Colonization of Hawaiian reef corals on new and denuded substrata in the vicinity of a Hawaiian power station

The colonization and growth of reef corals settling on new substrata (concrete and basalt) and on a denuded coral reef were studied over a seven-year period. The study area is in the vicinity of an outfall discharging thermal effluent from a Hawaiian power station, and both numbers and coverage of settled corals were found to increase exponentially with proximity to the outfall's discharge. Recruitment rates adjacent to the outfall were at least ten times greater than values previously reported for open ocean areas in Hawaii, and the estimated time for recovery of the coral community near the outfall was comparable to the most rapid that has been reported worldwide. By contrast, coral recruitment and recovery more distant from the outfall compared well with slower rates reported for other areas in Hawaii. Entrainment of coral planulae in water discharged into the area by the outfall is proposed to be the principal mechanism promoting the high coral colonization.     

The physiological response of reef corals to diel fluctuations in seawater temperature

An opportunity to explore the effects of fluctuating temperatures on tropical scleractinian corals arose when diurnal warming (as large as 4.7 °C) was detected over the rich coral communities found within the back reef of Moorea, French Polynesia. In April and May 2007, experiments were completed to determine the effects of fluctuating temperature on Pocillopora meandrina and Porites rus, and consecutive trials were used to expose them for 13 days to 26 °C, 28 °C (ambient conditions), 30 °C, or a fluctuating treatment ranging from 26 to 30 °C over 24 h. The multivariate response was assessed using maximum dark-adapted quantum yield of PSII (F_V/F_M), Symbiodinium density, chlorophyll-a content, and calcification. In trial 1, multivariate physiology of both species was significantly affected by treatments, with the fluctuating temperature resulting in a 17-45% decline in Symbiodinium density (relative to the ambient) matching that occurring at a constant 30 °C; F_V/F_M, chlorophyll-a content, and calcification, did not differ between the fluctuating and the steady treatments. In contrast, in trial 2 that utilized corals collected two weeks after those used in trial 1, the corals were unaffected by the treatments, likely due to an environment × trial interaction caused by seasonal declines in Symbiodinium density. Together, these results demonstrate that short transgressions to ecologically relevant high and low temperatures can elicit a potentially detrimental response equivalent to that occurring upon exposure to a constant high temperature. The dissimilar responses among dependent variables and consecutive trials underscore the importance of temporal replication and multivariate approaches in coral ecophysiology. It is likely that recent history has a stronger effect on the response of corals to treatments than is currently recognized.     

Transmission of growth anomalies between Indo-Pacific Porites corals

In this study we provide experimental evidence of transmission of growth anomalies (GAs) between corals. Twenty-four aquaria (16 experimental, 8 containing only apparently healthy corals) were set-up on Negros Island, Philippines, to test for direct-contact and waterborne transmission of GAs. Within seven weeks, two of 16 apparently healthy colonies placed in direct contact with colonies having GAs developed multiple GA lesions whose size and number increased over time. One of 16 apparently healthy colonies in experimental aquaria not touching any diseased colony also developed a GA, exhibiting a single lesion that did not increase in size. Apparently healthy colonies (n=24) in aquaria without a diseased colony remained unchanged.     

Reproductive ecology of Caribbean reef corals

The last decade has seen a resurgence of interest in the processes of sexual reproduction by scleractinian reef corals. Earlier investigations had focused fortuitously on brooding (planulating) species, which resulted in the general misconception that brooding was the main form of larval development of reef corals. More recent work on Indo-Pacific species has shown broadcast spawning and short annual reproductive periods to predominate. This report presents the reproductive patterns of eleven Caribbean coral species and attempts to explain the adaptive features and selective pressures that have led to the evolution of the four reproductive patterns described to date: (a) hermaphroditic broadcasters; (b) gonochoric broadcasters; (c) hermaphroditic broadcasters; (b) gonochoric brooders. Both (a) and (b) correlate with large colony size and short annual spawning periods; and (c) and (d) correlate with small colony size, multiple planulating cycles per year, and occupation of unstable habitats. Selection for outcrossing between long-lived individuals is proposed as the reason for gonochorism and for synchronous spawning of hermaphroditic broadcasters, and also for the large amount of sperm produced by hermaphroditic brooders. Selection for high rates of local recruitment is proposed as the force behind the evolution of brooding by species inhabiting unstable habitats and suffering high rates of adult mortality.     

Threatened reef corals of the world

A substantial proportion of the world's living species, including one-third of the reef-building corals, are threatened with extinction and in pressing need of conservation action. In order to reduce biodiversity loss, it is important to consider species' contribution to evolutionary diversity along with their risk of extinction for the purpose of setting conservation priorities. Here I reconstruct the most comprehensive tree of life for the order Scleractinia (1,293 species) that includes all 837 living reef species, and employ a composite measure of phylogenetic distinctiveness and extinction risk to identify the most endangered lineages that would not be given top priority on the basis of risk alone. The preservation of these lineages, not just the threatened species, is vital for safeguarding evolutionary diversity. Tests for phylogeny-associated patterns show that corals facing elevated extinction risk are not clustered on the tree, but species that are susceptible, resistant or resilient to impacts such as bleaching and disease tend to be close relatives. Intensification of these threats or extirpation of the endangered lineages could therefore result in disproportionate pruning of the coral tree of life.     

Response of Mediterranean coralline algae to ocean acidification and elevated temperature

The effects of elevated partial pressure of CO₂ ( p CO₂) and temperature, alone and in combination, on survival, calcification and dissolution were investigated in the crustose coralline alga Lithophyllum cabiochae . Algae were maintained in aquaria during 1 year at near-ambient conditions of irradiance, at ambient or elevated temperature (+3 °C) and at ambient [ca. 400 parts per million (ppm)] or elevated p CO₂ (ca. 700 ppm). Algal necroses appeared at the end of summer under elevated temperature first at 700 ppm (60% of the thallus surface) and then at 400 ppm (30%). The death of algae was observed only under elevated temperature and was two- to threefold higher under elevated p CO₂. During the first month of the experiment, net calcification was significantly reduced under elevated p CO₂. At the end of the summer period, net calcification decreased by 50% when both temperature and p CO₂ were elevated while no effect was found under elevated temperature and elevated p CO₂ alone. In autumn and winter, net calcification in healthy algae increased with increasing temperature, independently of the p CO₂ level, while necroses and death in the algal population caused a net dissolution at elevated temperature and p CO₂. The dissolution of dead algal thalli was affected by elevated p CO₂, being two- to fourfold higher than under ambient p CO₂. These results suggest that net dissolution is likely to exceed net calcification in L. cabiochae by the end of this century. This could have major consequences in terms of biodiversity and biogeochemistry in coralligenous communities dominated by these algae.     

Snorkeler damage to reef corals in the Maldive Islands

Rapid and intensive survey methods were used to measure coral breakage by snorkelers on a Maldivian resort reef. On the most impacted section of reef, breakage over a one month period was estimated at 17% of susceptible coral cover and 7% of total coral cover.     

Symbiont transmission and reproductive mode influence responses of three Hawaiian coral larvae to elevated temperature and nutrients

Elevated temperatures and nutrients are degrading coral reef ecosystems, but the understanding of how early life stages of reef corals respond to these stressors remains limited. Here, we test the impact of temperature (mean ~ 27 °C vs. ~ 29 °C) and nitrate and phosphate enrichment (ambient, + 5 µM nitrate, + 1 µM phosphate and combined + 5 µM nitrate with 1 µM phosphate) on coral larvae using three Hawaiian coral species with different modes of symbiont transmission and reproduction: Lobactis scutaria (horizontal, gonochoric broadcast spawner), Pocillopora acuta (vertical, hermaphroditic brooder) and Montipora capitata (vertical, hermaphroditic broadcast spawner). Temperature and nutrient effects were species specific and appear antagonistic for L. scutaria and M. capitata, but not for P. acuta. Larvae survivorship in all species was lowest under nitrate enrichment at 27 °C. M. capitata and L. scutaria survivorship increased at 29 °C. However, positive effects of warming on survivorship were lost under high nitrate, but phosphate attenuated nitrate effects when N/P ratios were balanced. P. acuta larvae exhibited high survivorship (> 91%) in all treatments and showed little change in larval size, but lower respiration rates at 29 °C. Elevated nutrients (+N+P) led to the greatest loss in larvae size for aposymbiotic L. scutaria, while positive growth in symbiotic M. capitata larvae was reduced under warming and highest in +N+P treatments. Overall, we report a greater sensitivity of broadcast spawners to warming and nutrient changes compared to a brooding coral species. These results suggest variability in biological responses to warming and nutrient enrichment is influenced by life-history traits, including the presence of symbionts (vertical transmission), in addition to nutrient type and nutrient stoichiometry.

     

Community assembly and diversification in Indo-Pacific coral reef fishes

Theories of species coexistence have played a central role in ecology and evolutionary studies of the origin and maintenance of biodiversity in highly diverse communities. The concept of niche and associated theories predict that competition for available ecological space leads to a ceiling in species richness that influences further diversification patterns. By contrast, the neutral theory supports that speciation is stochastic and diversity independent. We examined the phylogenetic community structure and diversification rates in three families and 14 sites within coral reef fish communities from the Indian and Pacific oceans. Using the phylogenetic relationships among 157 species estimated with 2300 bp of mitochondrial DNA, we tested predictions in terms of species coexistence from the neutral and niche theories. At the regional scale, our findings suggest that phylogenetic community structure shifts during community assembly to a pattern of dispersion as a consequence of allopatric speciation in recent times but overall, variations in diversification rates did not relate with sea level changes. At the local scale, the phylogenetic community structure is consistent with a neutral model of community assembly since no departure from a random sorting of species was observed. The present results support a neutral model of community assembly as a consequence of the stochastic and unpredictable nature of coral reefs favoring generalist and sedentary species competing for living space rather than trophic resources. As a consequence, the observed decrease in diversification rates may be seen as the result of a limited supply of living space as expected in a finite island model.     

Genomic insights into hybridization of reef corals

Coral Reefs - Hybridization plays a fundamental role in speciation and diversification of plants and animals. Hybridization among highly diverse assemblages of reef corals is well known and widely...     

Effects of water motion on reef corals

The Hawaiian reef coral Pocillopora meandrina Dana is restricted to turbulent environments. P. damicornis (L.) is most abundant on semi-protected reefs, while Montipora verrucosa (Lamarck) is characteristic of very calm environments. These species were grown in the laboratory under various conditions of water motion. Water motion influenced the growth, mortality, and reproductive rate, of each species differently. The differences may be attributed to morphological adaptations of the corals to their normal hydrodynamic environment. Water motion appears to influence corals by controlling the rate of exchange of material across the interface between the sea water and the coral tissue.     

Effects of intermittent flow and irradiance level on back reef Porites corals at elevated seawater temperatures

Corals inhabiting shallow back reef habitats are often simultaneously exposed to elevated seawater temperatures and high irradiance levels, conditions known to cause coral bleaching. Water flow in many tropical back reef systems is tidally influenced, resulting in semi-diurnal or diurnal flow patterns. Controlled experiments were conducted to test effects of semi-diurnally intermittent water flow on photoinhibition and bleaching of the corals Porites lobata and P. cylindrica kept at elevated seawater temperatures and different irradiance levels. All coral colonies were collected from a shallow back reef pool on Ofu Island, American Samoa. In the high irradiance experiments, photoinhibition and bleaching were less for both species in the intermittent high-low flow treatment than in the constant low flow treatment. In the low irradiance experiments, there were no differences in photoinhibition or bleaching for either species between the flow treatments, despite continuously elevated seawater temperatures. These results suggest that intermittent flow associated with semi-diurnal tides, and low irradiances caused by turbidity or shading, may reduce photoinhibition and bleaching of back reef corals during warming events.     

Extended geographic distribution of several Indo-Pacific coral reef diseases

Other than coral bleaching, few coral diseases or diseases of other reef organisms have been reported from Japan. This is the first report of lesions similar to Porites ulcerative white spots (PUWS), brown band disease (BrB), pigmentation response (PR), and crustose coralline white syndrome (CCWS) for this region. To assess the health status and disease prevalence, qualitative and quantitative surveys (3 belt transects of 100 m2 each on each reef) were performed in March and September 2010 on 2 reefs of the Ginowan-Ooyama reef complex off Okinawa, and 2 protected reefs off Zamani Island, in the Kerama Islands 40 km west of Okinawa. Overall, mean (±SD) disease prevalence was higher in Ginowan-Ooyama (9.7 ± 7.9%) compared to Zamami (3.6 ± 4.6%). Porites lutea was most affected by PUWS at Ooyama (23.1 ± 10.4 vs. 4.5 ± 5.2%). White syndrome (WS) mostly affected Acropora cytherea (12. 5 ± 18.0%) in Zamami and Oxipora lacera (10.2 ± 10%) in Ooyama. Growth anomalies (GA) and BrB were only observed on A. cytherea (8.3 ± 6.2%) and A. nobilis (0.8%) at Zamami. Black band disease affected Pachyseris speciosa (6.0 ± 4.6%) in Ooyama only. Pigmentation responses (PR) were common in massive Porites in both localities (2.6 ± 1.9 and 5.6 ± 2.3% respectively). Crustose coralline white syndrome (CCWS) was observed in both localities. These results significantly expand the geographic distribution of PUWS, BrB, PR and CCWS in the Indo-Pacific, indicating that the northernmost coral reefs in the western Pacific are susceptible to a larger number of coral diseases than previously thought.     

Species density and associations in Caribbean reef corals

The density of scleractinian corals on portions of two reefs in the Grenadine Islands, W. I. has been investigated by direct observation by SCUBA divers. Grid, transect, and random quadrat methods were compared with total samples to determine the precision and accuracy of these techniques. Transect methods were generally satisfactory provided at least 15% of a 400 m² total grid area was included in the sample. The data strongly indicated clumped distributions of all species, although numerical analysis does not indicate the distinct zones reported by other workers. Species associations based on Jaccard's coefficient and cluster analysis showed possible similarities in physical requirements, although few strong associations were found. Data based on 4 m² quadrats generally provided a more reliable estimate of species associations than did data based on 1 m² quadrats. It is suggested that surveys of these reef types may be better based on a number of parallel transects rather than a single transect, and that well-defined zones are more likely to be the exception than the rule.     

Feeding mechanisms and feeding strategies of Atlantic reef corals

The feeding behaviour of 35 species of Atlantic reef corals was examined in the laboratory and in the field. Observations were made during the day and at night, using freshly hatched brine shrimp nauplii and finely ground, filtered fresh fish as food sources. Three feeding strategies were observed: Group I–feeding by tentacle capture only; Group II–feeding by entanglement with a mucus net or mucus filaments; Group III–feeding by a combination of tentacle capture and mucus filament entanglement. Group I included corals of the families Poritidae and Pocilloporidae which were normally expanded during both day and night. Group II included corals of the family Agaricidae which were normally expanded at night and contracted during the day. Group III included corals of the other families examined which, with the exception of Dendrogyra cylindrus , were normally expanded only at night.
Feeding responses were elicited by both chemical and tactile stimuli. A preparatory feeding posture was assumed in response to chemical stimuli and consisted of horizontal positioning of the tentacles, elevation of the oral disk to form a cone-like mouth, a wide mouth opening and secretion of mucus by the epidermis of the oral disk. Following the assumption of the preparatory feeding posture, food capture and ingestive movements were elicited by tactile stimuli. However, food capture and ingestive movements were also elicited by chemical stimuli alone in those species which were normally contracted during the day.
While expanded corals captured food with their tentacles or with mucus filaments, contracted corals were able to feed by capturing fine particulate matter with mucus filaments only and thus acted as suspension feeders. By a combination of feeding strategies, reef corals were able to feed both day and night and a wide range of potential food ranging from fine particulate matter to large zooplankton was available to them.     

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.     

Destruction of corals and other reef animals by coral spawn slicks on Ningaloo Reef,Western Australia

In March 1989, most of the corals near Coral Bay, off the north-western coastline of Australia, spawned several nights earlier than usual. Flood, rather than ebb, tides at the time of spawning combined with light north-west winds and low swell conditions to restrict the dispersal of coral propagules and, as a result, large amounts of coral spawn were trapped in the bay, forming extensive slicks. Fish and other animals began to die almost immediately, and over the next few days, over 1 million fish, representing at least 80 species, were washed ashore. A survey of the benthic communities revealed extensive mortality of corals and other reef animals over an area of about 3 km². Live coral cover in this area decreased from 42.9% to 9.4% and several large coral colonies up to 10 m in diameter were killed. The observed mortality was presumably the result of hypoxia (oxygen depletion) created initially by the respiratory demand of the coral spawn and maintained by the biological oxygen demand of the decomposing spawn slicks and dead animals. Anecdotal reports of corals and other reef animals dying in the vicinity of coral spawn slicks on other reefs in Western Australia suggest that this phenomenon may be a relatively common event on shallow coral reefs where coral mass spawning occurs. These records and observations document, for the first time, a new source of natural disturbance that has a significant influence on the community structure of some coral reefs.