Distribution and abundance of the giant clams (Cardiidae: Bivalvia) on Kei Islands, Maluku, Indonesia

Triandiza T, Zamani NP, Madduppa H, Hernawan UE. 2019. Distribution and abundance of the giant clams (Cardiidae: Bivalvia) on Kei Islands, Maluku, Indonesia. Biodiversitas 20: 884-892. Giant clams, ecologically important bivalves in coral reefs, are under anthropogenic pressures in most parts of their range, necessitating the study of population status for conservation management. Here, we assessed species composition, distribution, size density, and habitat condition of giant clams in Kei Islands. A total of 9 reefs around the islands (Dar 1, Dar 2, Pulau Kur, Pulau Tanimbar Kei, Pulau Adranan, Pulau Dullah Laut, Difur, Labetawi, dan Ohoidertoom), were surveyed using quadrat-transect line in September-December 2017. We found five species of giant clams, i.e., Tridacna crocea, T. maxima, T. squamosa, T. noae, and Hippopus hippopus. Of these species, we report a new record for T. noae which was previously not known to be present in the region. The overall density was recorded at 0.0428 individual/m2. Juveniles clams were fewer than the adults clam, this may indicate that the survival rate of recruit is low. Most individuals were found living on dead coral algae substrate (75 %). Based on the findings, this study suggests that giant clam population in Kei Islands are imperiled, indicated by low population density and local extinction for species T. gigas and T. derasa. It is recommended to establish a protected area and restocking of giant clams by through implementing sasi laut (traditional law) with a minimum period of 5 years.

Reproduction of Megapitaria squalida (Bivalvia: Veneridae) in the Southeast Gulf of California, Mexico

Bivalves reproductive cycle varies according to the particular environmental conditions where they are found, and these reproductive details represent basic information for their capture, management and conservation strategies. With this objective, the reproductive cycle of the clam Megapitaria squalida, inhabiting the Southeast of the Gulf of California (Altata Bay, Sinaloa, Mexico), was studied using histology and changes in the number and size of oocytes, from June 2013 to June 2014. Histological analysis of the gonads showed spawning activity throughout the year, with two peaks. The first was registered in October and it was accompanied by the highest decrease of weight; the second was in February with the highest percentage of spawning population; besides, a resting period was observed in December. The sex-ratio (female:male) of the clam population was 1.08:1 (χ2 = 5.72, d.f. = 1, P < 0.05). Mean oocyte size and number were different (P < 0.05) among all sampling months and fluctuated from 34.6 ± 5.8 µm in June 2014, to 41.9 ± 6.8 µm in February 2014, and from 443.8 ± 424.5 in February 2014, to 1 214.4 ± 267.6 counted in April, respectively. With these results we suggest a protection season from October to November, when the most intense release of gametes occur in this population.

Studi Struktur dan Pertumbuhan Populasi Kerang Pokea (Batissa violacea var. celebensis, von Martens 1897) di Sungai Pohara Sulawesi Tenggara

AbstrakPokea merupakan bivalvia air tawar yang hidup di segmen muara. Bivalvia ini terus mengalami tekanan sejalan dengan peningkatan aktivitas kegiatan penangkapan dan menurunnya kualitas perairan. Penelitian ini bertujuan untuk mengetahui struktur dan pertumbuhan populasi kerang pokea di Sungai Pohara Sulawesi Tenggara. Penelitian ini dilaksanakan di segmen muara Sungai Pohara selama setahun dari bulan Maret 2007-Februari 2008. Parameter populasi (L∞ dan K) dan to masing-masing dianalisis dengan menggunakan pergerakan modus frekuensi panjang dan nilai L0=0.025. Pola pertumbuhan dianalisis menggunakan inverse von Bertalanffy sedangkan struktur populasi dianalisis menggunakan distribusi normal dari plot Bhattacharya yang secara keseluruhan terakomodasi pada program FiSAT II versi 3.0. Hasil penelitian menunjukkan bahwa lebar asimtotik dan koefisien pertumbuhan jantan dan betina masing-masing yaitu 7.16 cm, 0.59 dan 6.92 cm, 0.96. Oleh karenai tu, pertumbuhan pokea betina lebih cepat dibandingkan pokea jantan. Populasi kerang pokea tersebar pada berbagai kelompok ukuran yang mewakili ukuran muda, dewasa dan tua dengan nilai tengah berada pada 1.49 dan 6.01 yang menyebar pada tiga kelompok ukuran. Kelompok ukuran dominan pada jantan betina relatif berbeda yang tersebar pada nilai tengah masing-masing 1cm dan 2cm. Secara umum, struktur populasi pokea di Sungai Pohara relatif stabil.Key word : pokea, pertumbuhan, struktur, populasi, sungai, PoharaAbstractPokea clam was fresh water bivalve that lived on well into estuary segments. This bivalve have experienced in under pressure as activity increase in fishing events and decrease in water quality. This research aimed to understand the structure and growth population of pokea clam in Pohara river on Southeast Sulawesi. This research was conducted in estuary segment of Pohara river from March 2007 to February 2008. Parameters of population (L∞ dan K) and to were analyzed by using movements in modus of length frequency and Lo=0.025. Growth pattern was analyzed by using von Bertalanffy inverse, and population structure was analyzed by using normal distribution from Bhattacharya plot with full accommodation on FiSAT II version 3.0. The results of this research indicated that asymptotic width and growth coefficient for male and female were 7.16 cm, 0.59 cm, and 0.96 cm. Therefore, the growth of female pokea was faster than male. Pokea clam population spread to several size groups that represented as young, adult, and old with median 1.49 and 6.01. The dominant length measurement on male and female was relatively different which propagated in median 1 cm and 2 cm. Generally, population structure of pokea clam in Pohara river was relatively stable.Keyword: pokea, growth, structure, population, river, Pohara