokasi kajian menjadi 2 zona, upper litoral dan lower litoral. Sedangkan untuk biomasanya menggunakan silinder ukuran 30 cm x 60 cm. Pada setiap plot, dicuplik data spesies, densitas, dan pertumbuhan lamun meliputi biomasa, tinggi batang, panjang dan lebar daun. Kualitas air yang diukur meliputi kecerahan, tinggi muka air, kecepatan arus, salinitas, suhu, tinggi ombak, DO, pH, tekstur sedimen, dan nutrien berupa NH4, NO3, PO4, C-organik. Hasil menunjukkan ada 7 spesies terdistribusi tidak merata secara spasial dan temporal, spesies-spesies tersebut adalah Cymodocea rotundata, Cymodocea serrulata, Enhalus acoroides, Halodule uninervis, Syringodium isoetifolium, Thalassia hemprichii, dan Thalassodendron ciliatum. Variasi densitas spesies lamun antar lokasi kajian berkisar 13-855 individu/2,5 m2 yaitu spesies S. isoetifolium dan H. uninervis pada musim kemarau. Sedangkan pada musim hujan variasinya antara 2-215 individu/2,5 m2 pada zona upper litoral yaitu spesies E. acoroides dan T. ciliatum serta 2-231 individu/2,5 m2 pada zona lower litoral yaitu spesies T. hemprichii dan T. ciliatum. Penurunan cacah spesies dan densitas lamun pada musim hujan berhubungan dengan peningkatan nutrien terutama nitrat dan rendahnya cahaya. H. uninervis merupakan spesies lamun yang toleran terhadap nutrien tinggi sedangkan T. hemprichii toleran terhadap cahaya rendah. Tingginya nutrien memicu pertumbuhan algae epifitik yang mengganggu proses fotosintesis dan menyebabkan pertumbuhan lamun terganggu. Nutrien dan cahaya merupakan faktor-faktor yang menentukan kehadiran dan kemelimpahan lamun di Pantai Jepara.

The purpose of this research was to study the response of seagrass communities to the dry and wet seasons. The study areas were at Jepara Coast: Bandengan, abandon ponds, Prawean, and Pulau Panjang. The presence of seagrass communities was determined by the nutrients and light. In the wet season, high river discharge increased nutrients in the coastal waters. At location near the river, turbidity increased because of surface run off from the watershed. Data were collected using quadrat plots with two transects were placed across the litoral of upper and lower zones. At each transect of the zone, data was collected using the quadrat plot, 0.5 m x 0.5 m, with 10 replications. On each plot, number of species, density, and their growth include biomass, stem height, length and width of leaf were sampled. Parameter measured were water quality of light penetration, water level, current velocity, salinity, temperature, wave height, DO, pH, sediment texture, and nutrients of NH4, NO3, PO4, C-organic. The results showed there were 7 species of seagrass communities which distributed unevenly: Cymodocea rotundata, Cymodocea serrulata, Enhalus acoroides, Halodule uninervis, Syringodium isoetifolium, Thalassia hemprichii, and Thalassodendron ciliatum. The seagrass-species densities varied between locations. During the dry season, it between 13-855 individuals per 2.5 m2 (S. isoetifolium and H. uninervis). In contrast, during the rainy season was between 2-215 individuals per 2.5 m2 at upper littoral zone (E. acoroides and T. ciliatum) and 2-231 individuals per 2.5 m2 in the lower littoral zone (T. hemprichii and T. ciliatum). These variations were due to the increasing river discharges which increased the nutrients and turbidity. The two factors decreased the abundance of seagrass communities during wet season. H. uninervis was a seagrass species which was tolerant to high nutrient. While T. hemprichii was tolerant to turbidity. The high of nutrients triggerred the growth of epiphytic algae which interfered the process of photosynthesis and caused the growth of seagrass disturbed. Nutrients and light were factors that determined the presence and abundance of seagrass communities in Jepara Coast.

Kata Kunci : lamun, nutrien, cahaya, spesies toleran.