| 276831. |
- Selander, Erik, 1973, et al.
(författare)
-
Chemical signaling in the turbulent ocean-hide and seek at the Kolmogorov scale
- 2020
-
Ingår i: Fluids. - : MDPI AG. - 2311-5521. ; 5:2
-
Tidskriftsartikel (refereegranskat)abstract
- Chemical cues and signals mediate resource acquisition, mate finding, and the assessment of predation risk in marine plankton. Here, we use the chemical properties of the first identified chemical cues from zooplankton together with in situ measurements of turbulent dissipation rates to calculate the effect of turbulence on the distribution of cues behind swimmers as well as steady state background concentrations in surrounding water. We further show that common zooplankton (copepods) appears to optimize mate finding by aggregating at the surface in calm conditions when turbulence do not prevent trail following. This near surface environment is characterized by anisotropic turbulence and we show, using direct numerical simulations, that chemical cues distribute more in the horizontal plane than vertically in these conditions. Zooplankton may consequently benefit from adopting specific search strategies near the surface as well as in strong stratification where similar flow fields develop. Steady state concentrations, where exudation is balanced by degradation develops in a time scale of ~5 h. We conclude that the trails behind millimeter-sized copepods can be detected in naturally occurring turbulence below the wind mixed surface layer or in the absence of strong wind. The trails, however, shorten dramatically at high turbulent dissipation rates, above ~10−3 cm2 s−3 (10−7 W kg−1). © 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).
|
|
| 276832. |
- Selander, Erik, 1973, et al.
(författare)
-
Copepods drive large-scale trait-mediated effects in marine plankton
- 2019
-
Ingår i: Science Advances. - : American Association for the Advancement of Science (AAAS). - 2375-2548. ; 5
-
Tidskriftsartikel (refereegranskat)abstract
- Copyright © 2019 The Authors. Fear of predation may influence food webs more than actual predation. However, the mechanisms and magnitude of nonconsumptive predator effects are largely unknown in unicellular-dominated food webs such as marine plankton. We report a general mechanism of chemically induced predator effects in marine plankton. Copepods, the most abundant zooplankton in the oceans, imprint seawater with unique polar lipids—copepodamides—which trigger toxin production and bioluminescence in harmful dinoflagellates. We show that copepodamides also elicit defensive traits in other phytoplankton, inducing the harmful algal bloom-forming diatom Pseudo-nitzschia seriata to produce 10 times more toxins, and colony-forming diatoms to decrease colony size by half. A 1-year study in the northeast Atlantic revealed that natural copepodamide concentrations are high enough to induce harmful algal toxins and size reduction in dominant primary producers when copepods are abundant. We conclude that copepodamides will structure marine plankton toward smaller, more defended life forms on basin-wide scales.
|
|
| 276833. |
- Selander, Erik, 1973, et al.
(författare)
-
Copepods induce paralytic shellfish toxin production in marine dinoflagellates
- 2006
-
Ingår i: Proceedings of the Royal Society B-Biological Sciences. - : The Royal Society. - 0962-8452 .- 1471-2954. ; 273:1594, s. 1673-1680
-
Tidskriftsartikel (refereegranskat)abstract
- Among the thousands of unicellular phytoplankton species described in the sea, some frequently occurring and bloom-forming marine dinoflagellates are known to produce the potent neurotoxins causing paralytic shellfish poisoning. The natural function of these toxins is not clear, although they have been hypothesized to act as a chemical defence towards grazers. Here, we show that waterborne cues from the copepod Acartia tonsa induce paralytic shellfish toxin (PST) production in the harmful algal bloom-forming dinoflagellate Alexandrium minutum. Induced A. minutum contained up to 2.5 times more toxins than controls and was more resistant to further copepod grazing. Ingestion of non-toxic alternative prey was not affected by the presence of induced A. minutum. The ability of A. minutum to sense and respond to the presence of grazers by increased PST production and increased resistance to grazing may facilitate the formation of harmful algal blooms in the sea.
|
|
| 276834. |
- Selander, Erik, 1973, et al.
(författare)
-
Effects of food concentration on the behaviour of Oikopleura dioica
- 2003
-
Ingår i: Marine Biology. - 0025-3162. ; 142:2, s. 263-270
-
Tidskriftsartikel (refereegranskat)abstract
- Feeding behaviour of the pelagic tunicate Oikopleura dioica presented with a range of food concentrations (FC, 4-670 mug Cl-1) of the flagellate Isochrysis galbana was observed using video. Simultaneous bottle incubations provided clearance rate estimates. Tail beats per minute (TB), number of tail arrests or pauses (TA) and swimming speeds were recorded. TB decreased with increasing FC, from 521 to 355 min(-1), while TA increased from 17 to 35 min(-1). Aberrant behaviour with repeated TA was found if inlet filters were obstructed by larger particles or aquarium walls. Swimming speed was 1.0 0.4 mm s(-1), and the time spent swimming decreased with FC from 38 % to 11% of the time. Clearance rate decreased sharply with FC, from 4.3 to 0.11 ml ind(-1) h(-1), resembling a type II functional response with Michaelis-Menten parameters I-max = 113 mug C ind(-1) h(-1) and K-m = 27 mug Cl-1. Using TB, TA and a residual error term, a simple model to predict clearance rate from behavioural parameters was developed. Power functions of FC were fitted to each parameter, resulting in exponents of -0.047, -0.183 and -0.38, respectively. The error term includes passive clogging and food rejection at the mouth, and was according to the model the most important for shaping the functional response.
|
|
| 276835. |
- Selander, Erik, 1973, et al.
(författare)
-
Effects of nitrate and phosphate on grazer-induced toxin production in Alexandrium minutum
- 2008
-
Ingår i: Limnology & Oceanography. ; 53:2, s. 423-530
-
Tidskriftsartikel (refereegranskat)abstract
- Two strains of Alexandrium minutum were exposed to waterborne cues from copepod grazers in factorial combinations of nitrate and phosphate concentrations to evaluate the importance of grazer-induced paralytic shellfish toxin (PST) production under different nutrient regimes. In nitrate-rich treatments, the presence of waterborne cues from grazers resulted in significantly increased cell-specific PST content. In low nitrate treatments, however, waterborne cues from grazers did not result in any detectable increase in cell-specific PST content. The grazer-induced increase in cell-specific PST content in nitrate-rich treatments was comparable in size to the effects of nitrate in the absence of grazers. Effects of phosphate limitation were less consistent, resulting in increased PST content in nitrate-rich treatments in one of the A. minutum strains, but had no significant effect in the other. The ability of dinoflagellates to sense and respond to the presence of grazers by increased PST production may be one of the most important factors affecting cell-specific PST content under nitrogen replete conditions.
|
|
| 276836. |
- Selander, Erik, 1973, et al.
(författare)
-
Fight and flight in dinoflagellates? Kinetics of simultaneous grazer-induced responses in Alexandrium tamarense
- 2012
-
Ingår i: Limnology and Oceanography. - : Wiley. - 0024-3590 .- 1939-5590. ; 57:1, s. 58-64
-
Tidskriftsartikel (refereegranskat)abstract
- We monitored the kinetics of grazer-induced responses in the marine dinoflagellate Alexandrium tamarense. Chemical cues from each of three calanoid copepods (Calanus sp., Centropages typicus, and Acartia tonsa) induced increased toxicity and suppressed chain formation in A. tamarense. Both chemical and morphological responses augmented over 3 d. Toxicity subsequently averaged 299% higher than controls, and average biovolume 24% lower than controls because of suppression of chain formation in grazed treatments. Grazer-induced toxicity returned to control levels after approximately 11 d, equivalent to five cell divisions, and average biovolume returned to control levels within 1 to 4 d (one to two cell divisions). This suggests that dinoflagellates simultaneously reduce grazer encounter rates and increase chemical defense levels in the presence of copepod grazers. Media replacement experiments showed that the inducing cue(s) attenuate rapidly in seawater, which allows A. tamarense to adjust resource allocation to grazer-induced responses to follow fluctuations in grazer density. Grazer-induced responses, however, develop too slowly to be accounted for in short-term grazing experiments with laboratory cultures.
|
|
| 276837. |
- Selander, Erik, 1973, et al.
(författare)
-
Grazer cues induce stealth behavior in marine dinoflagellates
- 2011
-
Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 108:10, s. 4030-4034
-
Tidskriftsartikel (refereegranskat)abstract
- Chain formation is common among phytoplankton organisms but the underlying reasons and consequences are poorly understood. Here we show that chain formation is strongly impaired by waterborne cues from copepod grazers in the dinoflagellate Alexandrium tamarense. Chains of Alexandrium cells exposed to copepod cues responded by splitting into single cells or shorter chains. Motion analysis revealed significantly lower swimming velocities for single cells compared with chains, with two- to fivefold higher simulated predator encounter rates for two- and four-cell chains, respectively. In addition, the few remaining two-cell chains in grazed treatments were swimming at approximately half the speed of two-cell chains in treatments without grazers, which reduced encounter rates with grazers to values similar to that of single cells. Chain length plasticity and swimming behavior constitute unique mechanisms to reduce encounters with grazers. We argue that dinoflagellates can regulate the balance between motility and predator avoidance by adjusting chain length. The high predator encounter rate for motile chains may have contributed to the low prevalence of chain formation in motile phytoplankton compared with in nonmotile phytoplankton where chain formation is more common.
|
|
| 276838. |
- Selander, Erik, 1973, et al.
(författare)
-
Hydrodynamic properties and distribution of bait downstream of a zooplankton trap
- 2017
-
Ingår i: Journal of Plankton Research. - : Oxford University Press (OUP). - 0142-7873 .- 1464-3774. ; 39:6, s. 1020-1027
-
Tidskriftsartikel (refereegranskat)abstract
- The flow regime around a chemically baited trap is crucial for the trapping process and distribution of bait downstream of traps. We measured the flow field downstream of a trap prototype in flume experiments and mapped the distribution of bait using laser induced fluorescence. The trap produced a downstream wake, where flow recirculated towards the trap, allowing organisms slower than the free stream flow to interact with the trap. The chemical tracer revealed an average gradient with increasing concentrations towards the trap. Finally, we evaluated trap performance in field experiments. Traps with internal light caught on average 3.4 times more zooplankton than traps without light in short-term deployments (1 h). Trapping efficiency could be manipulated by chemical stimuli; A piece of fish (Salmo salar) inside traps deterred 79% of the zooplankton compared to traps without fish. We conclude that the flow regime around a cylindrical trap may facilitate trapping and that combined stimuli modalities may allow higher selectivity. The effective radius of the trap will depend on the surrounding flow and will likely be small when flow-rate exceeds swimming speed of targeted organisms. Finally, we propose applications for selective traps in aquaculture and pest management.
|
|
| 276839. |
- Selander, Erik, 1973, et al.
(författare)
-
Parasitic anemone infects the invasive ctenophore Mnemiopsis leidyi in the North East Atlantic
- 2010
-
Ingår i: Biological invasions. - : Springer Science and Business Media LLC. - 1387-3547 .- 1573-1464. ; 12:5, s. 1003-1009
-
Tidskriftsartikel (refereegranskat)abstract
- We report of the first finding of parasitic sea anemone larvae infecting the invasive ctenophore Mnemiopsis leidyi in the North East Atlantic. Parasitic anemone larvae are common in the native habitat of Mnemiopsis, but have not previously been reported from any of the locations where Mnemiopsis has been introduced. General morphology and 18S rRNA sequences support the identification of the larvae as Edwardsiella sp. Excised anemone larvae were reared through metamorphosis and confirmed the identification of the parasite. Both Mnemiopsis and Edwardsiella larvae were monitored weekly during 2007 and 2008 and parasitic larvae were recorded from September to November both years. The highest density was observed in September 2008 when Edwardsiidae larvae reached 2.3 ind m(-3). In 2008 total density of the parasite occasionally exceeded 40% of the host density and the potential consequences for Mnemiopsis population dynamics are discussed.
|
|
| 276840. |
- Selander, Erik, 1973, et al.
(författare)
-
Predator lipids induce paralytic shellfish toxins in bloom-forming algae
- 2015
-
Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 112:20, s. 6395-6400
-
Tidskriftsartikel (refereegranskat)abstract
- Interactions among microscopic planktonic organisms underpin the functioning of open ocean ecosystems. With few exceptions, these organisms lack advanced eyes and thus rely largely on chemical sensing to perceive their surroundings. However, few of the signaling molecules involved in interactions among marine plankton have been identified. We report a group of eight small molecules released by copepods, the most abundant zooplankton in the sea, which play a central role in food webs and biogeochemical cycles. The compounds, named copepodamides, are polar lipids connecting taurine via an amide to isoprenoid fatty acid conjugate of varying composition. The bloom-forming dinoflagel-late Alexandrium minutum responds to pico- to nanomolar concentrations of copepodamides with up to a 20-fold increase in production of paralytic shellfish toxins. Different copepod species exude distinct copepodamide blends that contribute to the species-specific defensive responses observed in phytoplankton. The signaling system described here has far reaching implications for marine ecosystems by redirecting grazing pressure and facilitating the formation of large scale harmful algal blooms.
|
|
