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Invited Talk
Recruitment on rocks, reefs and rafts in the sea: why invertebrate larvae settle when and where they do?
Hadfield MG*
Kewalo Marine Laboratory, University of Hawaii at Manoa, USA
*Email: hadfield@hawaii.edu
Benthic communities in the sea, whether growing on rocks, living biological coral reefs or floating objects such as ships, become established and remain so principally by recruitment of larvae of each of their component species from the water column. Whether released from their parent animals as sperm and eggs or as well developed stages, larvae of marine invertebrates must achieve the developmental capacity to recognize suitable recruitment sites, attach to them and undergo metamorphosis, a state referred to as “competence,” before recruitment can occur. The minimal pelagic period varies greatly across invertebrate larvae, correlating especially with pelagic-vs.-benthic early development, and whether or not the larvae feed in the plankton. This talk will explore the recruitment biology of larvae from coral reefs and fouling communities, including both feeding and non-feeding types, and the nature of cues that they utilize to indicate appropriate settlement sites (adsorbed vs. soluble cues). It will also explore the biological and physical nature of the communities into which larvae must recruit, and discuss how the minute larvae manage to recruit into good sites in the swirling, shearing flow that characterizes most marine habitats. Larvae types to be discussed include those of a polychaete worm, a bryozoan, a barnacle, an ascidian and a reef-building coral. Research approaches include both field studies and laboratory experiments.
Keywords: Larva, Recruitment, Metamorphosis, Settlement cues, Invertebrate
COI gene variability in established East Asian populations of the Caribbean bivalve Mytilopsis sallei (Dreissenidae)
Tan KS¹*, YT Wong², R Meier³
¹Tropical Marine Science Institute, National University of Singapore,
²Dept of Biological Sciences, National University of Singapore
*Email: tmstanks@nus.edu.sg
Mytilopsis sallei is one of a small number of tropical estuarine bivalves known to have successfully established themselves outside their native range in the Caribbean. Their occurrence in major ports of call in East Asia strongly suggests transport of larvae and/or adults by vessels. However, transfer pathways remain speculative, and direct evidence is difficult to obtain. Analysis of genetic variability between established populations may provide a means of tracing their movements. In this study, sequence variation in the 376-base-pair fragment of the mitochondrial cytochrome oxidase I (COI) gene of M. sallei was examined for the first time in 254 individuals from 11 discrete populations outside its native range from Singapore, India, Hong Kong and Taiwan. Some 15 haplotypes with variation over 24 nucleotide positions were identified, indicating high genetic diversity with no evidence of sex-specific sequences. Haplotype diversity ranged between 0.6 and 0.8 in eight Singapore populations, and an analysis of molecular variance showed that there was no significant genetic segregation in these eight Singapore populations examined. Haplotype diversity was equally high in a population from Visakhapatnam, India, but was slightly lower (0.5) in samples from Kaohsiung, Taiwan and those from Tolo Harbour, Hong Kong. Cladistic analyses showed that haplotypes were not segregated based on geographical location in East Asia. However, pair-wise analyses of the pooled Singapore population against those elsewhere indicated that there were significant differences between populations in Singapore and Hong Kong, and between Singapore and India. These differences can be attributed to two dominant haplotypes which characterise populations in Singapore and Taiwan on one hand, and those in Hong Kong and India in the other. Nevertheless, the two haplotypes were consistently present in all populations examined. The results suggest recent and possibly on-going, transfer of genetic material between Mytilopsis populations established in Asia in spite of their separation in physical distance and salinity.
Keywords: Alien invasive species, Dreissenidae, Mytilopsis, Bivalvia
Larval metamorphosis in barnacles: linking the internal and external ecologies
Khandeparker L*, AC Anil
National Institute of Oceanography, Dona Paula, Goa, India
*Email: klidita@nio.org
The ability of an organism to acquire information from the surrounding environment is an essential determinant of ecological function. The organism must sense and respond to the environmental and biological cues to behave in an ecologically appropriate manner. In the life cycle of a benthic organism the competitive larval stage is the transitory stage between the pelagic and the sessile life and its role in finding a suitable juvenile habitat is predominant. Microbes bridge the pelagic and benthic ecosystems by actively interacting with the metazoans in the water column. Surfaces submerged in the aquatic environment are rapidly covered by biofilms comprising of various microorganisms among which bacteria are major sources of chemical cues inhibiting or inducing larval settlement of marine invertebrates.
Barnacles (Cirripedia; Thoracica) are dominant components of the hard bottom inter-tidal zone of the marine habitat and form a major group of fouling organisms. They are also the organisms of major focus in marine antifouling research. There have been numerous empirical studies to elucidate the influence of different components of biofilm on barnacle settlement. Theses studies indicate that larvae can perceive the presence of suitable substratum while being in the water column and also have the capability to accept or reject a surface when in contact. Hence, both olfaction and contact chemoreception are equally important. Experiments carried out point out to the possibility that when the receptor sites for contact chemoreception are blocked the exploration of the surface is furthered through olfaction. In other words, it is possible to say that surface associated cues play a major role in mediating settlement and metamorphosis, whereas the water borne ones can act like signposts for the swimming larva.
Keywords: Barnacles, Biofilm, Settlement, Olfaction, Contact chemoreception
Invited Talk
Community stability in the face of environmental change:
things that matter
Martin Wahl*
IFM-GEOMAR, D-24105 Kiel, Germany
*Email:mwahl@ifm-geomar.de
Currently, natural benthic (i.e. stationary) communities experience environmental change of an unprecedented speed and amplitude. This may be caused by directly climate change related shifts of abiotic variables in a given habitat, changes in marine current patterns bathing a given site in new water bodies, the introduction of new biotic interactors, or the translocation of communities attached to motile substrata (e.g. ship hulls, floating litter). The stability of a given benthic community faced with the shift in biotic and abiotic environmental factors will determine how fast and how profoundly ecosystems change.
In a globally replicated experiment, environmental change was simulated by translocating hard bottom communities of 2 different successional stages between structurally similar habitats 100s of m to 10s of km away. This treatment simulated ship hull transport or change in current patterns.
Community stability was assessed as its inverse: the rate of structural convergence towards local hard bottom communities of identical age. This convergence was driven by 2 processes: mortality of introduced alien species and colonization of available space within the introduced community by local propagules.
Younger communities converged faster (i.e. were less stable) than older communities. Age is a sum parameter of other community properties such as free substratum, dominance, taxonomic and functional diversity all of which tend to change during succession.
Partial correlation allowed identifying the contribution of these parameters to community stability. Open substratum space and dominance reduced stability whereas taxonomic and functional diversity strengthen stability. The degree of dominance had the strongest negative impact on stability, functional richness the strongest positive effect. Despite substantial variability among biogeographic regions, together, these 4 community properties explain about 50% of the ‘global’ community stability.
Keywords: Benthic communities, Stability, Dominance, Functional richness, Biogeographic regions
Expression of biosynthetic gene cluster in sponge associated bacterium during co-cultivation experiment: Chemical warfare between bacterial neighbors
Thakur NL¹*, VA Grebenjuk², WEG Müller²
¹National Institute of Oceanography, Dona Paula, Goa, India,
²Institut für Physiologische Chemie, Abteilung Angewandte Molekularbiologie, Universität, Duesbergweg 6, D-55099 Mainz, Germany
*Email: thakurn @nio.org
The role of sponge surface-associated bacteria in host epibacterial chemical defense is well known. The production of antibacterial metabolites by sponge-associated bacteria confers a selective advantage to the producer for competition with other bacteria, populating the same ecological niche. In this investigation, a sponge associated bacterium SB2 (alpha-proteobacterium MBIC 3368) showed antibacterial activity against its bacterial neighbors. In SB2 bacterium a KS3 gene from polyketide synthases (PKSs) gene clusters was detected and it was predicted that this particular genetic machinery is responsible for the production of antibacterial metabolites. The regulation of PKS gene cluster was investigated in this microbe, upon challenging it with its competitor microbial strain SB6 (gamma-proteobacterium), isolated from the same sponge surface. In this co-cultivation experiment, the up-regulation was observed in PKS gene cluster (at RNA level) expression. Simultaneously, PKS cluster expression was investigated in comparison with the growth curve of SB2 bacterium. This experiment showed up-regulation of PKS cluster during late exponential phase and early stationary phase, which is reported to be a peak period of secondary metabolite production in bacteria. This investigation highlights the role of biosynthetic gene cluster in the defense strategy of bacteria against their competitors in the microfilm.
Keywords: Marine sponge, Bacteria, Antibacterial activity, Gene cluster, Up-regulation
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