Structure Of Coral Reefs Research Articles

Primacy of seascape connectivity effects in structuring coral reef fish assemblages

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 462:191-203 (2012) - DOI: https://doi.org/10.3354/meps09849 Primacy of seascape connectivity effects in structuring coral reef fish assemblages Andrew D. Olds*, Rod M. Connolly, Kylie A. Pitt, Paul S. Maxwell Australian Rivers Institute − Coast and Estuaries, School of Environment, Griffith University, Gold Coast, Queensland 4222, Australia *Email: a.olds@griffith.edu.au ABSTRACT: Connectivity has fundamental consequences for the productivity, persistence and management of coral reefs. The area and position of adjacent mangroves and seagrass can affect the demography of reef fish populations and the composition of reefal assemblages. To date, no studies have attempted to partition the influences of these habitats on reef fish assemblages. We used an exploratory seascape approach to separate the effects of connectivity with mangroves and seagrass on reef fish in Moreton Bay, Australia. We then compared the performance of seascape connectivity and reef complexity (i.e. coral cover, rugosity and area) in structuring these assemblages. Our results suggest a hierarchy of seascape connectivity effects, with reef fish assemblages being primarily distinguished by isolation (i.e. separation distance) from mangroves and secondarily by proximity (an index incorporating habitat isolation and area) to seagrass. Importantly, measures of reef complexity were only useful in separating reef fish assemblages within levels of connectivity with mangroves and seagrass. We demonstrate that neighbouring mangroves and seagrasses can exert different effects on reef fish assemblages, with 25% of all species being primarily influenced by mangroves and a different 25% being affected by seagrass. These findings have important implications for the design of marine reserve networks. They show that position in the seascape can be of greater significance than reef area or complexity to the composition of reef fish assemblages and highlight the value of incorporating seascape connectivity into conservation planning. KEY WORDS: Landscape · Mangrove · Seagrass · Fish · Nursery · Australia Full text in pdf format PreviousNextCite this article as: Olds AD, Connolly RM, Pitt KA, Maxwell PS (2012) Primacy of seascape connectivity effects in structuring coral reef fish assemblages. Mar Ecol Prog Ser 462:191-203. https://doi.org/10.3354/meps09849 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 462. Online publication date: August 21, 2012 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2012 Inter-Research.

How well do sunken vessels approximate fish assemblages on coral reefs? Conservation implications of vessel-reef deployments

The amount of artificial habitat (termed ‘artificial reef’, AR) in marine systems is rapidly increasing, yet the effect of most types of AR on reef communities remains unknown. We examined the role of well-established vessel-reefs in structuring coral reef fish assemblages by comparing assemblages on 7 World War II wrecks (>65 years old) to those on interspersed coral patch reefs of comparable size in a tropical lagoon. Fish abundance, species richness, diversity and feeding guild structure on wrecks were similar to natural reefs; however, species composition differed between the two reef types (R = 0.189–0.341, average dissimilarity: 67.3–68.8 %). Despite being more species-rich and diverse, fish assemblages on larger wrecks were less similar to assemblages on their adjacent natural reefs than smaller wrecks. Wrecks may also have affected fish abundance on adjacent natural reefs, with reefs adjacent to larger wrecks supporting higher abundances than reefs adjacent to smaller wrecks. Our results indicate that increases in vessel-reef habitat may not greatly affect reef fish assemblage parameters, but may affect the relative abundances of particular species.

The composition and structure of a protected coral reef in Cam Ranh Bay in the South China Sea

A nonstructural reef at Hon Nai Island in Cam Ranh Bay (southern Vietnam) was investigated. In comparison with most of the coastal continental and island coral reefs of this region, it is characterized by high species richness of reef-building corals, among them scleractinians. A total of 34 species of Acropora were found, which represent 80% of the total species composition of this scleractinian genus on the reefs of Vietnam and 25% on the reefs of the Indo-Pacific. Among 169 species of scleractinians found on the reef of Hon Nai, Favia sp. nov. was previously unknown to science. The vertical bionomic zonality of the reef corresponds to a zonal distribution of environmental factors and is similar to that on reefs of the Gulf of Siam and various areas of the Pacific and the Caribbean Basin. The thriving of the Hon Nai island reef may be connected with protective measures undertaken by the Government of Vietnam and the minimization of anthropogenic impacts due to the activities of the Sanest Co.

BIOPHYSICS, BIOENERGETICS AND MECHANISTIC APPROACHES TO ECOLOGY

Biophysics – the study of how the structure of individual plants and animals contributes to their function – has rarely been considered on the ecological scale. However, Mark Denny from Stanford University, USA, has a broader vision. Because the mechanisms that underpin individual performance

Classification of remote Pacific coral reefs by physical oceanographic environment

[1] The oceanographic environment is a key element in structuring coral reef ecosystems by setting the range of physical and chemical conditions in which coral reef-builders live. A cluster analysis of physical and chemical oceanographic data is used to classify coral habitats in the remote tropical and subtropical Pacific Ocean based on average temperature, temperature seasonal cycle, nutrient levels, salinity, aragonite saturation state, storm frequency, intense hurricane hits, and dissolved oxygen as well as temperature anomalies in degree heating weeks. The resulting seven geographic habitats are stable to perturbations in types of data used in the cluster analysis. Based on recent coral reef survey data in the area, the coral cover was related to the identified geographic regions. The habitats tend to be geographically clustered, and each is characterized by a unique combination of oceanographic conditions. Previous studies suggest coral reef habitats are associated with a uniform array of oceanographic conditions, while our results demonstrate that finer-scale variations in physical variables may control coral reef environments. The results better define the physical environment of remote coral reefs, forming a foundation for future work addressing physical habitat perturbation and anthropogenic impacts on reefs.

Physical habitat and social conditions across a coral reef shape spatial patterns of intraspecific behavioral variation in a demersal fish

AbstractAs coral reef ecosystems decline in health worldwide, reef‐associated fishes are being impacted by changes to their coral reef habitats. While previous studies have shown coral reef structure to affect the demography of reef fishes, changes in reef conditions may also impact the behavior of reef fishes as they cope with altered habitats. In this study, we examined spatial patterns of intraspecific behavioral variation in the bicolor damselfish (Stegastes partitus) across the fringing reefs of Curaçao (Caribbean Sea), and explored how this behavioral variation associated with physical and social conditions on the reef. Principal components analysis (PCA) condensed physical parameters of the reef into principal component 1 (PC1), comprising depth, coral cover (%), rugosity, and average hole size (cm2), and principal component 2 (PC2), which represented the number of holes. PC1, but not PC2, increased spatially across the reef as the habitat transitioned from coral rubble in the shallows to live coral on the reef slope. This transition in reef structure was paralleled by changes in social conditions including decreases in bicolor damselfish density in habitats with higher PC1 values. The behavior of bicolor damselfish also varied spatially with greater aggression and more frequent shelter use in habitats with lower PC1 values. Path analysis revealed robust associations between this behavioral variation and physical habitat conditions of the reef, indicating that physical – rather than social – habitat variation is the primary determinant of these spatial patterns of intraspecific behavioral variation. Taken as a whole, this coupling between physical reef structure and behavior suggests that reef fish may show altered behaviors on coral reefs degraded by anthropogenic impacts.

Land’s End

Land’s End

The role of sponge competition on coral reef alternative steady states

Sponges constitute an abundant and functionally important component of coral reef systems. Given their demonstrated resistance to environmental stress, it might be expected that the role of sponges in reef systems under modern regimes of frequent and severe disturbance may become even more substantial. Disturbances have recently reshaped the community structure of many Caribbean coral reefs shifting them towards a state of persistent low coral cover and often a dominance of macroalgae. Using competition and growth rates recorded from Glover's Atoll in Belize, we parameterise a mathematical model used to simulate the three-way competition between sponges, macroalgae and coral. We use the model to determine the range of parameters in which each of the three species might be expected to dominate. Emergent properties arise from our simple model of this complex system, and these include a special case in which heightened competitive ability of macroalgae versus coral may counter-intuitively prove to be advantageous to the persistence of corals. Importantly, we show that even under scenarios whereby sponges fail to invade the system, inclusion of this third antagonist can qualitatively affect the likelihood of alternative stable states – generally in favour of macroalgal dominance. The interplay between multi-species competition and predation is complex, but our efforts highlight a key process that has, until now, remained unexplored: the extent to which sponges dissipate algal grazing pressure by providing generalist fish with an alternative food source. We highlight the necessity of identifying the extent by which this process takes place in tropical systems in order to improve projections of alternative stable states for Caribbean coral reefs.

History of Ecological Sciences, Part 38B: Naturalists Explore North America, 1838–1850s

History of Ecological Sciences, Part 38B: Naturalists Explore North America, 1838–1850s

Government conservation policies on Mexican coastal areas: is ?top-down? management working?

Marine and terrestrial ecosystems are declining globally due to environmental degradation and poorly planned resource use. Traditionally, local government agencies have been responsible of the management of natural reserves to preserve biodiversity. Nonetheless, much of these approaches have failed, suggesting the development of more integrative strategies. In order to discuss the importance of a holistic approach in conservation initiatives, coastal and underwater landscape value and biological/environmental indicators of coral reef degradation were assessed using the study case of Zihuatanejo, Guerrero coastal area. This area shelters representative coral reef structures of the Eastern Pacific coast and its terrestrial biodiversity and archaeology enhance the high value of its coastal area. This study explored the landscape value of both terrestrial and marine ecosystems using the geomorphosite approach in two sites on the Zihuatanejo coastal area: Caleta de Chon and Manzanillo Beach. Sedimentation rate, water transparency, chlorophyll and total suspended solids were recorded underwater in each site for environmental characterization. 50 photo-quadrants on five transects were surveyed between 3-4m depth to record coverage (%) of living corals, dead corals, algae, sand and rocks. The conservation status of coral reefs was assessed by the coral mortality index (MI). Landscape values showed that both terrestrial and marine ecosystems had important scientific and aesthetic values, being Manzanillo Beach the site with the highest potential for conservation initiatives (TtV = 14.2). However, coral reefs face elevated sedimentation rates (up to 1.16 kg/m2d) and low water transparency (less of 5m) generated by coastal land use changes that have increased soil erosion in the adjacent coastal area. High coverage of dead corals (23.6%) and algae (up to 29%) confirm the low values in conservation status of coral reefs (MI = 0.5), reflecting a poorly-planned management. Current conditions are the result of "top-down" conservation strategies in Zihuatanejo, as Federal and Municipal authorities do not coordinate, disregard local community in coral reef management, and ignore the intimate relationship between the coastal and marine realms. This work confirms the importance of conservation strategies with a holistic approach, considering both terrestrial and marine ecosystems in coastal areas; and that these initiatives should include local coastal communities in management and decision-taking processes done by government authorities.

Unveiling the Role of Dps in the Organization of Mycobacterial Nucleoid

In order to preserve genetic information in stress conditions, bacterial DNA is organized into higher order nucleoid structure. In this paper, with the help of Atomic Force Microscopy, we show the different structural changes in mycobacterial nucleoid at different points of growth in the presence of different concentrations of glucose in the medium. We also observe that in Mycobacterium smegmatis, two different Dps proteins (Dps1 and Dps2) promote two types of nucleoid organizations. At the late stationary phase, under low glucose availability, Dps1 binds to DNA to form a very stable toroid structure. On the other hand, under the same condition, Dps2-DNA complex forms an incompletely condensed toroid and finally forms a further stable coral reef structure in the presence of RNA. This coral reef structure is stable in high concentration of bivalent ion like Mg2+.

Succession patterns in algal turf vegetation on a Caribbean coral reef

Over the past three decades, Caribbean coral reefs have drastically changed in structure and organization due to anthropogenically driven environmental changes. The prognostic trend indicates a shift from coral- to more algal-dominated reefs coupled with a loss in biodiversity and destabilization of reef structure. This study focuses on the composition of the most common algal growth form, the turf, and investigates turf succession within a fringing Caribbean coral reef. In a field study starting October 2007, we followed succession of turf algal assemblages grown on artificial substrata for periods of 15 up to 333 days at different water depths (5, 15 and 25 m). Species composition and abundance,biodiversity, total cover, and biomass were investigated and compared in uni- and multivariate analyses. Despite the pronounced change in coral reef structure over the past years, we found little difference from primary succession patterns described 30 years earlier. Succession patterns revealed a high diversity, mainly driven by the filamentous brown algal order Ectocarpales, the crustose green alga Pringsheimiella scutata at early stage, and diverse filamentous Cyanobacteria at later stages. Overall, the study provides insight into the early successional stages of coral reef vegetation by identifying the key species and discussing possible factors determining reef development in relation to environmental change.

Coral Reef Structure and Zonation of the Phoenix Islands

Atoll Research Bulletin, no. 589 : Phoenix Island Coral Reef Structure and Zonation of the Phoenix Islands.

History of Ecological Sciences, Part 37: Charles Darwin's Voyage on the Beagle

History of Ecological Sciences, Part 37: Charles Darwin's Voyage on the Beagle

Red Snapper Reproductive Biology in the Southern Gulf of Mexico

AbstractSex ratio, size at maturity, reproductive periodicity, ovarian development pattern, and spawning ground data for red snapper Lutjanus campechanus from the southern Gulf of Mexico were analyzed to understand this species' reproductive biology throughout its geographical distribution. Red snapper were sampled in 1999 and 2000 from commercial fishery catches taken on Campeche Bank at depths ranging from 43 to 130 m. Overall sex ratio (male: female) and sex ratios by size‐class did not differ significantly from a 1:1 ratio. First maturity was at a slightly smaller size in males (24.2 cm total length [TL]) than in females (28.3 cm TL), and maximum length percentages at first maturity were 28% for males and 34% for females. The length at which maturity was attained in 50% of females (L50) was 31.4 cm TL. The Campeche Bank red snapper stock had a protracted spawning period from February to November, with a spawning peak occurring in early fall. Vitellogenic oocytes were continually recruited from previtellogenic oocytes during the entire spawning season, with no gap between each oocyte development stage. This means that red snapper ovaries are asynchronous and that the species can be considered a heterochronal (batch) spawner with indeterminate annual fecundity. Females in spawning condition were collected from both the northeastern and northwestern areas of Campeche Bank, near submerged or emergent coral reef structures, and at depths between 48 and 117 m. These results generally agreed with those for red snapper stocks in others regions of the Gulf of Mexico and the Atlantic Ocean off the southeastern United States. However, reproductive periodicity in the Campeche Bank red snapper stock apparently displayed more of an insular pattern of extended spawning in comparison with the typical continental pattern of restricted spawning reported for other regions. The latitudinal differences observed in red snapper spawning seasons could also reflect a latitudinal gradient in the intensity of seasonal environmental constraints.

Cross-shelf variation in browsing intensity on the Great Barrier Reef

Herbivory is widely accepted as a key process determining the structure and resilience of coral reefs, with regional reductions in herbivores often being related to shifts from dominance by coral to leathery macroalgae. The removal of leathery macroalgae may therefore be viewed as a critical process on coral reefs. However, few studies have examined this process beyond a within-reef scale. Here, browsing activity was examined across the entire Great Barrier Reef shelf using bioassays of the leathery macroalga Sargassum to directly quantify algal removal. The assays revealed marked cross-shelf variation in browsing intensity, with the highest rates recorded on mid-shelf reefs (55.2–79.9% day-1) and decreasing significantly on inner- (10.8–17.0% day-1) and outer-shelf (10.1–10.4% day-1) reefs. Surprisingly, the variation in browsing intensity was not directly related to estimates of macroalgal browser biomass; rather, it appears to be shaped primarily by the local environment and behaviour of the component species. Removal rates across the inner- and mid-shelf reefs appear to be related to the attractiveness of the assays relative to the resident algal communities. Controlling for the influence of the resident algal communities revealed a positive relationship between removal rates and the biomass of a single macroalgal browsing species, Naso unicornis. In contrast, the low removal rates on the outer-shelf reefs displayed no relationship to algal or herbivore communities and appeared to reflect a negative behavioural response by the resident fishes to a novel, or unfamiliar, alga. These findings not only highlight the complexities of the relationship between fish presence and ecological function, but also the value of examining ecological processes across broader spatial scales.

New records of subtidal benthic marine algae from Wake Atoll, Central Pacific

Abstract The marine flora of Wake Atoll is phytogeographically interesting because the atoll is a small (6.5 km2) isolated coral reef structure located in the central Pacific between the north-western Hawaiian Islands and the Marshall Islands. Eighty-one of the 103 species of subtidal marine benthic algae collected in October 2005 and April–May 2007 during two NOAA cruises to Wake Atoll represent new records for the atoll. Previously published collections include five species collected in December 1841 during the US Exploring Expedition, 35 additional species representing collections made in June 1998 by US Fish and Wildlife personnel, and incidental specimens collected by various biologists and deposited in the Herbarium Pacificum of the Bishop Museum, Honolulu. The 121 species of marine benthic algae now documented from Wake Atoll contain components from the Hawaiian Islands and Marshall Islands, but show a closer resemblance to those of the Hawaiian Archipelago.

Territorial damselfishes facilitate survival of corals by providing an associational defense against predators

Territorial defense by the herbivorous damselfishes, Stegastes nigricans and S. lividus, benefits the hermatypic corals growing inside their territories. Coral diversity was significantly higher inside damselfish territories at 2 sites in Moorea, French Polynesia, and at 1 site in Guam, Mariana Islands. In Guam, this pattern was stable for at least 10 yr. Certain coral species, including Pocillopora damicornis, were found only inside damselfish territories at these sites. All fishes, including coral-feeding butterflyfishes, approaching territories of Stegastes spp. were vigorously chased. Colonies of P. damicornis inside territories were not preyed upon by any potential intruders. When transplanted outside of territories, colonies of P. damicornis were preyed upon rapidly by several species of butterflyfishes. Feeding rates of individual butterflyfishes on transplanted P. dami- cornis colonies were initially very high and decreased significantly over 30 min as accessible coral tissue was removed. In contrast, transplanted Porites rus, a major component of the reef outside of territories in Guam, attracted no predators. This study suggests that territorial damselfishes provide an associational defense for certain coral species that live inside their territories, whereas these species settling outside territories experience heavy predation, resulting in suppressed growth and negligible survival. This demonstrates the potential importance of this type of positive indirect interaction between species in structuring coral reef communities, that protection from predation by coral-feeding fishes is a mechanism by which damselfishes can enhance coral diversity on reefs, and that this association can remain stable for many years.

Importance of water-flow on the physiological responses of reef-building corals

The topographic complexity of coral reef structure naturally provides temporal and spatial variations in environmental factors. Among these physical environmental factors, water-flow is an important environmental factor in coral reef habitat that had been overlooked as a stress ameliorator for reef-building corals. This review will summarize the recent studies as well as previous findings concerning the effects of water-flow on corals. The interaction among major stress factors and water-flow will be discussed with special attention to the aspects of coral bleaching phenomenon.

Damselfish territories as a refuge for macroalgae on coral reefs

Herbivory is widely accepted as a key process determining the benthic community structure and resilience of coral reefs. Recent studies have mostly focused on the importance of roving herbivorous fishes in ecosystem processes. Here, we examine the role of territorial damselfish in shaping patterns of macroalgal distribution based on benthic surveys and macroalgal bioassays. The territory composition and effect of resident damselfish on the removal of Sargassum bioassays were quantified for six species of damselfish on Lizard Island, a mid-shelf reef in the northern Great Barrier Reef (GBR). The functional composition of algal communities within territories varied markedly among species. The territories of four species (Dischistodus perspicillatus, Dischistodus pseudochrysopoecilus, Plectroglyphidodon lacrymatus, and Stegastes nigricans) were characterized by algal turfs, while the territories of two species (Dischistodus prosopotaenia and Hemiglyphidodon plagiometopon) were characterized by foliose and leathery brown macroalgae. Sargassum, a generally rare alga on mid-shelf reefs, was a particularly common alga within D. prosopotaenia territories on the leeward side of the island but absent within their territories on the windward side of the island. D. prosopotaenia was the only species to retain the transplanted Sargassum, with only a minimal reduction in Sargassum biomass (1.1%) being recorded within their territories at both leeward and windward sites over a 24-h period. In contrast, reductions in Sargassum biomass were high in areas adjacent to D. prosopotaenia territories (83.8%), and within and adjacent to the territories of the five remaining damselfish species (76.2–92.5%). Overall, only one of the six damselfish species provided a refuge for leathery brown macroalgae and may facilitate the development of this macroalgae on mid-shelf reefs of the GBR