Disturbance and the structure of coral reef fish communities on the reef slope

Three levels of physical disturbance were applied to corals in permanent 10x10 m quadrats along a section of fringing reef at Lizard Island on the Great Barrier Reef to investigate the response of fish assemblages. Tabular and corymbose corals were overturned and left in situ, reducing total hard coral cover from ˜55% to ˜47%, ˜43%, and ˜34%. Despite pre-existing associations with benthic cover, all fish groups examined (pomacentrids, labrids, chaetodontids, and acanthurids) were resistent to benthic disturbances at the level and scale at which they were applied. Partial Mantel's tests, in combination with partial Canonical Correspondence Analysis enabled spatial and temporal variation to be factored out from experimental effects. Most of the variation in the fish community could be assigned to spatio-temporal variables, indicating that spatial structure over the reef landscape may moderate localised disturbance effects. This study indicates that coral reef fish assemblages may be more resistant to disturbance than many correlative studies would suggest, and highlights a need for further information on levels and scales of natural habitat disturbance in order to apply a structured approach to the experimental investigation of the importance of habitat in structuring coral-reef fish assemblages.     

Effects of alternate reef states on coral reef fish habitat associations

The present study describes ontogenetic shifts in habitat use for 15 species of coral reef fish at Rangiroa Atoll, French Polynesia. The distribution of fish in different habitats at three ontogenetic stages (new settler, juvenile, and adult) was investigated in coral-dominated and algal-dominated sites at two reefs (fringing reef and inner reef of motu). Three main ontogenetic patterns in habitat use were identified: (1) species that did not change habitats between new settler and juvenile life stages (60% of species) or between juvenile and adult stages (55% of species—no ontogenetic shift); (2) species that changed habitats at different ontogenetic stages (for the transition “new settler to juvenile stage”: 15% of species; for the transition “juvenile to adult stage”: 20% of species); and (3) species that increased the number of habitats they used over ontogeny (for the transition “new settler to juvenile stage”: 25% of species; for the transition “juvenile to adult stage”: 25% of species). Moreover, the majority of studied species (53%) showed a spatial variability in their ontogenetic pattern of habitat use according to alternate reef states (coral reef vs algal reef), suggesting that reef state can influence the dynamics of habitat associations in coral reef fish.     

Impacts of the live reef fish trade on populations of coral reef fish off northern Borneo

The live reef fish trade (LRFT) is one of the greatest but least-quantified sources of fishing pressure for several species of large coral reef fish across the Indo-Pacific. For the first time we quantify the localized impact of the LRFT. We collected data from three LRFT traders in northern Borneo, which yielded information on daily fishing effort and the species and mass of all fishes sold every day by individual fishers or vessels over 2, 3 and 8 years. Total monthly catch and relative abundance (catch-per-unit-effort) declined significantly in several species, including the most valuable species the Napoleon wrasse (Cheilinus undulatus, estimated changes of -98 and -78% over 8 years in catch and relative abundance, respectively) and lower-value bluelined groupers (Plectropomus oligocanthus: -99 and -81%) and Epinephelus groupers (-89 and -32%). These severe declines were rapid, species-specific and occurred in the first 2-4 years of the dataset and are, we believe, directly attributable to the LRFT. This has crucial implications for future data collection and monitoring if population collapses in other parts of the LRFT and similar wildlife trades are to be successfully detected.     

Bathymetry on a Carboniferous reef

Broadhurst, F. M. & Simpson, I. M.: Bathymetry on a Carboniferous reef.
In the Lower Carboniferous deposits of Castleton, Derbyshire, well bedded shelf limestones, apparently of shallow water origin, pass northwards into a marginal tract of poorly bedded apron-reef limestones which dip at about 30° downwards and away from the 'shelf'. Geopetal infillings of shell cavities in the apron-reef indicate only minor movement since deposition, and the observed dip must be due to deposition on a sloping sea floor. At certain times this sea floor was colonised by stromatolitic algae and corals such as Lithostrotion at the apron-reef crest where there was minimum water depth, followed to progressively increasing depths by (1) a fauna dominated by the coral Michelinia , (2) a fauna of small brachiopods, bryozoa, molluscs, trilobites, and other organisms and (3) a fauna dominated by Pseudamussium . At other times crinoidal debris was the dominant component of the apron-reef, when an alignment of crinoid stems parallel to the dip of the slope occurred at low levels, but a random orientation at the apronreef crest. Other sediments on the apron-reef are apparently devoid of macrofossils. Volcanic activity occurred during the development of the apron-reef, and it is suggested that uplift of the shelf area preceded the subaerial flow of a lava tongue which reached and plunged down the apron-reef slope and into the sea.     

Hindcast hurricane characteristics on the Belize barrier reef

Hurricane Greta was the most intense of the 1978 Atlantic hurricanes, with a minimum central pressure of 947 hPa (mb) just prior to passage across the Belize barrier reef in the western Caribbean. At Carrie Bow Cay, along the Belize barrier reef, 12 km south of the point where the storm crossed the barrier, coral reef damage was moderate and island damage rather extensive. Felled palm trees indicated that the most destructive storm force came from the SW, from across the barrier reef lagoon. Hindcasting of hurricane winds at Carrie Bow indicated that the palms probably fell in response to the most intense storm winds from the SW. Hindcast, significant waves at Carrie Bow reached a maximum height of 10.0 m with a period of 12.7 s. The largest waves that reached Carrie Bow from across the lagoon were hindcast to have a significant wave height of 2.8 m, significant period of 7.0 s and were responsible for construction of a storm berm at Carrie Bow, facing the lagoon.     

Nitrification on a coral reef.

We report that the algal pavement just behind the reef crest at Enewetak Atoll produces nitrate at measurable rates. In situ and in vitro incubations with N-Serve indicate that the autotrophic pathway involving two separate organisms is effective in this oxidation of ammonia to nitrate. Significant nitrification is indicated throughout the reef environment; Nitrobacter agilis has specifically been identified as at least one of the organisms responsible for the terminal oxidation of nitrite to nitrate.     

Changing dynamics of Caribbean reef carbonate budgets: emergence of reef bioeroders as critical controls on present and future reef growth potential

Coral cover has declined rapidly on Caribbean reefs since the early 1980s, reducing carbonate production and reef growth. Using a cross-regional dataset, we show that widespread reductions in bioerosion rates—a key carbonate cycling process—have accompanied carbonate production declines. Bioerosion by parrotfish, urchins, endolithic sponges and microendoliths collectively averages 2 G (where G = kg CaCO₃ m⁻² yr⁻¹) (range 0.96–3.67 G). This rate is at least 75% lower than that reported from Caribbean reefs prior to their shift towards their present degraded state. Despite chronic overfishing, parrotfish are the dominant bioeroders, but erosion rates are reduced from averages of approximately 4 to 1.6 G. Urchin erosion rates have declined further and are functionally irrelevant to bioerosion on most reefs. These changes demonstrate a fundamental shift in Caribbean reef carbonate budget dynamics. To-date, reduced bioerosion rates have partially offset carbonate production declines, limiting the extent to which more widespread transitions to negative budget states have occurred. However, given the poor prognosis for coral recovery in the Caribbean and reported shifts to coral community states dominated by slower calcifying taxa, a continued transition from production to bioerosion-controlled budget states, which will increasingly threaten reef growth, is predicted.     

Implications of reef ecosystem change for the stability and maintenance of coral reef islands

Coral reef islands are among the most vulnerable environments on Earth to climate change because they are low lying and largely constructed from unconsolidated sediments that can be readily reworked by waves and currents. These sediments derive entirely from surrounding coral reef and reef flat environments and are thus highly sensitive to ecological transitions that may modify reef community composition and productivity. How such modifications – driven by anthropogenic disturbances and on‐going and projected climatic and environmental change – will impact reef island sediment supply and geomorphic stability remains a critical but poorly resolved question. Here, we review the unique ecological–geomorphological linkages that underpin this question and, using different scenarios of environmental change for which reef sediment production responses can be projected, explore the likely resilience of different island types. In general, sand‐dominated islands are likely to be less resilient than those dominated by rubble grade material. However, because different islands typically have different dominant sediment constituents (usually either coral, benthic foraminifera or Halimeda) and because these respond differently to individual ecological disturbances, island resilience is likely to be highly variable. Islands composed of coral sands are likely to undergo major morphological change under most near‐future ecological change scenarios, while those dominated by Halimeda may be more resilient. Islands composed predominantly of benthic foraminifera (a common state through the Pacific region) are likely to exhibit varying degrees of resilience depending upon the precise combination of ecological disturbances faced. The study demonstrates the critical need for further research bridging the ecological–geomorphological divide to understand: (1) sediment production responses to different ecological and environmental change scenarios; and (2) dependant landform vulnerability.     

Augmented coral reef monitoring using a stationary reef monitoring system

Coral reef monitoring is a reliable tool to assess the effect of climate change as corals are sensitive to increases in water temperatures between 30 °C and 35 °C resulting in bleaching - a whitening process when the corals lose their color and the reefs begin to die. Existing satellite-based monitoring products facilitate coral bleaching monitoring over large spatial scales, but their use in predicting local scale stress that influences the bleaching severity across reefs is limited. In this paper, we describe a Stationary Reef Monitoring System (SRMS) that monitors the time evolution of coral reefs through the photography of nearby coral clusters. Simultaneously, the SRMS measures and records environmental parameters such as temperature, solar irradiance (PAR), and salinity in the waters surrounding the coral colonies. When deployed in the sea, the SRMS detected a 0.1–0.4 °C variability in temperature between the in situ and satellite datasets. The SRMS uses color photography along with quantitative data on environmental parameters to monitor the health of corals and eliminates the need for physical/visual verification of coral health by a diver. By this approach, one can determine the stress thresholds of corals and identify the vulnerable and resilient reefs so as to prioritize conservation efforts.     

Notes on the influence of particulate organic matter (POM) on light conditions at a coral reef of the Australian great barrier reef

On the outer slope of a coral reef in the Great Barrier Reef, at a depth of 11-12 in without artificial light, bright red and rose colours were observed to occur on coelenterates, because masses of floating luminescent bacteria in the environment.     

Photoinhibition of photosynthesis on a coral reef

Photoinhibition of macroalgae in the epilithic algal community (KAC) of coral reefs was studied using chlorophyll fluorescence techniques at One Tree Island, Great Barrier Reef, Australia. F_v/F_m (variable to maximum fluorescence, darkened samples) of shallow macroalgae declined by 50% on fine summer and winter days, recovering in late afternoon. Within a species, thalli from low-light habitats were more photoinhibited (2h at 1400μimol m^?2 s^?1) than those from high-light habitats. The sensitivity of Lobophora variegata (Phacophyta) and Chlorodesmis fastigiata (Chlorophyta) increased with depth (1 versus 20 m). However, shallow Halimeda tuna (Chlorophyta) plants growing between corals were more photoinhibited than those from deep, open areas. Photoinhibition and recovery were depth- and species-specific. Shallow Lobophora and Chlorodesmis maintained a greater degree of Q _A oxidation during photoinhibition. In deep thalli, reduced effective quantum yield of open photosystem II centres reflected lower proportions and excitation capture efficiencies of open centres. In Lobophora, zeaxanthin formation accompanied non-photochemical fluorescence quenching (NPQ), but in Chlorodesmis NPQ was limited and no zeaxanthin or antherxanthin formed. Higher photosynthetic efficiency in the lower storey of the EAC may compensate for photoinhibition in the upper storey, thereby reconciling photoinhibition of individual thalli with previous observations of no net inhibition of community productivity.     

Human impacts on the species-area relationship in reef fish assemblages

The relationship between species richness and area is one of the oldest, most recognized patterns in ecology. Here we provide empirical evidence for strong impacts of fisheries exploitation on the slope of the species–area relationship (SAR). Using comparative field surveys of fish on protected and exploited reefs in three oceans and the Mediterranean Sea, we show that exploitation consistently depresses the slope of the SAR for both power-law and exponential models. The magnitude of change appears to be proportional to fishing intensity. Results are independent of taxonomic resolution and robust across coral and rocky reefs, sampling protocols and statistical methods. Changes in species richness, relative abundance and patch occupancy all appear to contribute to this pattern. We conclude that exploitation pressure impacts the fundamental scaling of biodiversity as well as the species richness and spatial distribution patterns of reef fish. We propose that species–area curves can be sensitive indicators of community-level changes in biodiversity, and may be useful in quantifying the human imprint on reef biodiversity, and potentially elsewhere.     

Coral gardens: paternity and drug testing on the reef

An international team has used molecular genetics and chemical tagging to trace how baby clownfish travel from their mother's nest through the ocean to the anemone they will live on. More than one out of five juveniles came from nests that were only meters away, despite spending over a week drifting in ocean currents. Such surprising fidelity to a small area of the coral reef bodes well for efforts to preserve coral reef diversity with reserves.