Kontribusi ekosistem mangrove sebagai pemasok makanan ikan belanak (Liza subviridis)di perairan pantai utara konawe selatan Sulawesi Tenggara

Abstract

The most important ecological functions of mangrove forests are nutrient cycles and energy flows. Mangrove litter fall in the water decomposed by microorganisms that produce nutrients (partly in the form of particles of litter (detritus)) are utilized by fish, shrimp and crabs as food (Bengen 2000; Bengen and Dutton 2004). Mangrove leaf is the largest part of litter primary production available to consumers contributed significantly to the food chain in the coastal fishery resources (Lee 1995; Ananda et al. 2007; Berg and McClaugherty 2008). The amount and quality of the mangrove detritus are based on the dominant mangrove species in the ecosystem. A kind of fish that make use of detritus in a mangrove ecosystem as a food source (energy) is the Greenback mullet (L.subviridis) from mugilidae family. This study aims to determine the contribution of mangrove forests as a detritus supplier served as food and energy sources of mullet (L. subviridis) on the north coast of South Konawe. The research was carried out for six months from May - October 2011 on the north coast of South Konawe Southeast Sulawesi, covering Landipo Estuaryne waters and Oyster Cape. Data collection of mangrove species at each stationwas was done using Line transect plots with a size of 10 mx 10 m for tree and 5m x 5m for the pups (Bengen 2001). Production of detritus derived from mangrove litter was carried out by inserting as many as 10 grams of leaf litter in litter bags measuring 20 cm x 30 cm made of nylon with a mesh size of 2 mm. Then, the bags were put into other plastic bags with small holes in some parts so the waste products of decomposition in the bag will not go out making calsulation easy. The fish were collected using varying mesh size of monofilament gill nets. Biological parameters measured were feeding habits, condition factor, hepto and Gonado somatic index. Macronutrients of the detritus were determined by proximate analysis. Variations in water chemistry and physics variables were analyzed using Principal Component Analysis (PCA). Distribution of detritus production between stations were analyzed using Correspondent Analysis (CA) (Lagendre and Lagendre 1983; Bengen 2000). The results showed that the total energy generated by Rhizophora apiculata detritus was greater than Sonneratia alba detritus. Detritus of Rhizophora apiculata contribute better to the condition factor, Gonado and Hepato-Somatic Index of mullet fish (Liza subviridis) than detritus of Sonneratia alba on the north coast of South Konawe.

Fungsi ekologis terpenting dari hutan mangrove adalah dalam siklus nutrien dan aliran energi, dimana mangrove merupakan penghasil serasah yaitu materi organik yang telah mati yang terdapat di lantai hutan yang tersusun atas tumbuhan mati. Serasah mangrove yang jatuh di perairan mengalami dekomposisi oleh mikroorganisme yang menghasilkan zat hara (nutrient), dan sebagian lagi berupa partikel serasah (detritus) yang dimanfaatkan oleh ikan, udang dan kepiting sebagai makanannya (Bengen 2000). Detritus inilah yang merupakan sumber makanan dan energy bagi berbagai biota perairan termasuk berbagai juvenile, larva ikhtiofauna, krustacea serta kerang (shellfish) (Bengen dan Dutton 2004). Daun mangrove merupakan bagian terbesar dari produksi primer serasah yang tersedia untuk konsumen dan memiliki kontribusi yang signifikan terhadap rantai makanan dan sumberdaya perikanan di pesisir (Lee 1995; Ananda et al. 2007; Berg dan McClaugherty 2008) Besarnya sumbangan detritus dari ekosistem mangrove berkaitan dengan proses dekomposisi serasah dalam ekosistem mangrove. Melalui proses ini hara dalam jumlah yang cukup besar dapat dihasilkan (Valk dan Attiwill 1984). Hutan mangrove sebagai penghasil detritus yang merupakan sumber makanan bagi organisme laut. Salah satu jenis ikan yang memanfaatkan detritus dalam ekosistem mangrove sebagai sumber makanan (energi) adalah ikan belanak (Liza subviridis) dari famili mugilidae. Ikan belanak secara ekologis sangat penting dalam rantai makanan yang berperan dalam transfer energi dalam kehidupan di perairan estuari.