Keiji Yamashita

Genetic polymorphism of the adult medusae invading an electric power station and wild polyps of Aurelia aurita in Wakasa Bay, Japan

A large quantity of the jellyfish, Aurelia aurita , invade cooling water systems and cause serious problems at several electric power stations in Japan. In the present study, we examined intra—species genetic variation of A. aurita in Wakasa Bay, Japan in order to estimate the original polyp habitat of the adult medusae invading electric power stations. Total DNA was extracted from the adult medusae and the wild polyps, and polymerase chain reaction (PCR) was performed using the specific primers for amplification of nuclear internal transcribed spacer one (ITS-1) and mitochondrial cytochrome oxidase c subunit 1 (CO1). Then the DNA sequences of the PCR products were compared. The results showed genetic polymorphism of A. aurita in Wakasa Bay and locally specific frequency of each haplotype. The haplotype frequency, especially in CO1, of the adults collected at one of the power stations in Wakasa Bay was similar to that of the polyp colonies at harbours in the embayed area, not at another harbour in the western entrance of the bay. The polymorphic analysis is, therefore, thought to be useful for the determination of original polyp habitat as source of the adult medusae in relatively limited regions such as Wakasa Bay.

Larval Behavioral, Morphological Changes, and Nematocyte Dynamics During Settlement of Actinulae of Tubularia mesembryanthemum, Allman 1871 (Hydrozoa: Tubulariidae)

The marine colonial hydroid Tubularia mesembryanthemum produces a morphologically unique dispersive stage, the actinula larva. Detailed observations were made on the behaviors and nematocyte dynamics of actinula larvae during attachment and morphogenesis by employing microscopic and time lapse video techniques. These observations produced four primary results. (1) Actinula larvae demonstrated two forms of attachment: temporary attachment by atrichous isorhiza (AI)—nematocysts discharged from the aboral tentacle (AT) tips—and permanent settlement by cement secretion from the columnar gland cells of the basal protrusion. (2) During larval settlement, numerous AIs were discharged from the AT tips with sinuous movement and rubbing of the tentacles onto the substrata, leading to “nematocyte-printing” around the settlement site. (3) Simultaneous with the discharge of the AIs, migration of stenoteles, desmonemes, and microbasic mastigophores occurred, resulting in a dramatic change of nematocyte composition in the ATs after larval settlement. This was in parallel with changes in larval behavior and the tentacle function. (4) Nematocyte-printing behavior during settlement could be recognized as metamorphic behavior responsible for irreversible changes in AT function, from attachment to feeding and defense.

Calcium Dependence of Settlement and Nematocyst Discharge in Actinulae of the Hydroid Tubularia mesembryanthemum

The influence of Ca2+ and Mg2+ ions on both atrichous isorhiza (AI) discharge and settlement of actinular larvae of the hydroid Tubularia mesembryanthemum was investigated. Mg2+-supplemented artificial seawater (ASW) completely inhibited both events at a concentration of 206 mM, whereas lowered Mg2+ concentrations enhanced them. Ca2+ ions in the bathing solution highly regulated AI discharge and settlement, and Mg2+ ions may down-regulate these events. The effect of inorganic Ca2+-channel blockers, including Gd3+ and La3+, was also examined. Larval settlement was inhibited by Co2+, Ni2+, Cd2+, La3+, and Gd3+, with half inhibitory concentrations (IC50) of 5800, 260, 53, 45, and 7 {mu}M, respectively; AI discharge was also inhibited by these ions, with IC50 values of 6600, 500, 78, 41, and 5 {mu}M, respectively. These results suggest possible involvement of stretch-activated Ca2+ channels in the signal transmission of both AI discharge and larval settlement.

Cypris Larvae (Cirripedia: Balanomorpha) Display Auto-fluorescence in Nearly Species-specific Patterns

The identification of balanomorph larvae plays an important role in ecological study and for protection against biofouling. However, it is difficult to identify species of cyprids (settling larvae) of balanomorph barnacles, as they show remarkably similar morphology. Some authors have suggested distinguishing cyprids of different species by carapace length, pigmentation, and fine carapace detail. However, such criteria are only applicable to a narrow range of balanomorph species. Recently, we were have serendipitously found species-specific distribution of fluorescent substances in cultured cyprids obtained from adult balanomorph barnacles, collected near the coast of Japan. Fluorescent patterns (FPs) of cyprids from 11 species were classified into five major groups. Cyprids specimens collected from the field were estimated, based on the FPs and other morphological characteristics (pigmentation and carapace length), after which their species were identified using the following two criteria: the morphology of adults derived from the field cyprids that adhered to a culture dish, and cyprid 12S rRNA gene sequence. The results of species estimation by FPs largely corresponded to the correct species identification. Other FP groups were found in the field cyprids. This study of FPs should be helpful for identification of cyprid species.

Settlement Inhibitory Effects of Kureha's PGA (Polyglycolic Acid) Resin on Marine Sessile Organisms

2.1 試験生物 試験生物として,海産ヒドロ虫類クダウミヒドラ1 種(Ectopleura sp.)のアクチヌラ幼生,フジツボ類 タテジマフジツボ(Amphibalanus amphitrite)のキ プリス幼生,及び付着珪藻(Navicula ramosissima) を用いた(図 1). アクチヌラ幼生については,東播磨沿岸産クダウミ ヒドラポリプ群体を低温水槽で維持・飼育しながら, 幼生遊出直前の♀ポリプのみビーカー海水内に静置し, 随時,遊出した幼生をピペットで集めて試験に用いた. キプリス幼生については,姫路市沿岸産タテジマフ ジツボ成体から孵出したノープリウス幼生を,ビーカ ー海水中で浮遊珪藻を給餌しながら飼育し,得られた キプリス幼生を試験に用いた. 付着珪藻(Navicula ramosissima)については,増 養殖研究所より分譲された標準株を,藻類培養液 (KW21 にSi を添加)を用いて,人工照明下で移植・ 拡大培養したものを試験に用いた.