Coral Reef Habitats Research Articles

Resource use and impact of three herbivorous damselfishes on coral reef communities

Territorial damselfish are considered to be functionally important herbivores on coral reefs, promoting the abundance of preferred algae and depleting corals through a variety of ‘farming’ activities. However, the composition of algal and coral communities inside territories and patterns of feeding selectivity are known for only a few species. Here we compare substrata inside and next to territories of Plectroglyphidodon lacrymatus, P. dickii and Stegastes nigricans, 3 common damselfish in Papua New Guinea, and interpret patterns in relation to diets and patterns of feeding selectivity. The coral assemblages inside territories differed among fish species and also between defended and non-defended areas. Live corals dominated P. dickii territories, while those of P. lacrymatus and S. nigricans were primarily associated with algal substrata. Territories of P. lacrymatus were similar in coral composition to adjacent areas, while those of P. dickii and S. nigricans were associated with particular coral taxa. Territories of the 3 damselfish were similar in algal composition, with mixed turf algae (primarily blue-green algae Polysiphonia spp. and other filamentous red algae) more prominent inside territories and crustose coralline algae more prominent outside. Diets for the 3 species were also similar, as each species was primarily herbivorous and diets consisted of diatoms, blue-green algae, Polysiphonia spp. and other filamentous red algae. An experimental removal of P. lacrymatus showed that they promoted epiphyte loads without influencing macro-algal or coral cover. Our results suggest that while these 3 species of damselfish vary in their interactions with coral reef habitat, they selectively cultivate a similar range of epiphytic food algae on different substrata.

Uncommon diversity in developmental mode and larval form in the genus Macrophiothrix (Echinodermata: Ophiuroidea)

Development mode in the ophiuroid genus Macrophiothrix includes an unusual diversity of plank- tonic larval forms and feeding types. The modes of development for seven congeners that coexist in coral reef habitats at Lizard Island, Australia were com- pared using larvae generated from crosses over several reproductive seasons from 1999 to 2003. Three species (Macrophiothrix koehleri Clark, Macrophiothrix longi- peda Lamarck, Macrophiothrix lorioli Clark) develop from small eggs (<170 m) into typical obligately feed- ing planktonic (planktotrophic) pluteus larvae with four larval arm pairs. The remaining four species develop from larger eggs (¸230 m) into either faculta- tively-feeding or non-feeding (lecithotrophic) larval forms. The facultative planktotroph (Macrophiothrix rhabdota Clark) retains the ability to digest and beneWt from food but does not require particulate food to complete metamorphosis. Among the lecithotrophic species, Macrophiothrix caenosa Hoggett retains the pluteus morphology with four pairs of larval arms, but is incapable of feeding, depending instead on maternal provisions for larval development. The remaining two lecithotrophs have simpliWed larval morphologies with only a single pair of full length (Macrophiothrix nerei- dina Lamarck) or highly reduced (Macrophiothrix belli Doderlein) larval arms and no functional mouth or gut. This genus includes the Wrst example of facultative planktotrophy in ophiuroids, the Wrst example in echi- noderms of a complete pluteus morphology retained by a lecithotrophic larva, and three degrees of morpho- logical simpliWcation among lecithotrophic larval forms. Egg volume varies 20-fold among species and is related to variation in feeding mode, larval form, and development time, as predicted for the transition from planktotrophic to lecithotrophic development.

Towards a reefscape ecology: relating biomass and trophic structure of fish assemblages to habitat at Davies Reef, Australia

The complex relationship between coral reef fish assemblages and reef habitats at Davies Reef, a middle-shelf reef in the Great Barrier Reef, Australia, was approached from a reef- scape perspective. A reefscape merges the spatial patterns found in a reef with 3 ecological com- ponents: structure, function and change. The main objective of this study was to explore the rela- tionship between function (biomass and trophic structure of fish assemblages) and structure (reef habitat) within a reef. Three reef fish groups were defined using multi-dimensional scaling, and their similarity was evaluated using SIMPER analysis. From the benthic surveys conducted at the same sites we defined 3 reefscapes: A, 'encrusting non-Acropora', B, 'Acropora' and C, 'low den- sity massive non-Acropora'. Reefscape A was characterised by maximum fish species richness and biomass, while maximum fish diversity was found in Reefscape B. Reefscape C had the minimum values of fish biomass. The relationship between fish groups (using biomass as a proxy) and habi- tat was explored using redundancy analysis, which was also used to identify significant fish spe- cies within each reefscape. The relationship between the trophic structure (guilds) and habitat was explored using the 4th corner analysis, and this analysis revealed that substratum types differed in terms of their utility as proxies for associated fish species and trophic guilds. The present study stresses the importance of within-reef variability as a determinant of composition and relative abundance of local reef fish assemblages. It also suggests that, while loss or change of habitat structure (i.e. coral cover or change in the dominant coral type) could reduce species richness and biomass, some of the habitat features to which fishes cue are probably coarser geomorphological and environmental zones.

Initial and mid-term impacts of cyclone Erica on coral reef fish communities and habitat in the South Lagoon Marine Park of New Caledonia

The cyclone Erica (Class 5) hit the South Lagoon Marine Park of New Caledonia on 14 March 2003, in the midst of a survey conducted on coral reef fish and habitat of Larégnère and Crouy reefs. Such perturbation was exceptional for the area. Nine stations had already been sampled (8–11 March 2003) when the cyclone hit the reefs. These stations were sampled again just after the cyclone (23 March–15 April 2003) and 20 months later (14–16 November 2004). Erica had a significant initial impact on habitat characteristics. The fragile coral forms cover (branching, tubular and foliose) decreased significantly, resulting in a loss of habitat for the fish communities. Species richness and biomass of the commercial reef fish and the Chaetodontidae decreased just after Erica, but not the density. The species assemblage was modified on the stations with the lowest remaining live coral cover. The loss of shelter modified the behaviour of potential prey, which constituted unusual shoals and attracted predators. Twenty months after Erica, the habitat had not recovered and the broken coral colonies were transformed into rubble or colonized by algae. The nature of the mid-term impact on the fish communities was different and more significant than the initial impact. Species richness per station, density and biomass were significantly lower than before and just after Erica. This pattern was confirmed for all the main families, with the exception of Acanthuridae. A different fish assemblage was observed on all stations 20 months after Erica. Herbivorous species and benthic macro-invertebrate feeders associated with rubble replaced the coral associated species that characterized the assemblages before the cyclone. When a Class 5 cyclone affects an area where perturbations of such intensity are uncommon, its impact is immediate and the mid-term consequences are even more significant. A complete modification of the structure of the habitat and the fish assemblages is observed. The consecutive recovery should be a long process.

Defense mechanisms and antipredator behavior in two sympatric species of spiny lobsters, Panulirus argus and P. guttatus

The congeneric spiny lobsters Panulirus argus and P. guttatus co-occur throughout the Caribbean Sea, where they may share the coral reef habitat. Despite their phylogenetic closeness, both species have many different life-history traits that may partially explain their coexistence. However, even though both species may face the same predators, their defense mechanisms and antipredator strategies had not been compared. We compared the performance between species in 18 morphological and behavioral defense mechanisms commonly expressed by most spiny lobsters, including predator-avoidance mechanisms (activity schedule, sheltering behavior, delay to disturbance, and effect of conspecific damage-released scents on shelter choice) as well as antipredator mechanisms (body size, several parameters of the escape response and limb autospasy, clinging strength, antennal strength, and cooperative defense). As hypothesized, both species expressed all these defense mechanisms (except cooperative defense, shown only by P. argus), reflecting their phylogenetic closeness, but performed significantly differently in most, in accordance with their particular ontogenetic traits. Their comparative performance in individual defense mechanisms as well as the antipredator strategies displayed by groups of lobsters of each species in the presence of a common predator (the triggerfish Balistes vetula) showed that, in general, the defensive behavioral type of P. argus is more bold and that of P. guttatus more shy. Therefore, their distinct defensive behaviors contribute to their niche differentiation.

CONSEQUENCES OF PATCH REEF SPACING FOR DENSITY-DEPENDENT MORTALITY OF CORAL-REEF FISHES

The spatial configuration of habitat patches can profoundly affect a number of ecological interactions, including those between predators and prey. I examined the effects of reef spacing on predator-prey interactions within coral-reef fish assemblages in the Bahamas. Using manipulative field experiments, I determined that reef spacing influences whether and how density-dependent predation occurs. Mortality rates of juveniles of two ecologically dissimilar species (beaugregory damselfish and yellowhead wrasse) were similarly affected by reef spacing; for both species, mortality was density dependent on reef patches that were spatially isolated (separated by 50 m), and density independent on reef patches that were aggregated (separated by 5 m). A subsequent experiment with the damselfish demonstrated that a common resident predator (coney) caused a substantial proportion of the observed mortality, independent of reef spacing. Compared to isolated reefs, aggregated reefs were much more likely to be visited by transient predators (mostly yellowtail snappers), regardless of prey density, and on these reefs, mortality rates approached 100% for both prey species. Transient predators exhibited neither an aggregative response nor a type 3 functional response, and consequently were not the source of density dependence observed on the isolated reefs. These patterns suggest that resident predators caused density-dependent mortality in their prey through type 3 functional responses on all reefs, but on aggregated reefs, this density dependence was overwhelmed by high, density-independent mortality caused by transient predators. Thus, the spatial configuration of reef habitat affected both the magnitude of total predation and the existence of density-dependent mortality. The combined effects of the increasing fragmentation of coral reef habitats at numerous scales and global declines in predatory fish may have important consequences for the regulation of resident fish populations.

Characterizing the deep insular shelf coral reef habitat of the Hind Bank marine conservation district (US Virgin Islands) using the Seabed autonomous underwater vehicle

The benthic communities of the deep insular shelf at the Hind Bank marine conservation district (MCD), an important spawning aggregation site for groupers, were studied with the Seabed autonomous underwater vehicle (AUV) at depths between 32 and 54 m. Four digital phototransects provided data on benthic species composition and abundance of the insular shelf off St. Thomas, US Virgin Islands. Within the western side of the MCD, well-developed coral reefs with 43% mean living coral cover were found. The Montastrea annularis complex was dominant at all four sites between 33 and 47 m, the depth range where reefs were present. Maximum coral cover found was 70% at depths of 38–40 m. Quantitative determinations of sessile benthic populations, as well as the presence of motile megabenthic invertebrates and algae were obtained. The Seabed AUV provided new quantitative and descriptive information of a unique coral reef habitat found within this deeper insular shelf area.

Community structure of the family Pomacentridae along the Jordanian coast, Gulf of Aqaba, Red Sea

The spatial distribution and community structure of the family Pomacentridae were studied at different depths and sites along the coast of the Gulf of Aqaba in seagrass and coral reef habitats. Sixteen coastal sites along the Jordanian coast were studied by the visual census technique. A total of 151,134 pomacentrid fishes representing 23 species were observed during 188 visual censuses at 96 belt transects, and 4 additional species were observed outside the transect lines. Six species accounted for 85% of all individuals. Results from cluster analysis of the studied sites based on percentage of benthic cover revealed two main groups: the seagrass and the coral reef dominated sites. Fishes were most abundant at 12 m depths in the coral dominated sites, while fewer numbers were found at reef flat and seagrass sites. This was attributed to the shelter, structural complexity and food availability in the coral reef sites. Pomacentrus trichourus and Amphiprion bicinctus were the most common pomacentrid fishes. Teixeirichthys jordani was restricted to the northern coast of the Gulf of Aqaba. Multivariate analysis of the pomacentrid community revealed certain associations of fishes with different habitats. Within the large group of coral reef associated fishes we could distinguish the following three groups: a group of species that occur at 12 m deep transects such as Chromis weberi and C. pembae; a group of species that occur only in the reef flat such as Plectroglyphidodon leucozonus and P. lacrymatus; a group of the most dominant and most common species such as Neopomacentrus miryae and Pomacentrus trichourus.

Peyssonnelia imbricata sp. nov. (Peyssonneliaceae, Rhodophyta) from Puerto Rico, Caribbean Sea

Peyssonnelia imbricata sp. nov. occurs in shallow protected coral reef, mangrove and deep-reef habitats in southwestern Puerto Rico, Caribbean Sea. The species is characterized by its small imbricate blades which may form extensive colonies, vegetative production of new blades from the dorsal surface of parent blades, polyflabellate arrangement of hypothallial cells and its Peyssonnelia atropurpurea-type anatomy.

Interactions among Florida sponges. I. Reef habitats

Spatial interference competition is well described for many sessile marine invertebrates, but few studies have addressed interactions between neighboring sponges. We conducted transect surveys to assess interspecific interactions among sponges in coral reef habitats in Key Largo, Florida, USA. In total, 15 transect sites were surveyed at 5 reef locations with mean densities ranging from 13.0 ± 3.6 to 33.3 ± 5.9 sponges m -2 . The most abundant of over 43 sponge species observed were Amphimedon compressa, Aplysina cauliformis, Aplysina insularis, and Niphates erecta, while the least abundant were Hippospongia lachne, Ircinia campana, and Pseudaxinella lunaecharta. A nearest-neighbor technique was used to determine the degree and frequency of interactions between randomly selected sponge pairs. Overall, 40.4% of sponges occurred alone, 31.0% in proximity to, and 28.6% in contact with other sponge species. Among sponges in contact interactions, 18.7% were epibionts, 19.4% were basibionts, and a relationship could not be resolved for the remainder. Statistical analyses of the frequencies of each interaction category revealed that the ability to overgrow or resist overgrowth varied among species. For example, Aka coralliphagum, Ectyoplasia ferox, and Phorbas amaranthus occurred alone in >60% of their interactions and were never overgrown by other species with which they came into contact. In contrast, Agelas schmidti, Ircinia felix, Dysidea janiae, and Scopalina ruetzleri occurred alone in <30% of their interactions, with the first 2 species overgrown by, and the latter 2 overgrowing, most other species with which they came in contact. All contact interactions were further statistically examined, and 41 interspecific sponge pairs revealed significant overgrowth ability by 1 of the interacting species. While the over- growth ability of a species is dependent on sponge morphology, the ability to resist overgrowth is associated with the production of allelochemicals.

Connectivity of reef fish between mangroves and coral reefs: Algorithms for the design of marine reserves at seascape scales

Many species of coral reef fish undertake ontogenetic migrations between seagrass beds, mangroves, and coral reefs. A recent study from the Caribbean found that the availability of mangrove nursery habitat had a striking impact on the community structure and biomass of reef fish in their adult, coral reef habitat. The biomass of several species more than doubled when the reefs were connected to rich mangrove resources (defined as having at least 70 km of fringing Rhizophora mangle within a region of 200 km 2). Here, the results of this large-scale empirical study are translated into a series of algorithms for use in natural resource management planning. Four algorithms are described that identify (i) the relative importance of mangrove nursery sites, (ii) the connectivity of individual reefs to mangrove nurseries, (iii) areas of nursery habitat that have an unusually large importance to specific reefs, and (iv) priority sites for mangrove reforestation projects. The algorithms generate a connectivity matrix among mangroves and coral reefs that facilitates the identification of connected corridors of habitats within a dynamic planning environment (e.g., reserve selection algorithms).

Benthic cyanobacterial bloom impacts the reefs of South Florida (Broward County, USA)

Benthic cyanobacteria of the genus Lyngbya can form prominent mats and blooms in tropical and subtropical coral reef and seagrass habitats worldwide. A Lyngbya bloom on the reef tract offshore of Broward County, Florida, was first noted in 2002, and although it is seasonally variable in its distribution and abundance, it has persisted and spread over the past 3 years. In this study, the most abundant species of Lyngbya found in the blooms have been identified and compared to other species of Lyngbya by morphological and molecular methods. The most common species of Lyngbya is consistent with the properties of Lyngbya confervoides C. Agardh. The 16S ribosomal DNA sequence shares 88–92% identity with other known Lyngbya sequences, suggesting that this bloom consists primarily of a new, previously unsequenced species of Lyngbya. The second most common Lyngbya in the bloom is consistent with Lyngbya polychroa. This persistent bloom is a concern because it smothers octocorals and other invertebrates and negatively impacts these southeastern Florida reefs.

Low variation in partial cytochrome oxidase subunit I (COI) mitochondrial sequences in the coralline demosponge Astrosclera willeyana across the Indo-Pacific

Partial sequences of the mitochondrial DNA (mtDNA) gene cytochrome oxidase subunit 1 (COI) were analysed from individuals of the coralline demosponge Astrosclera willeyana sensu lato out of ten Indo-Pacific populations from the Red Sea to the central Pacific. This taxon is widely distributed in cryptic coral reef habitats of the Indo-Pacific and is regarded as a modern representative of long-extinct, formerly reef-building stromatoporoid-type sponges. The aims were to clarify phylogeographic and taxonomic relationships in this “living fossil” and to explore mitochondrial DNA sequence variation over a wide geographic range. Very low variability was observed across the Indo-Pacific, as only three COI haplotypes were identified, with a maximum p-distance of 0.418% and low nucleotide diversity (π=0.00049). Very low genetic structure was revealed among populations: Haplotype 1 was found in all specimens from nine Pacific populations (N=45), separated by distances of more than 7,000 km; haplotype 2 was restricted to the Red Sea population (N=4); haplotype 3 was only found in the Tuamoto specimens (N=7). COI data presented here do not support the hypothesis of at least two sibling species belonging to genus Astrosclera in the Pacific. Considering the maximum geographic distance of more than 20,000 km between sampled populations, mtDNA COI sequence variation observed here is among the lowest reported to date for a diploblastic taxon and adds to the growing evidence of a general mtDNA conservation in sponges. It is argued that this low mtDNA variation in A. willeyana s.l. is due to a low rate of mtDNA evolution caused by a combination of long generation time and low metabolic rate.

Threatened Fishes of the World: Rhincodon typus (Smith 1828) (Rhincodontidae)

Common name: Whale shark (E), requin-ba- leine (Fr), tiburon ballena (Sp), squalo balena (I), butanding (Philippines), ebisuzame (Ja- pan), tofu shark (Taiwan). Conservation sta- tus: IUCN Red List VU A1b,d, A2d. CITES Appendix II since November 2002. United Nations Convention on the Law of the Sea and the United Nations Agreement on straddling fish stocks and highly migratory fish stocks. Hunting prohibited by domestic legislation or decree in Western Australia, Tasmania, Philippines, Thailand, India, Maldives, Honduras, U.S. Atlantic waters and Gulf of Mexico (territorial seas), Florida state waters, Honduras, regional waters of Belize. Identification: The largest fish on planet earth. TL to 10-12 m, rarely to 18 m, and up to 21,000 kg body mass. Dorso-ventrally flattened and very broad head with body quickly tapering from robust shoulder girth to narrow caudal peduncle. Large, transverse and near-terminal mouth. Very large gill slits. Teeth numerous and minute. Gill slits large. Eyes lateral; spiracles behind eyes. First dorsal fin considerably larger than second and inserted ca. 2/3 posterior to snout. Three prominent, dorso-lateral ridges from shoulder to tail and terminating laterally at caudal peduncle. Caudal fin semi-lunate with no prominent sub-terminal notch. Body markings unique, consisting of checkerboard pattern of light spots, horizontal stripes and vertical bars against a dark background. Distribution: Wide range in tropical and temperate waters, with seasonal aggregated abundance in tropical to subtropical waters (except Mediterranean Sea). Abundance: Unknown, but evidence of declines in several areas where hunted as evidenced by rapid, recent declines in catch per unit effort and reduced sightings in neighboring areas.. Seasonally common (several dozen or more) at several near-shore continental and island locations (e.g. Atlantic Ocean: Belize and the Gulf of Mexico. Pacific Ocean: Sea of Cortez, Galapagos Islands, Bohol Sea and Coral Sea. Indian Ocean: the Seychelles, the Maldives, Andaman Sea, Christmas Island and Western Australia (Ningaloo Reef)). Habitat and ecology: Coastal in some seasons, pelagic in others and perhaps for much of life cycle. Evidence for long-distance migrations by some sharks. Movements may be related to ocean currents, water temperature and local, seasonal biological produc- tivity. Some evidence for trans-ocean basin movements and shorter seasonal migrations. Dives to more than 1000 m, may remain at depth for hours to weeks and tolerate ambient temperatures of 5-30C. Make regular excursions between the surface and depth in search of prey. Feed primarily on dense aggregations of crustaceans (e.g. euphausiids, copepods) and baitfishes (e.g. sardines, an- chovy). Suction filter-feeders, often assuming a head-up, tail-down posture when feeding. Young whale sharks have been found in the stomachs of a blue shark and a blue marlin. Virtually no free-ranging sharks observed at body lengths of 1-3 m. Adults have few natural predators, except perhaps for killer whales and white sharks. Reproduction: Ovoviviparous. Egg cases retained until embryos hatch. One shark captured off Taiwan had 300 embryos in utero in various developmental stages. Young ca. 55-60 cm long and 1 kg at birth and grow to 1.4 m long and 20 kg by 4 months later. Gestation duration unknown. May reproduce at 2 year intervals or more. Sexual maturity proposed at ca. 6 m and 10-30 years. Courtship and mating have never been observed. Differential distribution of sexes at among some sites suggests sexual segregation at times. Threats: Killed in coastal harpoon and net fisheries in Taiwan, the Philippines (banned in 1998), Indonesia, the Maldives (banned in 1995), India (banned in 2001) and Pakistan. Despite bans on hunting in several areas, functional enforcement is effectively minimal in most. Trade is largely driven by demand for meat for local con- sumption and fins for trade in shark fin soup market in Asia. Collisions with ships may also cause significant mortality. Greatest threats perhaps from unregulated killing and poaching in areas that may be seasonal residences for sharks that return at other seasons to distant home ranges and deterioration and destruction of important seasonal coral reef habitat feeding areas by direct exploitation of biotic and abiotic resources, coral bleaching events, and rapid climate change. Conservation recommendations: Conservation and management efforts should be coordinated at a regional and international scale with provisions for development of robust local enforcement regimes and illegal trade sanctions. Continued limits and bans on local and regional harvests and redirection to non- consumptive uses (e.g., managed ecotourism). Remarks: Several factors may make whale sharks particularly vulnerable to

Effects of artificial reefs on fish grazing in their vicinity: Evidence from algae presentation experiments

Artificial reefs have been suggested as a tool for conservation and restoration of marine habitats. However, the relationships between coral reef habitats and man-made structures are poorly understood. We experimentally tested whether artificial reefs change grazing patterns in their surrounding environment. We exposed heaps of the macroalgae, Ulva lactuca, to natural grazing, at various distances from three artificial reefs. Results suggest that artificial reefs change grazing patterns in the neighboring area. In all the locations examined grazing was 2-3 times higher near the artificial reefs than in control sites (p < 0.05). We suggest that herbivorous fishes are attracted to the artificial reefs, creating a zone of increased grazing. Therefore, while planning deployment of such artificial reefs it is necessary to consider their overall influence on their natural surroundings, in order to maintain the natural community trophic dynamics.

Trouble on the reef: the imperative for managing vulnerable and valuable fisheries

AbstractReef fishes are significant socially, nutritionally and economically, yet biologically they are vulnerable to both over‐exploitation and degradation of their habitat. Their importance in the tropics for living conditions, human health, food security and economic development is enormous, with millions of people and hundreds of thousands of communities directly dependent, and many more indirectly so. Reef fish fisheries are also critical safety valves in times of economic or social hardship or disturbance, and are more efficient, less wasteful and support far more livelihoods per tonne produced than industrial scale fisheries. Yet, relative to other fisheries globally, those associated with coral reefs are under‐managed, under‐funded, under‐monitored, and as a consequence, poorly understood or little regarded by national governments. Even among non‐governmental organizations, which are increasingly active in tropical marine issues, there is typically little focus on reef‐associated resources, the interest being more on biodiversityper seor protection of coral reef habitat. This essay explores the background and history to this situation, examines fishery trends over the last 30 years, and charts a possible way forward given the current realities of funding, capacity, development patterns and scientific understanding of coral reef ecosystems. The luxury live reef food‐fish trade is used throughout as a case study because it exemplifies many of the problems and challenges of attaining sustainable use of coral reef‐associated resources. The thesis developed is that sustaining reef fish fisheries and conserving biodiversity can be complementary, rather than contradictory, in terms of yield from reef systems. I identify changes in perspectives needed to move forward, suggest that we must be cautious of ‘fashionable’ solutions or apparent ‘quick fixes’, and argue that fundamental decisions must be made concerning the short and long‐term values of coral reef‐associated resources, particularly fish, for food and cash and regarding alternative sources of protein. Not to address the problems will inevitably lead to growing poverty, hardship and social unrest in many areas.

Passive acoustic monitoring of biological activity on coral reefs and in nearby waters

Monitoring the changing state of coral reef habitats is a challenging task that is exacerbated when the reefs in question are in remote locations. Physical sensors provide a wide range of measurements of local environmental variables, but do not give an indication of biological activity. The preliminary findings of an effort to use the ambient sound field as a means of characterizing and monitoring biological activity on coral reefs and surrounding waters are reported. Moored recording systems were developed to sample the sound field of reefs on Oahu, Hawaii for 1-min periods, at 30-min intervals, for 10 days at a time. Snapping shrimp produce the dominant acoustic energy on the reefs examined and exhibit clear diel acoustic trends. Peaks in activity consistently occur during crepuscular periods. At frequencies below 2 kHz, many fish sounds occur, which also exhibit distinct temporal variability. Cetacean sounds are also common, indicating the occurrence of an apex predator in the area. Many sounds can be detected automatically, making the examination of the sound field an efficient means of tracking acoustically active species. The results indicate that acoustic monitoring may be an effective means of tracking biological activity at locations where traditional surveys are impractical.

Macroalgal blooms on southeast Florida coral reefs: I. Nutrient stoichiometry of the invasive green alga Codium isthmocladum in the wider Caribbean indicates nutrient enrichment

Invasive blooms of the siphonaceous green algae Codium spp. have been considered a symptom of coastal eutrophication but, to date, only limited biochemical evidence supports a linkage to land-based nutrient pollution. Beginning in the summer of 1990, spectacular blooms of unattached Codium isthmocladum developed on deep coral reef habitats in southern Palm Beach County and northern Broward County, and in subsequent years, attached populations formed on reefs in northern Palm Beach County. To better understand the nutrition of these HABs, we collected C. isthmocladum and other reef macroalgae from various locations in southeast Florida as well as the wider Caribbean region for tissue C:N:P analysis in order to gauge variability in the type and degree of N- and/or P-limited growth. Widespread nutrient enrichment in floridian C. isthmocladum populations was evidenced by significantly higher tissue P (0.06% versus 0.04% of dry weight) and lower C:N (12 versus 19), C:P (425 versus 980), and N:P (35 versus 50) ratios compared to more nutrient-depleted Caribbean populations. To determine nutrient availability on southeast Florida's reefs, we sampled near-bottom waters at a variety of locations for DIN ( NH 4 + + NO 3 − + NO 2 −) and SRP analysis. In general, concentrations of NH 4 +, NO 3 − and SRP were all high on southeast Florida's reefs compared to values reported for Caribbean coral reefs. Although summertime upwelling provides episodic NO 3 − and SRP enrichment to reefs in southeast Florida, these transient nutrient pulses have not historically supported C. isthmocladum blooms. We suggest that the widespread P enrichment of C. isthmocladum tissue and water column DIN:SRP ratios <16:1 in southeast Florida drive this system toward N limitation where low level NH 4 + enrichment becomes of paramount importance. Hence, the recent C. isthmocladum blooms appear to be supported by increasing land-based nutrient pollution, particularly, sewage that is enriched in NH 4 + and SRP at a low N:P ratio (<10:1) critical to sustaining balanced growth during bloom formation.

Human-induced physical disturbances and their indicators on coral reef habitats: A multi-scale approach

This article aims to review 1) the major and most frequent human-induced physical disturbances and their consequences on coral reef habitats using a multi-scale approach, and 2) the scale-related indicators and conceptual aspects used to detect and measure the effects of these physical impacts. By physical disturbances, we mean direct perturbations that lead to the destruction/erosion of the carbonate framework. Human-induced direct physical disturbances are numerous from coastal development, tourism, harvesting, accidents and nuclear/weapon testing. Since methods for monitoring and measuring indicators are generally scale-implicit, coral reefs are first presented according to different ecological-spatial scales of organization, from colony to region (colony, reefscape, reef zone, whole reef, island and region). In this way, it is easier to link a couple {habitat, disturbance} to their potential indicators and to the descriptors they target. Three classes of descriptors, related to the response of the living component of coral reef ecosystem, are considered here: stony coral, reef fishes and the human uses. A synthesis of the different options for coral habitat assessments is proposed. We sort them according to their objectives (monitor, initial status or improvement of knowledge), their specificities (identification or not of a specific disturbances) and their scale of investigation (small, meso- or large scales). Usually, the majority of the indicators of human-induced disturbances are non-specific. They reveal that something is happening but not the actual causality and can only detect differences across time or space. A major weakness lies in the difficulty in deconvoluting the signals from a conjunction of stressors occurring at different scales. As such, a hierarchical concept of disturbances in coral reefs would be the next logical step to enhance our capabilities in monitoring and forecasting coral reefs status.

Using otolith microchemistry ofHaemulon flavolineatum (French grunt) to characterize mangroves and coral reefs throughout Turneffe Atoll, Belize: Difficulties at small spatial scales

We investigated whether the otolith chemistry ofHaemulon flavolineatum (French grunt), a nocturnally active fish, could be used as a means to differentiate individuals occupying mangrove and coral reef habitats. In 2003, adults were collected from 9 mangrove and 10 coral reef sites throughout Turneffe Atoll, Belize. Concentrations of trace elements were measured at the edge of sagittal otoliths by laser ablated inductively coupled plasma mass spectrometry. Results of a two-factor nested MANCOVA (sites nested within habitat and covariate of fish size), used to investigate whether significant differences in otolith elemental concentrations existed between habitats (i.e., mangrove versus reef) and among sites, indicated significant differences between habitats, in terms of lithium, magnesium, zinc, and rubidium (fish from mangroves had greater concentrations than those from coral reefs), as well as among sites (for several elements). Because elemental variability existed between habitats and among sites, we asked whether this variability was sufficient to differentiate habitats and sites using separate linear discriminant function analyses (LDFA). LDFA indicated that fish were classified to the habitat (mangrove or reef) from which they were collected with a moderate degree of accuracy (correct classification of 74% and 79% for mangrove and coral reef fish, respectively), but were poorly classified to the site from which they were collected (average correct classification of 46% with a range of 0–89%). Otolith microchemical investigations ofH. flavolineatum at Turneffe Atoll can be used to identify movement between habitats, yet due to the lack of unique site-specific chemical signatures likely caused by the nocturnal movement of individuals, it will not be possible to identify specific sites from which reef fish originated.