Intra-colonial response to Acroporid “white syndrome” lesions in tabular Acropora spp. (Scleractinia)

‘White syndrome’ is considered to be the most prevalent coral disease on the Great Barrier Reef, characterised by rapid rates of lesion progression and high levels of colony mortality. This study investigated the production and translocation of photoassimilates towards white syndrome lesions (WSLs) and artificially inflicted lesions in healthy and diseased colonies of tabular Acropora spp. to determine the intra-colonial response to white syndrome using ¹⁴C labelling. Translocation of ¹⁴C labelled photoassimilates was preferentially orientated away from active WSLs, with minimal ¹⁴C activity observed in the lesion borders, whilst artificial lesions (ALs) created directly opposite WSL borders showed significantly higher ¹⁴C activity, suggesting active translocation of photoassimilates for tissue regeneration. Transport of photoassimilates in healthy coral colonies was preferentially oriented towards ALs with a higher perimeter–area ratio, although translocation towards WSL boundaries was minimal even though the lesion perimeter was often the width of the colony (>200 cm). We suggest that the preferential orientation of photoassimilates away from WSLs may represent a deliberate strategy by the colony to induce a ‘shutdown reaction’ in order to preserve intra-colonial resources within areas of the colony that are more likely to survive and recover.     

Molecular diversity of symbiotic algae (zooxanthellae) in scleractinian corals of Kenya

In this first sequence analysis of ‘zooxanthellae’ (symbiotic algae of the genus Symbiodinium) in scleractinian corals in Africa, seven Kenyan species sampled in 2001–2002 were analysed by RFLP and sequencing of a PCR-amplified fragment of the LSU rRNA gene. Zooxanthellae of phylotypes A, C and D, all described previously in corals from other regions of the world, were detected. All sequences of phylotype D were identical, while phylotype C was variable, with 14 distinct sequences, seven of which clustered in a previously unreported subgroup of phylotype C, among the 22 samples. These data on the diversity of zooxanthellae in Kenyan corals 3–4 years after the 1998 bleaching event are of potential value for longitudinal studies of temporal changes in zooxanthella diversity in Kenyan corals, especially in relation to future large-scale bleaching episodes.     

Coralline algae as depth indicators in the Miocene carbonates of the Eratosthenes Seamount (ODP Leg 160, Hole 966F)

The abundance of the major coralline algal groups has been investigated and quantified in the coralline-rich facies of the Miocene shallow-water carbonates of the Eratosthenes Seamount (eastern Mediterranean, off-shore Cyprus). The analysis is based on the quantification of the most easily-recognizable groups of coralline algae in order to provide a user-friendly approach for palaeobathymetric reconstructions. Coralline algal distribution through the core suggests water depth estimates generally similar to those based on the composition of the skeletal assemblage and the benthic foraminiferal association in particular. The only noticeable difference occurs in the rhodolith and coral facies, where algal distribution suggests deeper waters than those indicated by benthic foraminifera. The distribution pattern of the major groups suggests that the ratio between Hapalidiales and Corallinales is the most reliable indicator of water-depth. The comparison with other models available in literature highlights a general zonation useful for the study of tropical, middle to late Miocene oligotrophic carbonates. Very shallow settings (0–20 m) are overwhelmingly dominated by Corallinales; in slightly deeper settings (20–40 m) Hapalidiales are more abundant, especially if the sea-floor is shaded (for example by a macrophyte canopy). Between 40 and 60 m, Hapalidiales dominate but Corallinales are still common, while below 60 m Corallinales are very rare. In non-oligotrophic environments this zonation is not reliable and, due to the reduced water clarity related to the high primary productivity, Hapalidiales clearly dominate even in very shallow settings.     

Enhanced ultraviolet radiation can terminate sexual reproduction in the broadcasting coral species Acropora cervicornis Lamarck

The effects of enhanced ultraviolet radiation (280-400 nm: UVR) on the fecundity of Acropora cervicornis were measured in field-transplanted colonies from 20 m to 1 m depth and vice versa at La Parguera, Puerto Rico. Fecundity was estimated from histological sections made from tissue samples obtained at different time intervals during the experimental period (March - August 2003). All colonies transplanted from 20 m to 1 m showed a 100% reduction in gonads per mesentery per polyp one month after transplantation, while those transplanted from 1 m to 20 m did not show any significant reduction in fecundity throughout the experimental period. The latter colonies did show however, a delay in the spawning times by releasing their gamete bundles approximately two-three weeks after the controls at 1 m and two months after the controls at 20 m suggesting an induced response as a consequence of changes in their daily light cycle due to less radiation (PAR and UVR) available at 20 m compared to 1 m. Control colonies at 20 m spawned after the full moon of June 2003, while the controls at 1 m spawned 5-6 days after the full moon of July 2003. While a possible reabsorption of the gametes occurred in A. cervicornis colonies transplanted from 20 m to 1 m, the expulsion of these gametes due to the sudden stress caused by the transplantation is not discarded. The results suggest that sudden increases in UVR can completely stop sexual reproduction in ramose broadcasting coral species, which in turn can affect the dominance of the species and the composition and structure of shallow reef environments.     

Fidelity of molluscan life and death assemblages on sublittoral hard substrata around granitic islands of the Seychelles

This study quantified the degree of coincidence between living and dead molluscan faunas in a shallow-water coral reef environment in the Indian Ocean. The results were compared with those from a similar life:death study in the northern Red Sea, and with those published for reef corals and soft substrata molluscs. The proportions of quantitatively important taxa are robust to sampling intensity, but fidelity indices and rank-order correlations are strongly influenced by quantitatively unimportant taxa. Distinct differences between life and death assemblages were recognized, which are due to distinct biases in the death assemblage. Bivalves that lived in close contact with living corals are preferentially overgrown after death and should provide considerable temporal and ecological information in a potential fossil record, as they will be preserved within a rapidly growing reef framework. Some gastropod taxa are preferentially transported into surrounding soft substrata postmortem. Here they will be affected by time-averaging and taphonomic disintegration typically occurring in sediments resulting in the associated loss of much temporal information. Most gastropod shells, however, are inhabited by hermit crabs postmortem, which may strongly alter the fossil gastropod community structure. The results are similar to a comparable study in the northern Red Sea, with a major exception being the strong dominance of hermit crab-inhabited gastropod shells in the death assemblage of the Seychelles. Comparison of life:death assemblages between hard and soft substrata, in keeping with the northern Red Sea study, showed the strong dominance of dead shells in the soft substrata with the converse on the hard substrata. This results from different accumulation conditions for dead shells in soft substrata. Fidelity indices are well suited to demonstrate that sedimentary death assemblages are typically remarkably robust reflections of local community composition but they do not record the strong biases in death assemblages of coral reef associated hard substrata molluscs and are therefore unsuitable for comparisons of life and death assemblages in reef environments.     

Habitat correlates of the distribution and biomass of Seychelles' reef fishes

Synopsis Relationships between quantitative measures of habitat type and the biomass of Chaetodon, Scarus and Parupeneus species were investigated across 35 reef sites in the Inner Seychelles Group. Multiple regression was used to determine the proportion of variance in biomass between sites which could be explained by depth, exposure, vertical relief, topographic complexity, live coral cover, coral rubble cover, rock cover, sand cover, underlying carbonate substrate, underlying sand substrate, underlying rock substrate and an index of fishing intensity. A significant proportion of the variance in biomass was explained by habitat variables and the index of fishing intensity for 7 of 12 Chaetodon species (23–52% of variance explained), 3 of 6 Parupeneus species (33–40%), and 10 of 13 Scarus species (14–46%). Within genera, different groups of habitat variables explained the variance in biomass for different species and, of the variables studied, only the proportion of underlying sand substrate failed to explain a significant proportion of the variance in biomass for any species. Quantitative relationships between the biomass of Chaetodon and habitat were often in accordance with those suggested by previous studies of their ecology, life-history and distribution at other Indo-Pacific locations. However, the habitat associations of the Parupeneus and some Scarus species have not been studied at other locations and clearly warrant further investigation. It was concluded that habitat was an important determinant of the distribution of many Seychelles reef fishes, but that the habitat variables examined were rarely the most important determinant of biomass. However, the inclusion of a procedure to collect habitat data provided a useful means by which to reduce the unexplained variance associated with visual census biomass estimates and therefore improves the possibility of elucidating the effects of other factors on the biomass of Seychelles reef fishes.     

Patterns of recruitment and spawning in Hawaiian reef fishes

Synopsis Recruitment of juvenile fishes to five 25 m² quadrats on an extensive natural reef in Kona, Hawaii was monitored over 51 months. Pronounced between-year variability in recruit abundance was evident for some species. Many exhibited strikingly low levels of recruitment. Overall recruitment was highly seasonal with a major peak in June and July, and a generally smaller, secondary peak in February and March. Recruitment was minimal during early winter (October–December) and a review of other studies similarly indicates minimal recruitment in Hawaii during this period. Spawning in Hawaiian fishes generally begins during the winter months of relatively low temperatures, increases during late winter and early summer and declines rapidly as maximum summer water temperatures are reached (September–October). Seasonal changes in food availability, ocean currents or salinity seem unlikely to be responsible for observed patterns of recruitment and spawning. Rather, the patterns appear to be most closely tied to changes in water temperature or photoperiod. Loss of propagules to offshore-moving eddies or other unfavorable currents may be responsible for the low levels of juvenile recruitment found in this and other Hawaiian studies. In Kona, at least 6 species of fishes recruited in pulses during quarter or new moon phases. Four other species have been reported elsewhere in Hawaii to recruit during either new or full moon phases. Lunar spawning periodicity was present in fewer than half of the species so far examined, and no single adaptive function for lunar periodicity was applicable to all species.     

A simple model of growth form-dependent recovery from disease in coral reef sponges, and implications for monitoring

For clonal organisms that can suffer high levels of partial mortality and still recover, the conditions that influence infection and development of disease (e.g., abiotic stressors, population density) may be very different from the conditions that influence recovery. Recovery from infectious disease may increase if an individual can mount a defense before infection spreads throughout its body. If pathogens spread within an organism from an initial infection point, growth form—in conjunction with size—can influence the amount of time before all the tissue is diseased, and recovery precluded. A simple model of pathogen progression within individual sponges predicts that species with massive growth forms will be most susceptible to being overwhelmed by pathogen infection, and branching species will be most likely to recover. These predictions may help to explain the seemingly contradictory observations that branching species had the greatest prevalence of disease, and massive species the greatest rate of loss, in a monitored coral reef community. Disease may be observed disproportionately frequently in the organisms that are most likely to recover, resulting in underestimation, by standard monitoring procedures, of the effect of disease on losses from the community.     

An analysis of fish community responses to coral mining in the Maldives

Synopsis Coral mining takes place on shallow reef flats at a number of localities in the Maldives, but not on the adjacent deeper reef slopes. A semi-quantitative census method for fish species abundance and biomass is described. Fish community structure is compared on mined and non-mined reef flats and their adjacent slopes using a variety of univariate, graphical/distributional and multivariate statistical techniques. In general, univariate and graphical distributional methods do not indicate significant differences between mined and non-mined localities with respect to the relative abundances and biomasses of species. Multivariate methods (both classification and ordination), however, indicate very clear-cut effects of mining on the reef flats, and also significant effects on reef slopes adjacent to mined flats. The effect was equally clear using non-quantitative (presence/absence) data. The fish species mainly responsible for the differences between mined and non-mined localities are identified, and the differences are explained in terms of the feeding biology of these species.     

Reef corals, zooxanthellae and free-living algae: a microcosm study that demonstrates synergy between calcification and primary production

A mature, high-biodiversity coral reef microcosm and its chambered subsets were used to examine the relationship between calcification and photosynthesis and its most critical biotic components. Whole ecosystem calcification at 4.0±0.2 kg (40±2 mol) CaCO₃ m⁻² year⁻¹ is related to its primary components (stony coral 17.6%, Halimeda 7.4%, Tridacna 9.0%, algal turf, coralline and foraminifera 29.4%, and miscellaneous invertebrates 36%). Through analysis of the microcosm's daily carbonate system, it is demonstrated that bicarbonate ion, not carbonate ion, is the principal component of total alkalinity reduction in the water column (thus, bicarbonate ion is the principal measured component of calcification as normally measured on reef transects). While chamber-isolated free-living algae remove carbon dioxide, and raise pH and carbonate ion equivalent to that in the microcosm as a whole, no total alkalinity reduction (calcification) occurs. On the other hand, chamber isolated stony corals remove considerable bicarbonate, with very little pH or carbonate ion elevation. Combining the non-calcifying free-living macroalgae Chondria with stony corals in chamber subsets, it is possible to remove more carbon dioxide (elevating pH) and thereby increase coral calcification rates by 60 and 120% above zooxanthellae-mediated rates to 20.6 kg (206 mol) and 18.5 kg (185 mol) CaCO₃ m⁻² year⁻¹ for Acropora and Montipora, respectively. These findings, which support the McConnaughey and Whelan hypothesis of bicarbonate ion neutralization in coral calcification, are easily demonstrated in the controlled microcosm environment.