Project description:Investigations of gut microbial diversity among fish to provide baseline data for wild marine fish, especially the carnivorous coral reef fishes of the South China Sea, are lacking. The present study investigated the gut microbiota of four carnivorous coral reef fishes, including Oxycheilinus unifasciatus, Cephalopholis urodeta, Lutjanus kasmira, and Gnathodentex aurolineatus, from the South China Sea for the first time using high-throughput Illumina sequencing. Proteobacteria, Firmicutes, and Bacteroidetes constituted 98% of the gut microbiota of the four fishes, and 20 of the gut microbial genera recovered in this study represent new reports from marine fishes. Comparative analysis indicated that the four fishes shared a similar microbial community, suggesting that diet type (carnivorous) might play a more important role in shaping the gut microbiota of coral reef fishes than the species of fish. Furthermore, the genera Psychrobacter, Escherichia-Shigella, and Vibrio constituted the core microbial community of the four fishes, accounting for 61-91% of the total sequences in each fish. The lack of the genus Epulopiscium in the four fishes was in sharp contrast to what has been found in coral reef fishes from the Red Sea, in which Epulopiscium was shown to be the most dominant gut microbial genus in seven herbivorous coral reef fishes. In addition, while unique gut microbial genera accounted for a small proportion (8-13%) of the total sequences, many such genera were distributed in each coral reef fish species, including several genera (Endozoicomonas, Clostridium, and Staphylococcus) that are frequently found in marine fishes and 11 new reports of gut microbes in marine fishes. The present study expands our knowledge of the diversity and specificity of gut microbes associated with coral reef fishes.
Project description:On coral reefs, fishes can facilitate coral growth via nutrient excretion; however, as coral abundance declines, these nutrients may help facilitate increases in macroalgae. By combining surveys of reef communities with bioenergetics modeling, we showed that fish excretion supplied 25 times more nitrogen to forereefs in the Florida Keys, USA, than all other biotic and abiotic sources combined. One apparent result was a positive relationship between fish excretion and macroalgal cover on these reefs. Herbivore biomass also showed a negative relationship with macroalgal cover, suggesting strong interactions of top-down and bottom-up forcing. Nutrient supply by fishes also showed a negative correlation with juvenile coral density, likely mediated by competition between macroalgae and corals, suggesting that fish excretion may hinder coral recovery following large-scale coral loss. Thus, the impact of nutrient supply by fishes may be context-dependent and reinforce either coral-dominant or coral-depauperate reef communities depending on initial community states.
Project description:Analysis of maximum depth of occurrence of 11 952 marine fish species shows a global decrease in species number (N) with depth (x; m): log10 N = -0·000422x + 3·610000 (r(2) = 0·948). The rate of decrease is close to global estimates for change in pelagic and benthic biomass with depth (-0·000430), indicating that species richness of fishes may be limited by food energy availability in the deep sea. The slopes for the Classes Myxini (-0·000488) and Actinopterygii (-0·000413) follow this trend but Chondrichthyes decrease more rapidly (-0·000731) implying deficiency in ability to colonize the deep sea. Maximum depths attained are 2743, 4156 and 8370 m for Myxini, Chondrichthyes and Actinopterygii, respectively. Endemic species occur in abundance at 7-7800 m depth in hadal trenches but appear to be absent from the deepest parts of the oceans, >9000 m deep. There have been six global oceanic anoxic events (OAE) since the origin of the major fish taxa in the Devonian c. 400 million years ago (mya). Colonization of the deep sea has taken place largely since the most recent OAE in the Cretaceous 94 mya when the Atlantic Ocean opened up. Patterns of global oceanic circulation oxygenating the deep ocean basins became established coinciding with a period of teleost diversification and appearance of the Acanthopterygii. Within the Actinopterygii, there is a trend for greater invasion of the deep sea by the lower taxa in accordance with the Andriashev paradigm. Here, 31 deep-sea families of Actinopterygii were identified with mean maximum depth >1000 m and with >10 species. Those with most of their constituent species living shallower than 1000 m are proposed as invasive, with extinctions in the deep being continuously balanced by export of species from shallow seas. Specialized families with most species deeper than 1000 m are termed deep-sea endemics in this study; these appear to persist in the deep by virtue of global distribution enabling recovery from regional extinctions. Deep-sea invasive families such as Ophidiidae and Liparidae make the greatest contribution to fish fauna at depths >6000 m.
Project description:BackgroundTwo processes may contribute to the formation of global centers of biodiversity: elevated local speciation rates (the center of origin hypothesis), and greater accumulation of species formed elsewhere (the center of accumulation hypothesis). The relative importance of these processes has long intrigued marine biogeographers but rarely has been tested.ResultsTo examine how origin and accumulation affected the Greater Caribbean center of diversity, we conducted a range-wide survey of mtDNA cytochrome b in the widespread Atlantic reef damselfish Chromis multilineata (N = 183) that included 10 locations in all four tropical Atlantic biogeographic provinces: the Greater Caribbean, Brazil, the mid-Atlantic ridge, and the tropical eastern Atlantic. We analyzed this data and re-evaluated published genetic data from other reef fish taxa (wrasses and parrotfishes) to resolve the origin and dispersal of mtDNA lineages. Parsimony networks, mismatch distributions and phylogenetic analyses identify the Caribbean population of C. multilineata as the oldest, consistent with the center of origin model for the circum-Atlantic radiation of this species. However, some Caribbean haplotypes in this species were derived from Brazilian lineages, indicating that mtDNA diversity has not only originated but also accumulated in the Greater Caribbean. Data from the wrasses and parrotfishes indicate an origin in the Greater Caribbean in one case, Caribbean origin plus accumulation in another, and accumulation in the remaining two.ConclusionOur analyses indicate that the Greater Caribbean marine biodiversity hotspot did not arise through the action of a single mode of evolutionary change. Reef fish distributions at the boundaries between Caribbean and Brazilian provinces (the SE Caribbean and NE Brazil, respectively) indicate that the microevolutionary patterns we detected in C. multilineata and other reef fishes translate into macroevolutionary processes and that origin and accumulation have acted in concert to form the Greater Caribbean biodiversity hotspot.
Project description:Pelagic predators are effective biological samplers of midtrophic taxa and are especially useful in deep-sea habitats where relatively mobile taxa frequently avoid observation with conventional methods. We examined specimens sampled from the stomachs of longnose lancetfish, Alepisaurus ferox, to describe the diets and foraging behaviors of three common, but poorly known deep-sea fishes: the hammerjaw (Omosudis lowii, n = 79, 0.3-92 g), juvenile common fangtooth (Anoplogaster cornuta, n = 91, 0.6-22 g), and juvenile Al. ferox (n = 138, 0.3-744 g). Diet overlap among the three species was high, with five shared prey families accounting for 63 ± 11% of the total prey mass per species. However, distinct differences in foraging strategies and prey sizes were evident. Resource partitioning was greatest between An. cornuta that specialized on small (mean = 0.13 ± 0.11 g), shallow-living hyperiid amphipods and O. lowii that specialized on large (mean = 0.97 ± 0.45 g), deep-dwelling hatchetfishes. Juvenile Al. ferox foraged on a high diversity of prey from both shallow and deep habitats. We describe the foraging ecologies of three midtrophic fish competitors and demonstrate the potential for biological samplers to improve our understanding of deep-sea food webs.
Project description:Deep seas have extremely harsh conditions including high hydrostatic pressure, total darkness, cold, and little food and oxygen. The adaptations of fishes to deep-sea environment apparently have occurred independently many times. The genetic basis of adaptation for obtaining their energy remains unknown. Mitochondria play a central role in aerobic respiration. Analyses of the available 2,161 complete mitochondrial genomes of 1,042 fishes, including 115 deep-sea species, detect signals of positive selection in mitochondrial genes in nine branches of deep-sea fishes. Aerobic metabolism yields much more energy per unit of source material than anaerobic metabolism. The adaptive evolution of the mtDNA may reflect that aerobic metabolism plays a more important role than anaerobic metabolism in deep-sea fishes, whose energy sources (food) are extremely limited. This strategy maximizes the usage of energy sources. Eleven mitochondrial genes have convergent/parallel amino acid changes between branches of deep-sea fishes. Thus, these amino acid sites may be functionally important in the acquisition of energy, and reflect convergent evolution during their independent invasion of the harsh deep-sea ecological niche.
Project description:Deep western boundary current (DWBC) was observed for the first time by an array of 6 current meter moorings southeast of the Zhongsha Islands in the South China Sea (SCS) deep basin during the period from August 2012 to January 2014. In the mean, the DWBC in the SCS flows southwestward with core velocity of 2.0 cm/s and a volume transport of 1.65 Sv (1 Sv = 1 × 106 m3/s). Its temporal variability is dominated by intraseasonal fluctuations with period around 90 days. The main axis of the DWBC, characterized by a low temperature core, tends not to shift with the 90-day fluctuation.