Coral reefs next to a major conurbation: a study of temporal change (1985-2011) in coral cover and composition in the reefs of Jakarta, Indonesia

Abstract

Coral reefs are diverse, ecologically important and globally threatened ecosystems. Numerous studies have reported on the threats to coral reefs, which include both local perturbations, such as pollution and overfishing, and widespread phenomena, such as bleaching. Here, we report on the history of the Jakarta Bay−Thousand Islands reef system from 1985 to 2011. Over this period, we recorded significant shifts in coral generic composition and an overall decline in coral cover with widely different trajectories between in-, mid-and offshore zones. In 1985, coral cover exhibited a clear on-to-offshore gradient with low coral cover inshore (10%), moderate cover midshore (49%) and high cover offshore (74%). The low coral cover inshore contrasts strongly with reports of high coral cover for inshore reefs in 1929. Inshore, coral cover declined from 10% in 1985 to < 5% in 1995. The greatest change in coral cover and composition, however, occurred in offshore reefs, where mean cover declined from 74 to < 20% between 1985 and 1995. Acropora species were particularly affected and declined from 36 to just 5% cover offshore. Recovery of coral cover occurred offshore between 1995 and 2005. From 2005 to 2011, however, a less severe loss in coral cover was observed. With the exception of inshore reefs, which appear to be on an ongoing trajectory of decline that started before the 1985 surveys, the reefs of the Jakarta Bay−Thousand Islands system have shown a propensity to recover.

Abundance and physiology of dominant soft corals linked to water quality in Jakarta Bay, Indonesia

“…Currently, the highest hard coral cover can be found at midshore sites (47%), with a subsequent significant decrease towards offshore (mean cover: 17–30%) (data based on Baum et al, 2015). A similar pattern in hard coral cover along the distance gradient from the mainland was also observed by Cleary et al (2014) for the Thousand Islands chain.…”

“…Although reefs within the bay once had thriving coral communities (Verstappen, 1953; Arifin, 2004; van der Meij, Suharsono & Hoeksema, 2010), they are now dominated by sand, rubble and algae, with a current hard coral cover of < 5% for nearshore reefs within JB. Mid- and offshore reefs along the Thousand Islands have highly variable reef conditions (< 20% hard coral cover to 50%) (Cleary et al, 2014; Baum et al, 2015). Considering that coral reefs are of huge economic and environmental importance in the area, supporting fisheries and tourist sectors and providing habitats with high productivity and diversity, there is a growing need to understand coral reef functioning.…”

27 years of benthic and coral community dynamics on turbid, highly urbanised reefs off Singapore

“…Quantifying changes in coral taxonomic community structure is also critical, because changes in total coral cover alone can be misleading as a measure of ecosystem state21. Long-term (i.e., spanning >20 years) studies of reef benthic and coral community structure are lacking for certain biogeographic regions and for reefs adjacent to heavily populated urbanised centers, including the biogeographic region known as the ‘coral triangle’2829, where most of the world’s reefs and the highest diversity of coral reef species occur. Many of the reefs in this region are close to very high human population densities, and have experienced extreme urbanisation over a relatively short time period.…”

Heavy metals in river and coast sediments of the Jakarta Bay region (Indonesia) — Geogenic versus anthropogenic sources

“…This is corroborated by other studies, which point to increasing metal contamination in the Jakarta Bay (Takarina, 2010). Enhanced metal contamination in combination with other human-induced stressors is also considered to have caused adverse effects on marine communities in the Jakarta Bay (van der Meij et al, 2009, Cleary et al, 2014. Discharge of untreated municipal wastewaters was shown to be most relevant for water quality (Dsikowitzky et al, in press-b).…”