Fine structure of naive and allogeneic challenged ampullae in Botrylloides subpopulation I from the Mediterranean coast of Israel

The external peripheral termini of vasculature in botryllid ascidians (ampullae) are important in the expression of effector mechanisms during histocompatibility reactions. We study here morphological changes to the microstructure during allorecognition in Botrylloides subpopulation I (SP1) from the Mediterranean coast of Israel, where special giant ampullae, called megaloampullae are developed hours after first allogeneic challenge. The basal part of each naive ampulla consists of a sheath of continuous squamous epithelial cells (1 μm×20 μm). At the tip of the ampullae, about 130 epithelial cells become columnar with wide apical pads (15 μm×5–10 μm), that contain electron-opaque “adhesive vesicles”. Foci of crystallizations were observed within the vesicles of some columnar cells. Ampullar epithelial cells develop internal folds that support tight attachments between circulating blood cells (most of them are pigment cells) and ampullar epithelium. During the histoincompatibility process, the tunic peripheral edge at the interaction area becomes highly convoluted. Filaments (up to 1.16 μm) accumulate in the interaction tunic matrix. Some of these filaments encircle destructed cells. Fragmented cell membranes are also found next to the reacting ampullae. The most characteristic feature of the Botrylloides SP1 rejection reaction is dilation of the ampullae. The ampullar epithelium becomes “curly” when megaloampullae are formed. Within the curly region, about 30% of the squamous epithelial cells are further stretched, up to 33 μm in length. Some additional mechanisms are suggested to explain the fast increase (up to seven times) in ampullar width that is recorded within a few hours from the first allogeneic contact.     

Photosynthetic characteristics of marine Synechococcus spp. with special reference to light environments near the bottom of the euphotic zone of the open ocean

The present study aimed to resolve the question why marine Synechococcus spp. abundantly occur even at the bottom of the euphotic zone in the Kuroshio are. Photosynthesis under such conditions was examined using simulated blue-green model light (BGL). Results indicated that photosynthesis of marine Synechococcus spp. under BGL is as active enough to support growth of these organisms. Examination of light-harvesting under BGL indicated that active photosynthesis is permitted by an unusually high abundance of phycoerythrin (PE), which is the main light-harvesting pigment for photosystem II (PSII), due to a phycobilisome (PBS) structure which is different from ordinary hemidiscoidals. Although the absorption maximum of PE is located at longer wavelengths than the energy maximum of BGL, PE was found to absorb BGL significantly. Thus, BGL cannot be a typical photosystem I (PSI) light. PSII is also significantly excited by BGL. Carotenoids, which largely absorb BGL, were found to be effective in light-harvesting for PSI. Based on the results obtained, possible reasons why marine Synechococcus spp. commonly occur in warm waters were discussed. Two strains of Synechococcus spp. isolated from the Gulf Stream in 1981 and from Kuroshio, Japan in 1983 were used in the present study.     

Remigration and growth of loggerhead turtles (<Emphasis Type="Italic">Caretta caretta</Emphasis>) nesting on Senri Beach in Minabe,Japan: life-history polymorphism in a sea turtle population

There are size-related differences in the use of feeding habitats (planktonic or benthic; oceanic or neritic) by adult female loggerhead sea turtles (Caretta caretta) within Japanese populations. We thus hypothesized that the differences may be reflected in their remigration and growth patterns, and investigated the relationships between body size and remigration intervals, growth rates, and remigration percentages, for female loggerheads nesting on a Japanese beach between 1991 and 2001. Although remigration intervals, growth rates, and remigration percentages were not significantly different among females, there were trends for longer remigration intervals and lower remigration percentages in smaller females. All females grew little. Considering these results along with previous findings, we speculated on the life-history strategy of female Japanese loggerheads.Communicated by T. Ikeda, Hakodate     

Cultures of the pelagic cyanophytes Trichodesmium erythraeum and T. thiebautii in synthetic medium

Trials for determination of culture conditions for the marine cyanophytes of Trichodesmium erythraeum and T. thiebautii were made with use of a synthetic medium. The Aquil medium, either with or without combined nitrogen, brought about stable growth of the two strains, T. erythraeum and T. thiebautii. However, they failed to grow in an ASP₇ medium. The failure was found to be due to the toxic effect of Tris-aminomethane, the pH-buffer in this medium. Two important chemical conditions for the stable growth of Trichodesmium spp. were revealed. (1) Stable growth was supported by Ca²⁺ at high concentrations; in a concentration lower than 0.9 mM, cell-lysis promptly occurred, while the cells could grow without cell-lysis at Ca²⁺ concentrations higher than 7.5 mM even at a salinity as low as 19 S. Ca²⁺ is probably essential for the osmotic regulation in this organism. (2) Phosphate-toxicity at high concentrations was at least partly due to heavy metal(s) contaminating the reagent of inorganic phosphate. After treatment with a Chelex-100 column, phosphate concentration could be increased up to four times the previous concentrations without toxicity.     

Night irradiance and synchronization of lunar release of planula larvae in the reef coral Pocillopora damicornis

Pocillopora damicornis (Linnaeus), which is known to release planula larvae on a monthly cycle, was grown in full daytime solar irradiance, but with four treatments of night irradiance: (1) natural night irradiance, (2) shifted-phase (total darkness during nights of full moon with artificial irradiance at lunar intensity on nights of new moon), (3) constant full moon (full lunar irradiance every night), and (4) constant new moon (total darkness every night). The reproductive cycle of the corals held in the shifted-phase treatment moved out of synchrony with the cycle of corals exposed to a natural lunar cycle of night irradiance. Two previously described types of P. damicornis were tested. The Type Y normally start releasing larvae at full moon, with peak production at third quarter. In the shifted-phase treatment they began releasing planulae at new moon (artificial full moon), with peak production at first quarter. The Type B corals, that normally start releasing planulae at new moon with peak production at first quarter, began to release planulae at full moon (artificial new moon), with peak production at third quarter. Populations of corals grown either in the constant full moon or constant new moon treatment quickly lost synchronization of monthly larva production, although production of planulae continued. Thus spawning is synchronized by night irradiance.Contribution No. 702 of the Hawaii Institute of Marine Biology     

Genetic variation in marine teleosts: High variability in habitat specialists and low variability in habitat generalists

Genetic variation was reviewed in 106 species of marine teleosts. Two heterozygosity estimates were used, one including all protein and enzyme loci and a second excluding the non-enzymatic protein loci. Mean heterozygosities are 0.055±0.036 based on all loci in 106 species and 0.060+0.038 based on enzymatic loci in 89 species. A significant negative correlation was noted between heterozygosity and the proportion of general protein loci included in the estimate. A comparison was made of heterozygosities among taxonomic orders and families, life zones, reproductive mode, geographical range and size. High levels of genetic variation are found in Clupeiformes, Atheriniformes, Pleuronectiformes, temperate pelagic, tropical, intertidal-sublittoral and wide-range species. Low levels of genetic variation are found in Gadiformes, Scorpaeniformes, temperate demersal, polar, and narrowrange species. The most striking differences in heterozygosities are between temperate demersal flatfishes and temperate demersal round fishes. It is suggested that much of the data can be explained by a habitat specialist-generalist model, with high heterozygosities in specialists and low heterozygosities in generalists, but that this is only one of a mosaic of factors which influence genetic variation.     

Light regulation of nitrate reductase in Ulya fenestrata (Chlorophyceae)

Observations were made on the behavior of nitrate reductase activity in the green alga Ulva fenestrata under controlled light:dark regimes. The activity of nitrate reductase (NR) was examined in response to normal seasonal photoperiods as well as in response to shortened or extended periods of darkness. NR activity exhibits a light-dependent diurnal rhythm under both normal summer and winter photoperiods, with a maximum in the early morning (2 to 2.5 h after the start of illumination). This peak of activity is followed by a lower steady-state level of activity which is sustained throughout the light period. There is a sustained minimal level of activity in darkness. The morning peak in activity is always observed as long as tissue is illuminated, irrespective of the previous light or dark treatments. As such, it appears that nitrate reductase activity in U. fenestrata is under circadian control. There is no major difference in the NR activity pattern between summer and winter plants, except that the peak activity values in winter plants are consistently much higher (5 times) than in summer plants. The study also suggests that illumination prior to the normal start of photoperiod triggers a different set of regulatory mechanisms, indicating that the physiological state of plants is important in dictating the NR activity response to illumination.Please address all correpondence and requests for reprints to G. J. Smith at his present address (Hopkins Marine Station)     

Benthic invertebrate larval response to substrate characteristics at settlement: Shelter preferences of the American lobsterHomarus americanus

The factors controlling shelter selection by the first post-larval stage of the American lobsterHomarus americanus were studied in the laboratory in 1988 using an experimental approach. The relative importance of shelter size, light level within shelters, number of shelter entrances, and presence of algal-film cover in and around them were investigated. Post-larvae showed a strong preference for opaque versus transparent shelters. No difference in post-larval selectivity was observed either for shelters of different widths or heights or between shelters with different numbers of entrances. Post-larvae showed no preference for microhabitats colonized by microorganisms compared to others without colonization. The intensity of the response measured suggests a possible hierarchical organization of the different cues involved in shelter selection, the light level within the shelter apparently being the most important. Simple linear regression was used to assess the effect of shelter area on the number of post-larvae occupying a shelter. Up to four post-larvae were observed simultaneously in a shelter of 40 cm² basal area, indicating that they can cohabit at settlement. The minimum shelter area necessary to the first post-larval stage was estimated to be about 3.25 cm². The results are discussed with reference to recent hypotheses concerning the mechanisms controlling larval settlement in other benthic species with relatively weak mobility during the larval and the post-larval phases.Contribution to the programmes of GIROQ (Groupe interuniversitaire de recherches océanographiques du Québec) and of the Institut Maurice-Lamontagne     

Decomposition and microbial dynamics for standing,naturally positioned leaves of the salt-marsh grass Spartina alterniflora

Decomposition of leaves of smooth cordgrass (Spartina alterniflora Loisel.) was monitored for two cohorts of leaves from September 1984 to May 1985 (autumn and winterspring) at Sapelo Island (31°23 N; 81°17 W). The leaves were tagged in plance at the ligule, rather than cut and placed in litterbags. Dead leaves were not abscised from shoots. Loss of organic mass from the attached leaves was at least 60 to 68% of the orginal values. Fungal mass, as measured by an enzyme-linked immunosorbent assay, formed > 98% of the microbial standing crops in two of three autumn samples, and in all samples for the colder, drier, winterspring cohort. Fungal mass was probably mostly in the form of the mycelium and pseudothecia of an ascomycete, Phaeosphaeria typharum (Desm.) Holm. Fungal dominance of microbial standing crops declined when autumn leaves bent downward and acquired a large sediment content (ash=35% of dry matter); the bacterial crop then rose to 7% of the total microbial crop. Microphotoautotrophic mass was always measurable, but was never more than 2% of the microbial crop. Carbon-dioxide fixation was much lower than carbon-dioxide release, and a substantial portion of the fixation may have been anaplerotic fungal fixation. Threeto 8 wk net fungal productivity (average per day) was much greater (16 to 26 times) than measured instantaneous bacterial productivity (extrapolated to per-day values) early in each decay period. Fungal productivity was negative late in the decay period. Fungal productivity was negative late in the decay period for autumn leaves, and was approximately equal to bacterial productivity late for winter-spring leaves. Net nitrogen immobilization was observed only late in the decay period for autumn leaves, implying that nearly all dead-leaf nitrogen was scavenged into fungal mass after the first sampling interval. Flux estimates for dead-leaf carbon indicated a flow of 11–15% of the original to fungal mass, 2% to bacterial mass, 15–21% to carbon dioxide, 10–12% to dissolved leachage, and 34–36% to small particles; 32–39% remained attached as shreds at the end of the study periods. Salt-marsh periwinkles (Littorina irrorata Say) appeared to be the major shredders of dead leaves and conveyors of leaf-particulate material to the marsh sediment, at least in those parts of the marsh where the snails are densely concentrated (usually areas of short- and intermediateheight cordgrass shoots).