Muscle tissue growth and muscle fibre dynamics in the tropical loliginid squid Photololigo sp. (Cephalopoda: Loliginidae)

Growth of somatic tissue in Photololigo sp. was examined in terms of muscle fibre recruitment and growth. Muscle blocks and muscle fibres were measured and size frequency distributions compared between different size-classes of squid. Muscle blocks increased in size as individuals grew. The size frequency distribution of the muscle blocks suggested that this increase was due to both the generation of new muscle fibres and an increase in the size of existing muscle fibres. The size frequency distribution of muscle fibres was very similar in all size-classes of squid examined, and the presence of small muscle fibres in all individuals suggested that fibre recruitment may be continuous. Growth of muscle tissue, by muscle fibre growth and recruitment, provides a mechanism to explain constant growth throughout the life cycle described for tropical squid. Two structural types of muscle fibres, mitochondria-poor and mitochondria-rich, are present in juvenile and adult squid. A weak relationship between the ratio of the two muscle fibre types and dorsal mantle length suggests that generation of mitochondria-rich fibres may not be influenced by growth

Cross-shelf distribution patterns of tropical juvenile cephalopods sampled with light-traps

This paper describes the cephalopod genera caught with light-traps at different locations and depths in the waters of the central Great Barrier Reef (GBR). Multiple stations were sampled in four locations: (1) the coastal GBR Lagoon, (2) inter-reef passages (Magnetic and Palm), (3) near-reef environments (Keeper, Helix, Faraday and Myrmidon) ranging from mid- to outer-shelf locations, and (4) the Coral Sea. A total of 13 cephalopod genera was caught from monthly cruises conducted from October to January of 1990-91 and 1991-92. Octopus, the most abundant juvenile cephalopod, was present in relatively high numbers at all shelf locations; few were caught in the Coral Sea. Photololigo, the most abundant squid, was rarely caught outside the GBR Lagoon. In contrast, Sthenoteuthis, the second most abundant squid, was caught at all locations. Deep samples from most locations were dominated by Octopus. Abralia was found only near the bottom of the GBR Lagoon; in contrast, Euprymna, the fourth most abundant genus, was collected only at the surface. Cephalopod communities from the GBR Lagoon had higher abundances of Octopus, Photololigo and Abralia compared with communities from the three other areas. Reef passages and reef locations shared similar communities, with the squid component dominated by Sthenoteuthis. Very low numbers of cephalopods were caught in the Coral Sea by light attraction. High concentrations of cephalopods detected in the middle of the GBR Lagoon are consistent with present knowledge about oceanographic processes over this shelf

Response of Antarctic terrestrial microarthropods to long-term climate manipulations

The terrestrial biota of the Antarctic Peninsula region are experiencing marked changes in climate, especially rising temperatures, precipitation, and UV-B radiation-a combination unique worldwide. These changes, combined with the inherent simplicity of terrestrial communities, have led to their use as "model systems" to predict the future climate change responses of biota at lower latitudes. However, studies integrating responses at different levels of the community trophic structure are lacking. We report here the consequences on the soil microarthropod community of a four-year, multivariate, climate-manipulation experiment carried out over vegetation near Palmer Station, Anvers Island, western Antarctic Peninsula. The experiment used a multifactorial randomized-block design, deploying filters to raise temperatures and reduce ultraviolet (UV)-B (280-320 nm) or both UV-B and UV-A (320-400 nm) radiation of existing vegetation, with further water and fertilizer amendment treatments. Seven microarthropod species recovered in sufficient numbers for statistical analyses showed considerable spatial aggregation independent of treatment, a feature typical of many soil invertebrates. Analyses using negative binomial generalized linear modeling identified further significant and consistent treatment impacts on both individual species and species groups. Relative to controls, manipulations increasing temperature decreased numbers of microarthropods (particularly Collembola), as did exposure to near-ambient levels of UV radiation (separate significant effects for both UV-A and UV-B), while water amendment increased numbers. The impacts of temperature and water are consistent with our understanding of the importance of these two environmental variables and their interaction in Antarctic terrestrial ecosystems. The negative impact of UV (-A or -B) on arthropod heterotroph and detritivore populations in the Antarctic terrestrial food web is likely to be a secondary consequence of UV impact on vegetation characteristics. This is, again, consistent with general predictions of the impact of changing UV climate on ecosystem function

Transitions during cephalopod life history: the role of habitat, environment, functional morphology and behaviour

Cephalopod life cycles generally share a set of stages that take place in different habitats and are adapted to specific, though variable, environmental conditions. Throughout the lifespan, individuals undertake a series of brief transitions from one stage to the next. Four transitions were identified: fertilisation of eggs to their release from the female (1), from eggs to paralarvae (2), from paralarvae to subadults (3) and from subadults to adults (4). An analysis of each transition identified that the changes can be radical (i.e. involving a range of morphological, physiological and behavioural phenomena and shifts in habitats) and critical (i.e. depending on environmental conditions essential for cohort survival). This analysis underlines that transitions from eggs to paralarvae (2) and from paralarvae to subadults (3) present major risk of mortality, while changes in the other transitions can have evolutionary significance. This synthesis suggests that more accurate evaluation of the sensitivity of cephalopod populations to environmental variation could be achieved by taking into account the ontogeny of the organisms. The comparison of most described species advocates for studies linking development and ecology in this particular group.Jean-Paul Robin, Michael Roberts, Lou Zeidberg, Isobel Bloor, Almendra Rodriguez, Felipe Briceño, Nicola Downey, Maite Mascaró, Mike Navarro, Angel Guerra, Jennifer Hofmeister, Diogo D. Barcellos, Silvia A.P. Lourenço, Clyde F.E. Roper, Natalie A. Moltschaniwskyj, Corey P. Green, Jennifer Mathe