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Predictions concerning the consequences of the oceanic uptake of increasing atmospheric carbon dioxide (CO2) have been primarily occupied with the effects of ocean acidification on calcifying organisms, particularly those critical to the formation of habitats (e.g. coral reefs) or their maintenance (e.g. grazing echinoderms). This focus overlooks direct and indirect effects of CO2 on non-calcareous taxa that play critical roles in ecosystem shifts (e.g. competitors). We present the model that future atmospheric [CO2] may act as a resource for mat-forming algae, a diverse and widespread group known to reduce the resilience of kelp forests and coral reefs. We test this hypothesis by combining laboratory and field CO2 experiments and data from 'natural' volcanic CO2 vents. We show that mats have enhanced productivity in experiments and more expansive covers in situ under projected near-future CO2 conditions both in temperate and tropical conditions. The benefits of CO2 are likely to vary among species of producers, potentially leading to shifts in species dominance in a high CO2 world. We explore how ocean acidification combines with other environmental changes across a number of scales, and raise awareness of CO2 as a resource whose change in availability could have wide-ranging community consequences beyond its direct effects.

Data on reef substrate composition and fish guild structure was extracted from filmed underwater surveys conducted in 1974 and 2000 at a coral reef in the Florida Keys. During the course of this 26-year interval the reef underwent a dramatic (>75 %) loss of stony coral cover, particularly acroporids, accompanied by significant increases in turf algae, crustose-coralline algae, octocorals, and macroalgae. At the same time, marked changes occurred in the structure of a guild of large herbivorous reef fishes. Total abundance declined, and the relative abundance of constituent species and functional groups changed as well. In contrast, we recorded no change in any measure of structural stability in either of two carnivorous fish guilds (lutjanids, haemulids) that feed by night in off-reef habitats. These results are generally consistent with the hypothesis that coral loss differentially impacts functionally dissimilar groups of fishes, according to dependency on reef substrates for food and/or shelter. The persistence of sizeable herbivore populations along with the relatively low (<16 %) macroalgal cover seen in 2000 suggests that coral loss at our study site was most likely due to bleaching and disease, rather than a response to macroalgal overgrowth. This study represents the first (and only) known study that simultaneously quantifies both a 'phase-shift' in reef substrate as well as concurrent changes in the structure of a reef fish assemblage at a single coral reef in the tropical western Atlantic region. [ABSTRACT FROM AUTHOR]

Predictions concerning the consequences of the oceanic uptake of increasing atmospheric carbon dioxide (CO2) have been primarily occupied with the effects of ocean acidification on calcifying organisms, particularly those critical to the formation of habitats (e.g. coral reefs) or their maintenance (e.g. grazing echinoderms). This focus overlooks direct and indirect effects of CO2 on non-calcareous taxa that play critical roles in ecosystem shifts (e.g. competitors). We present the model that future atmospheric [CO2] may act as a resource for mat-forming algae, a diverse and widespread group known to reduce the resilience of kelp forests and coral reefs. We test this hypothesis by combining laboratory and field CO2 experiments and data from 'natural' volcanic CO2 vents. We show that mats have enhanced productivity in experiments and more expansive covers in situ under projected near-future CO2 conditions both in temperate and tropical conditions. The benefits of CO2 are likely to vary among species of producers, potentially leading to shifts in species dominance in a high CO2 world. We explore how ocean acidification combines with other environmental changes across a number of scales, and raise awareness of CO2 as a resource whose change in availability could have wide-ranging community consequences beyond its direct effects. [ABSTRACT FROM AUTHOR]

The article focuses on a study about latitudinal variation in the consumption of the brown macroalgae Sargassum by fishes found in the Great Barrier Reef (GBR) in Australia. The study aims to explore herbivory on fleshy macroalgae as well as determine the rates of removal across regional scales. Results of the study are also presented including the high Sargassum tissue loss rates in the northern and central regions of GBR and the low rates in the southern region. Several factors behind the variation in the feeding propensity of herbivorous fishes across the regions are cited which include temperature, decrease in preference for the transplanted algae and topographic complexity.

Herbivory is a key process structuring plant communities in both terrestrial and aquatic ecosystems, with variation in herbivory often being related to shifts between alternate states. On coral reefs, regional reductions in herbivores have underpinned shifts from coral to dominance by leathery macroalgae. These shifts appear difficult to reverse as these macroalgae are unpalatable to the majority of herbivores, and the macroalgae suppress the recruitment and growth of corals. The removal of macroalgae is, therefore, viewed as a key ecological process on coral reefs. On the Great Barrier Reef, Sargassum is a dominant macroalgal species following experimentally induced coral–macroalgal phase-shifts. We, therefore, used Sargassum assays and remote video cameras to directly quantify the species responsible for removing macroalgae across a range of coral reef habitats on Lizard Island, northern Great Barrier Reef. Despite supporting over 50 herbivorous fish species and six macroalgal browsing species, the video footage revealed that a single species, Naso unicornis, was almost solely responsible for the removal of Sargassum biomass across all habitats. Of the 42,246 bites taken from the Sargassum across all habitats, N. unicornis accounted for 89.8% (37,982) of the total bites, and 94.6% of the total mass standardized bites. This limited redundancy, both within and across local scales, underscores the need to assess the functional roles of individual species. Management and conservation strategies may need to look beyond the preservation of species diversity and focus on the maintenance of ecological processes and the protection of key species in critical functional groups. [ABSTRACT FROM AUTHOR]

Herbivores are widely acknowledged as key elements maintaining the health and resilience of terrestrial and aquatic ecosystems. Understanding and quantifying the impact of herbivores in ecosystems are fundamental to our ability to manage these systems. The traditional method of quantifying the impact of herbivorous fishes on coral reefs has been to use transplanted pieces of seagrass or algae as ''bioassays''. However, these experiments leave a key question unanswered, namely: Which species are responsible for the impact being quantified? This study revisits the use of bioassays and tested the assumption that the visual abundance of species reflects their role in the removal of assay material. Using remote video cameras to film removal of assay material on an inner-shelf reef of the Great Barrier Reef, the species responsible for assay-based herbivory were identified. The video footage revealed that Siganus canaliculatus, a species not previously recorded at the study site, was primarily responsible for removal of macroalgal biomass. The average percentage decrease in thallus length of whole plants of Sargassum at the reef crest was 54 ± 8.9% (mean ± SE), and 50.4 ± 9.8% for individually presented Sargassum strands (for a 4.5-h deployment). Of the 14,656 bites taken from Sargassum plants and strands across all reef zones, nearly half (6,784 bites or 46%) were taken by S. canaliculatus, with the majority of the remainder attributable to Siganus doliatus. However, multiple regression analysis demonstrated that only the bites of S. canaliculatus were removing macroalgal biomass. The results indicate that, even with detailed observations, the species of herbivore that may be responsible for maintaining benthic community structure can go unnoticed. Some of our fundamental ideas of the relative importance of individual species in ecosystem processes may be in need of re-evaluation. [ABSTRACT FROM AUTHOR]

Many Caribbean reefs have experienced a phase-shift in community structure, the principle features being a decline in coral cover and an increase in macroalgal biomass. However, one Jamaican reef—Dairy Bull on the north shore near Discovery Bay—is once again dominated by scleractinian corals and several key species have returned. Living coral cover at 6-8 m depth at Dairy Bull has doubled over the past 9 years and is now ∼54%. The absolute cover of Acropora cervicornis was <1% in 1995, but increased to ∼11% by January 2004. During this time the cover of macroalgae decreased by 90%, from 45 to 6%. We speculate that long-lived colonies of Montastraea annularis may have facilitated the recovery of this reef by providing structural refugia. [ABSTRACT FROM AUTHOR]