Seasonal occurrence of balanomorph barnacle nauplius larvae in the region of the Antarctic Peninsula

Author Posting. © The Author(s), 2010. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Journal of Experimental Marine Biology and Ecology 392 (2010): 125-128, doi:10.1016/j.jembe.2010.04.016.Plankton samples taken along the west coast of the Antarctic Peninsula and in Bransfield Strait show widespread occurrence of Bathylasma corolliforme nauplius larvae during the austral spring, mid-October to the third week of December. During autumn, between the first week of May and early June there was a complete absence of balanomorph nauplii. This evidence shows periodicity in reproduction. There is a seemingly close correlation between the presence of these nauplii and the published data on phytoplankton biomass and seawater surface temperature.The research was supported by grants from the U.S. National Science Foundation Office of Polar Programs

Life-cycle and population dynamics of Rhincalanus gigas (Copepoda: Calanoida) in the Scotia Sea

A stage- and age-structured model was constructed to simulate stage-abundance patterns of Rhincalanus gigas in a data set consisting of over 80 yr of net-catch observations in the Scotia Sea. The model was initialised with the observed annual abundances of the Cl stage and the population developed according to pre-defined developmental stage durations, which varied according to life-cycle phenotype. Better fits to net-catch observations were achieved by models that allowed a number of different life-cycle phenotypes to co-exist in the population. In particular, a model in which 71 % of individuals reached adulthood in 2 yr (2 yr phenotype) and 29 % in 1 yr (1 yr phenotype) achieved the best fit. Of the 2 yr phenotypes, most individuals spent their 1st winter as a CIII, although a fraction passed this period as a CIV or CV. The 1 yr phenotypes entered their 1st winter as a CV but moulted through to adulthood before the following spring. During the productive period, the mortality rate of the early developmental stages was 0.1 d(-1), but this fell to 0.007 d(-1) as individuals developed beyond stage CIII. During the winter, the mortality rate fell further to 0.003 d(-1). Such rates meant that around 1.5 % of the copepodite population lived for 3 yr or more. Many of these spent 2 yr as an adult. Quantitative descriptions of development and mortality rates in the later stages of long-lived copepods are relatively few because of the difficulty in distinguishing the many generations in a typical population. As well as being the first to determine these rates in R. gigas, this study provides a methodological framework for determining such rates in other copepods with multi-year life cycles

Distribution, growth, diet and foraging behaviour of the yellow-fin notothen Patagonotothen guntheri (Norman)on the Shag Rocks shelf (Southern Ocean)

The distribution, total length (L-T) frequency and diet of Patagonotothen guntheri are described from 14 bottom trawl surveys conducted on the Shag Rocks and South Georgia shelves in the austral summers from 1986 to 2006. Patagonotothen guntheri (80-265 mm L-T) were caught on the Shag Rocks shelf from depths of 111 to 470 m, but no specimens were caught on the South Georgia shelf. Multiple cohorts were present during each survey and L-T-frequency analysis of these cohorts suggests that growth was slow (von Bertalanffy K = 0.133). Evidence from stomach contents and acoustic data (2005 and 2006) showed that P. guntheri is primarily a pelagic feeder, migrating from the sea floor towards the surface to feed during daylight. The diet of smaller fish (< 140 mm) was dominated by copepods, predominantly Rhincalanus gigas, whilst larger fish principally consumed the pelagic hyperiid amphipod, Themisto gaudichaudii and Antarctic krill Euphausia superba. Some larger fish also took benthic prey. (C) 2008 The Authors Journal compilation (C) 2008 The Fisheries Society of the British Isles

Growth rates of Antarctic krill, Euphausia superba: comparison of the instantaneous growth rate method with nitrogen and phosphorus stoichiometry

Zooplankton growth rates are hard to measure directly, and proxy measurements are desirable to encompass the variety of species and scales of interest. The growth rate hypothesis of stoichiometric theory states that a negative relationship exists between nitrogen: phosphorus (N: P) stoichiometry and growth rate, driven by cellular ribosomal ribonucleic acid (rRNA) content. Despite the wealth of literature on the growth rate hypothesis, there exist no practical demonstrations of its use in the marine literature. We thus investigated whether this hypothesis could be the basis of a technique to estimate growth rates of Euphausia superba by comparing, for the same individual krill, elemental stoichiometry and growth rates derived from the instantaneous growth rate (IGR) method. These growth rates were the first IGR measurements from South Georgia; from within a restricted area over the course of just 1 month, these rates were highly variable, from negative to near maximum rates recorded for the species. Although there were significant differences in N: P ratio and phosphorus content between individuals and schools, there was no relationship between N: P ratio and growth rate when data were grouped by school. Thus, our data do not support the predictions of the growth rate hypothesis at an intraspecific scale. However, when all data were pooled, the mean values of growth rate and N: P ratio did fit the interspecific relationship established previously for freshwater zooplankton. We suggest that krill maintain the biochemical machinery for high growth potential and maintain high growth in summer to take advantage of short-term fluctuations in food

Life-cycle phenotypic composition and mortality of Calanoides acutus (Copepoda: Calanoida) in the Scotia Sea: a modelling approach

A modelling approach was developed to identify the most likely composition of life-cycle phenotypes and mortality rates for Calanoides acutus found within the Scotia Sea. A stage- and age-structured model was parameterised with independent measurements of early copepodite stage duration, growth rate during the productive period and mortality and weight loss during the over-wintering period. Four possible life-phenotypes were simulated, varying according to whether (1) they spent their first winter as a CIV or CV stage, and (2) they persisted for between one and several years. The mortality rate coefficient during the epipelagic period was allowed to vary between 0.01 and 0.1 d(-1). Model runs determined the effect of all possible combinations of these variables on the abundance of the late copepodite stages, and predictions were compared to a comprehensive empirical data set, encompassing observations made over the last 60 yr. Best fits were achieved when 70% of the Scotia Sea population overwintered as a CV stage and 30% as CIV, with the majority of individuals reaching adulthood in their first year (after 1 overwintering period). During the epipelagic period, the population experienced mortality rate coefficients close to 0.06 d(-1). This high rate makes it unlikely that the earliest recruits survive to the end of the productive season. Predation was responsible for over 80% of mortality during winter. Starvation, which made up the remainder, mostly affected individuals that were spawned late in the season. The total rate of overwintering mortality was less than 0.007 d(-1). Sensitivity analyses demonstrated that model predictions were robust and identified the most likely causes of interannual and spatial variation in the observed data sets

Diatom fatty acid biomarkers indicate growth rates in Antarctic krill

We investigated the relationship between nutritional condition (levels of specific fatty acids) and growth increment (percentage growth per intermoult period, percentage IMP-1) for Antarctic krill (Euphausia superba) collected from the vicinity of South Georgia in the austral summer 2002. There were correlations between percentage IMP-1 and the concentration (gram: gram dry weight) of the diatom biomarker fatty acids, 16: 4(n-1) and 20: 5(n-3) in tissues of individual krill, suggesting that the abundance of diatoms in the environment of the krill in the intermoult period prior to moulting was a key determinant of change in body length, a proxy for growth. This substantiates the view that diatoms are crucial for supporting high growth rates of krill, either as a direct food source or, indirectly, by enhancing production of microzooplankton and mesozooplankton based food webs

Recruitment of Antarctic krill Euphausia superba in the South Georgia region: adult fecundity and the fate of larvae

The high concentration of adult Antarctic krill Euphausia superba Dana around South Georgia, Antarctica, is a product of immigration and not local recruitment. We investigated whether reproduction and early larval development are the cause of local recruitment failure. It was found that the majority of adult females were reproductively active in summer and that there was a comparatively high investment in the ovary, reaching up to 46% of the total wet weight of the krill. The corresponding egg batches were amongst the largest ever reported for E. superba. A semi-empirical model predicted that 11% of females completed just 1 spawning episode per year, 60% completed 2, and 29% completed 3 or more. On average, a South Georgian krill released 12 343 eggs yr–1. The eggs were unable to complete the descent–ascent developmental cycle on-shelf because the bathymetry was too shallow but, off-shelf, they were predicted to sink to between 490 and 520 m and return to the surface either as a metanauplius or 1st calyptopis stage with plenty of energy reserves remaining. Feeding conditions were adequate for the development of later larval stages once these reserves were exhausted. Although net surveys found calyptopis and early stage furcilia in the vicinity of South Georgia, numbers were mostly lower than predicted. Overall, reproduction or early stage development are successful in this region, leaving predation on larvae and advective export during winter as the main potential causes of local recruitment failure

Plankton community structure south and west of South Georgia (Southern Ocean): links with production and physical forcing

During late December 2004 and early January 2005 the plankton community to the south and west of South Georgia was investigated. Satellite imagery had shown the surface expression of a bloom over the southern shelf I month prior to the cruise, although by the time of sampling a well-defined sub-surface chl-a maximum was evident at 26 of the 57 stations located mainly at the western end of the southern shelf (and the bloom was declining). Nonetheless, integrated chl-a was still greater over the shelf than elsewhere (18-362 mg m(-2)). Macronutrient distributions essentially mirrored the distribution of chl-a biomass, with depletion greatest in the on-shelf waters at the western end of South Georgia, where the most intense surface bloom had occurred during the preceding November. Nearest neighbour clustering of microplankton and mesozooplankton data revealed the presence of two major station groups within each analysis with broadly congruent distributions. Within the microplankton analysis a southern and western shelf grouping of 18 stations was dominated by Corethron spp., Eucampia antarctica and Thalassiothrix spp. This group corresponded spatially to a shelf zooplankton grouping (12 of the 18 stations in both groups in common) in which mesozooplankton abundance was greatest. Here small copepods such as Oithona spp. and the neritic clausocalaniid Drepanopus forcipatus dominated, along with the thecate pteropod Limacina helicina, appendicularians and calanoid copepod naupliar stages. Acoustic doppler current profiler (ADCP) measurements indicated that water flow over the shelf was low and variable (< 15 cm s(-1)). In contrast the largest station groups in both ordinations were distributed along the southern shelf-break and further off-shelf in water flowing rapidly (up to 55 cm s(-1)) to the southeast. Nitzschia spp., Pseudonitzschia spp., and Fragilariopsis kerguelensis were abundant here, and the zooplankton, in addition to Oithona spp., was characterized by Metridia spp., Ctenocalanus spp., Oncaea spp., and the polychaete Pelagobia longicirrata. A third group of 13 stations disclosed by the mesoplankton ordination was confined to the north and west and generally comprised outer shelf stations in deeper waters. Here zooplankton abundance was less than in the adjacent major station groupings, although Calanus simillimus was considerably more abundant than in other groups. Relationships of both micro- and zooplankton ordinations with environmental variables were modest (Spearman rank correlation, rho w = 0.49-0.59), albeit complex, with interactions likely to have occurred over different timescales. High levels of ammonium over the shelf, probably resulting from microbial breakdown and zooplankton excretion, contributed most to explaining both ordinations, along with the Si(OH)(4):NO3 deficit ratio, a measure of past nutrient use. Model output from Ocean Circulation and Climate Advanced Modelling (OCCAM) supported ADCP-derived flow measurements. Specifically, release of particles along a transect to the southwest suggested there was an extended residence time (in excess of 3 months) over the southern shelf and a slow but significant northwards transport into the Georgia Basin. The spatial extent of the shelf and the current speed and direction implied that in situ production was locally important and had the potential to contribute significantly to downstream ecosystems. (C) 2007 Elsevier Ltd. All rights reserved

Spatial and Temporal Operation of the Scotia Sea Ecosystem

Analysis of the operation of ocean ecosystems requires an understanding of how the structure of the ecosystem is determined by interactions between physical, chemical and biological processes. Such analysis needs to consider the interactions across a wide range of spatial (approx. 10 m–10,000 km) and temporal (minutes to centuries) scales and trophic levels (primary producers to top predators) (Angel, 1994; Murphy et al., 1988;Werner et al., 2003). There are, however, few areas of the global ocean where there is sufficient knowledge to achieve such an integrated analysis (deYoung et al., 2004). Circulation patterns of the major ocean gyres, such as the North Atlantic and Pacific Oceans, involve movement of water masses through very different climatic regimes which favour distinctly different groups of organisms (Longhurst, 1998). Generating comprehensive views of the operation of oceanic ecosystems is complicated as a result of such heterogeneity in species distribution and ecosystem structure (Levin, 1990; Longhurst, 1998; Murphy et al., 1988). In contrast to othe

The science commons in health research: structure, function, and value

The “science commons,” knowledge that is widely accessible at low or no cost, is a uniquely important input to scientific advance and cumulative technological innovation. It is primarily, although not exclusively, funded by government and nonprofit sources. Much of it is produced at academic research centers, although some academic science is proprietary and some privately funded R&D enters the science commons. Science in general aspires to Mertonian norms of openness, universality, objectivity, and critical inquiry. The science commons diverges from proprietary science primarily in being open and being very broadly available. These features make the science commons particularly valuable for advancing knowledge, for training innovators who will ultimately work in both public and private sectors, and in providing a common stock of knowledge upon which all players—both public and private—can draw readily. Open science plays two important roles that proprietary R&D cannot: it enables practical benefits even in the absence of profitable markets for goods and services, and its lays a shared foundation for subsequent private R&D. The history of genomics in the period 1992–2004, covering two periods when genomic startup firms attracted significant private R&D investment, illustrates these features of how a science commons contributes value. Commercial interest in genomics was intense during this period. Fierce competition between private sector and public sector genomics programs was highly visible. Seemingly anomalous behavior, such as private firms funding “open science,” can be explained by unusual business dynamics between established firms wanting to preserve a robust science commons to prevent startup firms from limiting established firms’ freedom to operate. Deliberate policies to create and protect a large science commons were pursued by nonprofit and government funders of genomics research, such as the Wellcome Trust and National Institutes of Health. These policies were crucial to keeping genomic data and research tools widely available at low cost. Copyright Springer Science+Business Media, LLC 2007Patents, Genomics, Public domain, Open science, Intellectual property, Innovation, 031, 032, 034, 038,