Larval Settlement: The Role of Surface Topography for Sessile Coral Reef Invertebrates

For sessile marine invertebrates with complex life cycles, habitat choice is directed by the larval phase. Defining which habitat-linked cues are implicated in sessile invertebrate larval settlement has largely concentrated on chemical cues which are thought to signal optimal habitat. There has been less effort establishing physical settlement cues, including the role of surface microtopography. This laboratory based study tested whether surface microtopography alone (without chemical cues) plays an important contributing role in the settlement of larvae of coral reef sessile invertebrates. We measured settlement to tiles, engineered with surface microtopography (holes) that closely matched the sizes (width) of larvae of a range of corals and sponges, in addition to surfaces with holes that were markedly larger than larvae. Larvae from two species of scleractinian corals (Acropora millepora and Ctenactis crassa) and three species of coral reef sponges (Luffariella variabilis, Carteriospongia foliascens and Ircinia sp.,) were used in experiments. L. variabilis, A. millepora and C. crassa showed markedly higher settlement to surface microtopography that closely matched their larval width. C. foliascens and Ircinia sp., showed no specificity to surface microtopography, settling just as often to microtopography as to flat surfaces. The findings of this study question the sole reliance on chemical based larval settlement cues, previously established for some coral and sponge species, and demonstrate that specific physical cues (surface complexity) can also play an important role in larval settlement of coral reef sessile invertebrates.     

Profiling gene expression responses of coral larvae (Acropora millepora) to elevated temperature and settlement inducers using a novel RNA-Seq procedure

Elevated temperatures resulting from climate change pose a clear threat to reef-building corals; however, the traits that might influence corals' survival and dispersal during climate change remain poorly understood. Global gene expression profiling is a powerful hypothesis-forming tool that can help elucidate these traits. Here, we applied a novel RNA-Seq protocol to study molecular responses to heat and settlement inducers in aposymbiotic larvae of the reef-building coral Acropora millepora. This analysis of a single full-sibling family revealed contrasting responses between short- (4-h) and long-term (5-day) exposures to elevated temperatures. Heat shock proteins were up-regulated only in the short-term treatment, while the long-term treatment induced the down-regulation of ribosomal proteins and up-regulation of genes associated with ion transport and metabolism (Ca(2+) and CO(3)(2-)). We also profiled responses to settlement cues using a natural cue (crustose coralline algae, CCA) and a synthetic neuropeptide (GLW-amide). Both cues resulted in metamorphosis, accompanied by differential expression of genes with known developmental roles. Some genes were regulated only by the natural cue, which may correspond to the recruitment-associated behaviour and morphology changes that precede metamorphosis under CCA treatment, but are bypassed under GLW-amide treatment. Validation of these expression profiles using qPCR confirmed the quantitative accuracy of our RNA-Seq approach. Importantly, qPCR analysis of different larval families revealed extensive variation in these responses depending on genetic background, including qualitative differences (i.e. up-regulation in one family and down-regulation in another). Future studies of gene expression in corals will have to address this genetic variation, which could have important adaptive consequences for corals during global climate change.     

Characterization of a natural inducer of coral larval metamorphosis

External chemical signals used by scleractinian corals to recognize suitable substrata for larval settlement and metamorphosis were identified from crustose coralline red algae (CCA). A fragment of coral rubble with CCA induced larval metamorphosis of the scleractinian coral Pseudosiderastrea tayamai. A natural inducer and compounds that enhanced its effect in larval metamorphosis were isolated from the methanol extracts of coral rubble with CCA. A bromotyrosine derivative, 11-deoxyfistularin-3 (10^− 7 M) isolated from the CCA, induced the metamorphosis of P. tayamai larvae (27.5 ± 24.0%). In the presence of fucoxanthinol (10^− 9 M) and fucoxanthin (10^− 9 M), the percentage of metamorphosis induced by the bromotyrosine derivative was further enhanced to 87.8 ± 13.0 and 88.4 ± 17.8%, respectively. Both carotenoids are also found in the coral rubble with CCA. These results suggest that bromotyrosine derivative and carotenoids have a synergistic effect in the metamorphosis of P. tayamai larvae. The synergistic effect provides a higher selectivity for recruitment than a single-component natural inducer for recognizing suitable substrata for larval metamorphosis. Thus, the effect might offer a survival advantage for benthic marine invertebrates.     

Pharmacological induction of larval settlement and metamorphosis in the blue mussel Mytilus edulis L

The blue mussel Mytilus edulis L. is an important aquaculture and fouling species in northern seas. Although the general role of chemical cues for settlement of larvae of the blue mussel has been proposed, few studies have focused on induction of settlement and metamorphosis by pharmacological agents. In this study, the induction of larval settlement of the blue mussel by pharmacological compounds was investigated through a series of laboratory experiments with an aim of identifying artificial cues for laboratory bioassay systems in fouling and antifouling research. Gamma-aminobutiric acid (GABA), dihydroxyphenyl L-alanine (DOPA), isobutyl methylxanthine (IBMX) and acetylcholine chloride (ACH) at 10(-7)-10(-2) M as well as KCl at 10-40 mM K+ in excess of the level in normal seawater were tested for their inductive effect on larval settlement. In filtered seawater (FSW) < 9% of the larvae settled after 48 h. Elevated K+ and GABA levels had no effect on larval settlement and metamorphosis. DOPA at 10(-5) M and IBMX at 10(-6)-10(-4) M induced 41-83% larval settlement and ACH at 10(-7)-10(-5) M induced < 40% larval settlement. While the highest settlement rates were observed after 48 h exposure to the chemical, most of the larvae settled within 24 h. Compounds at concentrations of 10(-3)-10(-2) M were either toxic to larvae or retarded the growth of the post-larvae shell. Juveniles resulting from induction by lower concentrations of chemicals had a very high survival rate, completed metamorphosis and grew as well as the juveniles that metamorphosed spontaneously. IBMX at 10(-6)-10(-4) M and L-DOPA at 10(-5) M are effective agents for induction of settlement and metamorphosis for future studies using juvenile M. edulis.     

Coral larvae under ocean acidification: survival, metabolism, and metamorphosis

Ocean acidification may negatively impact the early life stages of some marine invertebrates including corals. Although reduced growth of juvenile corals in acidified seawater has been reported, coral larvae have been reported to demonstrate some level of tolerance to reduced pH. We hypothesize that the observed tolerance of coral larvae to low pH may be partly explained by reduced metabolic rates in acidified seawater because both calcifying and non-calcifying marine invertebrates could show metabolic depression under reduced pH in order to enhance their survival. In this study, after 3-d and 7-d exposure to three different pH levels (8.0, 7.6, and 7.3), we found that the oxygen consumption of Acropora digitifera larvae tended to be suppressed with reduced pH, although a statistically significant difference was not observed between pH conditions. Larval metamorphosis was also observed, confirming that successful recruitment is impaired when metamorphosis is disrupted, despite larval survival. Results also showed that the metamorphosis rate significantly decreased under acidified seawater conditions after both short (2 h) and long (7 d) term exposure. These results imply that acidified seawater impacts larval physiology, suggesting that suppressed metabolism and metamorphosis may alter the dispersal potential of larvae and subsequently reduce the resilience of coral communities in the near future as the ocean pH decreases.     

Antifouling properties of 10beta-formamidokalihinol-A and kalihinol A isolated from the marine sponge Acanthella cavernosa

Many soft-bodied sessile marine invertebrates such as sponges and soft corals defend themselves against fouling directly through the production of antifouling compounds, or indirectly through regulating the epibiotic microbes that affect larval settlement. In this study, 10beta-formamidokalihinol-A and kalihinol A were isolated and purified from the marine sponge Acanthella cavernosa (Dendy). The results indicated that both compounds inhibited the growth of bacteria isolated from the natural environment whereas kalihinol A suppressed larval settlement of a major fouling polychaete, Hydroides elegans with an EC50 of 0.5 microg ml(-1). Kalihinol A was incorporated in Phytagel that was exposed to the bacterial consortia in natural seawater for biofilm formation. Biofilms that developed on the Phytagel surfaces were analysed for bacterial abundance and bacterial species composition using a DNA fingerprinting technique, terminal restriction fragment length polymorphism (T-RFLP). The results showed that kalihinol A only slightly reduced bacterial abundance (t-test, p = 0.0497), but modified the bacterial species composition of the biofilms. Inhibition of H. elegans larval settlement was observed when biofilms developed under the influence of kalihinol A were exposed to larvae, suggesting that compounds like kalihinol A from the sponge A. cavernosa may change bacterial community composition on the sponge surface, which in turn, modulates larval settlement of fouling organisms.     

Induction of larval metamorphosis of the coral Acropora millepora by tetrabromopyrrole isolated from a Pseudoalteromonas bacterium

The induction of larval attachment and metamorphosis of benthic marine invertebrates is widely considered to rely on habitat specific cues. While microbial biofilms on marine hard substrates have received considerable attention as specific signals for a wide and phylogenetically diverse array of marine invertebrates, the presumed chemical settlement signals produced by the bacteria have to date not been characterized. Here we isolated and fully characterized the first chemical signal from bacteria that induced larval metamorphosis of acroporid coral larvae (Acropora millepora). The metamorphic cue was identified as tetrabromopyrrole (TBP) in four bacterial Pseudoalteromonas strains among a culture library of 225 isolates obtained from the crustose coralline algae Neogoniolithon fosliei and Hydrolithon onkodes. Coral planulae transformed into fully developed polyps within 6 h, but only a small proportion of these polyps attached to the substratum. The biofilm cell density of the four bacterial strains had no influence on the ratio of attached vs. non-attached polyps. Larval bioassays with ethanolic extracts of the bacterial isolates, as well as synthetic TBP resulted in consistent responses of coral planulae to various doses of TBP. The lowest bacterial density of one of the Pseudoalteromonas strains which induced metamorphosis was 7,000 cells mm(-2) in laboratory assays, which is on the order of 0.1-1% of the total numbers of bacteria typically found on such surfaces. These results, in which an actual cue from bacteria has been characterized for the first time, contribute significantly towards understanding the complex process of acroporid coral larval settlement mediated through epibiotic microbial biofilms on crustose coralline algae.     

Less inhibited with age? Larval age modifies responses to natural settlement inhibitors

As larvae of marine invertebrates age, their response to settlement cues can change. This change can have significant consequences to both the ecology of these organisms, and to their response to antifouling coatings. This study examines how larval age affects the settlement response of larvae to two naturally derived settlement inhibitors, non-polar extracts from the algae Delisea pulchra and Dilophus marginatus, the former of which contains compounds that are in commercial development as antifoulants. Two species of marine invertebrates with non-feeding larvae were investigated: the bryozoans Watersipora subtorquata and Bugula neritina. Larval age strongly affected larval settlement, with older larvae settling at much higher rates than younger larvae. Despite having strong, inhibitory effects on young larvae, the non-polar extracts did not inhibit the settlement of older larvae to the same degree for both species studied. The results show that the effects of ecologically realistic settlement inhibitors are highly dependent on larval age. Given that the age of settling larvae is likely to be variable in the field, such age specific variation in settlement response of larvae may have important consequences for host-epibiont interactions in natural communities.     

Settlement induction of Acropora palmata planulae by a GLW-amide neuropeptide

Complex environmental cues dictate the settlement of coral planulae in situ; however, simple artificial cues may be all that is required to induce settlement of ex situ larval cultures for reef re-seeding and restoration projects. Neuropeptides that transmit settlement signals and initiate the metamorphic cascade have been isolated from hydrozoan taxa and shown to induce metamorphosis of reef-building Acropora spp. in the Indo-Pacific, providing a reliable and efficient settlement cue. Here, the metamorphic activity of six GLW-amide cnidarian neuropeptides was tested on larvae of the Caribbean corals Acropora palmata, Montastraea faveolata and Favia fragum. A. palmata planulae were induced to settle by the exogenous application of the neuropeptide Hym-248 (concentrations ≥1 × 10⁻⁶ M), achieving 40–80% attachment and 100% metamorphosis of competent planulae (≥6 days post-fertilization) during two spawning seasons; the remaining neuropeptides exhibited no activity. Hym-248 exposure rapidly altered larval swimming behavior (<1 h) and resulted in >96% metamorphosis after 6 h. In contrast, M. faveolata and F. fragum planulae did not respond to any GLW-amides tested, suggesting a high specificity of neuropeptide activators on lower taxonomic scales in corals. Subsequent experiments for A. palmata revealed that (1) the presence of a biofilm did not enhance attachment efficiency when coupled with Hym-248 treatment, (2) neuropeptide-induced settlement had no negative effects on early life-history developmental processes: zooxanthellae acquisition and skeletal secretion occurred within 12 days, colonial growth occurred within 36 days, and (3) Hym-248 solutions maintained metamorphic activity following storage at room temperature (10 days), indicating its utility in remote field settings. These results corroborate previous studies on Indo-Pacific Acropora spp. and extend the known metamorphic activity of Hym-248 to Caribbean acroporids. Hym-248 allows for directed and reliable settlement of larval cultures and has broad applications to the study and rehabilitation of threatened Acropora populations in the Caribbean.     

Articulated coralline algae of the genus Amphiroa are highly effective natural inducers of settlement in the tropical abalone Haliotis asinina

The initiation of metamorphosis in marine invertebrates is strongly linked to the environment. Planktonic larvae typically are induced to settle and metamorphose by external cues such as coralline algae (Corallinaceae, Rhodophyta). Although coralline algae are globally abundant, invertebrate larvae of many taxa settle in response to a very limited suite of species. This specificity impacts population structure, as only locations with the appropriate coralline species can attract new recruits. Abalone (Gastropoda, Haliotidae) are among those taxa in which closely related species are known to respond to different coralline algae. Here we identify highly inductive natural cues of the tropical abalone Haliotis asinina. In contrast to reports for other abalone, the greatest proportion of H. asinina larvae are induced to settle and metamorphose (92.8% to 100% metamorphosis by 48 h postinduction) by articulated corallines of the genus Amphiroa. Comparison with field distribution data for different corallines suggests larvae are likely to be settling on the seaward side of the reef crest. We then compare the response of six different H. asinina larval families to five different coralline species to demonstrate that induction by the best inductive cue (Amphiroa spp.) effectively extinguishes substantial intraspecific variation in the timing of settlement.     

Convergent Antifouling Activities of Structurally Distinct Bioactive Compounds Synthesized Within Two Sympatric Haliclona Demosponges

A wide range of sessile and sedentary marine invertebrates synthesize secondary metabolites that have potential as industrial antifoulants. These antifoulants tend to differ in structure, even between closely related species. Here, we determine if structurally divergent secondary metabolites produced within two sympatric haliclonid demosponges have similar effects on the larvae of a wide range of benthic competitors and potential fouling metazoans (ascidians, molluscs, bryozoans, polychaetes, and sponges). The sponges Haliclona sp. 628 and sp. 1031 synthesize the tetracyclic alkaloid, haliclonacyclamine A (HA), and the long chain alkyl amino alcohol, halaminol A (LA), respectively. Despite structural differences, HA and LA have identical effects on phylogenetically disparate ascidian larvae, inducing rapid larval settlement but preventing subsequent metamorphosis at precisely the same stage. HA and LA also have similar effects on sponge, polychaete, gastropod and bryozoan larvae, inhibiting both settlement and metamorphosis. Despite having identical roles in preventing fouling and colonisation, HA and LA differentially affect the physiology of cultured HeLa human cells, indicating they have different molecular targets. From these data, we infer that the secondary metabolites within marine sponges may emerge by varying evolutionary and biosynthetic trajectories that converge on specific ecological roles.     

The chemical cue tetrabromopyrrole from a biofilm bacterium induces settlement of multiple Caribbean corals

Microbial biofilms induce larval settlement for some invertebrates, including corals; however, the chemical cues involved have rarely been identified. Here, we demonstrate the role of microbial biofilms in inducing larval settlement with the Caribbean coral Porites astreoides and report the first instance of a chemical cue isolated from a marine biofilm bacterium that induces complete settlement (attachment and metamorphosis) of Caribbean coral larvae. Larvae settled in response to natural biofilms, and the response was eliminated when biofilms were treated with antibiotics. A similar settlement response was elicited by monospecific biofilms of a single bacterial strain, Pseudoalteromonas sp. PS5, isolated from the surface biofilm of a crustose coralline alga. The activity of Pseudoalteromonas sp. PS5 was attributed to the production of a single compound, tetrabromopyrrole (TBP), which has been shown previously to induce metamorphosis without attachment in Pacific acroporid corals. In addition to inducing settlement of brooded larvae (P. astreoides), TBP also induced larval settlement for two broadcast-spawning species, Orbicella (formerly Montastraea) franksi and Acropora palmata, indicating that this compound may have widespread importance among Caribbean coral species.     

Metamorphic Competence, a Major Adaptive Convergence in Marine Invertebrate Larvae

Larvae from diverse marine-invertebrate phyla are able to respondrapidly to environmental cues to settlement and to undergo veryrapid metamorphic morphogenesis because they share the developmentaltrait of metamorphic competence. The competent state, characteristicof larvae as diverse as those of cnidarian planulae, molluscanveligers, and barnacle cyprids, is one in which nearly all requisitejuvenile characters are present in the larva prior to settlement.Thus metamorphosis, in response to more or less specific environmentalcues (inducers), is mainly restricted to loss of larva-specificstructures and physiological processes. Competent larvae oftwo "model marine invertebrates" studied in the authors' laboratory,the serpulid polychaete Hydroides elegans and the nudibranchPhestilla sibogae, complete metamorphosis in about 12 and 20hr, respectively. Furthermore, little or no de novo gene actionappears to be required during the metamorphic induction processin these species. Contrasting greatly with the slow, hormonallyregulated metamorphic transitions of vertebrates and insects,competence and consequent rapid metamorphosis in marine invertebratelarvae are conjectured to have arisen in diverse phylogeneticclades because they allow larvae to continue to swim and feedin the planktonic realm while simultaneously permitting extremelyfast morphological transition from larval locomotory and feedingmodes to a different set of such modes that are adaptive tolife on the sea bottom.     

Ontogenetic changes in responses to settlement cues by Anemonefish

Population connectivity for most marine species is dictated by dispersal during the pelagic larval stage. Although reef fish larvae are known to display behavioral adaptations that influence settlement site selection, little is known about the development of behavioral preferences throughout the larval phase. Whether larvae are attracted to the same sensory cues throughout their larval phase, or exhibit distinct ontogenetic shifts in sensory preference is unknown. Here, we demonstrate an ontogenetic shift in olfactory cue preferences for two species of anemonefish, a process that could aid in understanding both patterns of dispersal and settlement. Aquarium-bred na?ve Amphiprion percula and A. melanopus larvae were tested for olfactory preference of relevant reef-associated chemical cues throughout the 11-day pelagic larval stage. Age posthatching had a significant effect on the preference for olfactory cues from host anemones and live corals for both species. Preferences of olfactory cues from tropical plants of A. percula, increased by approximately ninefold between hatching and settlement, with A. percula larvae showing a fivefold increase in preference for the olfactory cue produced by the grass species. Larval age had no effect on the olfactory preference for untreated seawater over the swamp-based tree Melaleuca nervosa, which was always avoided compared with blank seawater. These results indicate that reef fish larvae are capable of utilizing olfactory cues early in the larval stage and may be predisposed to disperse away from reefs, with innate olfactory preferences drawing newly hatched larvae into the pelagic environment. Toward the end of the larval phase, larvae become attracted to the olfactory cues of appropriate habitats, which may assist them in identification of and navigation toward suitable settlement sites.     

Larval settlement preferences and post-settlement survival of the threatened Caribbean corals Acropora palmata and A. cervicornis

The settlement specificity of two threatened Caribbean corals, Acropora palmata and A. cervicornis, was tested by measuring their rates of larval metamorphosis in response to crustose coralline algae (CCA) and other substrata. In the no-choice experiments, the coral larvae were placed in six treatments: filtered seawater (FSW), a fragment of biofilmed dead skeleton of A. palmata, or a fragment of one of four species of CCA (Hydrolithon boergesenii, Porolithon pachydermum, Paragoniolithon solubile, and Titanoderma prototypum). Within each CCA treatment, there were three different substrata on which to settle and metamorphose: (1) the CCA surface, (2) the rock under the CCA, or (3) the plastic dish. The 5-day-old larvae of both A. palmata and A. cervicornis had similar rates of total metamorphosis (all substrata combined) in every treatment (excluding FSW) even in the absence of CCA. However, there were differences in larval behavior among the CCA species since the larvae settled and metamorphosed on different substrata in the presence of different CCA species. In the no-choice experiments the larvae of both corals had higher rates of metamorphosis on the top surfaces of H. boergesenii and/or T. prototypum than on P. pachydermum. In the choice experiments, the coral larvae were offered two species of CCA in the same dish. When given a choice, both species of coral larvae had more settlement and metamorphosis on the surface of H. boergesenii or T. prototypum or clean rock than onto the surface of P. solubile. After 6 weeks in the field, transplanted A. palmata recruits had approximately 15% survival on both T. prototypum and H. boergesenii, but A. cervicornis recruits only survived on T. prototypum (13%). Some, but not all, CCA species facilitated the larval settlement and post-settlement survival of these two threatened corals, highlighting the importance of benthic community composition for successful coral recruitment.     

The effects of the excretory-secretory products of fouling organisms on settlement of larvae of the sponge Halichondria panicea (Pallas, 1766) (Porifera: Demospongiae)

The effects of the excretory-secretory products (ESPs) of several fouling organisms on the larvae of the sponge Halichondria panicea were assessed in laboratory experiments. The ESPs of the brown alga Laminaria saccharina significantly stimulated larval settlement and metamorphosis, while the metabolites excreted by conspecific adult colonies were harmful to H. panicea larvae. The ESPs of the ascidians Styela rustica and Molgula citrina and the blue mussel Mytilus edulis impeded both the settlement and metamorphosis of the sponge larvae to varying degrees. The chemical cues of the bivalve Hiatella arctica had no significant effect on the number of settled larvae of H. panicea but retarded their metamorphosis.     

Differences in heat shock protein 70 expression during larval and early spat development in the Eastern oyster, Crassostrea virginica (Gmelin, 1791)

For a variety of species, changes in the expression of heat shock proteins (HSP) have been linked to key developmental changes, i.e., gametogenesis, embryogenesis, and metamorphosis. Many marine invertebrates are known to have a biphasic life cycle where pelagic larvae go through settlement and metamorphosis as they transition to the benthic life stage. A series of experiments were run to examine the expression of heat shock protein 70 (HSP 70) during larval and early spat (initial benthic phase) development in the Eastern oyster, Crassostrea virginica. In addition, the impact of thermal stress on HSP 70 expression during these early stages was studied. C. virginica larvae and spat expressed three HSP 70 isoforms, two constitutive, HSC 77 and HSC 72, and one inducible, HSP 69. We found differences in the expression of both the constitutive and inducible forms of HSP 70 among larval and early juvenile stages and in response to thermal stress. Low expression of HSP 69 during early larval and spat development may be associated with the susceptibility of these stages to environmental stress. Although developmental regulation of HSP 70 expression has been widely recognized, changes in its expression during settlement and metamorphosis of marine invertebrates are still unknown. The results of the current study demonstrated a reduction of HSP 70 expression during settlement and metamorphosis in the Eastern oyster, C. virginica.     

Changes in the proteome and phosphoproteome expression in the bryozoan Bugula neritina larvae in response to the antifouling agent butenolide

Larval attachment and metamorphosis, commonly referred to as larval settlement, of marine sessile invertebrates can be triggered or blocked by chemical cues and affected by changes in overall protein expression pattern and phosphorylation dynamics. This study focuses on the effects of butenolide, an effective larval settlement inhibitor, on larval settlement at the proteome level in the bryozoan Bugula neritina. Liquid‐phase IEF sample prefractionation combined with 2‐DE and MALDI‐TOF MS was used to identify the differentially expressed proteins. Substantial changes occurred both in protein abundance and in phosphorylation status during larval settlement and when settling larvae were challenged with butenolide. The proteins that responded to treatment were identified as structural proteins, molecular chaperones, mitochondrial peptidases and calcium‐binding proteins. Compared with our earlier results, both genistein and butenolide inhibited larval settlement of B. neritina primarily by changes in protein abundance and the phosphorylation status of proteins but have different protein targets in the same species. Clearly, to design potent antifouling compounds and to understand the mode of action of compounds, more studies on the effects of different compounds on proteome and phosphoproteome of different larval species are required.     

Behavior and development of larvae in the sponge Haliclona amboinensis

Sponges play important roles in marine ecosystems by contributing to habitat complexity and benthopelagic coupling of nutrients. Yet, the reproduction and settlement behaviors of diverse sponge species are not well understood. Here, we examined the brooding demosponge Haliclona amboinensis, which is common on shallow reefs in Bolinao, northwestern Philippines. Gravid sponges were found between the months of May and August, coinciding with warmer sea surface temperature. Sponges released parenchymella larvae from brood chambers in the mid‐morning, suggesting that light and temperature may serve as cues to initiate hatching. Larvae immediately swam toward the surface upon emergence and migrated to the bottom of the tanks 1–2 hr after release. The presence of light and crustose coralline algae induced high larval settlement. Metamorphosis proceeded rapidly in vitro, with larval cells spreading laterally on the substrate. The osculum was first visible at 3 days after settlement. The short pelagic duration of larvae in H. amboinensis promotes local recruitment and may be important for the maintenance of sponge populations in the face of disturbances.