Salps are common in oceanic waters and have higher per-individual filtration rates than any other zooplankton filter feeder. Although salps are centimeters in length, feeding via particle capture ...occurs on a fine, mucous mesh (fiber diameter d ∼0.1 μm) at low velocity (U = 1.6 ± 0.6 cm·s −1 , mean ± SD) and is thus a low Reynolds-number (Re ∼10 −3 ) process. In contrast to the current view that particle encounter is dictated by simple sieving of particles larger than the mesh spacing, a low-Re mathematical model of encounter rates by the salp feeding apparatus for realistic oceanic particle-size distributions shows that submicron particles, due to their higher abundances, are encountered at higher rates (particles per time) than larger particles. Data from feeding experiments with 0.5-, 1-, and 3-μm diameter polystyrene spheres corroborate these findings. Although particles larger than 1 μm (e.g., flagellates, small diatoms) represent a larger carbon pool, smaller particles in the 0.1- to 1-μm range (e.g., bacteria, Prochlorococcus) may be more quickly digestible because they present more surface area, and we find that particles smaller than the mesh size (1.4 μm) can fully satisfy salp energetic needs. Furthermore, by packaging submicrometer particles into rapidly sinking fecal pellets, pelagic tunicates can substantially change particle-size spectra and increase downward fluxes in the ocean.
A perceived recent increase in global jellyfish abundance has been portrayed as a symptom of degraded oceans. This perception is based primarily on a few case studies and anecdotal evidence, but a ...formal analysis of global temporal trends in jellyfish populations has been missing. Here, we analyze all available long-term datasets on changes in jellyfish abundance across multiple coastal stations, using linear and logistic mixed models and effect-size analysis to show that there is no robust evidence for a global increase in jellyfish. Although there has been a small linear increase in jellyfish since the 1970s, this trend was unsubstantiated by effect-size analysis that showed no difference in the proportion of increasing vs. decreasing jellyfish populations over all time periods examined. Rather, the strongest nonrandom trend indicated jellyfish populations undergo larger, worldwide oscillations with an approximate 20-y periodicity, including a rising phase during the 1990s that contributed to the perception of a global increase in jellyfish abundance. Sustained monitoring is required over the next decade to elucidate with statistical confidence whether the weak increasing linear trend in jellyfish after 1970 is an actual shift in the baseline or part of an oscillation. Irrespective of the nature of increase, given the potential damage posed by jellyfish blooms to fisheries, tourism, and other human industries, our findings foretell recurrent phases of rise and fall in jellyfish populations that society should be prepared to face.
During the past several decades, high numbers of gelatinous Zooplankton species have been reported in many estuarine and coastal ecosystems. Coupled with media-driven public perception, a paradigm ...has evolved in which the global ocean ecosystems are thought to he heading toward being dominated by “nuisance” jellyfish. We question this current paradigm by presenting a broad overview of gelatinous Zooplankton in a historical context to develop the hypothesis that population changes reflect the human-mediated alteration of global ocean ecosystems. To this end, we synthesize information related to the evolutionary context of contemporary gelatinous Zooplankton blooms, the human frame of reference for changes in gelatinous Zooplankton populations, and whether sufficient data are available to have established the paradigm. We conclude that the current paradigm in which it is believed that there has been a global increase in gelatinous Zooplankton is unsubstantiated, and we develop a strategy for addressing the critical questions about long-term, human-related changes in the sea as they relate to gelatinous Zooplankton blooms.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, IZUM, KILJ, NMLJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The term ‘biodiversity,’ while casually used in practice, is a complicated subject to measure, interpret, contextualize, and compare. Yet the possible advent of deep-sea mining in the mid-2020’s ...compels us to compare potential impacts of biodiversity loss across ecologically distant realms, a formidable task. Supplying the world’s green infrastructure is expected to lead to shortages of nickel, cobalt and other metals; meanwhile polymetallic nodules sitting atop the abyssal plains of the Clarion-Clipperton Zone (CCZ) of the Pacific Ocean contain billions of tons of nickel, cobalt, copper and manganese, enough to solve the supply issues. Implicit in society’s decision of whether to exploit this resource is a tradeoff of harm to biodiversity in the CCZ’s abyssal seafloor and its overlying water column, versus intensification of harm to rainforests and other terrestrial mining habitats. Here we frame the challenges of comparing biodiversity impacts across such different realms, spanning the gamut from normative to fundamental: ambiguities in definitions, lack of protocol standardization, physical challenges in measurement, difficulties to integrate measures among different taxonomic groups, profound differences between ecologically distant realms, contextual necessity to attribute value to mathematical index results, and constraints of current knowledge about species, ecosystems and system level impacts of biodiversity change. Quantitative biodiversity measures alone cannot rank one system above the other; measures must be supplemented with qualitative judgements of the tangible and intangible values of species and habitats to natural systems and to humans, along with consideration of other threats that they and we face.
Measurements of the defecation rate of Salpa thompsoni were made at several stations during two cruises west of the Antarctic Peninsula in 2004 and 2006. Rates were quantified in terms of number of ...pellets, pigment, carbon and nitrogen for a wide size range of both aggregate and solitary salps. Measured defecation rates were constant over several hours when salps were held at near-surface conditions from which they had been collected. The defecation rate per salp increased with both salp size and the ambient level of particulate organic matter (POM) in the upper water column. The weight-specific defecation rate ranged between 0.5 and 6% day⁻¹ of salp body carbon, depending on the concentration of available particulate matter in the water. Carbon defecation rates were applied to biomass estimates of S. thompsoni to calculate daily carbon defecation rates for the populations sampled during the two cruises. Dense salp populations of over 400 mg C m⁻² were calculated to produce about 20 mg C m⁻² day⁻¹, comparable to other major sources of vertical flux of organic material in the Southern Ocean. Measured sinking rates for salp fecal pellets indicated that the majority of this organic material could reach deep sediments within a few days, providing a fast and direct pathway for carbon to the deep ocean.
Jellyfish are usually perceived as harmful to humans and are seen as "pests". This negative perception has hindered knowledge regarding their value in terms of ecosystem services. As humans ...increasingly modify and interact with coastal ecosystems, it is important to evaluate the benefits and costs of jellyfish, given that jellyfish bloom size, frequency, duration, and extent are apparently increasing in some regions of the world. Here we explore those benefits and costs as categorized by regulating, supporting, cultural, and provisioning ecosystem services. A geographical perspective of human vulnerability to jellyfish over four categories of human well-being (health care, food, energy, and freshwater production) is also discussed in the context of thresholds and trade-offs to enable social adaptation. Whereas beneficial services provided by jellyfish likely scale linearly with biomass (perhaps peaking at a saturation point), non-linear thresholds exist for negative impacts to ecosystem services. We suggest that costly adaptive strategies will outpace the beneficial services if jellyfish populations continue to increase in the future.
Salps are barrel-shaped marine invertebrates that swim by jet propulsion. Morphological variations among species and life-cycle stages are accompanied by differences in swimming mode. The goal of ...this investigation was to compare propulsive jet wakes and swimming performance variables among morphologically distinct salp species (Pegea confoederata, Weelia (Salpa) cylindrica, Cyclosalpa sp.) and relate swimming patterns to ecological function. Using a combination of in situ dye visualization and particle image velocimetry (PIV) measurements, we describe properties of the jet wake and swimming performance variables including thrust, drag and propulsive efficiency. Locomotion by all species investigated was achieved via vortex ring propulsion. The slow-swimming P. confoederata produced the highest weight-specific thrust (T=53 N kg(-1)) and swam with the highest whole-cycle propulsive efficiency (eta(wc)=55%). The fast-swimming W. cylindrica had the most streamlined body shape but produced an intermediate weight-specific thrust (T=30 N kg(-1)) and swam with an intermediate whole-cycle propulsive efficiency (eta(wc)=52%). Weak swimming performance variables in the slow-swimming C. affinis, including the lowest weight-specific thrust (T=25 N kg(-1)) and lowest whole-cycle propulsive efficiency (eta(wc)=47%), may be compensated by low energetic requirements. Swimming performance variables are considered in the context of ecological roles and evolutionary relationships.
A molecular phylogeny of the Thaliacea GOVINDARAJAN, Annette F; BUCKLIN, Ann; MADIN, Laurence P
Journal of plankton research,
06/2011, Letnik:
33, Številka:
6
Journal Article
Recenzirano
Thaliaceans are gelatinous holoplanktonic tunicates comprised of around 72 described species in three orders: the Pyrosomatida (pyrosomes), Salpida (salps) and Doliolida (doliolids). Despite their ...interesting biology and important role in ocean ecosystems, relatively little is known about their evolutionary relationships with other tunicate lineages and with each other. Here, using 40 newly obtained 18S rDNA sequences, we present a molecular phylogeny of the Thaliacea. Our results show the pyrosomes branching off first and support their division into the Pyrostremmatinae and Pyrosomatinae. Within the Salpida, we found the subfamily Salpinae is paraphyletic with the morphologically divergent Cyclosalpinae. We also resolved the uncertainty regarding Weelia (Salpa) cylindrica, finding it to be relatively distantly related to Salpa aspera, Salpa maxima, Salpa fusiformis and Salpa thompsoni.
The least known component of the “biological pump” is the active transport of carbon and nutrients by diel vertical migration of zooplankton. We measured CO
2 respiration and dissolved organic carbon ...(DOC) excretion by individual species of common vertically migrating zooplankton at the US JGOFS Bermuda Atlantic Time-series Study (BATS) station. The inclusion of DOC excretion in this study builds on published research on active transport by respiration of inorganic carbon and allows a direct assessment of the role of zooplankton in the production of dissolved organic matter used in midwater microbial processes. On average, excretion of DOC makes up 24% (range=5–42%) of the total C metabolized (excreted+respired) and could represent a significant augmentation to the vertical flux that has already been documented for respiratory CO
2 flux by migrant zooplankton. Migratory fluxes were compared to other transport processes at BATS. Estimates of combined active transport of CO
2 and DOC by migrators at BATS averaged 7.8% and reached 38.6% of mean sinking POC flux at 150
m, and reached 71.4% of mean sinking POC flux at 300
m. DOC export by migrator excretion averaged 1.9% and reached 13.3% of annual DOC export by physical mixing at this site. During most of the year when deep mixing does not occur, diel migration by zooplankton could provide a supply of DOC to the deeper layers that is available for use by the microbial community. A carbon budget comparing migrant zooplankton transport to the balance of fluxes in the 300–600
m depth strata at BATS shows on average that the total migrant flux supplies 37% of the organic carbon remineralized in this layer, and that migrant DOC flux is more than 3 times the DOC flux gradient by diapycnal mixing. New estimates of active transport of both organic and inorganic carbon by migrants may help resolve observed imbalances in the C budget at BATS, but the magnitude is highly dependent on the biomass of the migrating community.
Siphonophores eat fish larger than their stomachs Pagès, Francesc; Madin, Laurence P.
Deep-sea research. Part II, Topical studies in oceanography,
12/2010, Letnik:
57, Številka:
24
Journal Article
Recenzirano
We report a collection of the siphonophore
Halistemma cupulifera, collected at 20 meters depth during a night SCUBA dive in the Sargasso Sea. One of its stomachs (gastrozooids) contained a ...leptocephalus larva of the eel
Ariosoma sp. folded in thirds to fit, but 8.3
cm in length fully extended. This finding shows that
in situ observations can reveal previously unknown trophic interactions that may be significant in a changing world ocean where gelatinous organisms seem to increase at the expense of fish.
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