Sea Anemone Aiptasiomorpha minuta (Verrill, 1867) as a Possible Agent to Control Biofouling in Oyster Culture and the Optimal Conditions for Its Mass Rearing under Laboratory Conditions

The potential use of the sea anemone Aiptasiomorpha minuta as an agent for controlling biofouling on cultured oysters and the optimum culture conditions for its mass culture were evaluated. Field experiments showed that nineteen species (eight phyla), including two seaweed species, sponges, hydroids, bryozoans, mollusk/bivalve species, barnacles, and tunicates were found as biofouling assemblages on the oyster collectors. The ability of A. minuta to accumulate biomass on oyster collectors, thus, minimizing colonization by problem species; was also demonstrated to promote better oyster growth, condition index, and survival. Favorable mass culture conditions of A. minuta in laboratory trials were found at 28 ◦C, fed with Artemia salina (1000 individuals/day), and at 23 psu for the optimum temperatures, diet regimen, and salinity, respectively. These mass culture conditions could be useful for the purpose of producing enough biomass for attaching the sea anemones, A. minuta, to oyster collectors. The use of A. minuta could be a preventive strategy against biofouling that may be useful for oyster farmers; it is safe from the viewpoint of food hygiene, and is also environment-friendly

Combination of macroalgae-conditioned water and periphytic diatom Navicula ramosissima as an inducer of larval metamorphosis in the sea urchins Anthocidaris crassispina and Pseudocentrotus depressus

The induction of larval metamorphosis in the sea urchins Anthocidaris crassispina and Pseudocentro(us depressus was investigated in the laboratory, using waters conditioned by 15 different macroalgae combined with the periphytic diatom Navicula ramosissima. Larvae of P. depressus did not metamorphose, but larvae of A. crassispina showed a high incidence of metamorphosis, especially in waters conditioned by coralline red algae or brown algae. High inductive activity for larval metamorphosis was detected in Corallina pi/ullfera-conditioned water during a 2.5-year investigation, but the activity was relatively low in February or March and in September, the off-growth seasons of the alga. By contrast, Ulva pertusa-conditioned water did not show metamorphosis-inducing activity except in spring or early summer. These results indicate that during their growth phase, red and brown algae release into their environment active substances that are involved in the larval metamorphosis of A. crassispina

Identification and Characterization of the Larval Settlement Pheromone Protein Components in Adult Shells of Crassostrea gigas: A Novel Function of Shell Matrix Proteins

The global decline of natural oyster populations emphasizes the need to improve our understanding of their biology. Understanding the role of chemical cues from conspecifics on how oysters occupy appropriate substrata is crucial to learning about their evolution, population dynamics, and chemical communication. Here, a novel role of a macromolecular assembly of shell matrix proteins which act as Crassostrea gigas Settlement Pheromone Protein Components in adult shells is demonstrated as the biological cue responsible for gregarious settlement on conspecifics. A bioassay-guided fractionation approach aided by biochemical and molecular analyses reveals that Gigasin-6 isoform X1 and/or X2 isolated from adult shells is the major inducing cue for larval settlement and may also play a role in postlarva–larva settlement interactions. Other isolated Stainsall-stainable acidic proteins may function as a co-factor and a scaffold/structural framework for other matrix proteins to anchor within this assembly and provide protection. Notably, conspecific cue-mediated larval settlement induction in C. gigas presents a complex system that requires an interplay of different glycans, disulfide bonds, amino acid groups, and phosphorylation crosstalk for recognition. These results may find application in the development of oyster aquacultures which could help recover declining marine species and as targets of anti-fouling agents

Transcriptome Dynamics of an Oyster Larval Response to a Conspecific Cue-Mediated Settlement Induction in the Pacific Oyster Crassostrea gigas

The molecular mechanisms underlying the conspecific cue-mediated larval settlement in Crassostrea gigas is not yet fully understood. In this study, we described and compared the transcriptomes of competent pediveligers (Pedi) and conspecific cue-induced postlarvae (PL). A total of 2383 candidate transcripts were identified: 740 upregulated and 1643 downregulated transcripts, after settlement. Gene Ontology analysis revealed active chitin binding, calcium ion binding, and extracellular region processes in both stages. Results showed that the differential expression trend of six candidate transcripts were consistent between the quantitative real-time PCR and transcriptome data. The differential transcript expression related to shell formation showed closely linked dynamics with a gene regulatory network that may involve the interplay of various hormone receptors, neurotransmitters, and neuropeptide receptors working together in a concerted way in the Pedi and PL stages. Our results highlight the transcriptome dynamics underlying the settlement of oysters on conspecific adult shells and demonstrate the potential use of this cue as an attractant for wild and hatchery-grown oyster larval attachment on artificial substrates. It also suggests the possible involvement of an ecdysone signal pathway that may be linked to a neuroendocrine-biomineralization crosstalk in C. gigas settlement

Nutritional effects on the visual system of the rotifer Brachionus plicatilis sensu stricto (Rotifera: Monogononta)

Rotifers have a light sensor called "eyespot" which is expected to be composed of rhodopsin. Based on the molecular feature of rhodopsin as regenerated with 11-cis-retinal, we hypothesized that phototactic behavior should be affected by the nutritional level of food; especially vitamin A availability. This study intended to address the following questions on the nutritional effects of using baker\u27s yeast (Saccharomyces cerevisiae) and Nannochloropsis oculata: how does diet affect the pigmented area and absorbance of the eyespot, and how do these changes characterize phototactic behavior and population growth in the monogonont rotifer Brachionus plicatilis sensu stricto. The pigmented area of the eyespot decreased to 14.7μm2 with baker\u27s yeast while it was maintained at the initial size of 82.9μm2 with N. oculata. Maximum absorbance of the eyespot was observed at a range of 470 to 525nm in the initial rotifers and it was not significantly changed with diet type and culture day. The value of the maximum absorbance was maintained with N. oculata, while it rapidly decreased on day 10 with baker\u27s yeast. Stronger positive phototaxis with N. oculata was observed under lower light intensity (0.1 and 0.5Wm-2) at 470nm. On the other hand, phototaxis with baker\u27s yeast became weak and no phototactic reactions were observed under the same lighting condition. From the genomic DNA database of rotifers, 12 putative opsin-relevant genes were identified. These results corroborate the hypothesis that rhodopsin is the visual pigment in the rotifer eyespot. Lack of vitamin A with baker\u27s yeast should induce reduction of the pigmented area and the sensitivity of the rotifer eyespot resulting in weak phototaxis. The population growth of rotifers showed different patterns related to the food type and light intensity. The lowest population growth (0.33-0.37day-1) was shown with baker\u27s yeast diet at 0.5Wm-2. This phenomenon may be significantly related to malnutrition on baker\u27s yeast which is deficient not only in vitamin A but also in fatty acids, vitamin B12 and its derivatives

Causes of decoupling between larval supply and settlement and consequences for understanding recruitment and population connectivity

Author Posting. © The Author(s), 2010. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Journal of Experimental Marine Biology and Ecology 392 (2010): 9-21, doi:10.1016/j.jembe.2010.04.008.Marine broadcast spawners have two-phase life cycles, with pelagic larvae and benthic adults. Larval supply and settlement link these two phases and are crucial for the persistence of marine populations. Mainly due to the complexity in sampling larval supply accurately, many researchers use settlement as a proxy for larval supply. Larval supply is a constraining variable for settlement because, without larval supply, there is no settlement. Larval supply and settlement may not be well correlated, however, and settlement may not consistently estimate larval supply. This paper explores the argument that larval supply (i.e., larval abundance near settlement sites) may not relate linearly to settlement. We review the relationship between larval supply and settlement, from estimates and biases in larval supply sampling, to non-behavioral and behavioral components, including small-scale hydrodynamics, competency, gregarious behavior, intensification of settlement, lunar periodicity, predation and cannibalism. Physical and structural processes coupled with behavior, such as small-scale hydrodynamics and intensification of settlement, sometimes result in under- or overestimation of larval supply, where it is predicted from a linear relationship with settlement. Although settlement is a function of larval supply, spatial and temporal processes interact with larval behavior to distort the relationship between larval supply and settlement, and when these distortions act consistently in time and space, they cause biased estimates of larval supply from settlement data. Most of the examples discussed here suggest that behavior is the main source of the decoupling between larval supply and settlement because larval behavior affects the vertical distribution of larvae, the response of larvae to hydrodynamics, intensification of settlement, gregariousness, predation and cannibalism. Thus, larval behavior seems to limit broad generalizations on the regulation of settlement by larval supply. Knowledge of the relationship is further hindered by the lack of a well founded theoretical relationship between the two variables. The larval supply- settlement transition may have strong general consequences for population connectivity, since larval supply is a result of larval transport, and settlement constrains recruitment. Thus, measuring larval supply and settlement effectively allows more accurate quantification and understanding of larval transport, recruitment and population connectivity.JP would like to thank WHOI Ocean Life Institute for partial funding. FP’s contribution is based upon research supported by the South African Research Chairs Initiative of the Department of Science and Technology and National Research Foundation

A Glycoprotein in Shells of Conspecifics Induces Larval Settlement of the Pacific Oyster Crassostrea gigas

Settlement of larvae of Crassostrea gigas on shell chips (SC) prepared from shells of 11 different species of mollusks was investigated. Furthermore, the settlement inducing compound in the shell of C. gigas was extracted and subjected to various treatments to characterize the chemical cue. C. gigas larvae settled on SC of all species tested except on Patinopecten yessoensis and Atrina pinnata. In SC of species that induced C. gigas larvae to settle, settlement was proportionate to the amount of SC supplied to the larvae. When compared to C. gigas SC, all species except Crassostrea nippona showed lower settlement inducing activities, suggesting that the cue may be more abundant or in a more available form to the larvae in shells of conspecific and C. nippona than in other species. The settlement inducing activity of C. gigas SC remained intact after antibiotic treatment. Extraction of C. gigas SC with diethyl ether (Et2O-ex), ethanol (EtOH-ex), and water (Aq-ex) did not induce larval settlement of C. gigas larvae. However, extraction of C. gigas SC with 2N of hydrochloric acid (HCl-ex) induced larval settlement that was at the same level as the SC. The settlement inducing compound in the HCl-ex was stable at 100°C but was destroyed or degraded after pepsin, trypsin, PNGase F and trifluoromethanesulfonic acid treatments. This chemical cue eluted between the molecular mass range of 45 and 150 kDa after gel filtration and revealed a major band at 55 kDa on the SDS-PAGE gel after staining with Stains-all. Thus, a 55 kDa glycoprotein component in the organic matrix of C. gigas shells is hypothesized to be the chemical basis of larval settlement on conspecifics