Patterns of use of space in a guild of territorial reef fishes

There exists on Heron Reef, at the southern end of the Great Barrier Reef, an 8-species guild of ecologically very similar, territorial, herbivorous reef fishes. All individuals of these species maintain territories on rubble substrata throughout juvenile and adult life. Territories are defended from all other guild members. Three rubble patches, each containing residents of 3 guild species: Pomacentrus apicalis, P. wardi, and Abudafduf lachrymatus, have been monitored for 12 to 18 months. This paper examines the patterns of use of space as shown by the antecedent and subsequent histories of sites chosen by 43 new colonists, and sites vacated through the loss of 34 residents on the rubble patches. In addition, variation through time is examined in the total amount of space held in territories on each rubble patch. The 3 species show similar preferences for space as colonists, although adult and juvenile colonists behave differently. Numbers of colonists detected on rubble patches are not proportional to the resident populations of the 3 species. Residents of the 3 species are equal in their abilities to enter spaces vacated through mortality, although they differ slightly in methods used to enter sites. They do not respond preferentially to sites previously occupied by any particular species. P. wardi shows a higher rate of mortality than the other species, and residents of this species are more often dislodged by new colonists. The total amount of space held on any rubble patch did not vary during the year from September, 1972 to October, 1973. The data are interpreted as supporting the hypothesis that the 3 species do not differ in their requirements for space on rubble patches, and that they are in competition for a short supply of such space. Differences exist in their strategies for obtaining and holding such space. These differences are important for explaining the continued presence of P. wardi on rubble patches. P. apicalis and a. lachrymatus are both specialists in holding territories on the upper reef slope. No differences have been detected in their requirements or competitive abilities. P. wardi is a fugitive species on the upper reef slope, coexisting because it maintains a refuge from competition by occupying some un-preferred sites off rubble patches.     

Life histories of large and small murexes (Prosobranchia: Muricidae)

One can predict the major features of a muricid's life history from its adult size. Most adults do not grow, and juveniles of all species grow 1 to 2 mm/month, so that larger adults have had fonger juvenile periods. Larger females deposit larger egg capsules and, since each of these contains more eggs, their clutches are larger. Small females deposit several clutches each year, and thus have relatively large annual fecundities. However, large females live longer, so each spawns many more eggs in her life-time than would a smaller female. From 90 to 99% of the juveniles die within their first year. However hatchings of small species are much more likely to complete their first year; a newly hatched Urosalpinx cinerea is 25 times more likely to survive long enough to breed once than a newly hatched Ceratostoma foliatum (Gmelin, 1791).     

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     

Poecilogony in an estuarine opisthobranch: planktotrophy, lecithotrophy, and mixed clutches in a population of the ascoglossan Alderia modesta

A San Diego population of the opisthobranch mollusc Alderia modesta (Lovén, 1844) exhibits poecilogony, the presence of two development modes within a single species. In spring, half of the adults spawned masses containing ∼300 eggs with a mean diameter of 68 μm. After 3 d, these egg masses hatched planktotrophic veligers with a maximum shell dimension of 116 μm. The remaining adults spawned masses containing ∼30 eggs with a mean diameter of 105 μm. These egg masses hatched after 5 to 6 d, releasing lecithotrophic larvae with a maximum shell dimension of 186 μm. About 1% of field-collected adults produced mixed clutches containing a continuum of larval sizes, spanning the size extremes of planktotrophy and lecithotrophy and hatching larvae with a mean maximum shell dimension of 152 μm. Adults producing planktotrophic and lecithotrophic larvae were interfertile, and no hybrid breakdown was observed through the F3 generation. When starved, adults which previously produced only lecithotrophic larvae switched to producing planktotrophic larvae or mixed clutches with both planktotrophic and lecithotrophic larvae. Sequence-polymorphisms from a portion of the mitochondrial cytochrome c oxidase I gene support the conclusion that the two reproductive morphs represent a single species. Most of the lecithotrophic larvae and a small percentage of the larvae from mixed clutches were metamorphically competent within 3 d of hatching. A. modesta is the only molluscan species as yet known to have both planktotrophic and pelagic lecithotrophic development within a single natural population. Received: 14 August 1997 / Accepted: 11 April 1998     

Hatching and viability of copepod eggs at two stages of embryological development: anoxic/hypoxic effect

The effects of low oxygen concentrations on the hatching and viability of copepod eggs at two stages of embryological development were investigated. Fully developed eggs from Acartia tonsa (Dana) and Labidocera aestiva (Wheeler) collected between July and September 1991 at Turkey Point, Florida, USA, hatched at lower oxygen concentrations than newly spawned eggs given the same incubation periods. Since many of the newly spawned eggs subsequently hatched when exposed to normoxic conditions, it is likely that the exposure to low oxygen delayed embryonic development. At oxygen concentrations where no initial hatching occurred, the subsequent hatching success of fully developed eggs of A. tonsa was higher than that of newly spawned eggs, indicating that newly spawned eggs were more sensitive to low oxygen concentrations. No such difference was observed for the eggs of L. aestiva.     

Time-lapse cinematography of feather stars (Echinodermata: Crinoidea) on the Great Barrier Reef,Australia: demonstrations of posture changes,locomotion, spawning and possible predation by fish

Aspects of feather star behavior and ecology were recorded by time-lapse cinematography approximately 1 frame min^-1 on the Great Barrier Reef, Australia over a 1 mo period in 1983. The current regime influenced body postures of most species studied, whether nocturnal or not. Moreover, feather stars of several species crawled on the substratum with their arms; each crawling episode lasted roughly 10 min, and the maximum speed attained was about 1 arm length min^-1. Nocturnal feather stars crawled to their nighttime feeding perches around dusk and crawled back to their daytime hiding places around dawn. Surprisingly, some species of feather stars living on the reef surface both day and night also crawled around at dawn and dusk for reasons that are not known. In the time-lapse films, and individual of Comanthus bennetti (sex undetermined) spawned for about 2 min just after dark on 5 July 1983. Another film showed possible predation on a feather star (Himerometra robustipinna) by a saddled coralfish (Chaetodon ephippium).     

Reproduction,recruitment and fragmentation in nine sympatric species of the coral genus Acropora

Multispecies assemblages of the coral genus Acropora occur commonly throughout the Indo-Pacific Ocean. Nine species from such an assemblage comprising 41 species of Acropora, at Big Broadhurst Reef on the Great Barrier Reef, were studied during 1981–1983. Similarities and differences in reproductive modes and timing, oocyte dimensions and fecundity, recruitment by larvae and by fragments, and mortality were recorded. All species had an annual gametogenic cycle, were simultaneous hermaphrodites, and had the same arrangement of gonads in polyps. In six species, most colonies released gametes on the same night of the year, in early summer, during a mass spawning event involving many coral genera. A seventh species had colonies spawning at this as well as other times of the year. Another species spawned in late summer, and gametes were not observed to mature in the last species. Eggs were very large (601 to 728 m geometric mean diameter) and fecundity of polyps low, compared with other corals; no reduction in oocyte numbers occurred during oogenesis. Reef-flat species had slightly bigger and fewer eggs than reef-slope species. All species recruited by larvae, but four also multiplied by fragmentation, either year-round or during occasional rough weather. Yearround fragmenters had few larval recruits; non-fragmenters had many, and a rough-weather fragmenter had an intermediate number of larval recruits. It was concluded that larval recruitment largely determined species composition, and that reduced larval recruitment was responsible for sparse distribution of fragmenting species. Subsequent mortality in some species and increase by fragmentation in others probably determined relative abundances.     

Effects of various environmental factors on egg development of several species of Acartia in Southern California

The hatching of the eggs of 3 Acartia species (A. tonsa, A. clausi, and Acartia sp. I) spawned in the laboratory and the eggs of Acartia (species undetermined) isolated from natural bottom sediments was examined under various environmental conditions (temperature, salinity and temperature combinations, oxygen concentration, illumination, and the presence of bottom mud). The range of temperature and salinity in which eggs hatched differed from one species to another. Egg hatching was inhibited under certain environmental conditions for all species, although egg viability under such conditions varied from one species to another. In relation to these findings, habitat separation of planktonic Acartia populations and the role of dormant eggs during their seasonal absence in the plankton of Southern California coastal waters are discussed.     

Nitrogen excretion by some demersal macrozooplankton in Heron and One Tree Reefs,Great Barrier Reef,Australia

Nitrogen excretion rates of demersal macrozooplankton were measured together with nitrogen concentrations in the water column and sediments in lagoons of Heron Reef and One Tree Reef, Great Barrier Reef, Australia, during August and November 1991. Excretion rates increased with body weight, and weight-specific excretion rates of the demersal macrozooplankton were comparable to those of pelagic zooplankton and meiofauna in the Great Barrier Reef. Values of demersal macrozooplankton abundance from previous studies and excretion rates from this study were combined to estimate fluxes of ammonium from demersal macrozooplankton in coral reef lagoons. The estimated fluxes in the water column and sediments were 12 M NH₄ m^-2 d^-1 and 34 M NH₄ m^-2d^-1, respectively. These fluxes were compared with reported fluxes of ammonium in coral reef lagoons in the Great Barrier Reef, Australia. The estimated flux from the demersal macrozooplankton in the water column was 29 and 9% of those reported for microheterotroph regeneration and phytoplankton utilization, respectively. It was 10% of the reported advective flux during periods of low advection and 13% of the maximum efflux from sediments computed from diffusion models. The estimated flux from the demersal macrozooplankton in the sediments exceeded those reported for meiofauna, and was 5 to 32% and 2 to 13% of those reported for ammonification and utilization in sediments, respectively. The potential importance of demersal macrozooplankton in mediating sediment-water column exchanges in the absence of diffusive effluxes and when they swarm is discussed.     

Resident mysids: community structure,abundance and small-scale distributions in a coral reef lagoon

Seasonal and diel variations in community structure and abundance of coral-reef lagoon mysids were examined at Davies Reef in the central region of the Great Barrier Reef (GBR) between June 1980 and May 1981. Twenty-five mysid species belonging to three subfamilies of the family Mysidae were captured during the study, with six new records for the GBR. The epibenthic mysid community differed from that in the overlying water, was faunistically uniform, but formed characteristic seasonal and diel groupings. The dominant epibenthic species were Erythrops sp., Anisomysis pelewensis, Doxomysis littoralis, A. laticauda, Prionomysis stenolepis, A. lamellicauda, and A. australis, five of which formed schools. Total mysid abundances ranged between 110 and 790 m^-3 with peak abundance in October. Schooling species occurred at local densities of up to 500 000 m^-3. Mysids were absent from shallow and midwater depths during the day, but were distributed throughout all depths at night with peak abundances in mid-water and deep layers. The dominant species in the water column at night were Pseudanchialina inermis, A. laticauda and Gastrosaccus indicus, in descending order of abundance. Lagoonal mysids contribute little to the food of sessile reef planktivores, as all but three species remain concentrated near or on the lagoon floor both day and night. The contribution of resident lagoon mysids to reef trophodynamics is probably through remineralization of lagoon detritus. Given the vast reef areas comprised of sandy lagoons, the large populations and relatively large size of lagoon mysids, this trophodynamic role may be of considerable importance.A.I.M.S. Contribution No. 477     

Tolerance of estuarine benthic diatoms to high concentrations of ammonia,nitrite ion,nitrate ion and orthophosphate

A carbon-14 assimilation method was used to determine action spectra and photosynthesis versus irradiance (P versus I) curves of natural populations of phytoplankton and zooxanthellae from a coral reef fringing Lizard Island in the Australian Barrier Reef. The action spectra were related to the phytoplankton species composition. The curves showed shade adaptation in phytoplankton from deeper waters and in the zooxanthellae. Rates of photosynthesis of zooxanthellae were shown to be highly but variably dependent on their host organisms. Photosynthetic production by zooxanthellae was about 0.9 gC m^-2 day^-1, which is about three times higher than phytoplankton production in the waters close to the reef.     

Synchronous spawnings of 105 scleractinian coral species on the Great Barrier Reef

Following observations of mass spawning of hermatypic corals on the Great Barrier Reef in 1981 and 1982, spawning dates were successfully predicted and documented at five reefs on the Central and Northern Great Barrier Reef in 1983. During the predicted times, 105 species from 36 genera and 11 families were observed to spawn. Of these, 15 species were shown to have an annual gametogenic cycle. All but two of the species observed during mass spawnings shed gametes which underwent external fertilization and development. Synchronous spawning was observed both within and between the five reefs studied, which were separated by as much as 5° of latitude (500 km) or almost a quarter of the length of the Great Barrier Reef. The mass spawning of corals took place on only a few nights of the year, between the full and lastquarter moon in late spring. Maturation of gametes coincided with rapidly rising spring sea temperatures. Lunar and diel cycles may provide cues for the synchronization of gamete release in these species. The hour and night on which the greatest number of species and individuals spawned coincided with low-amplitude tides. Multispecific synchronous spawning, or mass spawning, of scleractinian and some alcyonacean corals represents a phenomenon which is, so far, unique in both marine and terrestrial communities.     

Preferential incubation positions for different sized eggs and their influence on incubation period and hatching asynchrony in Snares crested (<Emphasis Type="Italic">Eudyptes robustus</Emphasis>) and yellow-eyed penguins (<Emphasis Type="Italic">Megadyptes antipodes</Emphasis>)

In crested penguins (Eudyptes spp.), second-laid eggs typically hatch before first eggs. Amongst a variety of factors that have been considered as mechanisms underlying this reversal, has been the idea that crested penguins can adjust the degree of hatching asynchrony by manipulating egg positions (i.e. placing the smaller first egg in the supposedly thermally disadvantaged anterior position) during incubation (termed Preferential Incubation Hypothesis). We tested this in the Snares crested penguin (Eudyptes robustus) and the closely related, but synchronously-hatching, yellow-eyed penguin (Megadyptes antipodes). Snares crested penguins were more likely to place their first eggs, which are smaller than second eggs, in the anterior incubation position than were yellow-eyed penguins, which have a clutch of two similar-sized eggs. But when yellow-eyed penguins, a non-brood reducing species, were provided with an artificial size-dimorphic clutch, they also placed smaller eggs more frequently in the anterior position, suggesting that a general preference exists among penguins to place smaller eggs in the anterior position. Egg temperatures of small first eggs of Snares crested penguins were higher in the anterior than in the posterior position. Large first eggs in lesser size-dimorphic clutches experienced high temperature differences in relation to position, while small first eggs in greater size-dimorphic clutches were incubated at similar temperatures. In yellow-eyed penguins, large eggs within clutches generally had higher egg temperatures than small eggs. Incubation periods of second eggs declined with increasing egg size. Egg-size variation, rather than egg positioning behaviour, influenced hatching patterns in Snares crested penguins. In lesser size-dimorphic clutches, second eggs were more likely to hatch first while in greater size-dimorphic clutches, small first eggs were more likely to hatch at the same time or before the second eggs. This was similar in yellow-eyed penguins, where second eggs hatched earlier in clutches with large first eggs. Our data contradicts the Preferential Incubation Hypothesis and we conclude that this hypothesis is unlikely to explain the reversed hatching asynchrony in crested penguins.Communicated by C. Brown     

Kinship recognition and grouping in hatchling green iguanas

Summary The research addressed two questions: (1) doIguana iguana hatchlings recognize their kin, and (2) what are the recognition mechanisms? Eggs were collected from wild and captive-raised females and hatched in semi-natural incubators. In the first experiment we used eggs from two females. One of the clutches was subdivided to be placed in different incubators. Immediately after emergence one of these hatchling groups was introduced into a 10 m x 10 m enclosure. At the same time we introduced hatchlings from another female. The remaining hatchling group was kept separate for 3 weeks and was then introduced into the same cage. Unrelated hatchlings separated from each other. Related but separated hatchlings grouped according to introduction date. In the second experiment we maintained eight kin groups in individual cages and two hatchlings per kin group in an additonal cage. Hatchlings from the mixed group showed no preference for their kin before physical contact with pure kin groups had occurred. After physical contact hatchling recognized their kin by feces smell. Body odor is likely to be also involved.     

Self- and cross-fertilization in scleractinian corals

The mating patterns of four species of hermaphroditic scleractinian coral were investigated in November 1984 at Orpheus Island on the Great Barrier Reef, Australia. Each of the species shed eggs and sperm into the water, with subsequent external development of larvae. Studies of gamete viability indicated that cross-fertilizations were possible until at least 6 h after spawning.Montipora digitata cross-fertilized exclusively,Acropora tenuis, Goniastrea aspera andG. favulus were capable of self-fertilization, but to varying extents. In all species, cross-fertilization was the dominant mating pattern.     

Seasonality and dynamics in coral reef macroalgae: variation in condition and susceptibility to herbivory

Seasonal variation in coral reef macroalgal size and condition is well documented, yet seasonal variability of herbivory on macroalgae by coral reef fishes is unknown. Herbivore feeding intensity was quantified monthly on an inner-shelf reef on the Great Barrier Reef, using Sargassum bioassays. Removal rates of transplants displayed high levels of variation with significantly higher rates of removal during the summer months. Differences in Sargassum plant size and condition suggest that the variability in herbivore feeding intensity is attributed primarily to the variation in the condition of the macroalgae, especially epiphyte loads. The dramatic changes in macroalgal removal reveal a considerable decrease in herbivore activity in the winter. This highlights the clear distinction between ‘summer’ and ‘winter’ months in terms of reef processes, emphasizing the high seasonal variation in macroalgal removal rates at different time of the year.     

Ecological studies of the coral predator Acanthaster planci in the south pacific

Ecological surveys involving over 500 man-days between 1966 and 1969 indicate that the coral-eating sea star, Acanthaster planci, is a normal component of the coral reef community throughout the tropical Pacific, and that its abundance in the past has probably been underestimated. The sea star is not uncommon in certain environments, particularly back-reef and lagoon slopes. Sheltered, inner reefs are generally preferred over less protected reefs. Recently reported population explosions of A. planci at Guam and on the Great Barrier Reef of Australia appear to be isolated, widely-separated, local infestations of unknown cause. The infestation on the Great Barrier Reef has not spread beyond the area off Cairns and Innisfail. Approximately 40 of the more than 1000 reefs comprising the Great Barrier Reef complex have been infested heavily.     

Amphibian embryo and parental defenses and a larval predator reduce egg mortality from water mold

Water molds attack aquatic eggs worldwide and have been associated with major mortality events in some cases, but typically only in association with additional stressors. We combined field observations and laboratory experiments to study egg stage defenses against pathogenic water mold in three temperate amphibians. Spotted salamanders (Ambystoma maculatum) wrap their eggs in a protective jelly layer that prevents mold from reaching the embryos. Wood frog (Rana sylvatica) egg masses have less jelly but are laid while ponds are still cold and mold growth is slow. American toad (Bufo americanus) eggs experience the highest infection levels. They are surrounded by thin jelly and are laid when ponds have warmed and mold grows rapidly. Eggs of all three species hatched early when infected, yielding smaller and less developed hatchlings. This response was strongest in B. americanus. Precocious hatching increased vulnerability of wood frog hatchlings to invertebrate predators. Finally, despite being potential toad hatchling predators, R. sylvatica tadpoles can have a positive effect on B. americanus eggs. They eat water mold off infected toad clutches, increasing their hatching success.     

Complex patterns of population structure and recruitment of <Emphasis Type="Italic">Plectropomus leopardus</Emphasis> (Pisces: Epinephelidae) in the Indo-West Pacific: implications for fisheries management

Here the population genetic structure of an ecologically and economically important coral reef fish, the coral trout Plectropomus leopardus, is investigated in the context of contemporary and historical events. Coral trout were sampled from four regions (six locations) and partial mtDNA D-loop sequences identified six populations (Fst = 0.89209, P < 0.0001): Scott Reef and the Abrolhos Islands in west Australia; the Great Barrier Reef (GBR), represented by northern and southern GBR samples; New Caledonia and Taiwan, with Taiwan containing two genetic lineages. Furthermore, this study identified source and sink populations within and among regions. Specifically, the northern population in west Australia (Scott Reef) was identified, as the source for replenishment of the Abrolhos population, whilst New Caledonia was a source for recruitment to the GBR. Based on these insights from a single mtDNA marker, this study will facilitate the development of rational management plans for the conservation of P. leopardus populations and therefore mitigate the risk of population declines from anthropogenic influences.     

Sexual reproduction in Acropora (Isopora) species (Coelenterata: Scleractinia)

Despite the wide range of morphological diversity among the Acropora (Isopora) colonies on Heron Island (Great Barrier Reef, Australia), only two reproductively isolated species were present from 1977 to 1982: A. cuneata (Dana, 1846) and A. palifera (Lamarck, 1816). Both species released planulae lacking zooxanthellae and were simultaneous hermaphrodites with testes and ovaries occurring on separate mesenteries within the same polyp. Oogenesis preceded spermatogenesis. Seasonal cycles of gametogenesis, embryogenesis and planulation occurred in the two species. Colonies of A. cuneata developed two cycles of gametes. One cycle matured near the first quarter moon in April and the other on the same lunar phase in June. Planulae release occurred from about September to December each year and was not correlated with lunar phase. Gametes of A. palifera ripened only once per annum, a few days after the last quarter moon in November, and planulation occurred from about January to March. Embryos were brooded in the coelenteron of the polyps in both species. Ova were fertilized in the mesenteries and embryos were retained within an envelope of mesoglea and gastrodermis, remaining attached to the mesentery by a stalk until the larvae matured and were released. A. palifera and A. cuneata were abundant in the unpredictable reef flat environment. However, their life-history traits, e.g. seasonal reproduction, delayed sexual maturity, large colony size and fairly long life span, were more specialised than had been predicted for this type of environment.