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Marine larval ecology is the study of the factors influencing the dispersing larval stage which is exhibited by many marine invertebrates and fishes. Marine organisms with a larval stage usually release large numbers of larvae into the water column, where the larvae develop and grow for a certain period of time before metamorphosing into adults. Many marine larvae are capable of dispersing long distances from their release site, although determining their actual dispersal distance is a significant challenge due to their microscopic size and the lack of an appropriate larval tracking method. Understanding dispersal distance, however, is important for a variety of reasons, including fisheries management, effective marine reserve design, and control of invasive species. == Theories on the evolution of a biphasic life history == Marine larval dispersal is one of the most important topics in marine ecology today. Most marine invertebrates and many fishes have evolved a life cycle involving a demersal adult and a pelagic larval stage or pelagic eggs that have the capacity to be transported long distances.〔Grosberg, R.K. and D.R. Levitan. 1992. For adults only? Supply-side ecology and the history of larval biology. Trends Ecol. Evol. 7: 130-133.〕 There are several theories behind why these organisms have evolved this biphasic life history:〔Swearer, S. E., J. S. Shima, M. E. Hellberg, S. R. Thorrold, G. P. Jones, D. R. Robertson, S. G. Morgan, K. A. Selkoe, G. M. Ruiz, and R. R. Warner. 2002. Evidence of self-recruitment in demersal marine populations. Bull. Mar. Sci. 70(1) Suppl.: 251-271.〕 *Larvae use a different food source than adults, which may decrease competition between life stages. *Pelagic larvae have the potential to disperse long distances, colonize new territory, and move away from habitat that has become overcrowded or otherwise unsuitable. *A long pelagic larval duration can help a species break its parasite cycles. *Pelagic larvae avoid benthic predators. Pelagic larval dispersal, however, is not without its risks. For example, while larvae do avoid benthic predators, they are exposed to a whole new suite of predators in the water column. == Larval development strategies == Marine larval development can be broadly classified into three strategies: direct development, lecithotrophic, and planktotrophic. Direct developers are characterized by a larval stage that has very low dispersal potential and usually looks like the adult form of the animal. These larvae are also known as “crawl-away larvae,” since numerous marine snails exhibit this type of development, and their larvae crawl away from the egg mass. Some species of frog also hatch this way. Lecithotrophic larvae generally have greater dispersal potential than direct developers. Many fish species and some benthic invertebrates have lecithotrophic larvae, which are provided with a source of nutrition to use during their dispersal, usually a yolk sac. Though some lecithotrophic species are capable of feeding in the water column, many, such as tunicates, are not, and must settle before depleting their food source. Consequently, these species have short pelagic larval durations and do not disperse long distances. Planktotrophic species, on the other hand, generally have fairly long pelagic larval durations and feed while in the water column. Consequentially, they have the potential to disperse long distances. This ability to disperse is one of the key adaptations of benthic marine invertebrates.〔Strathmann, R. R., T. P. Hughes, A. M. Kuris, K. C. Lindeman, S. G. Morgan, J. M. Pandolfi, and R. R. Warner. 2002. Evolution of local recruitment and its consequences for marine populations. Bull. Mar. Sci. 70(1) Suppl.: 377-396.〕 During their time in the water column, planktotrophic larvae feed on phytoplankton and small zooplankton, including other larvae. Planktotrophic development is the most common type of larval development, especially among benthic invertebrates. The relatively long time most planktotrophic larvae spend in the water column and their apparently low probability of successful recruitment led some early researchers to develop a “lottery hypothesis” that states animals release huge numbers of larvae to increase the chances that at least one will survive, and that larvae cannot influence their probability of success.〔Thorson, G. 1950. Reproductive and larval ecology of marine bottom invertebrates. Biol. Rev. Cambridge Philos. Soc. 25: 1-45.〕〔Roughgarden, J., Y. Iwasa, and C. Blaxter. 1985. Demographic theory for an open population with space-limited recruitment. Ecology 66: 54-67.〕〔Caley, M.J., M.H. Carr, M.A. Hixon, T.P. Hughes, G.P. Jones, and B. Menge. 1996. Recruitment and the local dynamics of open marine populations. Evolution 35: 1192-1205.〕 This hypothesis, though, views larval survival and successful recruitment as chance events, and numerous studies on larval behavior and ecology have shown this to be false.〔Kingsford, M. J., J. M. Leis, A. Shanks, K. C. Lindeman, S. G. Morgan, and J. Pineda. 2002. Sensory environments, larval abilities, and local self-recruitment. Bull. Mar. Sci. 70(1) Suppl.: 309-340.〕 Though it has been generally disproved, the larval lottery hypothesis does represent an important understanding of the difficulties faced by larvae during their time in the water column, particularly because it recognizes the low probability of larval survival. All three marine larval strategies face two major problems: avoiding predation and finding an appropriate site to settle. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Marine larval ecology」の詳細全文を読む スポンサード リンク
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