Experimental fragmentation reduces sexual reproductive output by the reef-building coral Pocillopora damicornis

Natural and anthropogenic disturbances may fragment stony reef corals, but few quantitative data exist on the impacts of skeletal fragmentation on sexual reproduction in corals. We experimentally fragmented colonies of the branching coral Pocillopora damicornis and determined the number and size of planula larvae released during one lunar reproductive cycle. Partially fragmented colonies significantly delayed both the onset and peak period of planula release compared with intact control colonies. Most fragments removed from the corals died within 11–18 days, and released few planulae. The total number of planulae released per coral colony varied exponentially with remaining tissue volume, and was significantly lower in damaged versus undamaged colonies. However, the number of planulae produced per unit tissue volume, and planula size, did not vary with damage treatment. We conclude that even partial fragmentation of P. damicornis colonies (<25% of tissue removed) decreases their larval output by reducing reproductive tissue volume. Repeated breakage of corals, such as caused by intensive diving tourism or frequent storms, may lead to substantially reduced sexual reproduction. Therefore, reef management should limit human activities that fracture stony corals and lead to decreases in colony size and reproductive output. Accepted: 2 February 2000     

Possible self-fertilization in the brooding coral Acropora (Isopora) brueggemanni

We examined gametogenesis and the periodicity of planula release in the brooding coral Acropora (Isopora) brueggemanni (Brook, 1893) on Akajima Island, Okinawa, Japan. We captured the moment when A. brueggemanni would be in the process of self-fertilization. Whole colonies of this species were cultured separately or together with other colonies in plastic containers. We observed no apparent periodicity of planula release in the collected colonies. A few planulae were released intermittently during the observation period, regardless of whether the colonies were cultured individually or with other colonies. Serial paraffin sections of A. brueggemanni showed follicle-like cells surrounding the oocyte during vitellogenesis. In September and October, some spermaries looked half-broken and some ova were surrounded by sperm or spermaries instead of follicle-like cells. Such ova were heart-shaped and may have been cells at the first cleavage stage. These observations suggest that the migration of spermaries and/or oocytes resulted in the close proximity of oocytes and sperm, which would allow self-fertilization. This possibility, together with the production of planula larvae by isolated colonies, suggests that this brooding coral engages in self-fertilization.     

Reproductive seasonality,settlement, and post-settlement mortality of Pocillopora damicornis (Linnaeus), at Lizard Island,Great Barrier Reef

Pocillopora damicornis (Linnaeus) has seasonal gametogenesis and planula release at Lizard Island, Great Barrier Reef, in contrast with several previous reports on the species at other locations. The number of planulae released and gonad development varied considerably among colonies sampled at the same time, but reproductive activity occurred predominantly in winter. P. damicornis planulae settled preferentially on algal-covered substrata, rather than bare coral substrata, but showed subsequent mortality inversely related to this settlement preference. Competition with algae and biological disturbance contribute to spat mortality at different stages of settlement and growth.     

Engineering of coral reef larval supply through transplantation of nursery-farmed gravid colonies

The continuous worldwide degradation of coral reefs raises an urgent need for novel active restoration techniques as traditional conservation practices have failed to impede the incessant reefs' decline. While applying the “gardening coral reefs” methodology in Eilat (Red Sea, Israel), we examined reproductive outputs of naturally-grown and outplanted, nursery-farmed Stylophora pistillata colonies from three coral-transplantation trials (November 2005, May 2007, and September 2008), along three reproductive seasons. Surprisingly, transplanted colonies showed better reproductive capacities than the natal Stylophora colonies during > 4 post-transplantation years. A higher percentage of nursery-farmed colonies released planula larvae as compared to naturally-grown colonies. Gravid transplants also shed more planulae per colony, yielding significantly augmented numbers of total planulae over naturally developed S. pistillata colonies. Our results indicate that nursery-grown corals may be used to enhance reef resilience by contributing to the larval pool, forming an engineered larval dispersal instrument for reef rehabilitation.     

Pattern of serotonin‐like immunoreactive cells in scyphozoan and hydrozoan planulae and their relation to settlement

The planulae of almost all investigated cnidarian species possess neuron‐like cells. The distribution of these cells is usually uneven throughout the long axis of the planula. The majority of these cells are located in the anterior half of the planula body. Scyphozoan planulae, as well as anthozoan planulae, have a sensory structure at the anterior pole called an apical organ, which is believed to take part in metamorphosis induction. Hydrozoan planulae also possess sensory cells. It has been previously shown in several cnidarian larvae that their neuronal cells contain the neurotransmitter, serotonin. The present study describes the peculiarities of serotonin‐like immunoreactive cells in Aurelia aurita (Scyphozoa) and Gonothyraea loveni (Hydrozoa) planulae. We show that several cells in the presumptive apical organ of A. aurita are immunoreactive to antibodies against serotonin, while G. loveni planulae have an accumulation of serotonin‐positive cells near the anterior pole. Additional serotonin‐like immunoreactive cells are found in the lateral ectoderm of both planulae. Treatment of A. aurita and G. loveni planulae with serotonin or its blockers show that serotonin is likely involved in the initiation of planula settlement.     

Elevated Temperature Alters the Lunar Timing of Planulation in the Brooding Coral Pocillopora damicornis

Reproductive timing in corals is associated with environmental variables including temperature, lunar periodicity, and seasonality. Although it is clear that these variables are interrelated, it remains unknown if one variable in particular acts as the proximate signaler for gamete and or larval release. Furthermore, in an era of global warming, the degree to which increases in ocean temperatures will disrupt normal reproductive patterns in corals remains unknown. Pocillopora damicornis, a brooding coral widely distributed in the Indo-Pacific, has been the subject of multiple reproductive ecology studies that show correlations between temperature, lunar periodicity, and reproductive timing. However, to date, no study has empirically measured changes in reproductive timing associated with increased seawater temperature. In this study, the effect of increased seawater temperature on the timing of planula release was examined during the lunar cycles of March and June 2012. Twelve brooding corals were removed from Hobihu reef in Nanwan Bay, southern Taiwan and placed in 23 and 28°C controlled temperature treatment tanks. For both seasons, the timing of planulation was found to be plastic, with the high temperature treatment resulting in significantly earlier peaks of planula release compared to the low temperature treatment. This suggests that temperature alone can influence the timing of larval release in Pocillopora damicornis in Nanwan Bay. Therefore, it is expected that continued increases in ocean temperature will result in earlier timing of reproductive events in corals, which may lead to either variations in reproductive success or phenotypic acclimatization.     

Lipid content of Favia fragum larvae: changes during planulation

Lipid content of planula larvae of the brooding scleractinian coral Favia fragum was analysed through a monthly planulation period. The average lipid content per dry weight of F. fragum planulae was 39%, which is low compared with other scleractinian coral species. Lipid content of planulae was significantly affected by the day of release and decreased during the planulation period.     

Planulation,larval biology,and early growth of the deep‐sea soft corals Gersemia fruticosa and Duva florida (Octocorallia: Alcyonacea)

Abstract. Although the reproductive biology and early life‐history stages of deep‐sea corals are poorly understood, such data are crucial for their conservation and management. Here, we describe the timing of larval release, planula behavior, metamorphosis, settlement, and early juvenile growth of two species of deep‐sea soft corals from the northwest Atlantic. Live colonies of Gersemia fruticosa maintained under flow‐through laboratory conditions released 79 planulae (1.5–2.5 mm long) between April and early June 2007. Peak planulation in G. fruticosa coincided with peaks in the chlorophyll concentration and deposition rates of planktic matter. Metamorphosis and settlement occurred 3–70 d post‐release. The eight primary mesenteries typically appeared within 24 h, and primary polyps grew to a height of ～6–10 mm and a stalk diameter of ～1 mm within 2–3 months. Planulae of Duva florida (1.5–2.5 mm long) were extracted surgically from several colonies and were successfully reared in culture. Primary polyps reached a height of ～3–4 mm within 2–3 months. No budding of primary polyps was observed in either species over 11–13 months of monitoring, suggesting a very slow growth rate.     

Synchronized release of medusae from three species of hydrozoan fire corals

 The release of medusae from three hydrozoan fire corals, Millepora dichotoma, M. murrayi and M. platyphylla, was investigated at three sites in southern Taiwan from February 1994 to July 1995. All three species were gonochoristic, and developed and released several batches of medusae between April and May. The duration of open ampulla appearing on the surface of coralla was short, about three months, and could be used to infer the reproductive season of the fire corals between April and May. No obvious lunar cycles of medusa release were found in these species. Medusa release started before dark at approximately 17:00 h and continued for several hours. Males began releasing medusae earlier than females. Synchronization of medusa release between colonies, i.e., the probability of occurring on the same nights, was significantly higher within a species than between different species. Hybridization in nature among the three species is, therefore, unlikely due to segregation in the spawning dates. Moreover, the synchronization within each species was often significantly higher within versus between sites. The free-swimming medusae released gametes within approximately one hour, and the spent medusae lived for a few more hours. Medusae may facilitate fertilization rates as a result of an apparently negatively geotactic swimming response that results in medusa aggregation at the surface. No differences in the sizes of medusae, eggs and sperm were detected among the three species; however, some characteristic differences of medusa nematocysts were found. Accepted: 25 September 1997     

Geographical variation in reproductive biology is obscured by the species problem: a new record of brooding in Porites cylindrica,or misidentification?

Little is known about the reproductive biology of corals from the Philippines, despite this archipelago being at the center of coral reef biodiversity. Here, we report on the reproductive biology of a branching poritid species provisionally identified as Porites cf. cylindrica in the Bolinao‐Anda reef complex (BARC), northwestern Philippines. Histological examination and ex situ planulation observations reveal P.cf. cylindrica colonies to be gonochoric brooders that release actively swimming zooxanthellate larvae. Planulation appeared to occur throughout the year and there was significant lunar periodicity in planular release. The mean peak of release occurred from the 25th to 29th lunar day or just before the new moon, while peak in diel timing in planulation occurred during daytime between 08:00–11:00 h. Elsewhere in the Pacific, Porites cylindrica colonies are reported to broadcast spawn. If our species identification is correct, then this is the first report of brooding in P. cylindrica. Although there are no apparent morphological differences between the coral in this study and P. cylindrica reported from other sites, an alternative explanation for our findings is that our provisionally identified Porites cf. cylindrica is a different species. If so, our findings further highlight how difficulties with species identification in corals can influence our understanding of geographical variation in reproductive biology.     

Reproductive biology, development, and planula behavior in the Caribbean gorgonian Pseudopterogorgia elisabethae

Abstract. The reproductive biology, development, and planula behavior of the gorgonian Pseudopterogorgia elisabethae were studied at 2 sites in the Bahamas between 1996 and 2001. Colonies were gonochoric, and females brooded planulae on the colony surface. Gonads were observed only in colonies 18 cm high or larger. Spawning was asynchronous within and between sites but was concentrated 2–10 days after the new moons from late November through early January. Fertilized eggs developed into planulae over 1–2 days and the planulae remained attached to the surface of the female colony for an additional 2–4 days. Planulae were negatively buoyant and field observations suggest that larvae may settle within tens of meters of the maternal colony. P. elisabethae is harvested for natural products, and information on the reproduction of this commercially important species is crucial to the understanding of its population biology and to the development of management plans for the conservation of the species.     

Reproductive biology of the Caribbean brooding octocoral Antillogorgia hystrix

The reproductive biology of the Caribbean gorgonian Antillogorgia hystrix was studied in the shallow‐water reefs of Cross Harbour, Great Abaco (The Bahamas) from 2009 to 2010. Antillogorgia hystrix is an internal brooder that reproduces annually. The population at Cross Harbour was gonochoric and the sex ratio was skewed toward females (~3:1). Oogenesis precedes spermatogenesis by several months, and lasts at least 9 months, with oocytes >100 μm in diameter first becoming visible in dissections of samples from February; mature oocytes are present in late October–November. The size of mature oocytes (400–900 μm in diameter) was greater than that of the spermaries, which were rarely larger than 400 μm. Brooded planulae were observed in polyps from early November to mid‐December, and planula release was observed in aquaria in December 2009, which suggests that planulation occurs continuously over this period. Planulae of A. hystrix contained dinoflagellate symbionts, presumably acquired during embryogenesis and/or by mature planulae while they were in the gastrovascular cavity of the polyp. Brooding is an uncommon reproductive strategy among Caribbean gorgonians and this is the first report of internal brooding in the genus Antillogorgia. The genus contains a number of sympatric species with different modes of reproduction, and knowledge of their reproductive biology is critical to understand their ecology and evolution.     

Contrasting reproductive strategies in three deep-sea octocorals from eastern Canada: Primnoa resedaeformis, Keratoisis ornata, and Anthomastus grandiflorus

Various aspects of reproduction were studied in three deep-sea octocorals belonging to the order Alcyonacea that co-occur at bathyal depths on the continental edge and the slope of eastern Canada. The main goals were to expand knowledge of deep-water heterotrophic corals and ascertain whether reproductive strategies could explain the known patterns of occurrence. Anthomastus grandiflorus is a gonochoric species with a female-biased sex ratio that exhibits internal fertilization and brooding of planula larvae. Conversely, Primnoa resedaeformis and Keratoisis ornata rely on broadcast spawning and external fertilization; their sexuality remains undetermined as spermatocysts were not found. In P. resedaeformis, the presence of mixed size classes of oocytes in samples from all months, depths, and locations studied suggests continuous oogenesis or overlapping development of oocyte cohorts, indicative of a gametogenic cycle spanning more than a year. No evidence of periodicity was found in this species, although it could have been masked by the striking bathymetric variation in potential relative fecundity (oocytes polyp⁻¹). The two other octocorals displayed a clear annual breeding pattern. Spawning in K. ornata and larval release in A. grandiflorus occurred in late summer and fall, respectively, possibly in response to environmental factors, as supported by shifts in the reproductive peak of A. grandiflorus across latitudes. The three species are presumed to share a nonfeeding larval mode, and data on their reproductive potential do not present any striking disparities. Published data on bycatches and video surveys in Atlantic Canada indicate that the gonochoric brooder A. grandiflorus is more widely distributed than the two free spawners, P. resedaeformis and K. ornata, which is contrary to common dispersal potential paradigms.     

Size variation of planulae and its effect on the lifetime of planulae in three pocilloporid corals

Dispersal of propagules plays an important role in the distribution of corals. Pocillopora damicornis, Seriatopora hystrix, and Stylophora pistillata are all brooders and release planulae having symbiotic zooxanthellae. Planulae showed a great size variation, especially at peaks of planulation, and we found negative correlations between zooxanthella density and planula size in S. hystrix and S. pistillata. Studies of the larval life of planulae under both light and dark conditions have revealed that larger planulae have a longer lifetime. When planulae of the same size were compared, it was found that they lived longer under light conditions than under dark conditions. These findings suggest that planulae utilize energy from photosynthetic products of zooxanthellae and that these corals enjoy long-distance dispersal by producing larger planulae with greater dispersal potential. It is conceivable that variation in the dispersal potential of planulae is a means of adaptation by which planulae can increase their chances of finding a suitable habitat.     

Reproduction and developmental pathways of Red Sea Xeniidae (Octocorallia,Alcyonacea)

This work on Red Sea alcyonaceans describes the reproductive patterns of 21 xeniid species. Gonochorism is the commonest sexual mode but simultaneous hermaphroditism was recorded in 4 species and brooding of planulae was observed in 15 species. The reproductive patterns of Xenia umbellata and Heteroxenia fuscescens were examined. X. umbellata exhibits seasonal spermatogenesis, continuous oogenesis and a 7 month period of planulation each year. H. fuscescens has continuous gametogenesis, and planulation occurs throughout the year, lacking any lunar pattern. The prolonged breeding season of H. fuscescens reflects intrapopulation asynchrony in larval development and subsequent maturation. Xeniids possess structurally similar gonads, but adopt diverse reproductive and developmental pathways.     

Reproductive cycles in tropical intertidal gastropods are timed around tidal amplitude cycles

Reproduction in iteroparous marine organisms is often timed with abiotic cycles and may follow lunar, tidal amplitude, or daily cycles. Among intertidal marine invertebrates, decapods are well known to time larval release to coincide with large amplitude nighttime tides, which minimizes the risk of predation. Such bimonthly cycles have been reported for few other intertidal invertebrates. We documented the reproduction of 6 gastropod species from Panama to determine whether they demonstrate reproductive cycles, whether these cycles follow a 2‐week cycle, and whether cycles are timed so that larval release occurs during large amplitude tides. Two of the species (Crepidula cf. marginalis and Nerita scabricosta) showed nonuniform reproduction, but without clear peaks in timing relative to tidal or lunar cycles. The other 4 species show clear peaks in reproduction occurring every 2 weeks. In 3 of these species (Cerithideopsis carlifornica var. valida, Littoraria variegata, and Natica chemnitzi), hatching occurred within 4 days of the maximum amplitude tides. Siphonaria palmata exhibit strong cycles, but reproduction occurred during the neap tides. Strong differences in the intensity of reproduction of Cerithideopsis carlifornica, and in particular, Littoraria variegata, between the larger and smaller spring tides of a lunar month indicate that these species time reproduction with the tidal amplitude cycle rather than the lunar cycle. For those species that reproduce during both the wet and dry seasons, we found that reproductive timing did not differ between seasons despite strong differences in temperature and precipitation. Overall, we found that most (4/6) species have strong reproductive cycles synchronized with the tidal amplitude cycle and that seasonal differences in abiotic factors do not alter these cycles.     

Inductive activity of the posterior tip of planula in the marine hydroid <Emphasis Type="Italic">Dynamena pumila</Emphasis>

Activity of organizer regions is required for body plan formation in the developing organism. Transplanting a fragment of such a region to a host organism leads to the formation of a secondary body axis that consists of both the donor’s and the host’s tissues (Gerhart, 2001). The subject of this study, the White Sea hydroid cnidarian Dynamena pumila L. (Thecaphora, Sertulariidae), forms morphologically advanced colonies in the course of complex metamorphosis of the planula larva. To reveal an organizer region, a series of experiments has been performed in which small fragments of donor planula tissues were transplanted to embryos at the early and late gastrula stage, as well as to planulae. Only transplantations of a posterior tip fragment of a donor planula to a host planula of the same age led, in the course of metamorphosis, to the formation of a secondary shoot, which involved up to 50% of the host’s tissues. After transplantations of tissue fragments of the anterior tip and the middle of the planula body, the formation of any ectopic structures was never observed. It was concluded that the posterior tip of the planula has organizer properties in Dynamena.     

Early Life History of the ‘Irukandji’ Jellyfish Carukia barnesi

Adult medusae of Carukia barnesi were collected near Double Island, North Queensland Australia. From 73 specimens, 8 males and 15 females spawned under laboratory conditions. These gametes were artificially mixed which resulted in fertilized eggs. Post fertilization, most eggs developed to an encapsulated planula stage and then paused for between six days and six months prior to hatching as ciliated planulae. The paused stage planulae were negatively buoyant and adhered to substrate. The first planula was produced six days post fertilization, lacked larval ocelli, remained stationary, or moved very slowly for two days prior to metamorphosis into primary polyps. Mature polyps reproduced through asexual reproduction via lateral budding producing ciliated swimming polyps, which in turn settled and developed into secondary polyps. Medusae production for this species was in the form of monodisc strobilation, which left behind polyps able to continue asexual reproduction.     

Cellular and intracellular pathways mediating the metamorphic stimulus in hydrozoan planulae

Summary Both the natural metamorphic stimulus (an unidentified bacterial product) and an artificial trigger of metamorphosis (Cs⁺) cause large calcium transients in planula cells of the hydrozoanMitrocomella polydiademata. When these transients are inhibited with calcium channel blockers, metamorphosis is also inhibited. All cells of theMitrocomella planula contain a calcium-specific photoprotein. The cells where the calcium transients occur during natural- and Cs⁺-induced metamorphosis have been visualized in normal and entoderm free planulae that lack ganglion cells, using a compound microscope coupled to an image intensifier and video camera. During bacteria- and Cs⁺-induced metamorphosis, groups of contiguous cells, occupying from about 10% to the entire visible surface of the planula, simultaneously exhibit calcium transients. When the cells that initiate a transient comprise only part of the planula surface, the calcium transient frequently propagates and can eventually involve every cell on the visible planula surface. There is no special site on the planula surface where calcium transients are more apt to be initiated. There is no indication that propagation of a flash in one direction is more likely than in another. The velocity of propagation is virtually the same in all directions. The only feature of the spatial distribution of bacteria- and Cs⁺-induced calcium transients that appears to be necessary for the induction of metamorphosis is that at least one transient must involve all of the surface cells of the planula. The spatial behavior of calcium transients is the same in entoderm free planulae (lacking ganglion cells) as in normal planulae. The propagation of these calcium transients most probably occurs via epithelial conduction. This metamorphic step involving calcium transients is probably the intercellular communication system that informs the cells of the planula that metamorphosis will commence.Metamorphosis inMitrocomella planulae can also be induced with phorbol esters. Calcium transients do not occur during phorbol ester-induced metamorphosis, indicating that they act at a different point in the metamorphic pathway. Calcium channel blockers do not inhibit phorbol ester-induced metamorphosis. Inhibitors of protein kinase-C, inhibit both phorbol ester-induced metamorphosis and Cs⁺- and bacteria-induced metamorphosis, but have no effect on the calcium transients induced by Cs⁺. This indicates that the calcium transient mediated step in the metamorphic pathway occurs prior to protein kinase-C activation. Calcium transients probably play a major role in activating protein kinase-C.     

The Embryonic Origin of Neurosensory Cells and the Role of Nerve Cells in Metamorphosis in Phialidium gregarium (Cnidaria,Hydrozoa)

Summary

The embryonic origin of the nervous system in Phialidium gregarium was investigated. Entoderm-free planulae, surgically produced by bisection at mid-gastrulation, and normal planulae were examined by light and electron microscopy to determine their cellular composition. The cell types that occur in the epidermis of the normal planula were described. The entoderm-free planulae were found to be devoid of interstitial cells and their derivatives, the nematocytes and ganglion cells. Neurosensory cells were present, however, indicating that they are derivatives of the ectodermal epithelium.

The role of nerve elements in the initiation of metamorphosis was also examined. Normal and entoderm-free planulae treated for four hours with 0.4% colchicine at two, three, or four days of development fail to undergo cesium-induced metamorphosis. Since such treatment in other hydrozoans eliminates interstitial cells and their derivatives [1-3], it might be argued that ganglion cells are necessary to initiate metamorphosis. The observation that entoderm-free planulae, devoid of interstitial cell derivatives, are capable of responding to induction by bacteria or cesium, however, indicates that in Phialidium the colchicine effect is on other cell types. The results are compared with findings for other Cnidaria.