Rapid assessment of different oxygenic phototrophs and single-cell photosynthesis with multicolour variable chlorophyll fluorescence imaging

We present a new system for microscopic multicolour variable chlorophyll fluorescence imaging of aquatic phototrophs. The system is compact and portable and enables microscopic imaging of photosynthetic performance of individual cells and chloroplasts using different combinations of blue, green, red or white light. Automated sequential exposure of microscopic samples to the three excitation colours enables subsequent deconvolution of the resulting fluorescence signals and colour marking of cells with different photopigmentation, i.e., cyanobacteria, green algae, red algae and diatoms. The photosynthetic activity in complex mixtures of phototrophs and natural samples can thus be assigned to different types of phototrophs, which can be quantified simultaneously. Here, we describe the composition and performance of the new imaging system and present applications with both natural phytoplankton and microalgal culture samples.     

Seabird use of discards from a nearshore shrimp fishery in the South Atlantic Bight,USA

Shrimp trawling is common throughout the southeastern and Gulf of Mexico coasts of the USA and is the primary contributor to fisheries discards in these regions. Tens of thousands of nearshore seabirds nest near shrimp trawling grounds in the USA, but to date, there has been no assessment of the relationship between seabirds and shrimp trawlers. We examined the taxonomic composition of bycatch, rate at which seabirds scavenged bycatch, and energy density of discarded bycatch in a nearshore commercial shrimp fishery. Bycatch was primarily comprised of demersal fish that are not typically accessible to the plunge-diving and surface-feeding seabirds that occur in the area. Hence, seabird diets in the region appear to be broadened taxonomically by the availability of discards. Results from discard experiments indicated that 70% of the nearly 5,500 items discarded by hand were scavenged by seabirds and that the fate of a discarded item was most strongly predicted by its taxonomic order. Laughing gulls scavenged the greatest proportion of discards, although brown pelicans were the only species to scavenge more discards than predicted based upon their abundance. Because this is the first such study in the region, it is difficult to ascertain the extent or intensity of the impact that discards have on nearshore seabirds. Nonetheless, our results suggest that it will be difficult for managers to clearly understand fluctuations in local seabird population dynamics without first understanding the extent to which these species rely upon discards. This may be especially problematic in situations where seabird populations are recovering following natural or anthropogenic stressors.     

A comparative analysis of sperm storage and mating strategies in five species of brachyuran crabs

Variation in female sperm storage is explained, in part, by the amount of sperm transferred at mating. Laboratory mating experiments were conducted on Eurypanopeus depressus and Rhithropanopeus harrisii from the Chesapeake Bay and Pachygrapsus transversus from Florida, while mated pairs of Uca beebei and U. terpsichores were collected from mudflats in Panama. All experiments and collections were conducted during the summer of 2006 and 2007. More sperm was transferred to larger than smaller females, and by species with long copulation durations (R. harrisii and E. depressus). These two species live in cryptic habitats, have high sperm/egg ratios, and likely store sperm across multiple broods. In contrast, P. transversus and U. beebei mate conspicuously, have short copulations, transfer fewer sperm, and have low sperm/egg ratios. Comparisons of sperm transfer across different mating strategies and habitats provide a better understanding of female sperm storage in the Brachyura.     

The role of intraguild predation in the population dynamics of small pelagic fish

In this paper, we argue that understanding marine ecosystem functioning requires a thorough appreciation of the role of intraguild predation to system dynamics. The theoretical predictions of intraguild predation models might explain some of the community features observed in marine ecosystems such as low diversity in upwelling and productive systems and species alternation in response to moderate external forcing. Finally, we argue that an ecosystem approach to fisheries requires that the size–structure of fish populations should be taken into account and that it is extremely important to account for the predators of early stages (eggs and larvae) to gain a thorough understanding of the key interactions between species.     

Life-history and demographic spatial variation in Mediterranean populations of the opportunistic polychaete <Emphasis Type="Italic">Ophryotrocha labronica</Emphasis> (Polychaeta,Dorvilleidae)

The spatial scale of life-history and demographic variation was investigated in the opportunistic polychaete Ophryotrocha labronica La Greca and Bacci. Individuals were collected along the Italian coasts from three thermally different biogeographical regions of the Mediterranean Sea. For each region, populations from four harbours were considered, and for each harbour, two sites were examined. Life-history and demographic traits were investigated after one generation under a common garden experiment, and their variation at the three spatial scales was assessed. All the traits showed high variability with regard to site. A number of life-history and all demographic traits also varied according to the biogeographical region. Conversely, no differences were found between harbours, suggesting that geographical isolation did not contribute to phenotypic variation. Results confirmed the central role of local conditions for the evolution of life history in species colonizing heterogeneous environments, but they also pointed to the importance of large-scale factors in shaping the phenotypic responses of O. labronica, demonstrating the need for a multi-scale approach for obtaining a good measure of natural variation in widespread opportunistic species.     

Prey selection in <Emphasis Type="Italic">Octopus rubescens</Emphasis>: possible roles of energy budgeting and prey nutritional composition

This study explores the relationship between energy budgeting and prey choice of Octopus rubescens. Seventeen male Octopus rubescens were collected between June 2006 and August 2007 from Admiralty Bay, Washington. Prey choices made by individuals in the laboratory deviated widely from those expected from a simple optimal foraging model. O. rubescens chose the crab Hemigrapsus nudus over the clam Nuttallia obscurata as prey by a ratio of 3:1, even though prey energy content and handling times suggested that this octopus could obtain 10 times more energy intake per unit time when choosing the latter compared to the former prey species. Octopus energy budgets were similar when consuming either of the prey species except for lipid extraction efficiency that was significantly higher in octopuses consuming H. nudus. This suggests that lipid digestibility may play an important role in the prey choice of O. rubescens.     

Mutualist-induced morphological changes enhance growth and survival of corals

Species interactions can induce morphological changes in organisms that affect their subsequent growth and survival. In Moorea, French Polynesia, epibiotic gammaridean amphipods induce the formation of long, branch-like coral “fingers” on otherwise flat, encrusting, or plating Montipora coral colonies. The fingers form as corals encrust tubes built by the amphipods and lead to significant changes in colony morphology. This study examines the costs and benefits of this association to the amphipods and corals and demonstrates that the interaction is a mutualism. Amphipods gain protection from predators by living within corals, and corals benefit by enhanced growth and survival. Benefits to the coral arise through direct effects due to the amphipods’ presence as well as through benefits derived from the altered colony morphology. This study demonstrates that induced morphological plasticity can be a mechanism for facilitation, adding to our knowledge of the roles mutualism, and phenotypic plasticity play in ecology.     

The reproductive ecology of the invasive ascidian, <Emphasis Type="Italic">Styela clava,</Emphasis> in Auckland Harbour,New Zealand

The ascidian Styela clava, native to the north-west Pacific, is an invasive species affecting New Zealand’s marine ecosystems, biodiversity and aquaculture operations. To provide detailed information on the reproductive biology of S. clava in New Zealand for post-border biosecurity management, long-term seasonal patterns of gametogenesis were determined from May 2006 to May 2008 in Auckland’s Waitemata Harbour (36°49′20″S, 174°45′85″E). Of particular interest was whether the critical 15°C threshold spawning temperature for reproduction observed in the Northern Hemisphere applied here to the first Southern Hemisphere study. S. clava gametogenesis followed a regular seasonal cycle with ripe gametes appearing as early as September and persisting to June; this time frame corresponds to the period when sea surface temperatures in the region first reach 15°C and with spawning occurring mainly during late summer to early autumn. From photoperiod manipulation, it was determined that spawning occurred at approximately 18:20. The extended reproductive period and a short generation time in the Waitemata Harbour provides a lengthy opportunity for S. clava to spread. Findings are discussed in relation to S. clava’s post-border management.     

Effect of starvation on the energy budget of two Asian horseshoe crab species: <Emphasis Type="Italic">Tachypleus tridentatus</Emphasis> and <Emphasis Type="Italic">Carcinoscorpius rotundicauda</Emphasis> (Chelicerata: Xiphosura)

Energy budget is one of the most studied parameters in aquatic animals under environmental challenge. To examine how prolonged starvation would affect their energy budget, respiration rate (RR), ammonia excretion rate (ER), oxygen consumption to ammonia–nitrogen excretion (O:N) ratio and scope for growth (SfG) representing the balance between energy intake and metabolic output, two Asian horseshoe crab species, Tachypleus tridentatus and Carcinoscorpius rotundicauda, were investigated in two feeding regimes (fed and starved) over a period of 7 weeks. No significant effects of species and time course, as well as their interaction, on absorption efficiency were observed in the fed treatments. For both species, RR and ER of the starved treatments significantly decreased, while their O:N ratio significantly increased during the experiment. However, such values for the fed treatments remained relatively stable over the study period. A rapid reduction in SfG was only apparent in the first week of the starved treatments for both species; thereafter, their SfG remained relatively constant. In the fed treatments, SfG of T. tridentatus was significantly lower than that of C. rotundicauda throughout the experiment. In general, C. rotundicauda showed a greater decrease in SfG under starvation than T. tridentatus, suggesting that they may have a more competitive life-history strategy for adjusting to poor nutritional conditions.