Responses of marine fouling communities to sewage abatement in Kaneohe Bay,Oahu, Hawaii

The development of marine fouling communities was followed as part of a sewage abatement study in Kaneohe Bay (Oahu, Hawaii). Panels immersed near the outfall during sewage discharge were dominated by dense mats of blue-green algae and diatoms. This mat was significantly lighter at this station when sewage did not flow into the bay, and it never developed on panels within the same sector of the bay but away from the influence of the outfall. Taxonomic diversity, and the frequency of filamentous algae and the serpulidHydroides elegans were reduced near the outfall during discharge. It is suggested that this reduction in diversity and abundance of certain key foulers is due to competitive exclusion by the dense blue-green and diatom mats, and is not a direct effect of the sewage effluent.     

Diversity and stability of herbivorous fishes on coral reefs

Biodiversity may provide insurance against ecosystem collapse by stabilizing assemblages that perform particular ecological functions (the "portfolio effect"). However, the extent to which this occurs in nature and the importance of different mechanisms that generate portfolio effects remain controversial. On coral reefs, herbivory helps maintain coral dominated states, so volatility in levels of herbivory has important implications for reef ecosystems. Here, we used an extensive time series of abundances on 35 reefs of the Great Barrier Reef of Australia to quantify the strength of the portfolio effect for herbivorous fishes. Then, we disentangled the contributions of two mechanisms that underlie it (compensatory interactions and differential responses to environmental fluctuations ["response diversity"]) by fitting a community-dynamic model that explicitly includes terms for both mechanisms. We found that portfolio effects operate strongly in herbivorous fishes, as shown by nearly independent fluctuations in abundances over time. Moreover, we found strong evidence for high response diversity, with nearly independent responses to environmental fluctuations. In contrast, we found little evidence that the portfolio effect in this system was enhanced by compensatory ecological interactions. Our results show that portfolio effects are driven principally by response diversity for herbivorous fishes on coral reefs. We conclude that portfolio effects can be very strong in nature and that, for coral reefs in particular, response diversity may help maintain herbivory above the threshold levels that trigger regime shifts.     

Variability of stable isotopes and maximum linear extension in reef-coral skeletons at Kaneohe Bay, Hawaii

Stable-isotope and growth records of coral skeletons are often used to reconstruct tropical paleoclimate, yet few surveys have systematically examined the natural variability in coral skeletal ¹³C, ¹⁸O and maximum linear skeletal extension (MLSE) across depth. Here, interspecific, intraspecific, and geographical variations in coral skeletal ¹³C, ¹⁸O, and MLSE were examined in the corals Porites compressa, P. lobata, and Montipora verrucosa grown at 1.7, 5.0, and 8.3 m depth from August 1996 to March 1997 at The Point Reef and Patch Reef #41 field sites in Kaneohe Bay, Hawaii. Coral skeletal ¹³C values significantly decreased with depth and differed between species, but did not vary between field sites. ¹⁸O values were not significantly different across depth within a species, but did differ among species and field sites. High-resolution analysis of the intra-annual variation in skeletal ¹³C and ¹⁸O in P. compressa at 2.0 m depth confirms that these isotopes reflect changes in solar irradiance and temperature, respectively. Changes in MLSE across depth were consistent within, but highly variable among, species. Peak MLSE occurred at 1.7, 5.0, and 8.3 m for P. lobata, P. compressa, and M. verrucosa, respectively. Such interspecific variation in MLSE patterns may be attributable to one or more of the following: increases in zooplankton in the diet, changes in metabolic processes, or changes in growth form with depth. Overall, these results imply that natural inter- and intraspecific variability in coral skeletal ¹³C, ¹⁸O, and MLSE should be considered when interpreting and comparing coral-based tropical paleoclimate data from various coral species, depths, and field sites. Received: 6 October 1998 / Accepted: 8 July 1999     

Ultraviolet photosensitivity and feeding in larval and juvenile coral reef fishes

The ability of young coral reef fishes to feed using solely ultraviolet-A (UV-A) radiation during ontogeny was examined using natural prey in experimental tanks. Larvae and juveniles of three coral reef fish species (Pomacentrus amboinensis, Premnas biaculeatus and Apogon compressus) are able to feed successfully using UV-A radiation alone during the later half of the pelagic larval phase. The minimum UV radiation intensities required for larval feeding occur in the field down to depths of 90–130 m in oceanic waters and 15–20 m in turbid inshore waters. There was no abrupt change in UV sensitivity after settlement, indicating that UV photosensitivity may continue to play a significant role in benthic juveniles on coral reefs. Tests of UV sensitivity in the field using light traps indicate that larval and juvenile stages of 16 coral reef fish families are able to detect and respond photopositively to UV wavelengths. These include representatives from families that are unlikely to possess UV sensitivity as adults due to the UV transmission characteristics of the ocular media. Functional UV sensitivity may be more widespread in young coral reef fishes than in the adults, and may play a significant role in detecting zooplanktonic prey.     

Geographical gradients of marine herbivorous fishes: patterns and processes

We present new data and the first rigorous analysis of latitudinal and thermal gradients of diversity, density and biomass of marine herbivorous fishes and review proposed explanatory mechanisms. Consistently, negative relationships between latitude, and positive relationships between sea surface temperature (SST), and relative richness and relative abundance of herbivorous fishes were found worldwide. Significant differences in the strength of gradients of richness and abundance with latitude and SST between tropical and extratropical zones were found consistently across ocean basins. Standardized sampling along the western Atlantic also showed negative relationships between latitude and total density and biomass. The trends, however, are driven by different components of the fish assemblages (i.e., scarids in the Caribbean and acanthurids in Brazil). Patterns of abundance along thermal gradients, generally associated with extensive latitudinal gradients, also were found at the local scale. Feeding rate of the ocean surgeonfish Acanthurus bahianus decreases with temperature more rapidly than the mean metabolic rate of teleost fishes. This relationship suggests a temperature-related physiological constraint. From the new standardized and comparative data presented and the review of the explanatory hypotheses, we conclude that temperature-related feeding and digestive processes are most likely involved in the distribution patterns of herbivorous fishes. Electronic Supplementary Material Supplementary material is available for this article at     

Associations between the abundance of piscivorous fishes and their prey on coral reefs: implications for prey-fish mortality

Few studies have examined predator-prey relationships in diverse communities such as those found on coral reefs. Here we examined patterns of spatial and temporal association between the local abundance of predator and prey fishes at Lizard Island on the Great Barrier Reef, Australia. We predicted that the nature of this association would have implications for patterns of prey-fish mortality. Strong positive relationships between prey and piscivore abundance were found throughout the study. Greater densities of predators and of prey were found on patch-reef habitats, compared with contiguous reef-slope habitats. Declines in prey-fish abundance on patch reefs were density-dependent and correlated with the densities of predators. The relative roles of recruitment and piscivore movement in determining patterns of predator and prey abundance were assessed from surveys of recruit densities and an intensive programme of tagging two species of rock-cod, Cephalopholis cyanostigma and C. boenak (Serranidae), over 2 years. Patterns of recruitment explained little of the variation in the abundance and distribution of piscivorous fish. If movement explains large-scale patterns of distribution, this was not evident from the tagging study. The two rock-cod species were highly sedentary, with individuals on patch reefs seldom moving among reefs. Individuals on reef slopes were also highly site-attached, although they moved greater distances than those on patch reefs. Although the mechanisms responsible remain to be determined, this study demonstrated strong associations between the abundance of piscivorous fish and their prey on coral reefs. This relationship appeared to be an important factor in producing density-dependent declines in the abundance of prey. Received: 30 April 2000 / Accepted: 22 September 2000     

Spatial and temporal patterns of recuruitment of juvenile coral reef fishes to coral habitats within “One Tree Lagoon”, great barrier reef

Recruitment of juvenile fishes to coral grids, each comprising 4 colonies of 3 species of coral (Acropora formosa, Seriatopora hystrix and Pocillopora damicornis), was examined at 4 widely separated sites within the lagoon of One Tree Reef over two successive summers and intervening months (November 1976–January 1978). Recruitment was highly seasonal, with most recruitment occurring during summer. For many species, numbers settling differed greatly from year to year with total numbers (over all sites) differing as much as an order of magnitude between summers. Many fish species demonstrated marked preference among the three coral species as settling sites. The distribution of each of the 20 commonest species across the 4 lagoon sites differed significantly from a random pattern. Differences of an order of magnitude were common in the numbers of a given species recruited to different sites. Each site was preferred by at least one species. In each of 5 cases examined, the pattern of settlement of the species across the 4 sites changed significantly from one summer to the next. The distribution of recruits of a number of species corresponded to the distribution of adults, but for other species there was no correspondence. It is concluded that, at the spatial scale examined, patterns of recruitment of some taxa are consistently more variable than those of other taxa. The implications of spatial variability of recruitment for the distribution of adult fish is discussed and the importance of being able to discriminate such natural variability from other kinds of change is stressed.     

Current and historic distribution and abundance of the inarticulated brachiopod, <Emphasis Type="Italic">Lingula reevii</Emphasis> Davidson (1880), in Kaneohe Bay,Oahu, Hawaii,USA

The inarticulated brachiopod, Lingula reevii Davidson (1880) is a filter-feeding invertebrate that burrows vertically in sandy or mixed sediments. Its only recorded occurrence is from Kaneohe Bay, Oahu, Hawaii, southern Japan, and Ambon, Indonesia. Past surveys of Kaneohe Bay populations suggested a distinct decrease in abundance following the diversion of sewage effluent from the bay in 1978/1979. In the summer of 2004 and 2007, visual surveys were conducted in areas of historical L. reevii abundance as well as in areas appearing to have suitable habitat. In 2004, approximately 2,950 m² at 20 sites within the bay were surveyed using quantitative belt transecting methods. A maximum density of 4 Lingula/m² was observed, a decrease from previous maximum estimates of 500 individuals/m² (Worcester, Dissertation, Zoology Department, University of Hawai′i, pp 49, 1969) and 100 individuals/m² (Emig, J Exp Mar Biol Ecol 52:47–61, 1981). When these 20 sites were revisited in 2007, many had fewer or no L. reevii; therefore, broader scale presence/absence surveys were conducted at 16 additional sites in the bay (also surveyed in 2004). The highest density of L. reevii found in 2007 was 0.94 individuals/m². The continued decline in abundance of L. reevii in Kaneohe Bay may be due, in addition to decreased organic enrichment from diversion of sewage discharge almost 30 years ago, to the more recent reduction of suitable habitat by the invasion of mat-forming alien algae species.     

Hydrography and distribution dynamics of larval and juvenile fishes in the coastal waters of the Tanshui River estuary,Taiwan, with reference to estuarine larval transport

Distribution dynamics of fish larvae and juveniles in the coastal waters of the Tanshui River, Taiwan was studied fortnightly using surface horizontal tows with a larval net in daytime during the period from early April through early June 1991. Environmental factors, including water temperature, salinity, dissolved oxygen, pH, transparency and depth at sampling stations, were also monitored. A total of 10737 fish eggs and 1387 individuals, representing 43 families and 93 species, was collected during five cruises from 12 stations in the coastal waters. Most fish were estuarine-dependent marine species. Liza macrolepis, Ambassis gymnocephalus, Terapon jarbua, Mullidae and Gobiidae were the most dominant, making up 64.7% of the total catch. Early life stages, including egg, preflexion, flexion and postflexion larvae were abundant in surface samples. However, yolk-sac larvae were absent in the surface water, probably due to an ontogenetic behavioral shift as a consequence of a change in specific weight during early development. The species composition of fish larvae and juveniles was related to the microhabitats found in the coastal waters. The physico-chemical conditions, along with ontogenetic behavior, played an important role in larval fish distribution in the coastal waters.     

Vertical and horizontal distribution of fish larvae near coral reefs at Lizard Island,Great Barrier Reef

Consistent patterns of horizontal distribution of fish larvae from plankton tows were found in shallow waters around Lizard Island, Great Barrier Reef during 1979 and 1980. Few types of larvae were most abundant in Lizard Lagoon, and none of these were old larvae. Forty percent of the 57 types of larvae studied differed in abundance between windward and downwind sides of the island. More types of old larvae were found in greatest abundance off the windward side of the island than the downwind side. Most types of larvae preferred deeper water (>3 m) during the day and moved upward at night, although a few types preferred upper (<3 m) or middle portions of the water column. These latter were more likely to descend at night or to maintain their day-time distribution than to move upward. Windward larvae [those more abundant off the windward (SE) side of the island] were more shallow-living than were downwind larvae, and were more likely to maintain their day-time distribution at night. The current patterns around Lizard Island were favourable for retention of larvae in both Lizard Lagoon and off the windward side of the island, if combined with certain vertical distributions of the larvae. However, while there was evidence for retention on the windward side of the island, there was no evidence for retention in Lizard Lagoon. Currents on the downwind side of the island were not favourable for retention of larvae and there was little evidence that larvae were retained there. Retention may be an accidental result of interaction between currents and larval behaviour, or the result of a strategy of retention by the larvae. These could not be distinguished in the present study.     

Natural parthenogenesis,larval and juvenile development,and geographical distribution of the coral reef asteroid Ophidiaster granifer

Ophidiaster granifer Lütken is a small cryptic coral reef asteroid found in the Indo-West Pacific. Its mode of reproduction, shown by aquarium observations and gonad histology, is parthenogenetic. This is the first confirmation of natural parthenogenesis in the phylum Echinodermata, despite many studies showing artificial parthenogenesis in echinoderms. Populations of O. granifer from Micronesia, New Guinea and the Great Barrier Reef consisted only of females: no testes or spermatogenesis were found in any individual at any stage of gonad development of ca 400 individuals. Regular year-round population censuses at Guam, Micronesia, revealed a distinct 0-year class which grew to sexual maturity in two years. There was an annual reproductive cycle with apparently-synchronous spawning in early winter. The large eggs, ca 0.6 mm diameter, develop into lecithotrophic larvae. Some larvae are planktonic, while some remain attached under the rocks. The latter develop through metamorphosis in situ. Parthenogenetic reproduction leading to both stationary and dispersed larvae may be related to the low fecundity and low population densities of this small asteroid.     

Temporal and spatial variability in coral recruitment on two Indonesian coral reefs: consistently lower recruitment to a degraded reef

Corals are the primary reef-building organisms, therefore it is key to understand their recruitment patterns for effective reef management. Coral recruitment rates and juvenile coral abundance were recorded in the Wakatobi National Marine Park, Indonesia, on two reefs (Sampela and Hoga) with different levels of environmental degradation (12.5 vs. 44 % coral cover with high and low sedimentation rates, respectively) to examine consistencies in recruitment patterns between years and seasons. Recruitment was measured on multiple panels at two sites on each reef (6–7 m depth) and cleared areas of natural reef. Although coral recruitment was twofold higher in 2008–2009 than in 2007–2008, and seasonal differences were identified, consistent significant differences in recruitment rates were found between the two reefs even though they are separated by only ~1.5 km. Recruitment rates and juvenile abundance were lower on the more degraded reef. These patterns are likely a consequence of differential pre- and post-settlement mortality as a result of the high sedimentation rates and degraded conditions and possibly reduced larval supply.     

Short-term temporal patterns of early recruitment of coral reef fishes in the tropical eastern Pacific

Short-term temporal patterns of recruitment have been described in a variety of coral reef fishes and have often been related with lunar and tidal cycles. While the relative importance of lunar and tidal factors in determining recruitment patterns has been difficult to assess, most studies have been done in the Caribbean and Indo-Pacific, where tidal amplitudes are small. We studied the short-term temporal dynamics of fish recruitment at Gorgona Island (tropical eastern Pacific), where there is a large tidal amplitude (~4.4 m). Every other day during three consecutive months in 1998, we directly measured the magnitude of reef fish recruitment to standardized coral units (SCUs) isolated from natural reefs. A total of 40 species from 21 families settled on the SCUs. Of 11 species with sufficient numbers for meaningful statistical analyses, two (Lutjanus guttatus and Pomacanthus zonipectus) had lunar recruitment with peaks near the new moon; three combined species of antennariids showed semilunar recruitment with peaks near moon quarters; and eight other species showed sporadic and aperiodic recruitment pulses. The contribution of lunar (moonlight intensity) and tidal factors (tidal amplitude and net tidal flow) to recruitment dynamics varied among species, although it was generally low (<18%) even among species with periodic patterns, except perhaps in L. guttatus. In this species, recruitment magnitude correlated negatively with moonlight intensity, accounting for 34.5% of the variance. Post-settlement predation by roving predators may be one cause of this relationship. In the remaining species, particularly those with sporadic and aperiodic recruitment pulses, stochastically varying weather and oceanographic events may be more important in determining temporal variation in recruitment.     

Diel patterns of abundance of presettlement reef fishes and pelagic larvae on a coral reef

Most presettlement reef fish settled at night at One Tree Island, Great Barrier Reef. Fish were sampled day and night using channel nets located on the reef crest, and a plankton-mesh purse-seine net in the lagoon (1992–1994). Catches of fish at night were generally tens to hundreds of times greater than those taken during the day. Preflexion fish, as well as postflexion and pelagic juveniles, were taken in greater numbers at night. Preflexion forms were a combination of those that had hatched from demersal eggs and later stages that had been transported over the reef crest. Highest numbers of postflexion and pelagic juvenile forms of Apogonidae, Blenniidae, Gobiesocidae, Gobiidae, Labridae, Lutjanidae, Mugiloididae, Mullidae, Pomacentridae, Scaridae, Serranidae and Tripterygiidae were found at night. Observations, while SCUBA diving, and purse-seine samples in the lagoon indicated that the only resident larvae were of the genera Spratelloides and Hypoatherina; most of the fishes caught in nets, therefore, were immigrants. Patch reefs, sampled for new settlers early in the morning and late in the day, indicated that the majority of apogonids (Apogon doederleini, >95%) settled at night. Although greater numbers of pomacentrids were found in morning counts (e.g. Pomacentrus wardi), if data were converted to an hourly rate, many pomacentrids showed a similar hourly rate of settlement day and night. Depth-stratified sampling in waters near One Tree Island (to 20 m) indicated that some taxa rise to the surface at night. This behaviour, perhaps combined with avoidance of diurnal predators may explain on-reef movement of potential settlers soon after dark. Studies on settlement cues, therefore, need to focus on night-related phenomena. Received: 3 March 2000 / Accepted: 20 June 2000     

Distribution patterns of larval myctophid fishes in the transition region of the western North Pacific

We examined the species composition and horizontal distribution of myctophid fish larvae in the transition region of the western North Pacific during the early summer. In total, 4,760 myctophid larvae were collected at 44 stations; 18 species of myctophids from 15 genera were collected, and the 8 most abundant species accounted for >95% of larvae. The distribution patterns of these larvae were well defined by the hydrographic structures of the study area including the Oyashio and Kuroshio fronts, the Subarctic Boundary, and a warm core ring. The horizontal distribution patterns of the eight dominant species were categorized into three groups: northern transition water (Stenobrachius nannochir, Tarletonbeania taylori, and Lampanyctus jordani), southern transition water (Symbolophorus californiensis, Diaphus theta, and Nannobrachium regale), and Kuroshio (Myctophum asperum and Diaphus garmani). The Subarctic Boundary defined the distributions of the northern and southern transition-water groups. The importance of areas of western North Pacific transition water as spawning and nursery grounds for subarctic, transitional, and subtropical myctophid fishes was indicated by the relationship between the horizontal distribution patterns of larvae, juveniles, and adults and the physical oceanographic structures.Communicated by T. Ikeda, Hakodate     

The relationship between population genetic structure and pelagic larval duration in coral reef fishes on the Great Barrier Reef

Pelagic larval duration (PLD) is a commonly used proxy for dispersal potential in coral reef fishes. Here we examine the relationship between PLD, genetic structure and genetic variability in geographically widespread and ecological generalist species from one coral reef fish family (Pomacentridae) that differs in mean larval duration by more than a month. The genetic structure was estimated in eight species using a mitochondrial molecular marker (D-loop) and in a sub-set of five species using nuclear molecular markers (ISSRs). Estimates of genetic differentiation were similar among species with pelagic larvae, but differed between molecular markers. The mtDNA indicated no structure in all species except one, while the ISSR indicated some structure between the sampling locations in all species. We detected a relationship between PLD and genetic structure using both markers. These relationships, however, were caused by a single species, Acanthochromis polyacanthus, which differs from all the other species examined here in lacking a larval phase. With this species excluded, there was no relationship between PLD and genetic structure using either marker despite a range of PLDs of more than 20 days. Genetic diversities were generally high in all species and did not differ significantly among species and locations. Nucleotide diversity and total heterozygosity were negatively related to maximum PLD but again these relationships were caused by A. polyacanthus and disappeared when this species was excluded. These genetic patterns are consistent with moderate gene flow among well-connected locations and indicate that at this phylogenetic level (i.e., within family) the duration of the pelagic larval phase is unrelated to the patterns of genetic differentiation.     

Bioerosion of coral reefs by two Hawaiian parrotfishes: species, size differences and fishery implications

Parrotfishes can be significant bioeroders and sediment producers on coral reefs. We quantified the bioerosion rates of two similarly sized Hawaiian parrotfishes with two different feeding modes (Scarus rubroviolaceus—a scraper and Chlorurus perspicillatus—an excavator). The results showed that feeding modes did not affect bioerosion rates but that bioerosion rates were size dependent, with largest individuals (S. rubroviolaceus 45–54 cm FL) bioeroding up to 380 ± 67 kg ind⁻¹ year⁻¹. The size for onset of bioerosion capabilities for both species was 15 cm. Grazing by the two species consumed 60% of the carbonate production of the fore reef area, suggesting that large parrotfishes in Hawaii are ecologically important bioeroders. As individual large S. rubroviolaceus contributed disproportionately more to bioerosion and sediment production than the equivalent biomass of smaller conspecifics, management strategies designed to retain normal reef bioerosion rates should seek to preserve the historical size structure of S. rubroviolaceus populations and to especially protect the larger size classes.     

Minimal genetic variation among samples of six species of coral reef fishes collected at La Parguera,Puerto Rico,and Discovery Bay,Jamaica

Intraspecific genetic variation among samples of six species of reef fishes,Chromis cyanea, Stegastes partitus, S. planifrons, S. leucostictus, S. dorsopunicans, andThalassoma bifasciatum collected over a 2 wk period in 1990 at La Parguera, Puerto Rico, USA and Discovery Bay, Jamaica, was evaluated using starch-gel electrophoresis. On average, products of 33 protein-coding loci were resolved in each species. Levels of polymorphism (0.95 criterion) ranged from 3.1% inS. dorsopunicans to 42.4% inC. cyanea. Estimates of genetic divergence among samples and indices of genetic subdivision were small in all six study species: mean genetic distances ranged from 0.000 to 0.002 and mean fixation indices ranged from 0.004 to 0.035. Estimates of numbers of migrants per generation (mN _e) ranged from 5.1 to 11.6, indicating that substantial genetic exchange probably occurs over the relatively large geographic distance (ca. 1000 km) separating coral reef communities of La Parguera and Discovery Bay. The estimates ofmN _e may be biased by a sampling strategy involving only two localities, and should therefore be interpreted with caution. With inferences based solely on allozyme frequency data under a primary assumption of neutrality, genetic substructuring of populations of the six study species on a macrogeographic scale appears virtually nonexistent.