A Paradigm Shift in the Trophic Importance of Jellyfish? Hays, Graeme C.; Doyle, Thomas K.; Houghton, Jonathan D.R.
Trends in ecology & evolution (Amsterdam),
November 2018, 2018-11-00, 20181101, Letnik:
33, Številka:
11
Journal Article
Recenzirano
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The past 30 years have seen several paradigm shifts in our understanding of how ocean ecosystems function. Now recent technological advances add to an overwhelming body of evidence for another ...paradigm shift in terms of the role of gelatinous plankton (jellyfish) in marine food webs. Traditionally viewed as trophic dead ends, stable isotope analysis of predator tissues, animal-borne cameras, and DNA analysis of fecal and gut samples (metabarcoding) are all indicating that many taxa routinely consume jellyfish. Despite their low energy density, the contribution of jellyfish to the energy budgets of predators may be much greater than assumed because of rapid digestion, low capture costs, availability, and selective feeding on the more energy-rich components. Feeding on jellyfish may make marine predators susceptible to ingestion of plastics.
Jellyfish are ubiquitous in the world’s oceans, can occur in very high densities and are increasing in abundance in some areas. Yet they have long been considered trophic dead ends that are ignored by most predators because of their low nutritional content.
New approaches are being used to examine the diet of marine predators including stable isotope analysis of predator tissues, animal-borne cameras, and DNA analysis of fecal and gut samples (metabarcoding). These new approaches have revealed that around the world’s oceans jellyfish are frequently consumed by a diverse range of marine predators including fish, birds, turtles, and various invertebrates including octopus, sea cucumbers, crabs, and amphipods.
Taken together, there is now overwhelming evidence that jellyfish are integral components of marine food webs and warrant attention for reasons far exceeding their impacts on human enterprise. Armed with an array of cutting-edge techniques we now have the capacity to drive such investigations forward like never before.
An optimal search theory, the so-called Lévy-flight foraging hypothesis, predicts that predators should adopt search strategies known as Lévy flights where prey is sparse and distributed ...unpredictably, but that Brownian movement is sufficiently efficient for locating abundant prey. Empirical studies have generated controversy because the accuracy of statistical methods that have been used to identify Lévy behaviour has recently been questioned. Consequently, whether foragers exhibit Lévy flights in the wild remains unclear. Crucially, moreover, it has not been tested whether observed movement patterns across natural landscapes having different expected resource distributions conform to the theory’s central predictions. Here we use maximum-likelihood methods to test for Lévy patterns in relation to environmental gradients in the largest animal movement data set assembled for this purpose. Strong support was found for Lévy search patterns across 14 species of open-ocean predatory fish (sharks, tuna, billfish and ocean sunfish), with some individuals switching between Lévy and Brownian movement as they traversed different habitat types. We tested the spatial occurrence of these two principal patterns and found Lévy behaviour to be associated with less productive waters (sparser prey) and Brownian movements to be associated with productive shelf or convergence-front habitats (abundant prey). These results are consistent with the Lévy-flight foraging hypothesis, supporting the contention that organism search strategies naturally evolved in such a way that they exploit optimal Lévy patterns.
Archaea and Bacteria constitute a majority of life systems on Earth but have long been considered inferior to Eukarya in terms of solute tolerance. Whereas the most halophilic prokaryotes are known ...for an ability to multiply at saturated NaCl (water activity (a(w)) 0.755) some xerophilic fungi can germinate, usually at high-sugar concentrations, at values as low as 0.650-0.605 a(w). Here, we present evidence that halophilic prokayotes can grow down to water activities of <0.755 for Halanaerobium lacusrosei (0.748), Halobacterium strain 004.1 (0.728), Halobacterium sp. NRC-1 and Halococcus morrhuae (0.717), Haloquadratum walsbyi (0.709), Halococcus salifodinae (0.693), Halobacterium noricense (0.687), Natrinema pallidum (0.681) and haloarchaeal strains GN-2 and GN-5 (0.635 a(w)). Furthermore, extrapolation of growth curves (prone to giving conservative estimates) indicated theoretical minima down to 0.611 aw for extreme, obligately halophilic Archaea and Bacteria. These were compared with minima for the most solute-tolerant Bacteria in high-sugar (or other non-saline) media (Mycobacterium spp., Tetragenococcus halophilus, Saccharibacter floricola, Staphylococcus aureus and so on) and eukaryotic microbes in saline (Wallemia spp., Basipetospora halophila, Dunaliella spp. and so on) and high-sugar substrates (for example, Xeromyces bisporus, Zygosaccharomyces rouxii, Aspergillus and Eurotium spp.). We also manipulated the balance of chaotropic and kosmotropic stressors for the extreme, xerophilic fungi Aspergillus penicilloides and X. bisporus and, via this approach, their established water-activity limits for mycelial growth (∼0.65) were reduced to 0.640. Furthermore, extrapolations indicated theoretical limits of 0.632 and 0.636 a(w) for A. penicilloides and X. bisporus, respectively. Collectively, these findings suggest that there is a common water-activity limit that is determined by physicochemical constraints for the three domains of life.
Many species are currently experiencing anthropogenically driven environmental changes. Among these changes, increasing noise levels are specifically a problem for species using acoustic signals ...(i.e., species relying on signals that use the same sensory modality as anthropogenic noise). Yet many species use other sensory modalities, such as visual and olfactory signals, to communicate. However, we have only little understanding of whether changes in the acoustic environment affect species that use sensory modalities other than acoustic signals. We studied the impact of anthropogenic noise on the common cuttlefishSepia officinalis, which uses highly complex visual signals. We showed that cuttlefish adjusted their visual displays by changing their color more frequently during a playback of anthropogenic noise, compared with before and after the playback. Our results provide experimental evidence that anthropogenic noise has a marked effect on the behavior of species that are not reliant on acoustic communication. Thus, interference in one sensory channel, in this case the acoustic one, affects signaling in other sensory channels. By considering sensory channels in isolation, we risk overlooking the broader implications of environmental changes for the behavior of animals.
Sessile organisms such as macroalgae located in the intertidal and shallow subtidal zones are subject to a hydrodynamically diverse environment, controlling the variation of intraspecific morphology ...and distribution. Kelp forests experience both waves and/or currents, yet, how kelp blade material mechanically differs between these various hydrodynamic environments and what drives the variation in strength and extensibility are not fully understood. Here, the mechanical properties, cellular composition and blade tissue thickness of the meristematic region and distal tips of the kelp Laminaria digitata blades were quantified and compared between seasons and among three hydrodynamic environments: wave dominated, current dominated and a benign hydrodynamic environment. Kelps associated with energetic environments, generally tended to be stronger yet more extensible than those growing in the benign hydrodynamic environment. Higher extensibility was located at the meristematic region whereas tissue was stronger in the distal tip of the blade. Linking both cellular composition and mechanical properties, results suggest enhancement of medulla cells in the meristematic region increases extensibility, potentially protecting the thallus during increased storm activity while growing in a wave/current exposed habitat. Investment in cortex cells towards the tip of the blade suggests an increase in strength of the region, which is susceptible to breakage. However, the lack of variation in the proportion of medulla and cortex cellular layers between distinct hydrodynamic environments revealed that the potential overall strategy for avoiding breakage in energetic hydrodynamic environments is that of investing energy into the increased thickness of blade tissue.
•Kelps in energetic conditions tend to be strong and extensible.•Meristematic tissue was more extensible than the distal tip.•Hydrodynamics did not influence the proportion of medullary or cortical tissue.•Kelp blade thickness increases in energetic environments to avoid breakage.
Marine renewables could form a significant part of the green energy mix. However, a potential environmental impact of tidal energy converters (TECs) is collision risk between a device and animal, ...which has been a significant barrier in the consenting process. While it is important to understand the number of collisions of an animal with the device, the relative speed at which an animal collides with the device, and the point on the animal where collision occurs, will determine whether a collision is fatal, which is important in understanding population-level impacts. Using a simulation-based collision risk model, this paper demonstrates a novel method for producing estimates of mortality. Extracting both the speed and the location of collisions between an animal and TEC, in this instance a seal and horizontal axis turbine, collision speed and location of collision are used to produce probabilities of mortality. To provide a hypothetical example we quantified the speed and position at which a collision occurs to estimate mortality and, using collision position, we determine all predicted collisions with the head of the animal as fatal, for example, whilst deeming other collisions non-fatal. This is the first collision risk model to incorporate speed at the point of contact and the location where the collision occurs on the animal, to estimate the probability of mortality resulting from a collision. The hypothetical scenarios outline how these important variables extracted from the model can be used to predict the proportion of fatal events. This model enables a comprehensive approach that ultimately provides advancements in collision risk modelling for use in the consenting process of TECs. Furthermore, these methods can easily be adapted to other renewable energy devices and receptors, such as wind and birds.
The redistribution of species has emerged as one of the most pervasive impacts of anthropogenic climate warming, and presents many societal challenges. Understanding how temperature regulates species ...distributions is particularly important for mobile marine fauna such as sharks given their seemingly rapid responses to warming, and the socio‐political implications of human encounters with some dangerous species. The predictability of species distributions can potentially be improved by accounting for temperature's influence on performance, an elusive relationship for most large animals. We combined multi‐decadal catch data and bio‐logging to show that coastal abundance and swimming performance of tiger sharks Galeocerdo cuvier are both highest at ~22°C, suggesting thermal constraints on performance may regulate this species' distribution. Tiger sharks are responsible for a large proportion of shark bites on humans, and a focus of controversial control measures in several countries. The combination of distribution and performance data moves towards a mechanistic understanding of tiger shark's thermal niche, and delivers a simple yet powerful indicator for predicting the location and timing of their occurrences throughout coastlines. For example, tiger sharks are mostly caught at Australia's popular New South Wales beaches (i.e. near Sydney) in the warmest months, but our data suggest similar abundances will occur in winter and summer if annual sea surface temperatures increase by a further 1–2°C.
Being able to predict how temperature regulates species distributions is particularly important for mobile marine animals such as sharks given their seemingly rapid responses to warming, and implications of human encounters with some dangerous species. We combined catch data and accelerometry tagging to show that coastal abundance and swimming activity of tiger sharks Galeocerdo cuvier are both highest at ~22°C. Our combination of distribution and performance data takes a step towards a mechanistic understanding of tiger shark's thermal niche, and delivers a simple indicator that may be useful for predicting coastal occurrences of this potentially dangerous species.
An oceanic cruise (October 2007) revealed the widespread occurrence of Pelagia noctiluca in the NE Atlantic just prior to a major fish kill induced by P. noctiluca in Irish coastal waters.
We are at a crossroads where many nation states, including the United Kingdom of Great Britain and Northern Ireland (UK), are committing to increased electricity production from “green energy”, of ...which tidal stream marine renewable energy is one such resource. However, many questions remain regarding the effects of tidal energy devices on marine wildlife, including seabirds, of which the UK has internationally important numbers. Guidelines are lacking on how best to use both well-established and novel survey methods to assess seabird use of tidal flow areas, leading to a data-rich but information poor (DRIP) situation. This review provides a conceptual framework for assessing the effects of tidal stream energy devices on seabirds, summarises current knowledge and highlights knowledge gaps. Finally, recommendations are given for how best to pursue knowledge on this topic.
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•Marine renewables are increasing while many seabird populations are in decline.•Effects on seabirds (e.g. collision, displacement) are difficult to measure.•Many tools to monitor seabird habitat use exist; which to select?•Guidance is given on tools to determine effects of tidal turbines on seabirds.
Leatherback turtles (Dermochelys coriacea) are obligate predators of gelatinous zooplankton. However, the spatial relationship between predator and prey remains poorly understood beyond sporadic and ...localized reports. To examine how jellyfish (Phylum Cnidaria: Orders Semaeostomeae and Rhizostomeae) might drive the broad-scale distribution of this wide ranging species, we employed aerial surveys to map jellyfish throughout a temperate coastal shelf area bordering the northeast Atlantic. Previously unknown, consistent aggregations of Rhizostoma octopus extending over tens of square kilometers were identified in distinct coastal "hotspots" during consecutive years (2003-2005). Examination of retrospective sightings data (>50 yr) suggested that 22.5% of leatherback distribution could be explained by these hotspots, with the inference that these coastal features may be sufficiently consistent in space and time to drive long-term foraging associations.
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