Reproduction in the Mediterranean endemic gorgonian Spinimuricea klavereni (Anthozoa,Octocorallia, Plexauridae)

Spinimuricea klavereni is a Mediterranean endemic gorgonian that is rarely encountered, probably because it typically occurs at depths below 50 m. It is exceptionally common in the northern Marmara Sea, with an unusually shallow upper depth limit of ~20 m. The reproductive biology of this species was studied during a one year period off Büyükada, in the northeastern Marmara Sea. Spinimuricea klavereni is a gonochoric broadcast spawner with an almost even sex ratio. Colonies were ~15 cm in height at first reproduction. Gametogenesis was continuous, characterized by high male and female fecundities year‐round. Oocytes and sperm sacs of all developmental stages were found throughout the year, with small‐sized oocytes and sperm sacs dominant throughout the year. The reproduction of S. klavereni did not seem to exhibit any marked seasonal pattern, unlike most other studied Mediterranean octocorals. Modest variation in gamete output was probably related to slight alterations in food availability and temperature. The non‐seasonal reproductive pattern we observed may be related to the low intra‐annual variation in temperature in the Marmara Sea, and the fact that the mesotrophic‐eutrophic level of productivity in the Marmara Sea can support the energetic requirements of continuous gametogenesis in this gorgonian. Whether these patterns are local adaptations or intrinsic characteristics for this Mediterranean endemic species remains to be studied.     

Early Life History of Deep-Water Gorgonian Corals May Limit Their Abundance

Deep-water gorgonian corals are long-lived organisms found worldwide off continental margins and seamounts, usually occurring at depths of ∼200–1,000 m. Most corals undergo sexual reproduction by releasing a planktonic larval stage that disperses; however, recruitment rates and the environmental and biological factors influencing recruitment in deep-sea species are poorly known. Here, we present results from a 4-year field experiment conducted in the Gulf of Maine (northwest Atlantic) at depths >650 m that document recruitment for 2 species of deep-water gorgonian corals, Primnoa resedaeformis and Paragorgia arborea. The abundance of P. resedaeformis recruits was high, and influenced by the structural complexity of the recipient habitat, but very few recruits of P. arborea were found. We suggest that divergent reproductive modes (P. resedaeformis as a broadcast spawner and P. arborea as a brooder) may explain this pattern. Despite the high recruitment of P. resedaeformis, severe mortality early on in the benthic stage of this species may limit the abundance of adult colonies. Most recruits of this species (∼80%) were at the primary polyp stage, and less than 1% of recruits were at stage of 4 polyps or more. We propose that biological disturbance, possibly by the presence of suspension-feeding brittle stars, and limited food supply in the deep sea may cause this mortality. Our findings reinforce the vulnerability of these corals to anthropogenic disturbances, such as trawling with mobile gear, and the importance of incorporating knowledge on processes during the early life history stages in conservation decisions.     

Linking micromorphism,brooding, and hermaphroditism in brachiopods: Insights from Caribbean Argyrotheca (Brachiopoda)

In extant brachiopods, parental brooding of the larvae occurs exclusively within Rhynchonelliformea. Methods of larval protection range from simple retention of the larvae within the mantle cavity, to sophisticated brood care within highly specialized brood pouches found in Argyrotheca and Joania (Terebratulida, Megathyridoidea), Gwynia (Terebratulida, Gwynioidea), and all Thecideoidea (Thecideida). Previous studies on the reproductive biology of Argyrotheca yielded contrasting results on the epithelial origin of the brood pouches in this genus. Here, representatives of different species of Argyrotheca from the Belize Barrier Reef were examined using histological section series. Brood pouches of four species, A. cf. schrammi and Argyrotheca sp. 1–3, are of the same basic structure, formed by invaginations of the anterior body wall and connected to the visceral cavity via the metanephridia. The same four species are simultaneously hermaphroditic, suggesting that fertilization is achieved, at least partly, through selfing. One species, Argyrotheca rubrocostata, differs significantly from all others as it has no brood pouch and gonochoric gonads. Thus, the presence of brood pouches and simultaneous hermaphroditism are concluded to be correlated within Megathyridoidea and proposed to be homologous traits of Joania and several but not all species of Argyrotheca, questioning the monophyletic status of both genera. In contrast to the brood pouches of Thecideoidea, lophophoral epithelium is not involved in the formation of the pouches of Argyrotheca and Joania. Therefore, megathyridoid and thecideoid brood pouches are not homologous but evolved independently within rhynchonelliform brachiopods. All brachiopods with brood pouches share a micromorphic form and a short life span, limiting the space and time available for gamete and larval development. We suggest that the brood pouches and the hermaphroditic gonads of Argyrotheca spp. and Joania compensate these limitations by minimizing the loss of gametes and larvae, and by maximizing the chances of successful fertilization. J. Morphol., 2013. © 2013 Wiley Periodicals, Inc.     

Reproduction and the unusual condition of hermaphroditism in Sarcophyton glaucum (Octocorallia,Alcyoniidae) in KwaZulu-Natal,South Africa

The genus Sarcophyton is an abundant soft coral on the marginal, high-latitude reefs in KwaZulu-Natal. A 2-year study on reproduction in the most common species,S. glaucum, revealed that gametogenesis in male and female colonies takes 9–10 and 16–18 mo, respectively, in this gonochoric, seasonal, broadcast spawner. Gametogenesis and spawning are synchronised in and between colonies, and with other common soft corals on the reefs. Spawning occurs annually in March between full and new moon with the release of spermsacs and the mature oocytes, the smaller oocytes being retained for further development. Thus far, the reproductive attributes of S. glaucum are comparable with other studies on the genus. However, the KwaZulu-Natal population of S. glaucum manifested the unusual attribute of hermaphroditism in 9% of the colonies, these having Stage I and II spermaries and predominantly Stage III and IV oocytes in their polyps. Small numbers of Stage I and II oocytes indicated that such colonies may be simultaneous hermaphrodites but this could not be confirmed. The complex reproductive strategy and associated measure of hermaphroditism in S. glaucum on KwaZulu-Natal reefs are discussed in terms of the species’ recruitment success in this marginal, high-latitude environment.     

Reproductive system morphology of Lightiella magdalenina (Crustacea,Cephalocarida): functional and adaptive implications

The reproductive systems of adults and larvae of Lightiella magdalenina were examined. Lightiella magdalenina, similar to the best-known cephalocarida species Hutchinsoniella macracantha, is a simultaneous hermaphrodite. Although the morphology of their reproductive system is similar, L. magdalenina differs from H. macracantha in exhibiting reduced fecundity: it lays one egg, not two, per reproductive event. This is due to asynchronous development of the oocytes inside the paired female reproductive structures, which determines the maturation of a single egg at a time. The reduced fecundity of L. magdalenina could be offset by the precocious release of oocytes from the germarium, which begins the vitellogenetic process during the last larval stages. Due to this process, after their last moult, reproductive adults can have a large number of advanced vitellogenic oocytes, reducing the time required for their maturation. A possible adaptive relationship between the halved fecundity with pre- and post-hatching parental care is discussed.     

Apoptosis in the digestive tract of herbivorous Rana pipiens larvae and carnivorous Ceratophrys ornata larvae: An immunohistochemical study

The lifespan of herbivorous Rana pipiens larvae is ～3 months, while that of carnivorous Ceratophrys ornata larvae is only about 2 weeks. During metamorphic climax, the larval gut shortens dramatically, especially in R. pipiens, and its luminal epithelium is replaced by adult‐type epithelium. To determine when programmed cell death occurs during the metamorphic restructuring of the gut, we prepared cross‐sections of the stomach, small intestine, and large intestine from representative larval stages and from juvenile frogs of both species. The sections were incubated with monoclonal antibody against active caspase‐3, one of the key enzymes in the apoptotic cascade. We observed apoptosis in some luminal epithelial cells in each of the three regions of the larval gastrointestinal tract of both species. However, apoptotic cells appeared earlier in larval stages of R. pipiens than C. ornata and few were seen in juvenile frogs of either species. The results demonstrate the occurrence of apoptosis in the metamorphic remodeling of the gut of both R. pipiens larvae and C. ornata larvae. J. Morphol., 2011. © 2011 Wiley Periodicals, Inc.     

Density-dependent individual growth of marble trout (<Emphasis Type="Italic">Salmo marmoratus</Emphasis>) in the Soca and Idrijca river basins,Slovenia

The aim of this field study was to investigate effects of estimated fish- and sea urchin herbivory on the reproductive potential of four species of macroalgae; Halimeda macroloba (Decasine), H. renschii (Hauck), Turbinaria ornata (Turner) and Padina boergesenii (Allender et Kraft). Fish and sea urchin herbivory were calculated based on reported consumption rates for their biomass estimates. We hypothesized that reduced herbivory would increase algal size and the reproductive potential, which may promote algal recruitment and be one of the driving mechanisms behind algal shifts and persistent algae-dominated reefs. Algae were investigated in field sites where the estimated fish- and or sea urchin herbivory differed. Our results suggest that algal fecundity of T. ornata and P. boergesenii are positively correlated to their size. Fecundity of T. ornata was higher and individuals grew larger in areas where estimated fish herbivory was lower. The two species of Halimeda grew larger and had higher fecundity in areas where estimated sea urchin herbivory was lower. P. boergesenii responded ambiguously to patterns in herbivory. Due to species-specific responses to different herbivores, it is difficult to generalize about effects of overfishing on algal fecundity. Handling editor: S. Wellekens     

Apoptosis in larval and frog skin of Rana pipiens,R. catesbeiana,and Ceratophrys ornata

Apoptosis (programmed cell death) occurs during normal development of anurans in organs such as gills, gut, and tail. For example, apoptotic cells have been reported in the luminal epithelium along the length of the digestive tract of both larvae and frogs; however, timing of the peak number of such cells varies in different species. The purpose of the present study was to ascertain whether apoptosis also varies by species during metamorphic restructuring of the skin (as larval epithelium is replaced by adult epidermis). To determine this, cross‐sections of dorsal skin from representative larval stages and frogs of Rana pipiens, R. catesbeiana, and Ceratophrys ornata were incubated with monoclonal antibody against active caspase‐3, one of the main enzymes in the apoptotic cascade. We observed apoptotic cells in the epidermis of the skin of the three species and found that such cells were more numerous in larval stages than in frogs and more abundant in the two ranid species than in C. ornata. These results contribute to our understanding of metamorphic changes in anuran skin. J. Morphol. 275:51–56, 2014. © 2013 Wiley Periodicals, Inc.     

Sexual reproduction of Hawaiian black corals,with a review of the reproduction of antipatharians (Cnidaria: Anthozoa: Hexacorallia)

Abstract. Black corals (Cnidaria: Antipatharia) are ecologically important members of the sessile invertebrate fauna, but due to their typical deep‐water environments (>50 m), very little is known about their basic biology, including reproduction. We used histological techniques to examine the sexual reproduction of members of eight species of antipatharians collected from the Hawaiian Islands over a wide depth range (10–1327 m). Gametes of all species examined were found in association with the primary transverse mesenteries, which in some cases reached into the cavity of lateral tentacles. Specimens contained either spermatocysts or oocytes, but never both within the same individual, suggesting either a gonochoric or a sequentially hermaphroditic mode of reproduction. No developing embryos or larvae were observed in any of the samples, indicating that fertilization and larval development likely occur externally in the water column and not internally within polyps. We compared our results with previously published information on the sexual reproduction of antipatharians. Our review suggests that in antipatharians, more generally, (1) entire colonies are either female or male (although sequential hermaphroditism cannot be ruled out in most cases and has been reported previously for one species), (2) gametes are confined to the primary transverse mesenteries in most species, and (3) there is no evidence of internal fertilization. Further studies are needed to determine whether gonochorism or sequential hermaphroditism is more prevalent within the Antipatharia, whether dimorphic polyps occur within this taxonomic order, and to examine the reproductive seasonality and larval behavior of individual species.     

Insemination,intrafollicular fertilization and development of the fertilization plug during gestation in Heterandria formosa (Poeciliidae)

The viviparous teleost Heterandria formosa is a remarkable species for its reproductive characters including: (a) the smallest oocyte in viviparous fish species; (b) a high level of matrotrophy with a complex placenta; and (c) the highest level of superfetation. Superfetation involves (d) the continuous development of oocytes and fertilization at the same time with embryos in gestation. The sequential fertilization of oocytes requires (e) storage of spermatozoa in the ovary. Among these characteristics, fertilization is of fundamental interest, specifically the intrafollicular fertilization of poeciliids, species that do not present micropyle, and the consequent formation of the fertilization plug, a structure developed at the periphery of the follicle where the entrance of spermatozoa occurs. Both processes intrafollicular fertilization and formation of the fertilization plug have been rarely described. There is only one study illustrating, the fertilization plug of H. formosa with a drawing. In the context of reproductive aspects of H. formosa, the goal of this study is to describe the morphology of the ovary during insemination, intrafollicular fertilization and development of the fertilization plug. After insemination, spermatozoa enter the ovary and occupy folds of the lamella near follicles of all stages of oogenesis, the delle, where the germinal epithelium establishes contact with the follicular epithelium. The results of the present study provide evidence that both epithelia open at the distal end of the delle, this morphological change allow that the spermatozoa to make contact with the zona pellucida of the oocyte. After fertilization, the delle becomes blocked by proliferation of cells of the germinal epithelium, to form the fertilization plug that persists throughout gestation. Abundant reticular fibers and blood vessels are seen around the fertilization plug. Persistence of the fertilization plug suggests that it could be the site where the juvenile will gain entrance to the ovarian lumen during birth.     

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.     

Benthic ctenophore (Order Platyctenida) reproduction,recruitment, and seasonality in south Florida

Reproductive structures, modes, and seasonal patterns of size–class abundances are examined in two benthic platyctene (Family Coeloplanidae) ctenophore species present in dissimilar shallow marine environments in subtropical southeast Florida. Coeloplana waltoni, a minute (1–3 mm body length) epizoic associate of octocorals, occurs in exposed environments often under turbulent conditions, and Vallicula multiformis (2–10 mm) commonly occurs epiphytically on macroalgae in protected, calm‐water environments. Reproductive activity in C. waltoni is most active during the warm‐water summer season (June–October); gonadal development in V. multiformis occurs year‐round, and is most pronounced during sea‐warming periods in late spring (May) and late summer to early autumn (August–October), with release of cydippid larvae. Both species are hermaphroditic brooders, exhibiting paedogenesis (early gonadal development) at body lengths approximately one‐third (Coeloplana) to one‐sixth (Vallicula) of maximum adult size. Juvenile individuals (<0.6 mm) increased in abundance in C. waltoni during the summer reproductive period, and large (≥1 mm) pink‐colored individuals comprised 50% or more of samples from July through September. Seasonal abundance of gravid individuals and the timing of cydippid larval release in V. multiformis did not correspond closely with juvenile or adult population densities. Asexual fragmentation occurred in both ctenophore species, but was observed more frequently in individuals of V. multiformis. This asexual mode of reproduction probably accounted in part for the discordance between ctenophore abundances and larval recruitment events by sexual means. Morphological structures and behaviors associated with reproduction are described in this study. Uncommon images of reproductive products (gametes, embryos, larvae), spawning events, brooding, and asexual fragmentation are included, some for the first time in the published literature.     

Phenology of sexual reproduction in the common coral reef sponge,Carteriospongia foliascens

Understanding processes that contribute to population maintenance is critical to the management and conservation of species. Despite this, very little is currently known about the reproductive biology of Great Barrier Reef (GBR) sponge species. Here, we established reproductive parameters including mode of sexuality and development, seasonality, sex ratios, gametogenesis, reproductive output, and size at sexual maturity for the common phototrophic intertidal sponge, Carteriospongia foliascens, in the central GBR over two reproductive cycles. A population sexual productivity index (PoSPi) integrating key reproductive parameters was formulated to compare population larval supply over time. This study shows that C. foliascens is reproductive all year round, gonochoric and viviparous, with larvae developing asynchronously throughout the mesohyl. The influence of environmental parameters relevant to C. foliascens reproduction [i.e., sea surface temperature (SST), photoperiod, and rainfall] was also examined, and SST was found to have the most significant effect on phenology. C. foliascens reproduction exhibited annual mono-cyclic patterns closely resembling SST fluctuations. Reproductive output was depressed at low SST (<23 °C) and increased at temperatures above 23 °C. Peak sperm release occurred at temperatures above 25 °C, while peak larval release occurred during the annual temperature maxima (>28 °C). A twofold increase in maximum larval production (PoSPi) in C. foliascens was observed in the second reproductive cycle, following a depressed PoSPi in the first cycle. This reduction in PoSPi in the first reproductive cycle was associated with elevated SST and rainfall, coinciding with one of the strongest La Niña events on record.     

Differences in reproductive strategies between obscure puffer Takifugu obscurus and ocellated puffer Takifugu ocellatus during their spawning migration

Reproductive strategies were compared between obscure puffer Takifugu obscurus and ocellated puffer Takifugu ocellatus captured in waters near Yangzhong Island in the lower reaches of the Yangtze River during the spawning migration season from February to June in two consecutive years (1995 and 1996). Results showed that obscure puffer and ocellated puffer have adopted different reproductive strategies, including different spawning times, different size at maturity, and different number and size of oocytes, resulting in two different larval sizes. In detail, the timing of the spawning migration and status of gonad development of obscure puffer was about 1 month earlier than that of ocellated puffer; the obscure puffer was obviously longer and heavier than ocellated puffer in both mature male and female fish; mean GSI of obscure puffer females (15.8%) was significantly higher than that of ocellated puffer females (14.6%); the average diameter of ocellated puffer eggs (1.49 ± 0.12 mm) was significantly larger than that of the obscure puffer (1.22 ± 0.08 mm); and obscure puffer females (320.8 oocytes mg^?1 somatic wet weight) had significantly higher relative fecundity than ocellated puffer females (125.2 oocytes mg^?1 somatic wet weight). These differences in reproductive strategies between two closely related species of the Takifugu genus indicate that both obscure puffer and ocellated puffer fit the r/K dichotomy. Obscure puffer shows K‐selected characters with maturity at relatively large size and r‐selected characters with relatively many and small offspring, whereas ocellated puffer shows r‐selected characters with maturity at a relatively small size and K‐selected characters with relatively few and large offspring.     

Sperm morphology of scleractinians from the Caribbean

This study compares the sperm morphology of 2 hermaphroditic (Diploria strigosa, Montastrea annularis) and 2 gonochoric (Siderastrea siderea, Dendrogyra cylindrus) Caribbean reef corals. The spermatozoa of the gonochoric species are morphologically more specialized than those of the hermaphrodites. The cytological differences are apparent in the formation of a Spitzenkörper and pro-acrosomal vesicles, a mitochondrial mass (Nebenkern) and a large lipid vesicle in the gonochorists studied. Harrison (1985) first demonstrated that sperm morphology is correlated with sexual reproductive pattern and systematic position in scleractinian corals, and this is supported by the results of this study. The possible functional and phylogenetic bases of sperm morphology are discussed and a brief outline is given of further studies required.     

The reproductive system of Osedax (Annelida,Siboglinidae): ovary structure,sperm ultrastructure,and fertilization mode

Osedax is a genus of siboglinid annelids in which the females live on dead vertebrate bones on the seafloor. These females have a posterior end that lies within the bone and contains the ovarian tissue, as well as the “roots” involved with bone degradation and nutrition. The males are microscopic and live as “harems” in the lumen of the gelatinous tube that surrounds the female trunk, well away from the ovary. Females are known to spawn fertilized primary oocytes, suggesting internal fertilization. However, little is known about sperm transfer, sperm storage, or the location of fertilization, and the morphology of the female reproductive system has not been described and compared with the reproductive systems of other siboglinids. A 3D‐reconstruction of the ovisac of Osedax showed ovarian tissue with multiple lobes and mature oocytes stored in a “uterus” before being released through the single oviduct. The oviduct emerges as a gonopore on the trunk and travels along the trunk to finally open to the seawater as a thin cylindrical tube among the crown of palps. Light and transmission electron microscopy of mature Osedax sperm revealed elongate heads consisting of a nucleus with helical grooves occupied by mitochondria. In contrast to other Siboglinidae, Osedax sperm are not packaged into spermatophores or spermatozeugmata, and Osedax females lack a discrete region for sperm storage. Transmission electron microscopy and fluorescence microscopy allowed detection of sperm associated with ovarian tissue of the female ovisac of four different Osedax species. This provides the first evidence for the site of internal fertilization in Osedax. A heart body was found in the circulatory system, as seen in other siboglinids and some other annelids. The possible presence of nephridia in the anterior ovisac region was also documented. These morphological features provide new insights for comparing the regionalization of Osedax females in relation to other siboglinids.     

Temporal variation in gametogenic cycles of vesicomyid clams

Summary

Sulfide-rich cold seeps in Monterey Canyon support dense communities of vesicomyid clams, which harbor chemosynthetic bacterial endosymbionts. Because these animals rely upon non-photosynthetic food sources, their life histories may be decoupled from seasonal phytoplankton productivity. We examined this hypothesis by investigating temporal changes in gametogenesis in two vesicomyid clam species. Clams were collected from two cold seeps (600 m and 900 m depths), and their gonads were removed and processed for histological analyses. Oocyte diameters and relative abundances of tissue types were measured in thin sections taken across the gonad. Mean oocyte diameters of Calyptogena kilmeri increased from August to November, 1994, but did not change by March, 1995. Relative proportions of ovarian tissue types (reproductive vs. somatic) also changed during this period, indicating reproductive seasonality. Analyses of Calyptogena pacifica tissues showed no significant change within a 3-month period. Existence of seasonal cycles for vesicomyid clams suggests that either (1) chemosynthetic production is seasonal or (2) reproductive output is tied to factors other than food production, such as synchrony of spawning to maximize fertilization success, or larval survival.     

Biology of the exotic zebra mussel,Dreissena polymorpha,in relation to native bivalves and its potential impact in Lake St. Clair

The zebra mussel, Dreissena polymorpha, is a new exotic species that was introduced into the Great Lakes as early as the fall of 1985. It differs markedly from native species of bivalves in its: (i) shell form; (ii) mode of life; (iii) reproductive potential; (iv) larval life cycle; (v) population dynamics; (vi) distribution, (vii) dispersal mechanisms; (viii) physiology; (ix) potential impact on the ecosystem; and (x) impact on society and the economy. In body form, it has an anterior umbone, a flat ventral surface with permanent aperature for the byssal apparatus and a shape that together make the animal well adapted for life on a hard surface. The shell has a zebra-stripe pattern, a heteromyarian muscle condition and lacks hinge teeth which make it easily identifiable from native bivalves. The zebra mussel is strongly byssate and has an epifaunal mode of life not seen in native bivalves. The species is dioecious and has external fertilization, the eggs developing into pelagic veligers which remains planktonic for approximately 4 weeks. Gametogenesis begins in late winter to early spring, veligers appear in the water column in late May to early June and disappear in mid to late October in Lake St. Clair. Adults live for about 2 years and have very rapid growth rates. Maximum shell lengths average 2.3 to 2.5 cm. Standing crops as high as 200 000 m^-2 are present in the 1-m depths of the Ontario shores. Infestations may be interfering with the normal metabolism of native unionid clams and there is potential of the unionid clam populations being reduced or even eliminated from Lake St. Clair.     

ONTOGENETIC CHANGES IN BUOYANCY,BREAKING STRENGTH,EXTENSIBILITY, AND REPRODUCTIVE INVESTMENT IN A DRIFTING MACROALGA TURBINARIA ORNATA (PHAEOPHYTA)1

Turbinaria ornata (Turner) J. Agardh is a tropical alga that disperses by detached, reproductively mature floating fronds. Material properties (breaking stress, breaking extension), buoyancy, and the proportion of reproductive tissue per frond were measured for juvenile, adult, and old fronds of T. ornata. Correlations between these factors indicate that as fronds age and become more reproductively mature, the tissue in their stipes (where they break) becomes weaker, more brittle, and the overall buoyancy of the frond increases. Measurement of drag force experienced by fronds from each ontogenetic stage allowed calculation of the environmental stress factor (ESF), which indicates the likelihood of detachment of a frond in the flow environment of its habitat. The ESF for fronds of each ontogenetic stage predicted that reproductively mature fronds (adult and old) break more readily than immature (juvenile) fronds. Increased proportions of reproductively mature fronds in floating rafts following storms compared with the proportion of mature fronds attached to the substratum support the ESF predictions. This combination of ontogenetic changes in material properties, buoyancy, and reproductive maturity in combination with the life history of T. ornata may contribute to the dispersal of this alga throughout French Polynesia.