Ontogenetic changes in size and shape of statoliths: implications for age and growth of the short-lived tropical squid Sepioteuthis lessoniana. (Cephalopoda: Loliginidae)

This study examined the relation between statolith and somatic growth in the tropical squid Sepioteuthis lessoniana. Five separate linear dimensions were measured on the statoliths of 103 individuals (17–245 mm mantle length). In addition the statoliths of 80 adults (82–245 mm mantle length) were weighed. Statolith increment analysis provided age estimates for 78 individuals. Statolith total length was correlated with age for squid less than ~60 days of age, although neither statolith total length nor weight was a useful predictor of age in older squid. Combining the five statolith dimensions to produce a description of statolith shape provided only slightly better estimates of age than statolith total length or weight alone. Statolith shape changed during ontogeny, developing from relatively elongate juvenile statoliths into the adult form with more robust dorsal and lateral domes. This development was reflected in wider spacing and superior optical definition of daily growth increments in the dorsal and lateral domes of adult statoliths, in relation to the slower growing rostrum. Growth of S. lessoniana statoliths does not appear to be strongly linked to mantle growth; both statolith total length and weight increase more slowly than mantle length

Heritability and fitness-related consequences of squid personality traits

Dumpling squid, Euprymna tasmanica, show consistent individual differences in behaviour that can be classified according to indices reflecting shy–bold, activity and reactivity responses. Using crosses of wild-caught single males to multiple females with known behavioural phenotypes, this study estimated patterns of additive genetic and residual variance in these behavioural traits from offspring of squid in two contexts, a threat (antipredator) and feeding (foraging) test. Genetic contributions to behavioural expression were dependent on test context. Behaviours in antipredator contexts had significant heritabilities (h2 = 0.2–0.8) while behaviours from foraging contexts had lesser additive genetic and greater residual components (h2 = 0.05–0.08). Personality trait variation in females was not related to her fecundity. Female boldness in foraging situations, which co-varied with body size, explained small but significant variation (∼21%) in brood hatching success, while successful fertilization was determined by positive assortion of mate pairs according to their shy–bold phenotype. These results are discussed in terms of the ecological and evolutionary significance of animal 'personality' traits in wild populations of animals

Size and characteristics of aggregations of moon jellyfish (Aurelia SP.) in Tasmania, Australia

Moon jellyfish, Aurelia spp., are found in marine and estuarine environments worldwide and can concentrate into dense aggregations within enclosed or semi-enclosed water bodies (e.g., Lucas et al. 1997, Purcell et al. 2000). Aggregations are often promoted by physical properties of the water body in which they occur and are commonly believed to facilitate sexual reproduction, rather than act as a defence against predation ortargetingfoodsources (Graham etal. 2001, Lucas 2001). The presence of!arge-scale aggregations of medusae, as a function offavourable conditions, has substantial ecological and economic consequences (Purcell et al. 2007). The distribution, abundance and life history characteristics of the genus Aurelia are highly variable spatially and temporally (e.g., Schneider & Brehrends 1994, Lucas et al. 1997). The pelagic medusa stage generally occurs seasonally and lives for several months (Lucas & Williams 1994, Miyake et al. 1997), but in some populations, medusae will live for 12 months or more (Kinoshita et al. 2006). Aurelia medusae are voracious feeders and are capable of modifying the seasonal composition and abundance of the planktonic community (Schneider & Brehrends 1994, Lucas et al. 1997). Secondary effects of high grazing pressure include increased phytoplankton biomass through reduced grazing pressure by copepods (Lindahl & Hernroth, 1983, Olsson et al. 1992, Moller & Riisgard 2007a) and decreased food availability for other zooplanktivores, which can have impacts through the food chain (Purcell & Arai 2001). Given their widespread distribution, occurrence in large aggregations and capacity to alter trophic dynamics, jellyfishes are potentially important consumers and transformers of energy and nutrients in the marine ecosystem (e.g., Watanabe & Ishii 2001, Pauly et al. 2009, Pitt et al. 2009). Determining the abundances and sizes of jellyfish in the oceans has proved difficult because of their large sizes, fragility and patchy distributions, both horizontally and vertically, and because their gelatinous bodies are difficult to tag (Purcell 2009). Also, the high water content of their tissues makes acoustic sampling difficult, although combined acoustic soundings and video recordings can monitor relatively reliably some jellyfish species, provided the target species can be distinguished from other co-occurring species acoustically (Bamstedt et al. 2003, Alvarez Columbo et al. 2009). Consequently, estimates of the extents, causes and effects of jellyfish blooms have rarely been conducted on a large scale (Purcell 2009). Aurelia sp. medusae periodically occur in dense monospecific aggregations in the sheltered waterways of southeast Tasmania, Australia (pl. 1). The medusae are morphologically similar to Aurelia aurita; however, they are genetically distinct from other species of Aurelia and have been designated as Aurelia sp. 7 (Dawson et al. 2005). Growth, survival and reproduction of the sessile, asexual, colonial phase of this species has been found to be regulated by a combination of density-dependent factors and environmental conditions, which are consequently important to the formation of jellyfish aggregations (Willcox et al. 2008). These aggregations, however, were largely unnoticed until they caused the deaths of cultured Atlantic Salmon in Tasmania, valued at millions of dollars. 'The objective of this study was to describe the biological characteristics of this species, as part of a larger study investigating mechanisms driving the intermittent occurrence of Aurelia sp. aggregations in southeast Tasmania. This included growth and reproduction of individuals in the aggregations, and estimating aggregation size and total biomass of medusae in the system. To achieve this, we developed a method to assess the abundance of jellyfish by combining aerial photography, underwater video photography and net sampling

Contrasting Responses to Harvesting and Environmental Drivers of Fast and Slow Life History Species

According to their main life history traits, organisms can be arranged in a continuum from fast (species with small body size, short lifespan and high fecundity) to slow (species with opposite characteristics). Life history determines the responses of organisms to natural and anthropogenic factors, as slow species are expected to be more sensitive than fast species to perturbations. Owing to their contrasting traits, cephalopods and elasmobranchs are typical examples of fast and slow strategies, respectively. We investigated the responses of these two contrasting strategies to fishing exploitation and environmental conditions (temperature, productivity and depth) using generalized additive models. Our results confirmed the foreseen contrasting responses of cephalopods and elasmobranchs to natural (environment) and anthropogenic (harvesting) influences. Even though a priori foreseen, we did expect neither the clear-cut differential responses between groups nor the homogeneous sensitivity to the same factors within the two taxonomic groups. Apart from depth, which affected both groups equally, cephalopods and elasmobranchs were exclusively affected by environmental conditions and fishing exploitation, respectively. Owing to its short, annual cycle, cephalopods do not have overlapping generations and consequently lack the buffering effects conferred by different age classes observed in multi-aged species such as elasmobranchs. We suggest that cephalopods are sensitive to short-term perturbations, such as seasonal environmental changes, because they lack this buffering effect but they are in turn not influenced by continuous, long-term moderate disturbances such as fishing because of its high population growth and turnover. The contrary would apply to elasmobranchs, whose multi-aged population structure would buffer the seasonal environmental effects, but they would display strong responses to uninterrupted harvesting due to its low population resilience. Besides providing empirical evidence to the theoretically predicted contrasting responses of cephalopods and elasmobranchs to disturbances, our results are useful for the sustainable exploitation of these resourcesVersión del editor4,411