Juvenile Corals Research Articles

INFLUENCE OF MINERAL ACCRETION INDUCED BY ELECTRIC CURRENT ON THE SETTLEMENT AND GROWTH OF THE SCLERACTINIAN CORAL POCILLOPORA DAMICORNIS (CNIDARIA, ANTHOZOA, HEXACORALLIA)

The effect of mineral accretion induced by electric current on settlement, growth, and survival of planula larvae and juvenile corals of Pocillopora damicornis was examined by both laboratory and field experiments. The laboratory experiment showed that the numbers of larvae settling on tiles with coralline algae and steel plates encrusted with limestone under no electric current condition were higher than that of other conditions. In the field, the highest survival rates of juvenile corals occurred under the lowest electric current density. However, there was no difference on the growth of juvenile corals between different electric current levels. The mineral accretion could potentially be used to enhance survival of juvenile corals for coral rehabilitation purpose.

Possible involvement of Tachylectin-2-like lectin from Acropora tenuis in the process of Symbiodinium acquisition

Most reef-building corals in tropical and subtropical areas symbiose with microalgae from the genus Symbiodinium (dinoflagellate) and depend on the photosynthate produced by the microalgae. The majority of corals acquire Symbiodinium from the surrounding environment through horizontal transfer, but the molecular mechanisms involved in the acquisition of Symbiodinium remain unknown. It has been hypothesized that carbohydrate-binding proteins, or lectins, of the host coral recognize cell surface carbohydrates of Symbiodinium in the process of acquiring symbionts. Thus, we examined the molecular mechanisms involving lectins and carbohydrates using model organism Acropora tenuis, a common reef-building coral, and Symbiodinium culture strains. Juvenile polyps acquire more cells of Symbiodinium strain NBRC102920 at 72–96 h of metamorphosis induction than in any other period. Glycosidase treatment of Symbiodinium inhibited the acquisition of Symbiodinium by juvenile coral polyps. The presence of carbohydrates D-galactose, N-acetyl-D-galactosamine, and N-acetyl-D-glucosamine at 10 mM also tended to decrease Symbiodinium acquisition. We isolated two N-acetyl-D-galactosamine binding lectins with apparent molecular masses of 14.6 and 29.0 kDa from A. tenuis, and de novo sequencing and cDNA cloning showed that the 29.0 kDa protein is Tachylectin-2-like lectin (AtTL-2). The anti-Tachylectin-2 antibody is suggested to bind specifically to AtTL-2. The antibody also inhibited binding of AtTL-2 to N-acetyl-D-galactosamine-resin and the acquisition of Symbiodinium by juvenile A. tenuis polyps. Based on these results, AtTL-2 is likely involved in the process of Symbiodinium acquisition.

NURSERY TECHNIQUES WITH JUVENILE CORAL TROUT, Plectropomus leopardus WITH DIFFERENT TYPES OF FOOD

ABSTRACT Feed management is a critical factor in the nursery activities because food serves as an energy for growth and survival rates. The study aimed to determine the best feeding to improve growth and survival rates. Cultured of coral trout grouper seeds were used for this research in 9 fiber tubs each of 0.8 tonnes of sea water volume with 3 treatments and 3 replicates. The feeding treatments were (a) commercial feeding pelle; (b) trash fish; and (c) feeding combinations (50% pellets and 50% trash fish). The initial length of coral trout grouper seeds were 3 cm long. The pellet used was a commercial pellet with dose of 5-10% biomass, while the trash fish was clupeid fish. Feeding times were twice a daya at 08:00 and 16:00 local time. A complete random design was used as an experiment design. Data was analysed using ANOVA and descriptive statistics. Water qualities during larva rearing included water temperature, pH, salinity, DO, ammonia, nitrite, and phosphate. The results showed that growth dan survical rates was significantly affected by combination feeding method (50% pellet and 50% trash fish) with growth rate of 0.08% cm/day and survival rate of 60.20±2.34%. Keywords: Feed, trash fish, juvenile coral trout grouper, growth, and survival.

Background level of risk and the survival of predator-naive prey: can neophobia compensate for predator naivety in juvenile coral reef fishes?

Neophobia--the generalized fear response to novel stimuli--provides the first potential strategy that predator-naive prey may use to survive initial predator encounters. This phenotype appears to be highly plastic and present in individuals experiencing high-risk environments, but rarer in those experiencing low-risk environments. Despite the appeal of this strategy as a 'solution' for prey naivety, we lack evidence that this strategy provides any fitness benefit to prey. Here, we compare the relative effect of environmental risk (high versus low) and predator-recognition training (predator-naive versus predator-experienced individuals) on the survival of juvenile fish in the wild. We found that juveniles raised in high-risk conditions survived better than those raised in low-risk conditions, providing the first empirical evidence that environmental risk, in the absence of any predator-specific information, affects the way naive prey survive in a novel environment. Both risk level and experience affected survival; however, the two factors did not interact, indicating that the information provided by both factors did not interfere or enhance each other. From a mechanistic viewpoint, this indicates that the combination of the two factors may increase the intensity, and hence efficacy, of prey evasion strategies, or that both factors provide qualitatively separate benefits that would result in an additive survival success.

Predicting climate-driven regime shifts versus rebound potential in coral reefs.

Climate-induced coral bleaching is among the greatest current threats to coral reefs, causing widespread loss of live coral cover. Conditions under which reefs bounce back from bleaching events or shift from coral to algal dominance are unknown, making it difficult to predict and plan for differing reef responses under climate change. Here we document and predict long-term reef responses to a major climate-induced coral bleaching event that caused unprecedented region-wide mortality of Indo-Pacific corals. Following loss of >90% live coral cover, 12 of 21 reefs recovered towards pre-disturbance live coral states, while nine reefs underwent regime shifts to fleshy macroalgae. Functional diversity of associated reef fish communities shifted substantially following bleaching, returning towards pre-disturbance structure on recovering reefs, while becoming progressively altered on regime shifting reefs. We identified threshold values for a range of factors that accurately predicted ecosystem response to the bleaching event. Recovery was favoured when reefs were structurally complex and in deeper water, when density of juvenile corals and herbivorous fishes was relatively high and when nutrient loads were low. Whether reefs were inside no-take marine reserves had no bearing on ecosystem trajectory. Although conditions governing regime shift or recovery dynamics were diverse, pre-disturbance quantification of simple factors such as structural complexity and water depth accurately predicted ecosystem trajectories. These findings foreshadow the likely divergent but predictable outcomes for reef ecosystems in response to climate change, thus guiding improved management and adaptation.

Wide field-of-view fluorescence imaging of coral reefs.

Coral reefs globally are declining rapidly because of both local and global stressors. Improved monitoring tools are urgently needed to understand the changes that are occurring at appropriate temporal and spatial scales. Coral fluorescence imaging tools have the potential to improve both ecological and physiological assessments. Although fluorescence imaging is regularly used for laboratory studies of corals, it has not yet been used for large-scale in situ assessments. Current obstacles to effective underwater fluorescence surveying include limited field-of-view due to low camera sensitivity, the need for nighttime deployment because of ambient light contamination, and the need for custom multispectral narrow band imaging systems to separate the signal into meaningful fluorescence bands. Here we describe the Fluorescence Imaging System (FluorIS), based on a consumer camera modified for greatly increased sensitivity to chlorophyll-a fluorescence, and we show high spectral correlation between acquired images and in situ spectrometer measurements. This system greatly facilitates underwater wide field-of-view fluorophore surveying during both night and day, and potentially enables improvements in semi-automated segmentation of live corals in coral reef photographs and juvenile coral surveys.

Geographic variation in long-term trajectories of change in coral recruitment: a global-to-local perspective

Compiled abundances of juvenile corals revealed no change over time in the Pacific, but a decline in the Caribbean. Using these analyses as a rationale, we explored recruitment and post-settlement success in determining coral cover using studies in the Caribbean (St John, Bonaire) and Pacific (Moorea, Okinawa). Juvenile corals, coral recruits, and coral cover have been censused in these locations for years, and the ratio of juvenile (J) to recruiting (R) corals was used to measure post-settlement success. In St John and Bonaire, coral cover was stable but different between studies, with the ratio of the density of juveniles to density of recruits (J:R) ~0.10; in Moorea, declines in coral cover were followed by recovery that was related to the density of juvenile corals 3 years before, with J:R ~0.40; and in Okinawa, a decline in coral cover in 1998 was followed by a slow recovery with J/R ~0.01. Coral cover was associated positively with juvenile corals in St John, and in Okinawa, the density of juvenile corals was associated positively with recruits the year before. J:R varied among studies, and standardised densities of juvenile corals declined in the Caribbean, but increased in the Pacific. These results suggest that differences in the post-settlement success may drive variation in coral community structure.

Rapid acclimation of juvenile corals to CO2 -mediated acidification by upregulation of heat shock protein and Bcl-2 genes.

Corals play a key role in ocean ecosystems and carbonate balance, but their molecular response to ocean acidification remains unclear. The only previous whole-transcriptome study (Moya etal. Molecular Ecology, 2012; 21, 2440) documented extensive disruption of gene expression, particularly of genes encoding skeletal organic matrix proteins, in juvenile corals (Acropora millepora) after short-term (3d) exposure to elevated pCO2 . In this study, whole-transcriptome analysis was used to compare the effects of such 'acute' (3d) exposure to elevated pCO2 with a longer ('prolonged'; 9d) period of exposure beginning immediately post-fertilization. Far fewer genes were differentially expressed under the 9-d treatment, and although the transcriptome data implied wholesale disruption of metabolism and calcification genes in the acute treatment experiment, expression of most genes was at control levels after prolonged treatment. There was little overlap between the genes responding to the acute and prolonged treatments, but heat shock proteins (HSPs) and heat shock factors (HSFs) were over-represented amongst the genes responding to both treatments. Amongst these was an HSP70 gene previously shown to be involved in acclimation to thermal stress in a field population of another acroporid coral. The most obvious feature of the molecular response in the 9-d treatment experiment was the upregulation of five distinct Bcl-2 family members, the majority predicted to be anti-apoptotic. This suggests that an important component of the longer term response to elevated CO2 is suppression of apoptosis. It therefore appears that juvenile A.millepora have the capacity to rapidly acclimate to elevated pCO2 , a process mediated by upregulation of specific HSPs and a suite of Bcl-2 family members.

Defended territories of an aggressive damselfish contain lower juvenile coral density than adjacent non-defended areas on Kenyan lagoon patch reefs

Jewel damselfish, Plectroglyphidodon lacrymatus, aggressively defend small territories on coral reefs in which they cultivate lawns of edible macroalgae. Pairwise frequency counts showed that juvenile coral density was lower inside damselfish territories than that in adjacent non-defended areas on lagoon patch reefs in Kenya. These differences in coral density decreased as coral size increased. Direct farming effects of the damselfish and indirect inhibitory effects from higher algal densities inside territories are both thought to be potentially responsible for the results attained herein. Damselfish territories can occupy a large proportion of a coral reef; territorial behaviour in fish may have greater impacts on reef structure, in particular the resilience and growth rate of juvenile corals, than previously appreciated.

Coupled dynamics of territorial damselfishes and juvenile corals on the reef crest

Territories of grazing fishes in the family Pomacentridae have been documented to cover a sub- stantial proportion of shallow, exposed coral reef fronts, and these fishes can have profound effects on benthic community composition, including the recruitment and post-settlement survival of scleractinian corals. However, current studies of territorial grazer effects on corals have focused on back-reef habitats. Territorial damselfishes occur in distinct behavioural guilds ranging from indeter- minate territorial grazers with thin algal turfs and low rates of territorial aggression to intensive territorial grazers with thick turfs and high rates of aggression. To determine the impact of territorial grazers on the establishment of juve- nile corals, we surveyed the reef crest habitat of Lizard Island, Great Barrier Reef, using fixed transects to assess the effects of indeterminate and intensive territorial grazers on juvenile coral abundance and taxonomic composition. In addition, the turnover of territorial pomacentrids was monitored as well as the effects of turnover on juvenile coral assemblages. Intensive territorial grazers were asso- ciated with a significantly lower juvenile coral abundance (34 % decrease), but neither intensive nor indeterminate grazer territories impacted juvenile coral taxonomic com- position. Over the course of 1 yr, there was a high rate of territorial turnover (39.7 %). Turnover from control plots to intensive damselfish territories was accompanied by a 44 % decrease in juvenile corals; conversely, turnover from intensive damselfish territories to control plots coin- cided with a 48 % increase in juvenile corals. These find- ings reveal two main conclusions. Firstly, the association between damselfish territories and the abundance and spatial turnover of juvenile corals strongly implies that territorial grazers have a negative effect on juvenile coral populations. Secondly, the unexpectedly high temporal turnover of damselfish territories indicates that damselfish- coral-algae linkages are highly dynamic, may be exten- sively influenced by local-scale effects, and have the potential to impact the structure of coral assemblages on coral reef fronts.

Linking benthic community structure to terrestrial runoff and upwelling in the coral reefs of northeastern Hainan Island

Near-shore coral reefs in northeastern Hainan Island are close to river mouths and aquaculture ponds, and also located at the center of the Qiongdong Upwelling (QDU). However, it is still unclear how terrestrial runoff and upwelling influence the community composition and spatial distribution of the benthos. During three cruises in 2010 and 2011 in Wenchang, northeastern Hainan Island, we determined a subset of environmental parameters in seawater (e.g. temperature, salinity, DO, dissolved inorganic nutrient (DIN), turbidity and transparency) and macroalgal δ15N and investigated the benthic communities (e.g. live coral cover, coral species richness, juvenile coral density, macroalgal cover and coverage of calcified algae) by video transect and visual census techniques at 10 stations (i.e. 1S–6D). The results showed that the QDU has influenced the reef waters in Wenchang. In 2011, the upwelling started in early May, peaked in July and disappeared in September and most upwelling events lasted for 1–2 weeks between May and July. The results also demonstrated that the reef water was nutrient enriched. Stations close to the river mouth and aquaculture ponds had higher levels of DIN and a higher percentage of ammonia in DIN, and there was consistently lower live coral cover, juvenile coral density and higher macroalgal cover. At some stations in this study, live coral cover was negatively correlated with macroalgal cover (i.e. 2S–6D). Live coral cover, species richness, and juvenile coral density all increased with the distance away from the river outlet and decreased with the rise of DIN. These results suggest that terrestrial runoff and upwelling stimulate nutrient enrichment, and that overgrowing macroalgae has an important influence on the coral communities in northeastern Hainan Island.

Onset and establishment of diazotrophs and other bacterial associates in the early life history stages of the coral Acropora millepora.

Early establishment of coral-microbial symbioses is fundamental to the fitness of corals, but comparatively little is known about the onset and succession of bacterial communities in their early life history stages. In this study, bacterial associates of the coral Acropora millepora were characterized throughout the first year of life, from larvae and 1-week-old juveniles reared in laboratory conditions in the absence of the dinoflagellate endosymbiont Symbiodinium to field-outplanted juveniles with established Symbiodinium symbioses, and sampled at 2 weeks and at 3, 6 and 12 months. Using an amplicon pyrosequencing approach, the diversity of both nitrogen-fixing bacteria and of bacterial communities overall was assessed through analysis of nifH and 16S rRNA genes, respectively. The consistent presence of sequences affiliated with diazotrophs of the order Rhizobiales (23-58% of retrieved nifH sequences; 2-12% of 16S rRNA sequences), across all samples from larvae to 12-month-old coral juveniles, highlights the likely functional importance of this nitrogen-fixing order to the coral holobiont. Dominance of Roseobacter-affiliated sequences (>55% of retrieved 16S rRNA sequences) in larvae and 1-week-old juveniles, and the consistent presence of sequences related to Oceanospirillales and Altermonadales throughout all early life history stages, signifies their potential importance as coral associates. Increased diversity of bacterial communities once juveniles were transferred to the field, particularly of Cyanobacteria and Deltaproteobacteria, demonstrates horizontal (environmental) uptake of coral-associated bacterial communities. Although overall bacterial communities were dynamic, bacteria with likely important functional roles remain stable throughout early life stages of Acropora millepora.

Identification of scleractinian coral recruits using fluorescent censusing and DNA barcoding techniques.

The identification of coral recruits has been problematic due to a lack of definitive morphological characters being available for higher taxonomic resolution. In this study, we tested whether fluorescent detection of coral recruits used in combinations of different DNA-barcoding markers (cytochrome oxidase I gene [COI], open reading frame [ORF], and nuclear Pax-C intron [PaxC]) could be useful for increasing the resolution of coral spat identification in ecological studies. One hundred and fifty settlement plates were emplaced at nine sites on the fringing reefs of Kenting National Park in southern Taiwan between April 2011 and September 2012. A total of 248 living coral spats and juveniles (with basal areas ranging from 0.21 to 134.57 mm2) were detected on the plates with the aid of fluorescent light and collected for molecular analyses. Using the COI DNA barcoding technique, 90.3% (224/248) of coral spats were successfully identified into six genera, including Acropora, Isopora, Montipora, Pocillopora, Porites, and Pavona. PaxC further separated I. cuneata and I. palifera of Isopora from Acropora, and ORF successfully identified the species of Pocillopora (except P. meandrina and P. eydouxi). Moreover, other cnidarian species such as actinarians, zoanthids, and Millepora species were visually found using fluorescence and identified by COI DNA barcoding. This combination of existing approaches greatly improved the taxonomic resolution of early coral life stages, which to date has been mainly limited to the family level based on skeletal identification. Overall, this study suggests important improvements for the identification of coral recruits in ecological studies.

Coral community responses to declining water quality: Whitsunday Islands, Great Barrier Reef, Australia

A five-year period (2002–2006) of below-median rainfall followed by a six-year period (2007–2012) of above-median rainfall and seasonal flooding allowed a natural experiment into the effects of runoff on the water quality and subsequent coral community responses in the Whitsunday Islands, Great Barrier Reef (Australia). Satellite-derived water quality estimates of total suspended solids (TSS) and chlorophyll-a (Chl) concentration showed marked seasonal variability that was exaggerated during years with high river discharge. During above-median rainfall years, Chl was aseasonally high for a period of 3 months during the wet season (February–April), while TSS was elevated for four months, extending into the dry season (March–June). Coinciding with these extremes in water quality was a reduction in the abundance and shift in the community composition, of juvenile corals. The incidence of coral disease was at a maximum during the transition from years of below-median to years of above-median river discharge. In contrast to juvenile corals, the cover of larger corals remained stable, although the composition of communities varied along environmental gradients. In combination, these results suggest opportunistic recruitment of corals during periods of relatively low environmental stress with selection for more tolerant species occurring during periods of environmental extremes.

Abundance and composition of juvenile scleractinian corals on a fringing reef (Little Reef) off San Andres Island, Colombian Caribbean

Colombian Caribbean reefs have deteriorated significantly over the last three decades. Coral recruitment is an important demographic process that determines the replenishment of populations and the natural potential for recovery of reef ecosystems after perturbations. We studied the composition and abundance of juvenile corals on a fringing reef (Little Reef) off San Andres Island, Colombia, using 1 m2 quadrats (N = 33) spread randomly on the reef. We surveyed a total of 190 juvenile corals belonging to seven families and 15 species, with a total density of 5.75 ± 3.47 (mean ± SD) juveniles m−2. The population of juvenile corals was dominated by species of the genera Favia, Agaricia and Porites (85.8%), while the adult population was dominated by Diploria, Acropora and Orbicella (78.4%). Most (71.6%) juveniles were between 1.1 and 2.0 cm. The most abundant species was Favia fragum (67 individuals), while Agaricia agaricites was the most frequently occurring (26.9%), covering the highest percentage (76.9%) of the substrate and having the largest Importance Value Index (44.6%). The community of juvenile corals on Little Reef was dominated by species that brood planulae while the adult community was dominated by species that spawn gametes. Furthermore, the two most abundant juvenile coral species had negatively skewed size–frequency distributions, indicating low recent recruitment. This study provides a demographic baseline for monitoring future changes in recruitment patterns.

Ecology. How do coral reefs recover?

Experiments on juvenile coral and fish behavior may have implications for reef restoration efforts [Also see Research Article by Dixson et al. ]

RETRACTED: Chemically mediated behavior of recruiting corals and fishes: a tipping point that may limit reef recovery.

Coral reefs are in global decline, converting from dominance by coral to dominance by seaweed. Once seaweeds become abundant, coral recovery is suppressed unless herbivores return to remove seaweeds, and corals then recruit. Variance in the recovery of fishes and corals is not well understood. We show that juveniles of both corals and fishes are repelled by chemical cues from fished, seaweed-dominated reefs but attracted to cues from coral-dominated areas where fishing is prohibited. Chemical cues of specific seaweeds from degraded reefs repulsed recruits, and cues from specific corals that are typical of healthy reefs attracted recruits. Juveniles were present at but behaviorally avoided recruiting to degraded reefs dominated by seaweeds. For recovery, degraded reefs may need to be managed to produce cues that attract, rather than repel, recruiting corals and fishes.

Corals and reef fish choose nice homes

Reef Ecology Young animals tend to disperse into new habitats. Can we use populations in protected areas to colonize nearby recovering or overused habitats? It seems that for corals and reef fish, the answer may be no. Dixson et al. show that dispersing juvenile corals and reef fish were overwhelmingly attracted to healthy reefs but were repelled by seaweeds that colonize degraded reefs (see the Perspective by Bruno). Thus, even species that appear passive in their choice of habitat may have stronger preferences than we thought. Science , this issue p. [892][1]; see also p. [879][2] [1]: /lookup/doi/10.1126/science.1255057 [2]: /lookup/doi/10.1126/science.1258556

Nutrient availability affects the response of juvenile corals and the endosymbionts to ocean acidification

The interactive effects of nutrient availability and ocean acidification on coral calcification were investigated using post‐settlement juvenile corals of Acropora digitifera cultured in nutrient‐sufficient or nutrient‐depleted seawater for 4 d and then exposed to seawater with different partial pressure of carbon dioxide (PCO2) conditions (38.8 or 92.5 Pa) for 10 d. After the nutrient pretreatment, corals in the high nutrient condition (HN corals) had a significantly higher abundance of endosymbiotic algae than did those in the low nutrient condition (LN corals). The high abundance of endosymbionts in HN corals was reduced as a result of subsequent seawater acidification, and the chlorophyll a per algal cell increased. The photosynthetic oxygen production rate by endosymbionts was enhanced by the acidified seawater regardless of the nutrient treatment, indicating that the reduction in endosymbiont density in HN corals due to acidification was compensated for by the increase in chlorophyll a per cell. Though the photosynthetic rate increased in the acidified conditions for both LN and HN corals, the calcification rate significantly decreased for LN corals but not for HN corals. The acquisition of nutrients from seawater, rather than the increase in alkalinity caused by photosynthesis, might effectively alleviate the negative response of coral calcification to seawater acidification, suggesting that the response of corals and their endosymbionts to ocean acidification can be influenced by nutrient conditions.

Coral reef community composition in the context of disturbance history on the Great Barrier Reef, Australia.

Much research on coral reefs has documented differential declines in coral and associated organisms. In order to contextualise this general degradation, research on community composition is necessary in the context of varied disturbance histories and the biological processes and physical features thought to retard or promote recovery. We conducted a spatial assessment of coral reef communities across five reefs of the central Great Barrier Reef, Australia, with known disturbance histories, and assessed patterns of coral cover and community composition related to a range of other variables thought to be important for reef dynamics. Two of the reefs had not been extensively disturbed for at least 15 years prior to the surveys. Three of the reefs had been severely impacted by crown-of-thorns starfish outbreaks and coral bleaching approximately a decade before the surveys, from which only one of them was showing signs of recovery based on independent surveys. We incorporated wave exposure (sheltered and exposed) and reef zone (slope, crest and flat) into our design, providing a comprehensive assessment of the spatial patterns in community composition on these reefs. Categorising corals into life history groupings, we document major coral community differences in the unrecovered reefs, compared to the composition and covers found on the undisturbed reefs. The recovered reef, despite having similar coral cover, had a different community composition from the undisturbed reefs, which may indicate slow successional processes, or a different natural community dominance pattern due to hydrology and other oceanographic factors. The variables that best correlated with patterns in the coral community among sites included the density of juvenile corals, herbivore fish biomass, fish species richness and the cover of macroalgae. Given increasing impacts to the Great Barrier Reef, efforts to mitigate local stressors will be imperative to encouraging coral communities to persist into the future.