Michael J. Risk

Reef degradation and coral biodiversity in indonesia: Effects of land-based pollution, destructive fishing practices and changes over time

Species-area curves calculated from line-intercept transect surveys on 15 reefs in three regions of Indonesia allow estimation of the relative decrease in within-habitat coral species diversity associated with different types of reef degradation. Reefs subject to land-based pollution (sewage, sedimentation, and/or industrial pollution) show 30–50% reduced diversity at 3 m, and 40–60% reduced diversity at 10 m depth relative to unpolluted comparison reefs in each region. Bombed or anchor damaged reefs are ca 50% less diverse in shallow water (3 m depth) than are undamaged reefs in the same region, but at 10 m depth the relative decrease is only 10%. Comparison reefs in the Java Sea are ca 20% less diverse than their counterparts in Ambon, Maluku. The results, compared with a previous survey in the Spermonde Archipelago found a 25% decrease in generic diversity of corals on two reefs resampled after 15 years. The decreased diversity on reefs subject to land-based pollution implies a dramatic, rapid decrease in Indonesian reef-based fisheries resources.

Normal Coral Growth Rates on Dying Reefs: Are Coral Growth Rates Good Indicators of Reef Health?

Massive coral growth rates may be poor indicators of coral reef health where coral reefs are subject to combined eutrophication and sedimentation. Massive coral growth (vertical extension) rates on polluted reefs were not different from extension rates on unpolluted reefs, while live coral cover was low and bioerosion intensity high, leading to net reef erosion and death of the polluted reefs. These combined patterns of coral growth rates, coral cover and bioerosion were documented on reefs affected by land-based pollution in the Java Sea, South Sulawesi and Ambon, Indonesia. Acid-insoluble content in coral skeletons reflected land-based pollution stress on reefs more reliably than did coral extension rates. Coral skeletal density was lower on polluted Java Sea reefs than on unpolluted reefs used as reference sites, but coral calcification rates were not significantly different. The most eutrophied Java Sea reefs had net carbonate loss, indicating net reef erosion, while a fringing reef adjacent to mangroves and two unpolluted coral cays both had positive net carbonate production. Coral growth and reef growth were decoupled, in that coral growth rates did not reliably predict rates of reef accretion. The apparently paradoxical combination of normal to rapid coral growth and net reef erosion on polluted reefs illustrates the need for a whole-reef perspective on coral reef health.

Bioerosion in Acropora across the continental shelf of the Great Barrier Reef

The degree of internal bioerosion was examined in the dead basal portions of live branches of the scleractinian coral Acropora formosa collected from six reefs across the continental shelf in the central region of the Great Barrier Reef, Australia. The bioeroders included the sponges Cliona spp. and Cliothosa spp., the boring bivalve Lithophaga sp., and sipunculid and polychaete worms. Total internal bioerosion exhibited higher means and variances inshore and at the mid-shelf than the outer shelf specimens, which were characterized by low means and low variances. Bioerosion by Cliothosa and all sponges combined declined slightly across the shelf. Bivalves accounted for a small proportion of the internal bioerosion in A. formosa. The bioerosion pattern exhibited by worms (polychaetes and sipunculids) was similar in pattern to that of the sponges. All groups exhibited lowest levels of bioerosion at the outer shelf. Highest variance in the data was observed at the intra-branch/intra-colony and the intercolony levels. Inter-site variance was high in worms and vivalves. Boring sponges generally dominated the bioeroder community. The relative abundance of Cliona declined on the outer shelf while the relative abundance of worms increased. Percent bioerosion in Acropora formosa was 2–3 times higher than in Porites lobata in this region. The low level of bioerosion at the outer shelf versus the inner- and mid-shelf areas may be partially due to lower levels of productivity and lower concentrations of terrestrially derived organic matter. Other potential factors may include higher fish grazing/predation activity on the outer shelf.

Nitrogen-15 Signals of Anthropogenic Nutrient Loading in Reef Corals

The 15N content of tissue from the coral Porites lobata was enriched, relative to corals from reference sites, at 5 of 7 Indo-Pacific sewage-affected reefs. Enrichment was as high as 3.7‰. The δ13C of sewage-affected corals suggests they maintained a high degree of autotrophic nutrition. 15N-enriched wastewater dissolved inorganic nitrogen (DIN), derived from untreated sewage, is the most likely cause for enrichment in coral tissue 15N, though changes in coral nutrition, metabolism and zooxanthellae population dynamics are possible additional factors. Isotopic measurements of coral tissue can provide a simple means of detecting wastewater uptake by corals.

Supershrimp: Deep Bioturbation in the Strait of Canso, Nova Scotia

Axius serratus, a crustacean thought to be extremely rare, was discovered in large numbers in polluted regions of the Strait of Canso. The shrimp may live deeper than 3 meters in the sediment; burrows are kept open to at least 2.5 meters. Sediment contained in old filled burrows is anomalous in its distribution of particle size and its content of water, organic carbon, and trace elements. These anomalous qualitites affect the geotechnical properties of sediments on the sea floor.

Mollusc Shell Encrustation and Bioerosion Rates in a Modern Epeiric Sea: Taphonomy Experiments in the Java Sea, Indonesia

Abstract Mollusc shells of several species were deployed on racks and on the seafloor for up to two years on eutrophic and mesotrophic reefs in the Java Sea, a modern epeiric sea. Taphonomic indicators of shell preservation decreased during the study, but some ligament, periostracum, and shell color persisted throughout. Shell fragmentation was negligible except for species with easily chipped margins; weight loss was less than 5% for sturdy shells and up to 15% for shells with chipped margins. Shells deployed in mesh bags on the sediment surface had low encrustation and bioerosion, probably because of partial or complete burial. Areal encrustation on shells in bags was greater at the mesotrophic site than the eutrophic site, but animal encrustation and biovolume of encrusters was greater at the eutrophic site. Shells elevated on racks were encrusted rapidly at all sites; animal encrustation rates were correlated positively with productivity, and biovolume of encrusters was greater on nearshore eutrophic reefs than on offshore mesotrophic reefs. Bioerosion rates were variable but also tended to be higher at the more productive site. Natural shells also exhibited a positive, though less strong correlation with productivity suggesting that encrustation intensity and shell bioerosion may serve as relative indicators of productivity in the fossil record.

Reef classification by coral morphology predicts coral reef conservation value

Coral reefs can be classified using triangular diagrams based on coral morphology; these taxonomy-independent classes predict several aspects of conservation value for coral reefs. Conservation classes (CCs) of 1, 2, 3 or 4 were assigned to reef sites dominated by massive and submassive corals (CC 1), foliose or branching non-Acropora corals (CC 2), Acropora corals (CC 3), or approximately equal mixes of these three end-members (CC 4). When applied to 15 Indonesian coral reefs, aggregrate conservation class, the average of the conservation class of all sites on that reef, was a reliable predictor of coral species richness, habitat complexity, and rare coral species occurrence. Aggregate conservation class predicted these aspects of conservation value more reliably than the reef condition index currently used in southeast Asia, live coral cover, or coral mortality. Definitions of reef status based solely on percentage of live coral cover should be supplemented with other indices such as conservation class that more accurately predict biodiversity value and fisheries potential. Coral morphology triangles and conservation class can be used in zoning marine protected areas and other coral reef biodiversity conservation efforts.

Calcification of exposed filaments of endolithic algae, micrite envelope formation and sediment production

ABSTRACT Iceland spar (calcite) crystals, placed in the shallow subtidal marine environment at Discovery Bay, Jamaica, are infested by the filamentous endolithic (boring) alga Ostreobium sp. Within 25 days after the crystals are placed in the sea, filaments project from the substrate into the sea; between 65 and 95 days the exposed filaments become completely calcified by low Mg calcium carbonate, both internally and externally. The submarine precipitation of calcium carbonate occurs only upon dead filaments and takes place at a geologically very rapid rate. The breakage of exposed calcified filaments is estimated to produce about 1 cm3/m2/yr of micrite-size carbonate. This is a source of mud-size materials, not only in the back reef and reef lagoon, but also within the reef itself. The coalescence of dense populations of exposed calcified filaments could produce a micrite envelope about a grain, without the destruction or alteration of the grain periphery associated with the classical mechanisms of micrite envelope formation Such micrite envelopes would be wholly constructive in origin, the product of precipitation of calcium carbonate on algal filaments outside the substrate, rather than within it.

The use of δ15N in assessing sewage stress on coral reefs.

While coral reefs decline, scientists argue, and effective strategies to manage land-based pollution lag behind the extent of the problem. There is need for objective, cost-effective, assessment methods. The measurement of stable nitrogen isotope ratios, delta(15)N, in tissues of reef organisms shows promise as an indicator of sewage stress. The choice of target organism will depend upon study purpose, availability, and other considerations such as conservation. Algae are usually plentiful and have been shown faithfully to track sewage input. The organic matrix of bivalve shells can provide time series spanning, perhaps, decades. Gorgonians have been shown to track sewage, and can provide records potentially centuries-long. In areas where baseline data are lacking, which is almost everywhere, delta(15)N in gorgonians can provide information on status and trends. In coral tissue, delta(15)N combined with insoluble residue determination can provide information on both sewage and sediment stress in areas lacking baseline data. In the developed world, delta(15)N provides objective assessment in a field complicated by conflicting opinions. Sample handling and processing are simple and analysis costs are low. This is a method deserving widespread application.

Paleotemperatures From Deep-Sea Corals: Overcoming ‘Vital Effects’

Abstract Thirty-five azooxanthellate (non-photosynthetic) corals belonging to 18 species were collected at sites ranging from the Norwegian Sea to the Antarctic and of depths ranging from 10 to 5220 m. All specimens showed distinct, well-defined linear correlations between carbonate oxygen and carbon isotopic composition, with slopes ranging from 0.23 to 0.67 (mean 0.45 ± 0.9) and linear correlation r2 values that averaged 0.89. These pronounced isotopic disequilibria have, to date, rendered azooxanthellate corals unsuitable for use in paleothermometry. Most, but not all, of the heaviest skeletal δ18O values reached or approached equilibrium. If the isotopically-heavy ends of the δ18O vs δ13C regression lines reliably approximated isotopic equilibrium with seawater, these values could be used to estimate the temperature of the water in which the coral grew. The δ13C values of the heavy ends of each line, however, were always depleted compared to carbon isotopic equilibrium with ambient bicarbonate by varying amounts. Despite the disequilibria, a reliable method for obtaining paleotemperature data was obtained. It was found that, if a δ18O vs δ13C regression line from an individual coral could be generated, the δ18Oarag value corresponding to δ13Carag = δ13Cwater and corrected for δ18Owater was a linear function of temperature: δ18O = −0.25 T(°C) + 4.97.