Comparative population genetic structure of marine gastropods (Littorina spp.) with and without pelagic larval dispersal

 Population genetic theory predicts that marine animal species with planktonic larvae will have less genetic structure than those with direct development. We compared the genetic structure of four species of littorinid snails – two with planktonic egg capsules that hatch as planktonic larvae and two with benthic egg masses that hatch as crawl-away juveniles. We used DNA sequencing and single stranded conformational polymorphism (SSCP) to assess sequence variation in a 480 bp fragment of the mitochondrial cytochrome b gene and then used an analysis of molecular variance (AMOVA) to estimate Φ_st for populations from the northeastern Pacific coast. One of the two direct-developing species, Littorina subrotundata, had a moderate amount of population structure (Φ_st=0.209) as expected but the other direct-developing species, L. sitkana, was nearly fixed for a single haplotype that made it impossible to precisely estimate Φ_st. One of the two planktonic-developing species, L. scutulata, did not show any significant population structure (Φ_st=0.004). In contrast to our expectations, the other planktonic-developing species, L. plena, showed some weak but statistically significant population structure (Φ_st=0.052). We discuss how differences in population genetic structure between species with the same type of development may reflect differences in their historical demography. Received: 22 December 1999 / Accepted: 24 July 2000     

Ultraviolet photosensitivity and feeding in larval and juvenile coral reef fishes

The ability of young coral reef fishes to feed using solely ultraviolet-A (UV-A) radiation during ontogeny was examined using natural prey in experimental tanks. Larvae and juveniles of three coral reef fish species (Pomacentrus amboinensis, Premnas biaculeatus and Apogon compressus) are able to feed successfully using UV-A radiation alone during the later half of the pelagic larval phase. The minimum UV radiation intensities required for larval feeding occur in the field down to depths of 90–130 m in oceanic waters and 15–20 m in turbid inshore waters. There was no abrupt change in UV sensitivity after settlement, indicating that UV photosensitivity may continue to play a significant role in benthic juveniles on coral reefs. Tests of UV sensitivity in the field using light traps indicate that larval and juvenile stages of 16 coral reef fish families are able to detect and respond photopositively to UV wavelengths. These include representatives from families that are unlikely to possess UV sensitivity as adults due to the UV transmission characteristics of the ocular media. Functional UV sensitivity may be more widespread in young coral reef fishes than in the adults, and may play a significant role in detecting zooplanktonic prey.     

Genetic connectivity among color morphs and Pacific archipelagos for the flame angelfish, <Emphasis Type="Italic">Centropyge loriculus</Emphasis>

Color variation is used in taxonomic classification of reef fishes, but it may not reliably indicate evolutionary divergence. In the central Pacific, there are three color morphs of the flame angelfish, Centropyge loriculus: a red morph that occurs primarily in the Hawaiian archipelago, the endemic Marquesan color morph with reduced black markings, and an orange morph that occurs throughout the rest of Oceania. The red and orange morphs co-occur at Johnston Atoll (1,300 km south of Hawai’i), but intermediate forms have not been reported. To determine whether the three color morphs represent distinct evolutionary lineages, we compared 641 base pairs of mitochondrial cytochrome b. Forty-one closely related haplotypes were observed in 116 individuals. Analysis of molecular variance (AMOVA) indicated no significant genetic structure among color morphs (Φ_ST = 0.011, P = 0.147). Likewise, there was no significant pairwise structure between sampling locations, separated by up to 5,700 km, after a Bonferroni correction (Φ_ST = 0.000–0.080, P = 0.0130–0.999). Genetic studies in conjunction with larval distribution data indicate that Centropyge species are highly dispersive. While there is a strong geographic component to the distribution of color morphs in C. loriculus, we find no evidence for corresponding genetic partitioning. We do not rule out an adaptive role for color differentiation, but our data do not support emerging species.     

Population connectivity in the temperate damselfish <Emphasis Type="Italic">Parma microlepis</Emphasis>: analyses of genetic structure across multiple spatial scales

This study investigated the utility of microsatellite markers for providing information on levels of population connectivity for a low dispersing reef fish in New South Wales (NSW), Australia, at scales ≤400 km. It was hypothesized that the temperate damselfish Parma microlepis, which produces benthic eggs and has limited post-settlement dispersal, would exhibit spatial genetic structure and a significant pattern of isolation-by-distance (IBD). A fully nested hierarchical sampling design incorporating three spatial scales (sites, location and regions, separated by 1–2, 10–50 and 70–80 km respectively) was used to determine genetic variability at seven microsatellite loci. Broad-scale genetic homogeneity and lack of IBD was well supported by single and multi-locus analyses. The proportion of the total genetic variation attributable to differences among regions, locations or sites was effectively zero (Φ/R-statistics ≤0.007). The geographic distribution of genetic diversity and levels of polymorphism (H _E 0.21–0.95) indicate high mutation rates, large effective population sizes, and high rates of gene flow. Significant gene flow may be driven by factors influencing pre-settlement dispersal, including the East Australian Current (EAC) and habitat continuity. Genetic connectivity may not reflect demographically important connectivity, but does imply that P. microlepis populations are well connected from an evolutionary perspective. Total observed genetic diversity was accounted for within 1–2 km of reef and could be represented within small Marine Protected Areas. Reef fishes in NSW which have life histories similar to P. microlepis (e.g. pre-settlement durations ≥2 weeks) are also likely to exhibit genetic homogeneity. Genetic markers are, therefore, most likely to provide information on demographically relevant connectivity for species with lower dispersal capabilities, small population sizes, short life spans, and whose habitats are rare, or patchily distributed along-shore. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Local and regional genetic connectivity in a Caribbean coral reef fish

Coupled bio-physical models of larval dispersal predict that the Costa Rica–Panama (CR–PAN) reefs should constitute a demographically isolated region in the western Caribbean. We tested the hypothesis that CR–PAN coral reef fish populations would be isolated from Mesoamerican Barrier Reef System (MBRS) populations. To test that, we assessed population genetic structure in bicolor damselfish (Stegastes partitus) from both regions. Adult fish were genotyped from five reefs in CR–PAN and from four reefs along the MBRS at 12 microsatellite loci. Between-region F _ST (F _ST = 0.0030, P < 0.005) and exact test (x ² = 74.34, df = 18, P < 0.0001) results indicated that there is weak but significant genetic differentiation between regions, suggesting some restriction in connectivity along the Central American coastline, as predicted by bio-oceanographic models. Additionally, there is among-site genetic structure in the CR–PAN region, relative to the MBRS and between regions, suggesting higher self-recruitment within CR–PAN. This finding may be explained by differences in habitat characteristics.     

Evidence of limited gene flow in three species of coral reef fishes in the lagoon of New Caledonia

Allozyme variation was used to investigate the genetic structure of the coral reef fishes Stegastes nigricans, Epinephelus merra and Acanthurus triostegus around New Caledonia. Each species was sampled from each of three sites in the ≃1000 km circumference of the lagoon of New Caledonia. Allelic variation was recorded for each species at 14, 13 and 17 loci, respectively, and heterozygosity diversity (H s) was 0.082, 0.065 and 0.116, respectively. Analysis of genetic differentiation between sites produced inconsistent results between species, with spatial heterogeneity in two species (S. nigricans, F st  = 0.038; A. triostegus, F st = 0.049) and homogeneity in one species (E. merra, F st = 0.000). Hydrological and climatic data from the lagoon suggest that the eastern and western sides of the lagoon are isolated, since they lie in water masses of different origin. This may explain the genetic differentiation and restricted gene flow found at a local scale for S. nigricans and A. triostegus. Homogeneity in populations of E. merra is discussed in relation to its low genetic diversity and its reproductive behaviour. Received: 23 April 1997 / Accepted: 25 September 1997     

Low levels of global genetic differentiation and population expansion in the deep-sea teleost <Emphasis Type="Italic">Hoplostethus atlanticus</Emphasis> revealed by mitochondrial DNA sequences

The orange roughy Hoplostethus atlanticus is a well-known commercial species with a global distribution. There is no consensus about levels of connectivity among populations despite a range of techniques having been applied. We used cytochrome c oxidase subunit I (COI) and cytochrome b sequences to study genetic connectivity at a global scale. Pairwise Φ_ST analyses revealed a lack of significant differentiation among samples from New Zealand, Australia, Namibia, and Chile. However, low but significant differentiation (Φ_ST = 0.02–0.13, P < 0.05) was found between two Northeast Atlantic sites and all the other sites with COI. AMOVA and the haplotype genealogy confirmed these results. The prevalent lack of genetic differentiation is probably due to active adult dispersal under the stepping-stone model. Demographic analyses suggested the occurrence of two expansion events during the Pleistocene period.     

Among-habitat variation in herbivory on Sargassum spp. on a mid-shelf reef in the northern Great Barrier Reef

Herbivory is widely acknowledged as a key process determining the benthic community structure and resilience of coral reefs. Despite numerous studies that have examined herbivory across reef gradients in the Caribbean, few studies have directly quantified this process on Pacific reefs. Bioassays of two species of erect macroalgae (Sargassum swartzii and S. cristaefolium) were used to quantify variation in grazing intensity across seven habitats of varying depth and wave exposure on a mid-shelf reef in the northern Great Barrier Reef. Removal rates of Sargassum varied significantly among habitats, with both species displaying broadly similar patterns. The shallow habitats on the exposed aspect of the reef (i.e. reef crest, flat and back reef) experienced the highest reductions in mass (81.4–91.6% day⁻¹) for both S. swartzii and S. cristaefolium, while the deeper exposed habitats (reef slope and base) displayed the lowest reductions (3.8–13.4% day⁻¹) over a 24 h period. In contrast, the grazing intensity varied between the two species in the three habitats on the leeward aspect of the reef. Reductions in mass remained relatively high for S. swartzii on the patch reef and sheltered reef base and flat (62.7–76.5% day⁻¹) but were considerably lower for S. cristaefolium (37.9–63.5% day⁻¹) across the same habitats. Surprisingly, the rates of removal of Sargassum displayed no relationship with the density or biomass of roving herbivorous fishes or those species known to consume erect macroalgae, either collectively or independently. These results suggest that the relationship between browsing rates and herbivorous fish biomass is complex and may be driven by species that are underestimated in visual surveys. Direct quantification of browsing intensity using assays revealed a different pattern to inferences based on herbivore densities and highlights the potential difficulties of evaluating ecosystem processes based on visual census data alone.     

Coral mortality following extreme low tides and high solar radiation

Extreme tidal events are one of the most predictable natural disturbances in marine benthic habitats and are important determinants of zonation patterns in intertidal benthic communities. On coral reefs, spring low tides are recurrent disturbances, but are rarely reported to cause mass mortality. However, in years when extremely low tides coincide with high noon irradiances, they have the potential to cause widespread damage. Here, we report on such an event on a fringing coral reef in the central Great Barrier Reef (Australia) in September 2005. Visual surveys of colony mortality and bleaching status of more than 13,000 corals at 14 reef sites indicated that most coral taxa at wave-protected sites were severely affected by the event. Between 40 and 75% of colonies in the major coral taxa (Acropora, Porites, Faviidae, Mussidae and Pocilloporidae) were either bleached or suffered partial mortality. In contrast, corals at wave-exposed sites were largely unaffected (<1% of the corals were bleached), as periodic washing by waves prevented desiccation. Surveys along a 1–9 m depth gradient indicated that high coral mortality was confined to the tidal zone. However, 20–30% of faviid colonies were bleached throughout the depth range, suggesting that the increase in benthic irradiances during extreme low tides caused light stress in deeper water. Analyses of an 8-year dataset of tidal records for the area indicated that the combination of extended periods of aerial exposure and high irradiances occurs during May–September in most years, but that the event in September 2005 was the most severe. We argue that extreme low-tide, high-irradiance events are important structuring forces of intertidal coral reef communities, and can be as damaging as thermal stress events. Importantly, they occur at a time of year when risks from thermal stress, cyclones and monsoon-associated river run-off are minimal.     

Mortality is associated with social rank in the clown anemonefish (<Emphasis Type="Italic">Amphiprion percula</Emphasis>)

Elucidating the causes of post-recruitment mortality is a vital step toward understanding the population dynamics of coral reef fishes. Predation is often considered to be the primary proximate cause of mortality. It has, however, proven difficult to discern the relative contributions of predation and other processes, such as competition for food, shelter, or mates, to patterns of mortality. To determine which other processes might be important drivers of mortality patterns, factors related to mortality in the clown anemonefish Amphiprion percula (Lacepède, 1802) were examined. Patterns of mortality will not be driven by predation in A. percula, because these fish are well protected from predators by their close association with sea anemones. Mortality rates were based on the disappearance of known individuals from a population of 201, in 57 groups, during a 1-year field study (in 1997), in Madang Lagoon, Papua New Guinea. Mortality rate of A. percula was low (14% per annum) compared to other coral reef fish, probably due to the protection from predators afforded by the anemone. Six factors (reef, depth, anemone diameter, number of individuals, density, and standard length) showed no association with the probability of mortality (P>0.05). Rank was the only factor associated with the probability of mortality (P<0.03); low-rank individuals (ranks 4–6) suffered a higher mortality rate than high-rank individuals (ranks 1–3) (P<0.01). The most likely explanation for this pattern was that competition for rank, amongst individuals within an anemone, resulted in some individuals evicting their subordinates. Individuals probably competed for rank because it conferred access to reproduction, and not because it conferred access to food or shelter. Such competition for reproduction will be intense whenever some individuals obtain a greater share of reproduction than others do, and it may be an important process influencing the dynamics of coral reef fish populations.Electronic Supplementary Material Supplementary material is available for this article if you access the article at . A link in the frame on the left on that page takes you directly to the supplementary material.Communicated by J.P. Grassle, New Brunswick     

Mitochondrial control region sequence analyses indicate dispersal from the US East Coast as the source of the invasive Indo-Pacific lionfish Pterois volitans in the Bahamas

Lionfish are popular aquarium fish from the Indo-Pacific that have invaded the western Atlantic. Two species, Pterois volitans and P. miles, were well established along the United States east coast before the first lionfish were reported from the Bahamas in 2004, where they quickly dispersed throughout the archipelago by 2007. The source of the Bahamian lionfish invasion has been in question because of the hypothesized low connectivity between Florida and Bahamas reef species as well as the temporal lag in their arrival in the Bahamas. Mitochondrial control region haplotypes (680 bp) were determined and analyzed for lionfish specimens from the Bahamas, North Carolina, and two sites within their native range (Indonesia and the Philippines). Exact tests, pairwise F _st and AMOVA analyses all showed no significant differentiation between the Bahamas and North Carolina specimens. The similarity between the Bahamas and North Carolina lionfish was also reflected in a minimum spanning network and neighbor-joining distance tree generated from the data. Sequence analyses also revealed the presence of only Pterois volitans, as no P. miles were detected in the Bahamian sample. These results indicate that the source of the Bahamian lionfish is egg and larval dispersal from the United States east coast population, and support previous models of reef fish dispersal that suggest a low level of connectivity between the Bahamas and east coast of Florida.     

Genetic diversity and relatedness of the mangrove Rhizophora mangle L. (Rhizophoraceae) using amplified fragment polymorphism (AFLP) among locations in Florida, USA and the Caribbean

Rhizophora mangle L. is a widespread mangrove species in the Western Hemisphere. Mangrove habitat loss and their importance to coastal and reef ecosystems make greater understanding of their genetic structure useful for conservation and management. An amplified fragment polymorphism (AFLP) analysis was performed on samples from Florida and the Caribbean to discover the genetic structure present. R. mangle had variable genetic diversity not related to latitude; P ranged 7 %–92 %. Some other factor, perhaps human impact, has caused low genetic diversity in some populations. Across Florida R. mangle populations varied in genetic diversity with less diversity (G_st?=?0.195) and greater gene flow on the Atlantic coast (Nm =2.07) than on the Gulf coast (G_st?=?0.717, Nm?=?0.197). Gene flow between Caribbean islands was low (Nm?=?0.386) compared to continental populations (Nm?=?1.40), indicating that long distance dispersal is not common between islands. Analysis of molecular variance (AMOVA) analysis showed significant deviations from Hardy-Weinberg expectations at the level of region among subpopulations and overall genetic difference among subpopulations for R. mangle. One implication for management is that small continental populations and island populations may be genetically isolated and distinct from each other.     

Phylogeography of two Atlantic squirrelfishes (Family Holocentridae): exploring links between pelagic larval duration and population connectivity

Genetic surveys of reef fishes have revealed high population connectivity within ocean basins, consistent with the assumption that pelagic larvae disperse long distances by oceanic currents. However, several recent studies have demonstrated that larval retention and self-recruitment may be higher than previously expected. To assess connectivity in tropical reef fishes, we contribute range-wide mtDNA surveys of two Atlantic squirrelfishes (family Holocentridae). The blackbar soldierfish, Myripristis jacobus, has a pelagic juvenile phase of about 58 days, compared to about 71 days (~22% longer) in the longjaw squirrelfish, Holocentrus ascensionis. If the pelagic duration is guiding dispersal ability, M. jacobus should have greater population genetic structure than H. ascensionis. In comparisons of mtDNA cytochrome b sequences from 69 M. jacobus (744 bp) and 101 H. ascensionis (769 bp), both species exhibited a large number of closely related haplotypes (h=0.781 and 0.974, π=0.003 and 0.006, respectively), indicating late Pleistocene coalescence of mtDNA lineages. Contrary to the prediction based on pelagic duration, M. jacobus has much less population structure (φ_ST=0.008, P=0.228) than H. ascensionis (φ_ST=0.091, P<0.001). Significant population partitions in H. ascensionis were observed between eastern, central and western Atlantic, and between Brazil and the Caribbean in the western Atlantic. These results, in combination with the findings from 13 codistributed species, indicate that pelagic larval duration is a poor predictor of population genetic structure in Atlantic reef fishes. A key to understanding this disparity may be the evolutionary depth among corresponding taxonomic groups of “reef fishes”, which extends back to the mid-Cretaceous and encompasses enormous diversity in ecology and life history. We should not expect a simple relationship between pelagic larval duration and genetic connectivity, among lineages that diverged 50–100 million years ago.     

Genetic differentiation among populations of a broadcast spawning soft coral, Sinularia flexibilis, on the Great Barrier Reef

The genetic structure of 12 reef populations of the soft coral Sinularia flexibilis (Octocorallia, Alcyoniidae) was studied along the Great Barrier Reef (GBR) at a maximum separation of 1,300 km to investigate the relative importance of sexual and asexual reproduction, genetic differentiation and gene flow among these populations. S. flexibilis is a widely distributed Indo-Pacific species and a gamete broadcaster that can form large aggregations of colonies on near-shore reefs of the GBR. Up to 60 individuals per reef were collected at a minimum sampling scale of 5 m at two sites per reef, from December 1998 to February 2000. Electrophoretic analyses of nine polymorphic allozymes indicated that genotypic frequencies in most populations and loci did not differ significantly from those expected from Hardy–Weinberg predictions. Analysis of multi-locus genotypes indicated a high number of unique genotypes (N _go) relative to the number of individuals sampled (N) in each reef population (range of 0.69–0.95). The maximum number of individuals likely to have been produced sexually (N*) was similar to the number of individuals sampled (i.e. N*:N ˜ 1), suggesting that even repeated genotypes may have been produced sexually. These results demonstrated a dominant role of sexual reproduction in these populations at the scale sampled. Significant genetic differentiation between some populations indicated that gene flow is restricted between some reefs (F _ST=0.026, 95% CI= 0.011 − 0.045) and even between sites within reefs (F _ST=0.041, 95% CI=0.027 − 0.055). Nevertheless, there was no relationship between geographic separation and genetic differentiation. Analyses comparing groups of populations showed no significant differentiation on a north-south gradient in the GBR. The pattern in the number of significant differences in gene frequencies in pairwise population comparisons, however, suggested that gene flow may be more restricted among inner-shelf reef populations near to the coast than among mid/outer-shelf populations further from the coast. Received: 10 July 2000 / Accepted: 5 October 2000     

Small-scale genetic structure in the sea palm Postelsia palmaeformis Ruprecht (Phaeophyceae)

Documenting the scale of movement among populations is an important challenge for marine ecology. Using nine microsatellite markers, evidence of genetic structure in a marine kelp, the sea palm Postelsia palmaeformis Ruprecht, was examined in the vicinity of Cape Flattery, Washington state, USA (48° 24′ N, 124°44′ W). Genetic clustering analysis implemented without reference to geographic structure strongly suggested that a number of distinct genetic clusters existed among the 245 plants sampled in August in the years 1997–2001. Subsequent analysis showed that clustering was associated with geographically defined populations both among (km scale) and within (m scale) sampling sites. F _st analysis of geographically defined populations revealed significant genetic differentiation among populations of plants as little as 5 m apart, evidence of genetic structuring at even smaller scales, and a sharp increase in F _st across populations separated by up to 23 m. F _st values were also high and approximately unchanging (F _st=0.470) for populations separated by greater distances (up to 11 km), consistent with a scenario of rare dispersal by detached, floating plants carried by variable currents. The results corroborate natural history observations suggesting that P. palmaeformis has extremely short (1–3 m) spore dispersal distances, and indicate that the dynamics of sea palm populations are more affected by local processes than recruitment from distant populations.     

Effects of Human Population Density and Proximity to Markets on Coral Reef Fishes Vulnerable to Extinction by Fishing

Coral reef fisheries are crucial to the livelihoods of tens of millions of people; yet, widespread habitat degradation and unsustainable fishing are causing severe depletion of stocks of reef fish. Understanding how social and economic factors, such as human population density, access to external markets, and modernization interact with fishing and habitat degradation to affect fish stocks is vital to sustainable management of coral reef fisheries. We used fish survey data, national social and economic data, and path analyses to assess whether these factors explain variation in biomass of coral reef fishes among 25 sites in Solomon Islands. We categorized fishes into 3 groups on the basis of life‐history characteristics associated with vulnerability to extinction by fishing (high, medium, and low vulnerability). The biomass of fish with low vulnerability was positively related to habitat condition. The biomass of fishes with high vulnerability was negatively related to fishing conducted with efficient gear. Use of efficient gear, in turn, was strongly and positively related to both population density and market proximity. This result suggests local population pressure and external markets have additive negative effects on vulnerable reef fish. Biomass of the fish of medium vulnerability was not explained by fishing intensity or habitat condition, which suggests these species may be relatively resilient to both habitat degradation and fishing. Efectos de la Densidad de Poblaciones Humanas y la Proximidad del Mercado sobre Peces de Arrecifes de Coral Vulnerables a la Extinción     

Inter-oceanic genetic differentiation among albacore (<Emphasis Type="Italic">Thunnus alalunga</Emphasis>) populations

Albacore (Thunnus alalunga) is a highly migratory pelagic species distributed in all tropical and temperate oceans. Recent analyses using both mitochondrial DNA (mtDNA) and nuclear DNA markers have demonstrated genetic subdivision within and between Atlantic and Pacific populations. However, although numerous biological differences have been reported for Atlantic and Mediterranean albacore, the genetic differentiation for these basins has not been demonstrated. We characterized 373 base pairs of nucleotide sequence from the mitochondrial DNA control region of 134 individuals collected in the Pacific (n=30), the northeast (NE) Atlantic (n=54) and the Mediterranean (n=50). Analysis of molecular variance (AMOVA) revealed a small, but highly significant, proportion of genetic variation separating these three regions (_st =0.041; P=0.009), a pattern also supported by pairwise comparisons. These results demonstrate for the first time the genetic distinctiveness of the Mediterranean albacore from the NE Atlantic population giving support to the current management practices based on separate units. This outcome is concordant with reported migratory movements related to reproductive behavior between the NE Atlantic and the Mediterranean Sea. Additionally, the phylogenetic analyses of DNA sequences revealed the presence of a shallow genetic discontinuity with no geographic association. These two phylogroups are more likely the result of the demographic history of this species (i.e. long demographic stable history) as opposed to historical vicariance as has been proposed for other highly migratory fishes.Communicated by P.W. Sammarco, Chauvin     

Phylogeography of the Indo-Pacific parrotfish Scarus psittacus: isolation generates distinctive peripheral populations in two oceans

Phylogenetic, phylogeographic, population genetic and coalescence analyses were combined to examine the recent evolutionary history of the widespread Indo-Pacific parrotfish, Scarus psittacus, over a geographic range spanning three marine biogeographic realms. We sequenced 164 individuals from 12 locations spanning 17,000 km, from 55oE to 143oW, using 322 base pairs of mitochondrial control region (D-loop). S. psittacus displayed high haplotype (h = 0.83–0.98), but low nucleotide (<1%) diversity. Most (>83%) genetic variation was within populations. AMOVA revealed significant partitioning and identified five geographic groups. These included one central population and four populations peripheral to the centre. The central population occupied reefs from Western Australia to Tahiti and represented the central Indo-Pacific biogeographic realm. Cocos Keeling was distinct from central and western Indo-Pacific biogeographic realms occupying a position intermediate to these. Peripheral populations (Hawaii, Marquesas) represented the eastern Indo-Pacific biogeographic realm, while Seychelles represented the western Indo-Pacific biogeographic realm. All but the central population expanded (<163 kya). Whilst all populations experienced major sea level and SST changes associated with Pleistocene glaciation cycles, the genetic structure of the central population was relatively homogenous unlike the remaining genetically distinctive populations.     

Nutrient transfer in a marine mutualism: patterns of ammonia excretion by anemonefish and uptake by giant sea anemones

Many symbioses involve multiple partners in complex, multi-level associations, yet little is known concerning patterns of nutrient transfer in multi-level marine mutualisms. We used the anemonefish symbiosis as a model system to create a balance sheet for nitrogen production and transfer within a three-way symbiotic system. We quantified diel patterns in excretion of ammonia by anemonefish and subsequent absorption by host sea anemones and zooxanthellae under laboratory conditions. Rates of ammonia excretion by the anemonefish Amphiprion bicinctus varied from a high of 1.84 μmole g⁻¹ h⁻¹ at 2 h after feeding, to a basal rate of 0.50 μmole g⁻¹ h⁻¹ at 24–36 h since the last meal. Conversely, host sea anemones Entacmaea quadricolor absorbed ammonia at a rate of 0.10 μmole g⁻¹ h⁻¹ during the daytime in ammonia-enriched seawater, but during the night reduced their absorption rate to near zero, indicating that ammonia uptake was driven by zooxanthella photosynthesis. When incubated together, net ammonia excretion was virturally zero, indicating that host anemones absorbed most of the ammonia produced by resident fish. Adult anemonefish weighed about 11 g under laboratory conditions, but on the coral reef may reach up to 64 g, resulting in a maximal potential ammonia load of >200 μmole h⁻¹ produced by two adult fish during daylight hours. In contrast, host sea anemones weighed about 47 g in the laboratory, but under field conditions, large individuals may reach 680 g, so their maximal ammonia clearance rates may reach about 70 μmole h⁻¹ during the daytime. As such, the ammonia load produced by adult anemonefish far exceeds the clearance rate of host anemones and zooxanthellae. Ammonia transfer likely occurs mainly during the daytime, when anemonefish consume zooplankton and excrete rapidly, and in turn the zooxanthellae are photosynthetically active and drive rapid ammonia uptake. We conclude that zooplanktivorous fishes that form mutualisms with coral reef cnidarians may serve as an important link between open water and benthic ecosystems, through the transfer of large quantities of nutrients to zooxanthellate hosts, thus enhancing coral reef productivity.     

Extremes, plasticity, and invariance in vertebrate life history traits: insights from coral reef fishes

Life history theory predicts a range of directional generic responses in life history traits with increasing organism size. Among these are the relationships between size and longevity, mortality, growth rate, timing of maturity, and lifetime reproductive output. Spanning three orders of magnitude in size, coral reef fishes provide an ecologically diverse and species-rich vertebrate assemblage in which to test these generic responses. Here we examined these relationships by quantifying the life cycles of three miniature species of coral reef fish from the genus Eviota (Gobiidae) and compared their life history characteristics with other reef fish species. We found that all three species of Eviota have life spans of < 100 days, suffer high daily mortality rates of 7-8%, exhibit rapid linear growth, and matured at an earlier than expected size. Although lifetime reproductive output was low, consistent with their small body sizes, short generation times of 47-74 days help overcome low individual fecundity and appear to be a critical feature in maintaining Eviota populations. Comparisons with other coral reef fish species showed that Eviota species live on the evolutionary margins of life history possibilities for vertebrate animals. This addition of demographic information on these smallest size classes of coral reef fishes greatly extends our knowledge to encompass the full size spectrum and highlights the potential for coral reef fishes to contribute to vertebrate life history studies.