Settlement Cues Research Articles

Use of chemical cues by coral reef animal larvae for habitat selection

AB Aquatic Biology Contact the journal Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections AB 19:231-238 (2013) - DOI: https://doi.org/10.3354/ab00532 Use of chemical cues by coral reef animal larvae for habitat selection David Lecchini1,2,*, Yohei Nakamura3 1USR 3278 CNRS-EPHE, CRIOBE, 98729 Moorea, French Polynesia 2Laboratoire d’Excellence ‘CORAIL’, 98729 Moorea, French Polynesia 3Graduate School of Kuroshio Science, Kochi University, 783 8502 Kochi, Japan *Email: lecchini@univ-perp.fr ABSTRACT: The present study explored the importance of chemical cues for habitat selection by fish (6 species), crustacean (1 species), and cephalopod (1 species) larvae in a 4-channel choice flume at Ishigaki Island, Japan. The larval attraction toward chemical cues from reef patches (seagrass bed patch, live coral patch, dead coral patch, and control water; Expt 1) and microhabitats within a given reef patch (live coral colonies, dead coral colonies, seagrass, and conspecifics; Expt 2) was tested in a 4-channel choice flume. The results in Expt 1 showed that 3 fish species used chemical cues to move significantly towards reef patches: Chromis viridis toward live coral patch water and Lutjanus fulviflamma and L. gibbus toward seagrass bed patch water. In Expt 2, 6 of 8 species (4 fishes, 1 cephalopod, and 1 crustacean) used chemical cues to move significantly toward conspecific water (Apogon properuptus, C. viridis, Dascyllus reticulatus, L. fulviflamma, Octopus cyanea, and Palaemonidae sp.). Overall, these results suggest that marine species can actively select settlement habitats according to olfactory cues (more specially, cues from conspecifics). Moreover, these results highlight the importance of conspecific cues over other types of information (reef patch and microhabitat) for habitat selection. Social aggregation of fish, crustacean, and cephalopod larvae with older conspecifics may be the result of individuals using conspecific ‘guides’ to potentially find beneficial resources (availability of resources and low mortality). KEY WORDS: Sensory mechanisms · Settlement cues · Fish · Crustacean · Cephalopod Full text in pdf format PreviousNextCite this article as: Lecchini D, Nakamura Y (2013) Use of chemical cues by coral reef animal larvae for habitat selection. Aquat Biol 19:231-238. https://doi.org/10.3354/ab00532 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AB Vol. 19, No. 3. Online publication date: October 24, 2013 Print ISSN: 1864-7782; Online ISSN: 1864-7790 Copyright © 2013 Inter-Research.

Habitat configuration and availability influences the settlement of temperate reef fishes (Tripterygiidae)

To survive, most benthic marine organisms must find suitable settlement habitat. For reef fishes, settlement habitat is often structurally complex, spatially heterogeneous, and dynamic. Consequently, successful settlement is likely to be determined by an interaction between larval delivery and behavior, habitat availability, and structural characteristics (e.g., configuration) of the habitat itself. We examined the effects of habitat configuration and availability on the settlement of New Zealand triplefins (Tripterygiidae), using a field experiment that comprised three habitat treatments and evaluated effects over naturally varying levels of larval supply. Our results suggest that settler density and total settlement are shaped by both the availability and spatial configuration of habitat patches. Highest total settlement occurred in larger, more clumped habitat patches. Lowest total settlement occurred in more dispersed habitat patches of the same size and smaller isolated patches. The densities of recently settled triplefins were lowest in the dispersed patches, and high in both isolated patches and the clumped patches. We speculate that dispersed patches may comprise a lower quality habitat, and/or provide a weaker settlement trigger for both physical and biological reasons. Clumped patches, on the other hand, may provide a stronger settlement cue via baffling of currents, or may represent a higher quality habitat for recently settled triplefins, triggering higher settlement. Our findings indicate that habitat availability can influence abundance of recently settled fish, but the landscape architecture is an equally important determinant of settlement success for triplefins.

Growth, settlement and survival ofDicathais orbita(Neogastropoda, Mollusca) larvae in response to temperature, diet and settlement cues

The southern Australian whelk, Dicathais orbita, is a potential candidate for aquaculture, as both seafood and for bioactive compound production. Larval rearing experiments to determine the effects of temperature and diet on the growth and survival of D. orbita larvae under laboratory conditions comprised five different unicellular algal diets of two brown algal species; Isochysis galbana and Chaetoceros muelleri, two green algae; Tetraselmis seucica and Nannochloropsis oculata, and a mixture of all four strains for larvae maintained at 16 and 22°C. Absolute growth, specific growth rate (SGR) and survival were determined regularly. Larvae reared at 22°C on a mixed diet, or brown algae, performed significantly better than those reared on green algal diets alone. Preliminary trials with settlement cues were undertaken on different aged larvae to determine when larvae become competent. An array of natural cues (carrion, Xenostrobus pulex, adult mucus and Ulvella lens), as well as concentrations of KCl was tested. KCl(concentration of 20 mM) induced the greatest settlement, however, no larvae metamorphosed under the conditions provided. This study confirms long-lived planktotrophic larval development for Dicathais orbita with higher development rates at the higher water temperatures. Further studies will optimize culture conditions and cues for settlement and metamorphosis.

Otx2 expression and implications for olfactory imprinting in the anemonefish, Amphiprion percula

SummaryThe otx2 gene encodes a transcription factor (OTX2) essential in the formation of the brain and sensory systems. Specifically, OTX2-positive cells are associated with axons in the olfactory system of mice and otx2 is upregulated in odour-exposed zebrafish, indicating a possible role in olfactory imprinting. In this study, otx2 was used as a candidate gene to investigate the molecular mechanisms of olfactory imprinting to settlement cues in the coral reef anemonefish, Amphiprion percula. The A. percula otx2 (Ap-otx2) gene was elucidated, validated, and its expression tested in settlement-stage A. percula by exposing them to behaviourally relevant olfactory settlement cues in the first 24 hours post-hatching, or daily throughout the larval phase. In-situ hybridisation revealed expression of Ap-otx2 throughout the olfactory epithelium with increased transcript staining in odour-exposed settlement-stage larval fish compared to no-odour controls, in all scenarios. This suggests that Ap-otx2 may be involved in olfactory imprinting to behaviourally relevant settlement odours in A. percula.

Localization of sensory mechanisms utilized by coral planulae to detect settlement cues

AbstractCoral planulae are induced to settle and metamorphose by contact with either crustose coralline algae or marine bacterial biofilms. Larvae of two coral species, Pocillopora damicornis and Montipora capitata, which respond to different metamorphic cues, were utilized to investigate the sensory mechanisms used to detect metamorphic cues. Because the aboral pole of the coral planula is the point of attachment to the substratum, we predicted that it is also the point of detection for cues. To determine where sensory cells for cues are localized along the body, individual larvae were transversely cut into oral and aboral portions at various levels along the oral–aboral axis, and exposed to settlement‐inducing substrata. Aboral ends of M. capitata metamorphosed, while oral ends continued to swim. However, in larvae of P. damicornis, ¾ oral ends (i.e., lacking the aboral pole) were also able to metamorphose, indicating that the cells that detect cues may be distributed along the sides of the body. These cells do not correspond to FMRFamide‐immunoreactive cells that are present throughout the body. Cesium ions induced both aboral and oral ends of larvae of both species to settle, suggesting that oral ends have not lost their capacity to metamorphose, despite lacking sensory cells to detect natural cues. To determine whether sensory cells in larvae of P. damicornis are restricted to one side of the body, swimming behavior over substrata was observed in larvae labeled with diI, a red fluorescent lipophilic membrane stain. The larvae were found to rotate around the oral–aboral axis, with their surface against the substratum, not favoring a particular side for detecting cues. While clarifying the regions of the larval body important for settlement and metamorphosis in coral planulae, we conclude that significant differences between coral species may be due to differences in the distribution of sensory structures in relation to different planular sizes.

Chemical Ecology of Marine Angiosperms: Opportunities at the Interface of Marine and Terrestrial Systems

This review examines the state of the field for chemically mediated interactions involving marine angiosperms (seagrasses, mangroves, and salt marsh angiosperms). Small-scale interactions among these plants and their herbivores, pathogens, fouling organisms, and competitors are explored, as are community-level effects of plant secondary metabolites. At larger spatial scales, secondary metabolites from marine angiosperms function as reliable cues for larval settlement, molting, or habitat selection by fish and invertebrates, and can influence community structure and ecosystem function. Several recent studies illustrate the importance of chemical defenses from these plants that deter feeding by herbivores and infection by pathogens, but the extent to which allelopathic compounds kill or inhibit the growth of competitors is less clear. While some phenolic compounds such as ferulic acid and caffeic acid act as critical defenses against herbivores and pathogens, we find that a high total concentration of phenolic compounds within bulk plant tissues is not a strong predictor of defense. Residual chemical defenses prevent shredding or degradation of plant detritus by detritivores and microbes, delaying the time before plant matter can enter the microbial loop. Mangroves, marsh plants, and seagrasses remain plentiful sources of new natural products, but ecological functions are known for only a small proportion of these compounds. As new analytical techniques are incorporated into ecological studies, opportunities are emerging for chemical ecologists to test how subtle environmental cues affect the production and release of marine angiosperm chemical defenses or signaling molecules. Throughout this review, we point to areas for future study, highlighting opportunities for new directions in chemical ecology that will advance our understanding of ecological interactions in these valuable ecosystems.

Recruitment constraints in Singapore's fluted giant clam (Tridacna squamosa) population--a dispersal model approach.

Recruitment constraints on Singapore's dwindling fluted giant clam, Tridacna squamosa, population were studied by modelling fertilisation, larval transport, and settlement using real-time hydrodynamic forcing combined with knowledge of spawning characteristics, larval development, behaviour, and settlement cues. Larval transport was simulated using a finite-volume advection-diffusion model coupled to a three-dimensional hydrodynamic model. Three recruitment constraint hypotheses were tested: 1) there is limited connectivity between Singapore's reefs and other reefs in the region, 2) there is limited exchange within Singapore's Southern Islands, and 3) there exist low-density constraints to fertilisation efficacy (component Allee effects). Results showed that connectivity among giant clam populations was primarily determined by residual hydrodynamic flows and spawning time, with greatest chances of successful settlement occurring when spawning and subsequent larval dispersal coincided with the period of lowest residual flow. Simulations suggested poor larval transport from reefs located along the Peninsular Malaysia to Singapore, probably due to strong surface currents between the Andaman Sea and South China Sea combined with a major land barrier disrupting larval movement among reefs. The model, however, predicted offshore coral reefs to the southeast of Singapore (Bintan and Batam) may represent a significant source of larvae. Larval exchange within Singapore's Southern Islands varied substantially depending on the locations of source and sink reefs as well as spawning time; but all simulations resulted in low settler densities (2.1–68.6 settled individuals per 10,000 m2). Poor fertilisation rates predicted by the model indicate that the low density and scattered distribution of the remaining T. squamosa in Singapore are likely to significantly inhibit any natural recovery of local stocks.

Zooxanthellae presence acts as a settlement cue for aposymbiotic planulae of the Caribbean CoralMontastraea faveolata

Settlement of Caribbean coral planulae with and without zooxanthellae was followed in response to four different settlement environments; one harboring zooxanthellae, one harboring crustose coralline algae (CCA) and one containing zooxanthellae and CCA. Aposymbiotic planulae of Montastraea faveolata settled preferably in both environments where zooxanthellae were present. Planulae of Agaricia humilis, that already possessed zooxanthellae through maternal inheritance, showed no preference for either settlement environment. These results suggest that planulae that lack zooxanthellae actively respond to the presence of zooxanthellae upon settlement and preferably settle in areas where zooxanthellae are present. Early successful acquisition of symbionts likely enhances recruitment success as symbionts provide the settler with additional resources to increase survival probabilities and enhance early growth.

Examining the Use of Mass Transplantation of Brooding and Spawning Corals to Support Natural Coral Recruitment in Sulawesi/Indonesia

AbstractCoral transplantation is frequently advocated as a possible means of coral reef rehabilitation. One of the purported benefits of transplantation is a positive effect of transplants on coral recruitment by sexual reproduction of transplants (“seeding”) and/or settlement cues generated by the presence of live coral (“attraction”). However, evidence for this assertion is scarce. Here, we investigated the effect of coral transplantation on larval recruitment. A total of 6,164 fragments of four coral species (acroporids and pocilloporids) were transplanted at three sites in North Sulawesi, Indonesia. Coral recruitment onto limestone settlement plates was examined every 3 months and on concrete structures at the end of the study (≥15 months) in the presence and absence of transplants. Transplant survival after 1 year ranged between 20 and 30% for pocilloporids and between 40 and 80% for acroporids. Transplantation had no consistent effect on the number of coral recruits on the settlement plates or on the concrete structures. Recruitment was relatively high compared to other locations in the region and fluctuated seasonally, with increased rates in all treatments during peaks of reproduction. We conclude that, in the presence of high background recruitment and detrimental environmental conditions, coral transplantation may not be an effective method to boost coral recruitment. The provision of stable substrate for settlement in the form of artificial reefs, combined with improved management to reduce chronic stressors, constitutes a better use of resources.

Single-species bacteria in sediments induce larval settlement of the infaunal polychaetes Polydora cornuta and Streblospio benedicti

Larval settlement of the infaunal spionid polychaetes Polydora cornuta and Streblospio benedicti is mediated by sediment-associated microorganisms. To investigate if larval preference for certain sediment is guided by individual sediment-associated bacteria, 13 bacterial isolates (5 phyla) obtained from the natural habitat of adult polychaetes (Wadden Sea, Germany) in 2008 were screened in still-water, no-choice settlement assays. Two isolates (α-Proteobacterium-Strain DF11 and Flavobacterium-Strain 54) significantly triggered larval settlement in comparison with sterile sediment. In still-water, multiple-choice settlement assays comprising natural and sterile sediment and sediment re-inoculated with isolates DF11 and 54, significant preferences for natural sediment and sediment containing bacterial isolates at 108 cells g−1 were observed. Larval settlement was influenced by bacterial abundance in sediment but the correlation was not strictly positive; thus, maximum larval settlement in response to single bacterial species may occur at certain optimum densities. Non-viable or suspended bacteria and water-soluble bacterial products did not induce larval settlement, suggesting that sediment-associated bacterial settlement cues for P. cornuta and S. benedicti were either produced in situ and/or consisted of heat-labile bacterial products.

Reproduction, larval development and settlement of the intertidal serpulid polychaeteSpirobranchus cariniferus

Serpulid polychaetes are often important components of marine communities, yet current knowledge of serpulid reproduction, development and settlement is largely based on the study of only a few species. This study examined whether spawning and sexual development of the mid-intertidal serpulidSpirobranchus cariniferusare typical of patterns observed in other serpulids, and also examined the effect of diet on larval development and identified cues that induce metamorphosis. Populations ofS. cariniferuson the east and west coasts of New Zealand's North Island had an extended spawning season with a high proportion (75–100%) of individuals carrying ripe gametes at any given time from the late spring to early autumn, consistent with other serpulid species. However, contrary to proposed patterns of sexual development in serpulids, sex-ratios and average male and female body masses suggestS. cariniferusare not protandric hermaphrodites. A diet experiment revealed that larval growth was fastest when provided with a mixed diet of three algal species. Solutions of 3-isobutyl-1-methylxanthine at a concentration of 10−4M were potent inducers of metamorphosis inS. cariniferuslarvae, revealing that competence is reached by 13–15 days after fertilization. When exposed to surfaces coated with conspecific tube or tissue homogenates, 6% of competent larvae settled and metamorphosed on surfaces coated with tube homogenate whereas none settled on tissue homogenate or in the controls, suggesting specific cues are required for settlement and the likely presence of a settlement cue in the tubes of adult worms, consistent with the highly gregarious distribution of the species.

Larval Settlement, Early Growth and Survival ofHaliotis tuberculatacoccineausing Several Algal Cues

Settlement of Haliotis tuberculata coccinea larvae was examined in the presence of crustose coralline algae (CCA), Ulvella lens, and Ulva rigida. Germlings of the 2 green macroalgae of different age, enrichment level, and in combination were tested as settlement cues, and CCA was tested as a positive control. Larval settlement was the highest on CCA (61 %) tailed by a 45-day-old mix of U. lens and U. rigida (52%) and 45-day-old U. rigida (46%). Settlement was the lowest (about 3%) on a mix of 4-day-old U. lens and U. rigida and 45-day-old enriched or unenriched U. lens. In all treatments, postlarvae were fed for 4 wk with a mix of diatoms (Amphora sp., Proschkinia sp., Nitzschia sp., and Navicula incerta); postlarval growth was the best on the 45-day-old mix of U. lens and U. rigida. This substrate was also the best of the green macroalgae germlings substrates tested for settlement induction and provided good survival rates. The substrate protein content correlated negatively with larval settlement and survival. The algal cues were differentiated by their fatty acid composition. Fatty acids such as 18:ln-7, 18:2n-6, 16:4n-3, arachidonic acid, and eicosapentaenoic acid were suggested to affect settlement and survival. The fatty acids correlated with settlement were different from the ones associated with survival rates, except eicosapentaenoic acid, which correlated with both. The results of this study show the high value of U. rigida for H. tuberculata postlarvae, and the influence of substrate age on the settlement success.

Evidence for the involvement of p38 MAPK activation in barnacle larval settlement.

The barnacle Balanus ( = Amphibalanus) amphitrite is a major marine fouling animal. Understanding the molecular mechanism of larval settlement in this species is critical for anti-fouling research. In this study, we cloned one isoform of p38 MAPK (Bar-p38 MAPK) from this species, which shares the significant characteristic of containing a TGY motif with other species such as yeast, Drosophila and humans. The activation of p38 MAPK was detected by an antibody that recognizes the conserved dual phosphorylation sites of TGY. The results showed that phospho-p38 MAPK (pp38 MAPK) was more highly expressed at the cyprid stage, particularly in aged cyprids, in comparison to other stages, including the nauplius and juvenile stages. Immunostaining showed that Bar-p38 MAPK and pp38 MAPK were mainly located at the cyprid antennules, and especially the third and fourth segments, which are responsible for substratum exploration during settlement. The expression and localization patterns of Bar-p38 MAPK suggest its involvement in larval settlement. This postulation was also supported by the larval settlement bioassay with the p38 MAPK inhibitor SB203580. Behavioral analysis by live imaging revealed that the larvae were still capable of exploring the surface of the substratum after SB203580 treatment. This shows that the effect of p38 MAPK on larval settlement might be by regulating the secretion of permanent proteinaceous substances. Furthermore, the level of pp38 MAPK dramatically decreased after full settlement, suggesting that Bar-p38 MAPK maybe plays a role in larval settlement rather than metamorphosis. Finally, we found that Bar-p38 MAPK was highly activated when larvae confronted extracts of adult barnacle containing settlement cues, whereas larvae pre-treated with SB203580 failed to respond to the crude adult extracts.

Characterization of biofilm exudates and their effects on settlement of mussel (Perna canaliculus) larvae

Settlement-inducing cues for larvae of the green-lipped mussel, Perna canaliculus, were characterized from biofilm exudates of mono-species bacteria. Biofilm exudates of Macrococcus sp. AMGM1 and Bacillus sp. AMGB1, previously known to induce settlement of P. canaliculus larvae, were chosen for this study. An innovative step-wise multi-technique approach, including physical methods (molecular weight fractionation and heat treatment) and chemical methods (crude fractionation, sub-sample fractionation, sequential fractionation, lipid fractionation and protease treatment), was used to characterize the chemical cues from these bacterial biofilm exudates. The resulting fractions obtained from these methods were individually tested for their ability to induce larval settlement. Results from the settlement assays indicate that settlement cues from Macrococcus sp. AMGM1 were between 1–3, 3–10 and 10–30kDa. These molecules were thermo-labile to over 70°C, and contained polar proteins and non-polar lipoprotein molecules. Protease-treated biofilm exudates did not elicit a settlement response, indicating the involvement of proteins from Macrococcus sp. AMGM1 in the larval settlement process. In addition, settlement cues from Bacillus sp. AMGB1 were found to be between 10–30 and 30–50kDa, were stable to up to 100°C, and contained glycolipid molecules. These results provide evidence for the presence of multiple settlement cues in the biofilm exudates from both Macrococcus sp. AMGM1 and Bacillus sp. AMGB1. This study provides a comprehensive and inexpensive set of biochemical techniques, which can be used in a step-wise manner, to deduce partial chemical identity of both inductive and non-inductive settlement cues produced by biofilm exudates. The results can be used to decipher complex bacterially mediated larval settlement processes for P. canaliculus and other marine invertebrates.

Carbonate Mineral Saturation State as the Recruitment Cue for Settling Bivalves in Marine Muds

After a pelagic larval phase, infaunal bivalves undergo metamorphosis and transition to the underlying sediments to begin the benthic stage of their life history, where they explore and then either accept or reject sediments. Although the settlement cues used by juvenile infaunal bivalves are poorly understood, here we provide evidence that carbonate saturation state is a significant chemical cue in both direct observation laboratory studies and field manipulations. In the laboratory, plantigrade-stage Mercenaria mercenaria (200 μm shell height) showed a significant positive relationship between percent burrowed and Ωaragonite, with an increasing probability of settlement with increasing saturation state. In the field, we increased bivalve recruitment by a factor of three in a 30-day field study by raising the pH (∼0.3) and saturation state of surface sediments by buffering sediments with crushed shell (CaCO3). The susceptibility of infaunal bivalves to dissolution mortality and the tight coupling of other sedimentary biogeochemical processes with carbonate dynamics suggest that mineral thermodynamics may be an overarching cue new settlers are responding to.

Immunity through early development of coral larvae

As a determinant of survival, immunity is likely to be significant in enabling coral larvae to disperse and successfully recruit, however, whether reef-building coral larvae have immune defenses is unknown. We investigated the potential presence and variation in immunity in the lecithotrophic larvae of Acropora tenuis through larval development. Enzymes indicative of tyrosinase and laccase–type melanin-synthesis were quantified, and the concentration of three coral fluorescent proteins was measured over six developmental stages; egg, embryo, motile planula, planula post-exposure to crustose coralline algae (CCA; settlement cue), settled, settled post-exposure to Symbiodinium (endosymbiont). Both types of melanin-synthesis pathways and the three fluorescent proteins were present in A. tenuis throughout development. Laccase-type activity and red fluorescence increased following exposure of planula to CCA, whereas tyrosinase-type activity and cyan fluorescence increased following settlement. No change was detected in the measured parameters following exposure to Symbiodinium. This study is the first to document coral larval immune responses and suggests the melanin-synthesis pathways have disparate roles-the laccase-type potentially non-immunological and the tyrosinase-type in cytotoxic defense. Our results indicate that corals have the potential to resist infection from the earliest life history phase.

Effects of Eutrophication, Seasonality and Macrofouling on the Diversity of Bacterial Biofilms in Equatorial Coral Reefs

Biofilms play an important role as a settlement cue for invertebrate larvae and significantly contribute to the nutrient turnover in aquatic ecosystems. Nevertheless, little is known about how biofilm community structure generally responds to environmental changes. This study aimed to identify patterns of bacterial dynamics in coral reef biofilms in response to associated macrofouling community structure, microhabitat (exposed vs. sheltered), seasonality, and eutrophication. Settlement tiles were deployed at four reefs along a cross-shelf eutrophication gradient and were exchanged every 4 months over 20 months. The fouling community composition on the tiles was recorded and the bacterial community structure was assessed with the community fingerprinting technique Automated Ribosomal Intergenic Spacer Analysis (ARISA). Bacterial operational taxonomic unit (OTU) number was higher on exposed tiles, where the fouling community was homogenous and algae-dominated, than in sheltered habitats, which were occupied by a variety of filter feeders. Furthermore, OTU number was also highest in eutrophied near-shore reefs, while seasonal variations in community structure were most pronounced in the oligotrophic mid-shelf reef. In contrast, the macrofouling community structure did not change significantly with seasons. Changes in bacterial community patterns were mostly affected by microhabitat, seasonal and anthropogenically derived changes in nutrient availability, and to a lesser extent by changes in the macrofouling community structure. Path analysis revealed a complex interplay of various environmental and biological factors explaining the spatial and temporal variations in bacterial biofilm communities under natural conditions.

Size dependence, facilitation, and microhabitats mediate space competition between coral and crustose coralline algae in a spatially explicit model

Coral interacts both positively and negatively with different types of crustose coralline algae (CCA) throughout the coral life cycle. These interactions range from settlement cues and facilitation by “promoter” CCA species to settlement inhibition, preemptive competition for space, and overgrowth of smaller coral colonies by “inhibitor” CCA species. Corals coexist with CCA in healthy coral reefs despite appearing to be weaker space competitors than inhibitor CCA. We use spatially explicit stochastic simulations of size dependent interactions between individual coral colonies and CCA patches to explore how CCA affects the recovery of corals after disturbance in homogenous and heterogeneous habitat. Specifically, we look at whether positive or negative interactions have a larger effect on coral growth and survival and whether events during recruitment or interactions between CCA and established colonies have larger impacts on coral cover and persistence. We find that competition for space through preemption and overgrowth is the primary factor driving coral dynamics, overshadowing settlement processes. Coexistence of coral and CCA is difficult if not impossible to achieve in homogenous landscapes unless corals are more effective than CCA at preempting space. Microhabitats that protect coral settlers from overgrowth allow vulnerable coral to persist and replace refuge coral that has died, but additional mechanisms such as competitive reversals or patchy CCA mortality are required for coral persistence outside of protected microhabitats. Through these models we identify mechanisms that have been rarely studied but are potentially critical for the survival of coral in areas where CCA is a dominant competitor.

Observed and modeled larval settlement of a reef fish to the Florida Keys

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 453:201-212 (2012) - DOI: https://doi.org/10.3354/meps09641 Observed and modeled larval settlement of a reef fish to the Florida Keys S. Sponaugle1,*, C. Paris2, K. D. Walter1, V. Kourafalou3, E. D’Alessandro1 1Marine Biology and Fisheries, 2Applied Marine Physics, and 3Meteorology and Physical Oceanography, Rosenstiel School of Marine and Atmospheric Science, University of Miami, 4600 Rickenbacker Causeway, Miami, Florida 33149, USA *Email: ssponaugle@rsmas.miami.edu ABSTRACT: The bipartite life history of most marine organisms leads to complex patterns of replenishment in benthic populations. High variation in adult spawning, dynamic oceanographic currents, and often unknown larval behaviors create challenges in accurately predicting spatial and temporal patterns in the supply and settlement of pelagic larvae to nearshore juvenile habitats. Yet, understanding and predicting larval exchange underlies population dynamics, ecological interactions, and conservation practices. We compared observed patterns of larval settlement of the bicolor damselfish Stegastes partitus (Pomacentridae) along the Florida Keys, USA, to those obtained through model simulations using a high-resolution biophysical model parameterized with species-specific early life-history information. Light traps intercepted settlement-stage larvae, and divers censused new recruits at 2 replicate reefs in each of the upper (eastern) (UK) and lower (western) Keys (LK) during 6 peak settlement periods. Damselfish settlement and recruitment to the LK consistently exceeded that to the UK. Remarkably, model simulations successfully explained 70% of temporal variation in settlement within each region. However, the model did not capture the relative magnitude of observed settlement between the regions: settlement was either overestimated in the UK or underestimated in the LK. Potential causes include weak larval settlement cues or larval ability to navigate and swim to settlement habitat in the UK, higher larval condition and survival in the more productive waters of the LK, or substantial spatial variation in reproductive output. Connectivity matrices indicate that a majority of S. partitus settlement to the Florida Keys is sourced from Keys populations. KEY WORDS: Larval dispersal · Recruitment · Population connectivity · Stegastes partitus · Biophysical model Full text in pdf format PreviousNextCite this article as: Sponaugle S, Paris C, Walter KD, Kourafalou V, D’Alessandro E (2012) Observed and modeled larval settlement of a reef fish to the Florida Keys. Mar Ecol Prog Ser 453:201-212. https://doi.org/10.3354/meps09641 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 453. Online publication date: May 07, 2012 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2012 Inter-Research.

Histamine is a modulator of metamorphic competence in Strongylocentrotus purpuratus (Echinodermata: Echinoidea).

BackgroundA metamorphic life-history is present in the majority of animal phyla. This developmental mode is particularly prominent among marine invertebrates with a bentho-planktonic life cycle, where a pelagic larval form transforms into a benthic adult. Metamorphic competence (the stage at which a larva is capable to undergo the metamorphic transformation and settlement) is an important adaptation both ecologically and physiologically. The competence period maintains the larval state until suitable settlement sites are encountered, at which point the larvae settle in response to settlement cues. The mechanistic basis for metamorphosis (the morphogenetic transition from a larva to a juvenile including settlement), i.e. the molecular and cellular processes underlying metamorphosis in marine invertebrate species, is poorly understood. Histamine (HA), a neurotransmitter used for various physiological and developmental functions among animals, has a critical role in sea urchin fertilization and in the induction of metamorphosis. Here we test the premise that HA functions as a developmental modulator of metamorphic competence in the sea urchin Strongylocentrotus purpuratus.ResultsOur results provide strong evidence that HA leads to the acquisition of metamorphic competence in S. purpuratus larvae. Pharmacological analysis of several HA receptor antagonists and an inhibitor of HA synthesis indicates a function of HA in metamorphic competence as well as programmed cell death (PCD) during arm retraction. Furthermore we identified an extensive network of histaminergic neurons in pre-metamorphic and metamorphically competent larvae. Analysis of this network throughout larval development indicates that the maturation of specific neuronal clusters correlates with the acquisition of metamorphic competence. Moreover, histamine receptor antagonist treatment leads to the induction of caspase mediated apoptosis in competent larvae.ConclusionsWe conclude that HA is a modulator of metamorphic competence in S. purpuratus development and hypothesize that HA may have played an important role in the evolution of settlement strategies in echinoids. Our findings provide novel insights into the evolution of HA signalling and its function in one of the most important and widespread life history transitions in the animal kingdom - metamorphosis.