Lanna Cheng

Increased oceanic microplastic debris enhances oviposition in an endemic pelagic insect

Plastic pollution in the form of small particles (diameter less than 5 mm)—termed ‘microplastic’—has been observed in many parts of the world ocean. They are known to interact with biota on the individual level, e.g. through ingestion, but their population-level impacts are largely unknown. One potential mechanism for microplastic-induced alteration of pelagic ecosystems is through the introduction of hard-substrate habitat to ecosystems where it is naturally rare. Here, we show that microplastic concentrations in the North Pacific Subtropical Gyre (NPSG) have increased by two orders of magnitude in the past four decades, and that this increase has released the pelagic insect Halobates sericeus from substrate limitation for oviposition. High concentrations of microplastic in the NPSG resulted in a positive correlation between H. sericeus and microplastic, and an overall increase in H. sericeus egg densities. Predation on H. sericeus eggs and recent hatchlings may facilitate the transfer of energy between pelagic- and substrate-associated assemblages. The dynamics of hard-substrate-associated organisms may be important to understanding the ecological impacts of oceanic microplastic pollution.

Prochloron : a microbial enigma

1.Introduction.- 2. Collection and Handling of Prochloron and Its Hosts.- Collection and Handling.- Didemnum molle.- Diplosoma virens.- Diplosoma similis.- Trididemnum cyclops.- Lissoclinum punctatum.- Lissoclinum voeltzkowi.- Lissoclinum patella.- Treatment of Prochloron cells.- Conclusion.- 3. Prochloron in Symbiosis.- Photosynthesis.- Translocation.- Formation of the Symbiosis.- Biochemical Interactions between the Symbionts.- Other Interactions between the Symbionts.- References.- 4. Physiological and Cellular Features of Prochloron.- Photosynthetic Features of Prochloron.- Carbon Metabolism.- Photosynthesis-Irradiance Relationships.- Respiratory Behavior and Carbon Balance in Prochloron.- Properties of the Photosynthetic Pigments and Membranes of Prochloron.- Pigments and Pigment-Protein Complexes.- Why Has Prochloron a Chlorophyll a + b Harvesting System?.- Physiology of the Prochloron-Ascidian Association.- Photosynthesis and Respiration of Symbiotic Didemnids.- Nitrogen Assimilation.- Obligate Nature of Symbiosis.- Some Suggested Physiological Requirements for the Culture of Prochloron.- Conclusion.- References.- 5. Biochemical Features of Prochloron.- General Features of Enzyme Isolation.- Enzymes of Photosynthetic Carbon Metabolism.- Ribulose 1,5-Bisphosphate Carboxylase-Oxygenase.- Phosphoribulose Kinase.- Enzymes of Glucan Synthesis and Storage Carbohydrates.- Lipophilic Components.- Lipid and Sterol Composition.- Pigments.- Properties of Membrane Fractions.- Miscellaneous Compounds and Metabolic Investigations.- Proteins and Amino Acids.- Cell Wall Components.- Nucleic Acids.- Nitrogen Metabolism.- Conclusion.- References.- 6. Phylogenetic Considerations of Prochloron.- Phylogenetic Position.- Phylogentic Rank.- Possible Relationship to Chloroplasts.- References.- 7. The Cytology of Prochloron.- The Cell Wall.- Thylakoids.- Inclusions.- Nucleic Acids.- Conclusion.- References.- 8. A Status Report on Prochlorothrix hollandica a Free-Living Prochlorophyte.- Epilogue.- Author Index.

Intracellular Symbiosis of a Photosynthetic Prokaryote, Prochloron sp., in a Colonial Ascidian

Cells of a symbiotic prokaryote, Prochloron sp., in colonies of a tropical ascidian, Lissoclinum punctatum, occur not only outside but also inside cells of the host. Cells of these photosynthetic symbionts of ascidians have previously been reported only extracellularly. The intracellular and extracellular symbionts do not differ morphologically. The host cells carrying the symbionts are freely distributed in the ascidian tunic. They probably endocytize the symbionts and then retain them within a vacuole. Since the intracellular prokaryotes showed no evidence of rejection or degeneration, this association between tunic phagocytes of L. punctatum and cells of Prochloron sp. seems to constitute a stable symrnbiosis, comparable to the postulated ancestral association between heterotrophic cells and the photosynthetic prokaryotes which gave rise to chloroplasts. Additional key words: algae, cyanobacteria, plastid evolution, prochlorophytes, tunicates Chloroplasts are photosynthetic organelles found in all photosynthetic eukaryotes. There is now convincing evidence from molecular biological studies on 16S-rRNA and RNA polymerase subunit (rpo Cl) and ribulose-bisphosphate carboxylase genes (Seewaldt & Stackebrandt 1982; Palenik & Haselkorn 1992; Urbach et al. 1992; Shimada et al. 1995) that these organelles originated from prokaryotic photosynthetic endosymbionts (cyanobacteria) engulfed and retained by heterotrophic host cells (Lewin 1981; Margulis 1981). Symbiotic photosynthetic prokaryotes are therefore of interest in relation to the evolution of chloroplasts. Prochloron is a genus of unicellular prokaryotes with the same chlorophyll pigments, chl a and b, as those in the chloroplasts of green algae and all other green plants (Lewin 1976). Prochlorophyta/Prochlorales was originally established (Lewin 1976, 1977; Florenzano et al. 1986) for prokaryotes that bear chl. a and b, lack bilin pigments, and generate oxygen in photosynthesis; molecular phylogenetic studies, however, indicate that this is a polyphyletic group whose members arose within the cyanobacterial radiation and should be treated as members of Cyanophyta/Cyanobacteria (Palenik & Haselkorn 1992; Urbach et al. 1992; Shimada et al. 1995). Cells of Prochloron occur in coral reef areas, almost exclusively as symbionts of colonial didemnid ascidians (Lewin & Cheng 1989). There the symbionts are normally associated with external or internal colony surfaces, but outside the host cells. Prochloron didemni LEWIN 1977 was originally described from the outer surfaces of didemnid colonies; but since no prochloron cells have been cultured in vitro, and specific distinctions remain to be established, we will refer to the symbionts in this paper simply as Prochloron sp. We present here the first report of Prochloron sp. as an intracellular symbiont in a didemnid ascidian, Lissoclinum punctatum KOTT 1977. Recent molecular biological data (Palenik & Haselkorn 1992; Urbach et al. 1992) indicate that the phylogenetic affinities of chloroplasts are closer to other cyanobacteria than to Prochloron, but we suggest that intracellular Prochloron can be regarded as a model of the ancestral green plastid.

Photosynthetic characteristics of Prochloron sp./ascidian symbioses

The prokaryotic green alga Prochloron sp. (Prochlorophyta) is found in symbiotic association with colonial didemnid ascidians that inhabit warm tropical waters in a broad range of light environments. We sought to determine the light-adaptation features of this alga in relation to the natural light environments in which the symbioses are found, and to characterize the temperature sensitivity of photosynthesis and respiration of Prochloron sp. in order to assess its physiological role in the productivity and distribution of the symbiosis. Colonies of the host ascidian Lissoclinum patella were collected from exposed and shaded habitats in a shallow lagoon in Palau, West Caroline Islands, during February and March, 1983. Some colonies from the two light habitats were maintained under conditions of high light (2 200 μE m−2 s−1) and low light (400 μE m−2 s−1) in running seawater tanks. The environments were characterized in terms of daily light quantum fluxes, daily periods of light-saturated photosynthesis (Hsat), and photon flux density levels. Prochloron sp. cells were isolated from the hosts and examined for their photosynthesis vs irradiance relationships, respiration, pigment content and photosynthetic unit features. In addition, daily P:R ratios, photosynthetic quotients, carbon balances and photosynthetic carbon release were also characterized. It was found that Prochloron sp. cells from low-light colonies possessed lower chlorophyll a/b ratios, larger photosynthetic units sizes based on both reaction I and reaction II, similar numbers of reaction center I and reaction center II per cell, lower respiration levels, and lower Pmax values than cells from high-light colonies. Cells isolated from low-light colonies showed photoinhibition of Pmax at photon flux densities above 800 μE m−2 s−1. However, because the host tissue attenuates about 60 to 80% of the incident irradiance, it is unlikely that these cells are normally photoinhibited in hospite. Collectively, the light-adaptation features of Prochloron sp. were more similar to those of eukaryotic algae and vascular plant chloroplasts than to those of cyanobacteria, and the responses were more sensitive to the daily flux of photosynthetic quantum than to photon flux density per se. Calculation of daily minimum carbon balances indicated that, though high-light cells had daily P:R ratios of 1.0 compared to 4.6 for low-light cells, the cells from the two different light environments showed nearly identical daily carbon gains. Cells isolated from high-light colonies released between 15 and 20% of their photosynthetically-fixed carbon, levels sufficient to be important in the nutrition of the host. Q10 responses of photosynthesis and respiration in Prochloron sp. cells exposed briefly (15–45 min) to temperatures between 15° and 45°C revealed a discontinuity in the photosynthetic response at the ambient growth temperatures. The photosynthetic rates were found to be more than twice as sensitive to temperatures below ambient (Q10=3.47) than to temperatures above ambient (Q10=1.47). The Q10 for respiration was constant (Q10=1.66) over the temperature range examined. It appears that the photosynthetic temperature sensitivity of Prochloron sp. may restrict its distribution to warmer tropical waters. The ecological implications of these findings are discussed in relation to published data on other symbiotic systems and free-living algae.

Distribution of the oceanic insects Halobates (Hemiptera: Gerridae) off the south coast of Japan

Specimens of ocean skaters Halobates were collected off the south coast of Japan in the East China Sea in 1995, and from the Kumano‐nada Sea to the East China Sea in 1998 and 1999. Three species were identified: H. micans, H. germanus and H. sericeus. We found two species co‐occurring in comparable densities in different years, a phenomenon not hitherto reported in other regions of the ocean. We discuss distributions of the three Halobates species with special reference to the influence of the Kuroshio Current, temporal variations of sea‐surface temperature, and monsoonal winds.

Mass Oviposition and Egg Development of the Ocean-Skater Halobates sobrinus (Heteroptera: Gerridae)

We report the first observation of mass oviposition by the oceanskater Halobates sobrinus White in the eastern tropical Pacific Ocean. We netted, in one scoop, 833 insects and a single egg mass with an estimated 70,000 eggs on a plastic gallon (3.785-liter) milk jug. Evidently anthropogenic debris could provide potentially important oviposition substrates for Halobates spp. in the open ocean. Freshly laid eggs incubated at 26-32C hatched within 8-10 days. Eggs kept at temperatures below 22C did not hatch even after 20 days.

Skaters of the seas – comparative ecology of nearshore and pelagic Halobates species (Hemiptera: Gerridae), with special reference to Japanese species

Abstract The insects overwhelm all other organisms of the world in species numbers and diversity. However, there are relatively few insects that inhabit the sea. Most of them are confined to the intertidal zone, with only five species of sea skaters, genus Halobates, having been successful in colonizing the open ocean. We discuss the ecology of both coastal and pelagic Halobates and the closely related genus Asclepios, focusing on their distribution ranges and adaptive strategies to marine environments accompanied by brief discussions of their biology. Updated information on the known localities for three species of Asclepios and some 40 coastal species of Halobates are presented. Many species live in vulnerable coastal habitats exposed to environmental pollution and coastal development. As a case study we trace the historical changes in populations of three Japanese sea skaters, Asclepios shiranui, Halobates matsumurai and H. japonicus, all designated as endangered species. For oceanic Halobates, we present an updated distribution map along with global current systems and sea-surface temperatures, examine interactions between distribution ranges and physical factors at the air–sea interface and discuss spatio-temporal variations in populations of each species. Finally, we infer the life history strategy of oceanic Halobates through theoretical considerations.

The sea-skater Halobates (Heteroptera: Gerridae) – probable cause for extinction in the Mediterranean and potential for re-colonisation following climate change

Sea-skaters in the genus Halobates Eschscholtz 1822 include some of the most specialised water striders and are found in tropical and subtropical seas around the world. Even though species of Halobates occur in both the Atlantic Ocean and the Red Sea, no extant sea-skater has been reported from the Mediterranean Sea. A fossil, Halobates ruffoi Andersen et al., 1994, described from Middle–Upper Eocene (45 Ma) Italy indicates that sea skaters were present in this part of the world in the past. Other geological evidence points to dramatic changes in the Mediterranean Sea during the Tertiary and Quaternary that may have led to their later extinction. In this paper we review briefly the distribution, systematics, evolution and ecology of Halobates, and discuss the potential for the Mediterranean to be recolonised following expected environmental changes due to global warming.

Chemical Composition and Behavioral Responses of the Marine Insect Halobates hawaiiensis (Heteroptera: Gerridae)

Halobates is the only insect genus with representatives in the open ocean. How adults find one another at sea has long been an intriguing issue. Since chemical communications have been demonstrated in a related marine veliid Trochopus, and laboratory bioassays indicated behavioral differences between males and females when insect extracts were presented, we carried out similar studies on Halobates. Analyses of surface lipid constituents of female and male Halobates hawaiiensis revealed marked differences. Palmitic and oleic acid, major constituents in the male extracts, were absent in the female extract, whereas nonacosenol, dominating the female extracts, was not detected in the male extracts. Analyses of nymphal extracts indicated an intermediate chemical profile. Surface waxes of all insect stages investigated showed nonacosanol and isononacosanol to be main components. “Headspace” analyses of airborne chemicals showed high levels of 4-hydroxy-4-methyl-2-pentanone and benzaldehyde from the male, whereas benzyl alcohol was the main component in the female mixture

Occurrence and density of Halobates micans (Hemiptera: Gerridae) in the eastern South Indian Ocean

Two species of ocean skaters, Halobates germanus and Halobates micans, live in the tropical and subtropical waters of the Indian Ocean. From December 1992 to December 1993, Halobates was intensively sampled in the easternmost region of the South Indian Ocean (13–18.5°S, 114–121E°), from which there have been a small number of records of Halobates. No H. germanus was caught, but a total of 1190 H. micans were collected, with densities estimated at 13 900–28 100 individuals/km2. This suggests that H. micans lives in the study area at high densities comparable to those in the Atlantic and the Pacific Oceans. We also discuss the possible effects of ocean currents and winds on the geographic distributions of the two Halobates species in the eastern South Indian Ocean.