Vicariance across major marine biogeographic barriers: temporal concordance and the relative intensity of hard versus soft barriers

The marine tropics contain five major biogeographic regions (East Pacific, Atlantic, Indian Ocean, Indo-Australian Archipelago (IAA) and Central Pacific). These regions are separated by both hard and soft barriers. Reconstructing ancestral vicariance, we evaluate the extent of temporal concordance in vicariance events across three major barriers (Terminal Tethyan Event (TTE), Isthmus of Panama (IOP), East Pacific Barrier, EPB) and two incomplete barriers (either side of the IAA) for the Labridae, Pomacentridae and Chaetodontidae. We found a marked lack of temporal congruence within and among the three fish families in vicariance events associated with the EPB, TTE and IOP. Vicariance across hard barriers separating the Atlantic and Indo-Pacific (TTE, IOP) is temporally diffuse, with many vicariance events preceding barrier formation. In marked contrast, soft barriers either side of the IAA hotspot support tightly concordant vicariance events (2.5 Myr on Indian Ocean side; 6 Myr on Central Pacific side). Temporal concordance in vicariance points to large-scale temporally restricted gene flow during the Late Miocene and Pliocene. Despite different and often complex histories, both hard and soft barriers have comparably strong effects on the evolution of coral reef taxa.     

A rare hybridization event in two common Caribbean wrasses (genus <Emphasis Type="Italic">Halichoeres</Emphasis>; family Labridae)

Molecular tools were used to evaluate the hybrid status of a specimen with intermediate colour pattern between Halichoeres bivittatus and Halichoeres garnoti from Belize. Phylogenetic analyses of the two species, eight Halichoeres species from new and old world lineages and two outgroups showed that the study species are closely related and that H. garnoti is the maternal contributor to the putative hybrid specimen, based on partial mitochondrial COI data. Direct sequencing of Intron 1 of the nuclear ribosomal protein S7 identified H. bivittatus as sister to H. garnoti with the putative hybrid specimen in an intermediate position, due to heterozygosity at nucleotides alternatively fixed in the two putative parent species. This is consistent with the hybrid status of the specimen, with parental contributions from both H. garnoti and H. bivittatus. These results, combined with no evidence of introgression between the two parent species (based on the mtDNA and the single investigated nuclear marker) and the biogeography and ecology of these species suggests that this is a rare event with minimal evolutionary implications.     

Human exploitation shapes productivity–biomass relationships on coral reefs

Coral reef fisheries support the livelihoods of millions of people in tropical countries, despite large‐scale depletion of fish biomass. While human adaptability can help to explain the resistance of fisheries to biomass depletion, compensatory ecological mechanisms may also be involved. If this is the case, high productivity should coexist with low biomass under relatively high exploitation. Here we integrate large spatial scale empirical data analysis and a theory‐driven modelling approach to unveil the effects of human exploitation on reef fish productivity–biomass relationships. We show that differences in how productivity and biomass respond to overexploitation can decouple their relationship. As size‐selective exploitation depletes fish biomass, it triggers increased production per unit biomass, averting immediate productivity collapse in both the modelling and the empirical systems. This ‘buffering productivity’ exposes the danger of assuming resource production–biomass equivalence, but may help to explain why some biomass‐depleted fish assemblages still provide ecosystem goods under continued global fishing exploitation.     

Historical and contemporary determinants of global phylogenetic structure in tropical reef fish faunas

Identifying the main determinants of tropical marine biodiversity is essential for devising appropriate conservation measures mitigating the ongoing degradation of coral reef habitats. Based on a gridded distribution database and phylogenetic information, we compared the phylogenetic structure of assemblages for three tropical reef fish families (Labridae: wrasses, Pomacentridae: damselfishes and Chaetodontidae: butterflyfishes) using the net relatedness (NRI) and nearest taxon (NTI) indices. We then related these indices to contemporary and historical environmental conditions of coral reefs using spatial regression analyses. Higher levels of phylogenetic clustering were found for fish assemblages in the Indo‐Australian Archipelago (IAA), and more particularly when considering the NTI index. The phylogenetic structure of the Pomacentridae, and to a lower extent of the Chaeotodontidae and Labridae, was primarily associated with the location of refugia during the Quaternary period. Phylogenetic clustering in the IAA may partly result from vicariance events associated with coral reef fragmentation during the glacial periods of the Quaternary. Variation in the patterns among fish families further suggest that dispersal abilities may have interacted with past habitat availability in shaping the phylogenetic structure of tropical reef fish assemblages.     

Pelagic Subsidies Underpin Fish Productivity on a Degraded Coral Reef

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Evolution and biogeography of marine angelfishes (Pisces: Pomacanthidae)

Phylogenetic relationships among angelfishes (Pomacanthidae) and their putative sister taxon, the butterflyfishes (Chaetodontidae), were examined using 12S and 16S mitochondrial DNA sequences. ML and MP trees were highly congruent with good basal resolution. Monophyly of the two families was supported, although a clade comprising the Chaetodontidae and one of the outgroups, the Scatophagidae, formed the sister clade to the Pomacanthidae. All genera and subgenera within the Pomacanthidae were examined. The relationships among the 24 representative species were consistent with traditional generic boundaries, with the exception of the genus Centropyge, but differed from previous phylogenies. Estimated ages of divergence based on trans-isthmian pairs were compared with independent fossil evidence. Trans-isthmian estimates were highly conservative, while fossil-calibrated estimates were most consistent with available evidence. Fossil calibrated estimates suggest that the family has been impacted by both the Terminal Tethyan Event and the closure of the Isthmus of Panama. Within the family, ecological diversity and species-level diversification are restricted primarily to a single pygmy angelfish clade with an origin near the Oligocene-Miocene boundary.     

Evolution and mechanics of long jaws in butterflyfishes (family Chaetodontidae)

We analyzed the functional morphology and evolution of the long jaws found in several butterflyfishes. We used a conservative reanalysis of an existing morphological dataset to generate a phylogeny that guided our selection of seven short- and long-jawed taxa in which to investigate the functional anatomy of the head and jaws: Chaetodon xanthurus, Prognathodes falcifer (formerly Chaetodon falcifer), Chelmon rostratus, Heniochus acuminatus, Johnrandallia nigrirostris, Forcipiger flavissimus, and F. longirostris. We used manipulations of fresh, preserved, and cleared and stained specimens to develop mechanical diagrams of how the jaws might be protruded or depressed. Species differed based on the number of joints within the suspensorium. We used high-speed video analysis of five of the seven species (C. xanthurus, Chel. rostratus, H. acuminatus, F. flavissimus, and F. longirostris) to test our predictions based on the mechanical diagrams: two suspensorial joints should facilitate purely anteriorly directed protrusion of the lower jaw, one joint should allow less anterior protrusion and result in more depression of the lower jaw, and no joints in the suspensorium should constrain the lower jaw to simple ventral rotation around the jaw joint, as seen in generalized perciform fishes. We found that the longest-jawed species, F. longirostris, was able to protrude its jaws in a predominantly anterior direction and further than any other species. This was achieved with little input from cranial elevation, the principal input for other known lower jaw protruders, and is hypothesized to be facilitated by separate modifications to the sternohyoideus mechanism and to the adductor arcus palatini muscle. In F. longirostris the adductor arcus palatini muscle has fibers oriented anteroposteriorly rather than medial-laterally, as seen in most other perciforms and in the other butterflyfish studied. These fibers are oriented such that they could rotate the ventral portion of the quadrate anteriorly, thus projecting the lower jaw anteriorly. The intermediate species lack modification of the adductor arcus palatini and do not protrude their jaws as far (in the case of F. flavissimus) or in a purely anterior fashion (in the case of Chel. rostratus). The short-jawed species both exhibit only ventral rotation of the lower jaw, despite the fact that H. acuminatus is closely related to Forcipiger.     

Life history patterns shape energy allocation among fishes on coral reefs

Although critically important, the link between animal life histories and ecosystem energetics is seldom explored. In the pursuit of ecological simplification, ecosystem properties are typically described by models based on static counts, where organisms are aggregated into trophic- or size-based groups. Consequently, output is often based on an assumption that larger group biomass equals greater energetic contribution. Here, we modelled the individual growth of over 58,000 fishes from 74 genera within a coral reef ecosystem to investigate the role and importance of taxon-specific life histories to the division, spatial distribution and relative contribution of biomass production within 14 coral reef fish families. Rank changes among families in standing biomass to biomass production indicated that small cryptic families (e.g. Gobiidae and Blenniidae) exhibit collective growth potentials equal to or exceeding those of many other common families composed of individuals with body-sizes 1–3 orders of magnitude larger. Remaining at high risk of predation throughout their lives as a consequence of their small size, these cryptic fishes also provide a constant food resource and supply of reproductive energy to coral reefs throughout the year. Enhanced further by the strength and diversity of their trophic relationships within food webs, the highly productive nature of these small cryptic fishes suggests they make a substantial contribution to the flow of energy in coral reef ecosystems via predatory pathways. It appears that life histories leave a strong imprint on ecosystem energy fluxes and illustrate the importance of incorporating taxon-specific features when assigning values to key ecosystem processes. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

High herbivory despite high sediment loads on a fringing coral reef

Coral Reefs - Algal turfs are expected to increasingly dominate the benthos of coral reefs in the Anthropocene, becoming important sources of reef productivity. The sediments trapped within algal...     

Suppression of herbivory by macroalgal density: a critical feedback on coral reefs?

Coral reefs globally are in decline, with some reefs undergoing phase shifts from coral-dominance to degraded states dominated by large fleshy macroalgae. These shifts have been underpinned by the overharvesting of herbivorous fishes and represent a fundamental change in the physical structure of these reefs. Although the physical structure provided by corals is regarded as a key feature that facilitates herbivore activity, the influence of the physical structure of macroalgal stands is largely unknown. Using transplanted Sargassum, the largest coral reef macroalga, we created habitat patches of predetermined macroalgal density (0.25-6.23 kg m(-2)). Remote video cameras revealed both grazing and browsing fishes avoided high density patches, preferring relatively open areas with low macroalgal cover. This behaviour may provide a positive feedback leading to the growth and persistence of macroalgal stands; increasing the stability of phase shifts to macroalgae.