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

Abstract

<jats:p>The Karimunjawa Islands are situated in the offshore Jepara region of Central Java with abundant coastal and marine resources including coral reefs. The reef geomorphology appears typical of fringing reefs worldwide comprising reef flat, reef crest and reef slope. The reef geomorphic profiles are generally gently sloping seaward with slightly raised reef crest along the reef edge. The reefs slope moderately (15-30°) at the upper forereef slope (~ 5-10 m deep) and tend to drop steeply, sometimes almost vertical, at depths of 10-30 m. The coral communities are found from the intertidal to a depth of about 15 m, with the most vigorous development occurring between 1.5 to 5 m. The reef flats have a low coral cover and are extensively covered by a mixture of seagrass beds and carbonate sand. The reef crests, which mark boundaries between reef flat and upper forereef slope, are mainly colonized by mixed Acropora corals, mainly A. Hyacinthus. The forereef slopes have substantial coral growth prevailing mixed branching Acropora, Porites cylindrica and Porites sp. Sediments on the reef flats are mainly bioclastic materials derived from reef-erosion, including coral fragments, mollusks, foraminifera, red algae, Halimeda, Echinodermata, aggregate, quartz and lithic fragments. Seagrass beds, mainly Enhalus, occur on the inner reef flat and are gradually shifted to macroalgae, predominantly Sargassum. The study provides a basic requirement for fisheries management and environmental monitoring for a mid-Sunda Shelf within a biodiversity “hotspot”.</jats:p>

Assessment of Empirical Near-Shore Bathymetry Model Using New Emerged PlanetScope Instrument and Sentinel-2 Data in Coastal Shallow Waters

“…A similar pattern is also shown by the SDB results from the PlanetScope combination of coastal blue and yellow (CBY) imagery. Transect 1 is taken from the coastline to the optical deep waters boundary, where this boundary is generally characterized by an increase in base height in the reef crest area [33]. The shallow water area of the western part of Kemujan Island generally forms a valley, where according to observations [34] based on transects at relatively the same location it can be seen that the bathymetry near the coast tends to be gentle, which then becomes deeper to form a valley before finally rising to become shallower in the reef crest area.…”

“…According to [33], shallow water, especially optically, is a water area that can be penetrated by sunlight until it reaches the bottom of the water effectively. The NDWI transformation results that were successfully obtained were then used to cut a specific study area in the optically shallow waters around the waters of Kemujan Island.…”