Restoration of coral populations in light of genetic diversity estimates

Due to the importance of preserving the genetic integrity of populations, strategies to restore damaged coral reefs should attempt to retain the allelic diversity of the disturbed population; however, genetic diversity estimates are not available for most coral populations. To provide a generalized estimate of genetic diversity (in terms of allelic richness) of scleractinian coral populations, the literature was surveyed for studies describing the genetic structure of coral populations using microsatellites. The mean number of alleles per locus across 72 surveyed scleractinian coral populations was 8.27 (±0.75 SE). In addition, population genetic datasets from four species (Acropora palmata, Montastraea cavernosa, Montastraea faveolata and Pocillopora damicornis) were analyzed to assess the minimum number of donor colonies required to retain specific proportions of the genetic diversity of the population. Rarefaction analysis of the population genetic datasets indicated that using 10 donor colonies randomly sampled from the original population would retain >50% of the allelic diversity, while 35 colonies would retain >90% of the original diversity. In general, scleractinian coral populations are genetically diverse and restoration methods utilizing few clonal genotypes to re-populate a reef will diminish the genetic integrity of the population. Coral restoration strategies using 10–35 randomly selected local donor colonies will retain at least 50–90% of the genetic diversity of the original population. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Phylogenetic community ecology and the role of social dominance in sponge-dwelling shrimp

When functional traits are evolutionarily conserved, phylogenetic relatedness can serve as a proxy for ecological similarity to examine whether functional differences among species mediate community assembly. Using phylogenetic- and trait-based analyses, we demonstrate that sponge-dwelling shrimp (Synalpheus) assemblages are structured by size-based habitat filtering, interacting with competitive exclusion mediated by social system. Most shrimp communities were more closely related and/or more similar in size than randomized communities, consistent with habitat filtering facilitated by phylogenetically conserved body size. Those sponges with greater space heterogeneity hosted shrimp communities with greater size diversity, corroborating the importance of size in niche use. However, communities containing eusocial shrimp - which cooperatively defend territories - were less phylogenetically related and less similar in size, suggesting that eusociality enhances competitive ability and drives competitive exclusion. Our analyses demonstrate that community assembly in this diverse system occurs via traits mediating niche use and differential competitive ability.     

Elevated carbon dioxide affects behavioural lateralization in a coral reef fish

Elevated carbon dioxide (CO(2)) has recently been shown to affect chemosensory and auditory behaviour, and activity levels of larval reef fishes, increasing their risk of predation. However, the mechanisms underlying these changes are unknown. Behavioural lateralization is an expression of brain functional asymmetries, and thus provides a unique test of the hypothesis that elevated CO(2) affects brain function in larval fishes. We tested the effect of near-future CO(2) concentrations (880 μatm) on behavioural lateralization in the reef fish, Neopomacentrus azysron. Individuals exposed to current-day or elevated CO(2) were observed in a detour test where they made repeated decisions about turning left or right. No preference for right or left turns was observed at the population level. However, individual control fish turned either left or right with greater frequency than expected by chance. Exposure to elevated-CO(2) disrupted individual lateralization, with values that were not different from a random expectation. These results provide compelling evidence that elevated CO(2) directly affects brain function in larval fishes. Given that lateralization enhances performance in a number of cognitive tasks and anti-predator behaviours, it is possible that a loss of lateralization could increase the vulnerability of larval fishes to predation in a future high-CO(2) ocean.     

VARIABILITY IN THE PRIMARY SITE OF PHOTOSYNTHETIC DAMAGE IN SYMBIODINIUM SP. (DINOPHYCEAE) EXPOSED TO THERMAL STRESS1

Exposure to elevated temperature is known to cause photosynthetic inhibition in the coral symbiont Symbiodinium sp. Through the use of the artificial electron acceptor, methyl viologen, this study identified how reduced photosynthetic capacity occurs as a result of inhibition up‐ and/or downstream of ferredoxin in Symbiodinium sp. in hospite and in culture. Heterogeneity between coral species and symbiont clades was identified in the thermal sensitivity of photosynthesis in the symbionts of the scleractinian corals Stylophora pistillata and Pocillopora damicornis, as well as among Symbiodinium cultures of clades A, B, and C. The in hospite symbionts of S. pistillata and the cultured clade C Symbiodinium both exhibited similar patterns in that their primary site of thermal inhibition occurred downstream of ferredoxin at 32°C. In contrast, the primary site of thermal inhibition occurred upstream of ferredoxin in clades A and B at 32°C, while at 34°C, all samples showed combined up‐ and downstream inhibition. Although clade C is common to both P. damicornis and S. pistillata, the manner of thermal inhibition was not consistent when observed in hospite. Results showed that there is heterogeneity in the primal site of thermal damage in Symbiodinium among coral species and symbiont clades.     

Learn and live: predator experience and feeding history determines prey behaviour and survival

Determining how prey learn the identity of predators and match their vigilance with current levels of threat is central to understanding the dynamics of predator–prey systems and the determinants of fitness. Our study explores how feeding history influences the relative importance of olfactory and visual sensory modes of learning, and how the experience gained through these sensory modes influences behaviour and survival in the field for a juvenile coral reef damselfish. We collected young fish immediately prior to their settlement to benthic habitats. In the laboratory, these predator-naïve fish were exposed to a high- or low-food ration and then conditioned to recognize the olfactory cues (odours) and/or visual cues from two common benthic predators. Fish were then allowed to settle on reefs in the field, and their behaviour and survival over 70 h were recorded. Feeding history strongly influenced their willingness to take risks in the natural environment. Conditioning in the laboratory with visual, olfactory or both cues from predators led fish in the field to display risk-averse behaviour compared with fish conditioned with sea water alone. Well-fed fish that were conditioned with visual, chemical or a combination of predator cues survived eight times better over the first 48 h on reefs than those with no experience of benthic predator cues. This experiment highlights the importance of a flexible and rapid mechanism of learning the identity of predators for survival of young fish during the critical life-history transition between pelagic and benthic habitats.     

Human activity selectively impacts the ecosystem roles of parrotfishes on coral reefs

Around the globe, coral reefs and other marine ecosystems are increasingly overfished. Conventionally, studies of fishing impacts have focused on the population size and dynamics of targeted stocks rather than the broader ecosystem-wide effects of harvesting. Using parrotfishes as an example, we show how coral reef fish populations respond to escalating fishing pressure across the Indian and Pacific Oceans. Based on these fish abundance data, we infer the potential impact on four key functional roles performed by parrotfishes. Rates of bioerosion and coral predation are highly sensitive to human activity, whereas grazing and sediment removal are resilient to fishing. Our results offer new insights into the vulnerability and resilience of coral reefs to the ever-growing human footprint. The depletion of fishes causes differential decline of key ecosystem functions, radically changing the dynamics of coral reefs and setting the stage for future ecological surprises.     

Specialization in habitat use by coral reef damselfishes and their susceptibility to habitat loss

While it is generally assumed that specialist species are more vulnerable to disturbance compared with generalist counterparts, this has rarely been tested in coastal marine ecosystems, which are increasingly subject to a wide range of natural and anthropogenic disturbances. Habitat specialists are expected to be more vulnerable to habitat loss because habitat availability exerts a greater limitation on population size, but it is also possible that specialist species may escape effects of disturbance if they use habitats that are generally resilient to disturbance. This study quantified specificity in use of different coral species by six coral‐dwelling damselfishes (Chromis viridis, C. atripectoralis, Dascyllus aruanus, D. reticulatus, Pomacentrus moluccensis, and P. amboinensis) and related habitat specialization to proportional declines in their abundance following habitat degradation caused by outbreaks of the coral eating starfish, Acanthaster planci. The coral species preferred by most coral‐dwelling damselfishes (e.g., Pocillopora damicornis) were frequently consumed by coral eating crown‐of‐thorns starfish, such that highly specialized damselfishes were disproportionately affected by coral depletion, despite using a narrower range of different coral species. Vulnerability of damselfishes to this disturbance was strongly correlated with both their reliance on corals and their degree of habitat specialization. Ongoing disturbances to coral reef ecosystems are expected, therefore, to lead to fundamental shifts in the community structure of fish communities where generalists are favored over highly specialist species.     

Isolation and characterization of 16 microsatellite loci in the humbug damselfish, Dascyllus aruanus (family Pomacentridae)

Here we report on 16 microsatellite loci designed for the damselfish Dascyllus aruanus. All loci were tested on 98 individuals and were polymorphic (seven to 35 alleles). Expected heterozygosity ranged from 0.705 to 0.942. Six loci showed Hardy-Weinberg disequilibrium due to the occurrence of null alleles. Cross-species amplifications conducted within the genus Dascyllus (D. carneus, D. strasburgi, D. trimaculatus) lead to polymorphic fragments in 32 out of 48 tests. These 16 loci will enable future research into the behavioural ecology and population ecology of Dascyllus aruanus throughout the Indo-Pacific.     

Microsatellite loci for assessing genetic diversity, dispersal and clonality of coral symbionts in 'stress-tolerant' clade D Symbiodinium

Reef corals harbouring clade D Symbiodinium spp. (endosymbiotic dinoflagellates) appear more tolerant of environmental stress. As sea surface temperatures rise, symbioses involving Symbiodinium D may increase in prevalence. For this reason, eight polymorphic microsatellite loci were developed for clade D Symbiodinium. From the analysis of 132 samples originating from cnidarian hosts in the Atlantic, Pacific and Indian Oceans, 4 to 35 alleles were found at each haploid locus and diversity indices ranged from 0.35 to 0.97. Population genetic analyses of these symbionts should reveal how environmental perturbations affect genetic diversity, geographical distributions, and possible host-range expansions to new coral species.