Sedimentary Environment of a Modern Carbonate Platform of Karimunjawa Islands, Central Java

Abstract

Sitting in a biodiversity "hotspot" of the mid-Sunda Shelf region, Karimunjawa Islands have currently been the priority for marine biodiversity conservation. Knowledge of surface sediments on modern carbonate platform is one of essential information to support conservation policies, but such has received little attention from reef researchers. This study describes the sediment characteristics of the selected modern carbonate platforms of Karimunjawa Islands through integrated sediments and satellite data analysis. Textural group of sediments indicates that moderate to poorly sorted gravelly sands are dominant with no grading pattern concerning geomorphological and habitat succession from landward to seaward. Sediment compositions are predominantly bioclastic components, comprising coral and mollusks as the highest and the second highest estimated order of abundance. The reworked grains and rock fragments, although present, are not volumentary abundant. The carbonate sedimentary facies is primarily composed of mud-lean packstone with additional proportion of grainstone and packstone. There are only slight distinct sedimentological characteristics for all benthic habitats as shown by the principal component analysis revealing overlap relationship between sediment parameters and benthic habitats. The study provides the first characterization of sediments which operate on the modern carbonate platform of Karimunjawa Islands along with their controlling factors and specialized nature.

Coral Reef Community Changes in Karimunjawa National Park, Indonesia: Assessing the Efficacy of Management in the Face of Local and Global Stressors

“…Karimunjawa was chosen as a study site because of its size, age and importance [18], and to compliment the efforts of the Indonesian Coral Reef Rehabilitation and Management Program (COREMAP) in order to deepen the coverage national reef resources [26,44]. Research was conducted in the dry season (May to October), when the prevailing eastward flow of surface current present during the northwest monsoon is in reverse, and salinity is higher (35 PSU compared to 31 PSU during monsoon) [20]. All data presented here, including photo quadrats, are freely available to download at [45].…”

“…This includes 132 km 2 of coral reefs, including fringing reefs which extend 100 m to 1000 m off rocky slopes of the larger islands of Kemunjan and Kariminjawa, platform reefs such as Menjangan Besar and Menjangan Kecil developed on sand-topped banks, and coral cays [19]. Reefs in the park generally have wide gently sloping reef flats, with steeply sloping (30 • ) upper fore reef zones where coral abundance is highest, and often a steeper lower fore reef that drops beyond 10 m [20]. These reefs are part of the Coral Triangle, a biogeographic area known to be the global hotspot of marine diversity, and the park hosts a rich diversity of species.…”

“…All three global coral bleaching events impacted corals in the park: the 1997-1998 global coral bleaching led to coral mortality rates of 50-60%, and mass bleaching was also reported in 2010. Mean monthly ocean temperatures in Karimunjawa range from 28.3 • C in August to 29.8 • C in April (based on long term average from 2007 to 2020 [20,36]). Between 2015 and 2016 sustained warmer-than-usual conditions were reported in the park with temperatures rising from October 2015 through April 2016 where they peaked around 30.5 • C [37].…”

“…All surveys were conducted on SCUBA using a custom-built diver operated underwater propulsion vehicle, which had an integrated camera system consisting of three synchronised Canon 5D-MKII cameras [43]. High-resolution (21 mp) images of the benthos were taken every two meters along a 700 m linear transect, following the upper fore reef slope contour at a depth of~7-9 m. These shallow slopes were targeted as the area of the most living coral growth [20]. Images were geo-referenced using a surface GPS unit tethered to the diver.…”

Reef geomorphology and associated habitats of Karimunjawa Islands, Indonesia: a spatial approach to improve coastal and small islands management

“…Until recently, there have been only few studies of substrates and habitats mapping from a geomorphological perspective in Indonesia (Solihuddin et al, 2019), despite the fact that Indonesian Archipelago contains some of the most diverse of island groups across the globe (Kuenen, 1933). Study of coral reefs has been focused on ecological studies with very limited studies linked to an understanding of reef geomorphology and coastal geology.…”