Peter A. Todd

Environmental impacts of dredging and other sediment disturbances on corals: A review

A review of published literature on the sensitivity of corals to turbidity and sedimentation is presented, with an emphasis on the effects of dredging. The risks and severity of impact from dredging (and other sediment disturbances) on corals are primarily related to the intensity, duration and frequency of exposure to increased turbidity and sedimentation. The sensitivity of a coral reef to dredging impacts and its ability to recover depend on the antecedent ecological conditions of the reef, its resilience and the ambient conditions normally experienced. Effects of sediment stress have so far been investigated in 89 coral species (~10% of all known reef-building corals). Results of these investigations have provided a generic understanding of tolerance levels, response mechanisms, adaptations and threshold levels of corals to the effects of natural and anthropogenic sediment disturbances. Coral polyps undergo stress from high suspended-sediment concentrations and the subsequent effects on light attenuation which affect their algal symbionts. Minimum light requirements of corals range from <1% to as much as 60% of surface irradiance. Reported tolerance limits of coral reef systems for chronic suspended-sediment concentrations range from <10 mg L(-1) in pristine offshore reef areas to >100 mg L(-1) in marginal nearshore reefs. Some individual coral species can tolerate short-term exposure (days) to suspended-sediment concentrations as high as 1000 mg L(-1) while others show mortality after exposure (weeks) to concentrations as low as 30 mg L(-1). The duration that corals can survive high turbidities ranges from several days (sensitive species) to at least 5-6 weeks (tolerant species). Increased sedimentation can cause smothering and burial of coral polyps, shading, tissue necrosis and population explosions of bacteria in coral mucus. Fine sediments tend to have greater effects on corals than coarse sediments. Turbidity and sedimentation also reduce the recruitment, survival and settlement of coral larvae. Maximum sedimentation rates that can be tolerated by different corals range from <10 mg cm(-2) d(-1) to >400 mg cm(-2) d(-1). The durations that corals can survive high sedimentation rates range from <24 h for sensitive species to a few weeks (>4 weeks of high sedimentation or >14 days complete burial) for very tolerant species. Hypotheses to explain substantial differences in sensitivity between different coral species include the growth form of coral colonies and the size of the coral polyp or calyx. The validity of these hypotheses was tested on the basis of 77 published studies on the effects of turbidity and sedimentation on 89 coral species. The results of this analysis reveal a significant relationship of coral sensitivity to turbidity and sedimentation with growth form, but not with calyx size. Some of the variation in sensitivities reported in the literature may have been caused by differences in the type and particle size of sediments applied in experiments. The ability of many corals (in varying degrees) to actively reject sediment through polyp inflation, mucus production, ciliary and tentacular action (at considerable energetic cost), as well as intraspecific morphological variation and the mobility of free-living mushroom corals, further contribute to the observed differences. Given the wide range of sensitivity levels among coral species and in baseline water quality conditions among reefs, meaningful criteria to limit the extent and turbidity of dredging plumes and their effects on corals will always require site-specific evaluations, taking into account the species assemblage present at the site and the natural variability of local background turbidity and sedimentation.

Morphological plasticity in scleractinian corals.

When describing coral shape and form the term phenotypic plasticity, i.e. environment‐induced changes in morphology, is often used synonymously with intraspecific variation. Variation, however, may simply be due to genetic differentiation (polymorphism). Of the 1314 extant scleractinian coral species, less than 20 have been tested for plastic responses. Morphological plasticity has important implications for coral identification, as skeletal features used in coral systematics are directly affected by environment. Furthermore, plastic changes can indicate how corals acclimatise to environmental change. The studies that have examined phenotypic plasticity in corals experimentally can be divided into two groups, i.e. ‘non‐clonal’—those that have transplanted whole colonies or fragments of colonies (but not treated the fragments as clones) to new environments, and ‘clonal’—those that have transplanted colony fragments and used them as clone‐mates. The use of clone‐mates is preferable as it facilitates the identification of among‐genotype variation for plasticity. The heterogeneous nature of the reef environment makes identifying the parameters that affect coral morphology difficult in the field, but there are also many problems conducting suitable aquarium experiments. Nevertheless, evidence to date suggests light and water movement are the most important variables inducing change. As these factors are known to be axiomatic to coral growth, it is possible that associated plastic changes in corals are adaptive; however, this hypothesis is yet to be tested rigorously.

Impacts of pollution on marine life in Southeast Asia

Pollutants, originating from both land and sea, are responsible for significant lethal and sub-lethal effects on marine life. Pollution impacts all trophic levels, from primary producers to apex predators, and thus interferes with the structure of marine communities and consequently ecosystem functioning. Here we review the effects of sediments, eutrophication, toxics and marine litter. All are presently major concerns in Southeast Asia (SE Asia) and there is little indication that the situation is improving. Approximately 70% of SE Asia’s human population lives in coastal areas and intensive farming and aquaculture, rapid urbanization and industrialisation, greater shipping traffic and fishing effort, as well as widespread deforestation and nearshore development, are contributing towards the pollution problem. As SE Asia encompasses approximately 34% of the world’s reefs and between a quarter and a third of the world’s mangroves, as well as the global biodiversity triangle formed by the Malay Peninsular, the Philippines, and New Guinea, the need to reduce the impacts of marine pollution in this region is all the more critical.

More evidence for pervasive paraphyly in scleractinian corals: systematic study of Southeast Asian Faviidae (Cnidaria; Scleractinia) based on molecular and morphological data.

Coral taxonomy and systematics continue to be plagued by a host of problems. Due to high phenotypic variability within species, morphological approaches have often failed to recognize natural taxa, and molecular techniques have yet to be applied to many groups. Here, we summarize the levels of paraphyly found for scleractinian corals and test, based on new data, whether paraphyly is also a significant problem in Faviidae, the second-most speciose hermatypic scleractinian family. Using both DNA sequence and morphological data we find that, regardless of analysis technique (maximum parsimony, maximum likelihood and Bayesian likelihood), many conventional taxonomic groups are not monophyletic. Based on two mitochondrial markers (COI and a noncoding region) that we amplified for 81 samples representing 41 faviid species and 13 genera, five genera that are represented by more than one species are paraphyletic, as is the family Faviidae. The morphological characters currently used to identify these corals similarly fail to recover many genera. Furthermore, trees based on both data types are incongruent, and total evidence analysis does little to salvage conventional taxonomic groupings. Morphological convergence, phenotypic variability in response to the environment, and recent speciation are likely causes for these conflicts, which suggest that the present classification of corals is in need of a major overhaul. We propose more detailed studies of problematic faviid taxa using standardized morphological, mitochondrial, and nuclear genetic markers to facilitate combining of data.

Morphological variation in the polyps of the scleractinian coral Favia speciosa (Dana) around Singapore

A photographic technique was used to examine morphological differences in the living polyps of Favia speciosa sampled from three sites around Singapore. Eight characters were measured, seven of which differed significantly between the three study sites. Sedimentation rates and character size were much higher at the site closest to the mainland than at the two sites further from shore. Land reclamation and dredging contribute to high sediment rates in Singapore waters; these rates decrease with increasing distance from shore. Large polyps close to the main island of Singapore are possibly a plastic, or selected for, response to high levels of sediment.

Towards a phylogenetic classification of reef corals: the Indo-Pacific genera Merulina, Goniastrea and Scapophyllia (Scleractinia, Merulinidae)

Recent advances in scleractinian systematics and taxonomy have been achieved through the integration of molecular and morphological data, as well as rigorous analysis using phylogenetic methods. In this study, we continue in our pursuit of a phylogenetic classification by examining the evolutionary relationships between the closely related reef coral genera Merulina, Goniastrea, Paraclavarina and Scapophyllia (Merulinidae). In particular, we address the extreme polyphyly of Favites and Goniastrea that was discovered a decade ago. We sampled 145 specimens belonging to 16 species from a wide geographic range in the Indo‐Pacific, focusing especially on type localities, including the Red Sea, western Indian Ocean and central Pacific. Tree reconstructions based on both nuclear and mitochondrial markers reveal a novel lineage composed of three species previously placed in Favites and Goniastrea. Morphological analyses indicate that this clade, Paragoniastrea Huang, Benzoni & Budd, gen. n., has a unique combination of corallite and subcorallite features observable with scanning electron microscopy and thin sections. Molecular and morphological evidence furthermore indicates that the monotypic genus Paraclavarina is nested within Merulina, and the former is therefore synonymised.

Chronic light reduction reduces overall resilience to additional shading stress in the seagrass Halophila ovalis

Seagrasses have substantial capacity to survive long periods of light reduction, but how acclimation to chronic low light environments may influence their ability to cope with additional stress is poorly understood. This study examines the effect of temporal light reduction by adding two levels of shading to Halophila ovalis plants in two meadows with different light histories, one characterized by a low light (turbid) environment and the other by a relatively high light (clear) environment. Additional shading resulted in complete mortality for both shading treatments at the turbid site while the clear site showed a pattern of decreased shoot density and increased photochemical efficiency (Fv/Fm) with increased shading. These contrasting results for the same species in two different locations indicate that acclimation to chronic low light regimes can affect seagrass resilience and highlights the importance of light history in determining the outcome of exposure to further (short-term) stress.

Citations: poor practices by authors reduce their value.

SIR — Scientists and whole institutes are frequently judged by the number of citations of their papers in scientific journals, and project funding depends on it. But, as Clint Kelly and Michael Jennions note in Correspondence (‘H-index: age and sex make it unreliable’ Nature 449, 403; 2007), the context and relevance of citations are crucial in reaching this judgement. Researchers from developing nations often face another problem. In the name of local issues and the national interest, they are required to publish in national journals that rarely find a place among cited journals and have a very limited circulation abroad. For example, a study of the Thomson Scientific Essential Science Indicators (ESI) during the past five years has found that the National Geophysical Research Institute (NGRI) in Hyderabad, India, scores among the top 1% of institutions publishing in the geosciences. During this period, the NGRI had 2,338 citations of 657 papers (www.incites.com/institutions/2007menu.html). But if it had not published more than half its publications in national journals — not all of which figure in the ESI database — the NGRI could have been ranked even nearer the top. In formulating their criteria, publications from institutes and by individuals in local and national journals should also be taken into account: this could be done by assigning some weighted average. The total number of publications in national journals not counted by the ESI would then be considered and weighted in order to arrive at a more appropriate index. D. C. Mishra National Geophysical Research Institute, Uppal Road, Hyderabad 500 007, Andhra Pradesh, India

Plastic corals from Singapore: 1

Figure captions: The explanatory texts for Figures 1 and 2 were accidentally omitted. The images, taken 15 weeks after reciprocal transplantation, were of a single genotype from each species (Figure 1 = Favia speciosa, Figure 2 = Diploastrea heliopora) and were characteristic of the results in general. BMSL = below mean sea level. TSS = total suspended solids. The figure captions should have read as follows: Figs. 1a and 2a. Cyrene Reef: shallow site (2.2 m BMSL), 4 km from mainland. Sedimentation rate = 25.08 (SE = 9.57) mg cm d; total suspended solids (TSS) = 12.99 (SE = 1.81) mg l. Figs. 1b and 2b. Cyrene Reef: deep site (7.6 m BMSL), 4 km from mainland. Sedimentation rate = 16.24 (SE = 7.28) mg cm d; TSS = 15.63 (SE = 2.37) mg l. Both species exhibit pigmentation loss. Figs. 1c and 2c. Pulau Hantu: shallow site (2.3 m BMSL), 7 km from mainland. Sedimentation rate = 19.84 (SE = 5.61) mg cm d; TSS = 9.30 (SE = 0.96) mg l. F. speciosa polyps appear to be tightly ‘packed’; buds have formed on D. helipora. Figs. 1d and 2d. Pulau Hantu: deep site (8.9 m BMSL), 7 km from mainland. Sedimentation rate = 12.02 (SE = 3.35) mg cm d; TSS = 11.83 (SE = 0.92) mg l. The tissue of D. helipora is almost translucent; F. speciosa polyps are spaced widely. Figs. 1e and 2e. Raffles Lighthouse: shallow site (2.4 m BMSL), 13 km from mainland. Sedimentation rate = 14.56 (SE = 2.93) mg cm d; TSS = 9.37 (SE = 0.76) mg l. The polyps of both species are more exsert than at Cyrene Reef shallow site. Figs. 1f and 2f. Raffles Lighthouse: deep site (7.0 m BMSL), 13 km from mainland. Sedimentation rate = 3.91 (SE = 1.28) mg cm d; TSS = 9.72 (SE = 0.58) mg l. Pigmentation loss is less pronounced here than at the other two deep sites. Coral Reefs (2003) 22: 306 DOI 10.1007/s00338-003-0318-1

Fluctuations in coral health of four common inshore reef corals in response to seasonal and anthropogenic changes in water quality

Environmental drivers of coral condition (maximum quantum yield, symbiont density, chlorophyll a content and coral skeletal growth rates) were assessed in the equatorial inshore coastal waters of Singapore, where the amplitude of seasonal variation is low, but anthropogenic influence is relatively high. Water quality variables (sediments, nutrients, trace metals, temperature, light) explained between 52 and 83% of the variation in coral condition, with sediments and light availability as key drivers of foliose corals (Merulina ampliata, Pachyseris speciosa), and temperature exerting a greater influence on a branching coral (Pocillopora damicornis). Seasonal reductions in water quality led to high chlorophyll a concentrations and maximum quantum yields in corals, but low growth rates. These marginal coral communities are potentially vulnerable to climate change, hence, we propose water quality thresholds for coral growth with the aim of mitigating both local and global environmental impacts.