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Abstract Euphausiids are important prey for many marine organisms and often occur in patchy aggregations. Euphausiid predators, such as blue whales, may become concentrated in the vicinity of these aggregations. We investigated an area called Nine Mile Bank (NMB) near San Diego, California, defined by an area of steep bathymetry, to determine whether the frequent whale sightings in that locality can be explained by the distribution of euphausiids across the bank and by the vertical distribution of euphausiids in the water column.Thysanoessa spinifera, the strongly preferred blue whale prey euphausiid in this area, was consistently more abundant on the bank or inshore of it than offshore. In contrast,Euphausia pacifica,a minor blue whale prey item, was much more abundant and distributed across the study region. Adults of both species were concentrated in a stratum corresponding to the feeding depth of blue whales. Other euphausiids that form a negligible part of the blue whale diet also showed no association with NMB. Both blue whales and their primary prey speciesThysanoessa spiniferawere more abundant on or inshore of the bank than offshore, suggesting that the bank may serve as an offshore limit of high prey abundance that helps to concentrate blue whales.
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Retention of blue‐green cryptophyte organelles by Mesodinium rubrum and their effects on photophysiology and growth
Abstract As chloroplast‐stealing or “kleptoplastidic” lineages become more reliant on stolen machinery, they also tend to become more specialized on the prey from which they acquire this machinery. For example, the ciliateMesodinium rubrumobtains > 95% of its carbon from photosynthesis, and specializes on plastids from theTeleaulaxclade of cryptophytes. However,M. rubrumis sometimes observed in nature containing plastids from other cryptophyte species. Here, we report on substantial ingestion of the blue‐green cryptophyteHemiselmis pacificabyM. rubrum, leading to organelle retention and transient increases inM. rubrum's growth rate. However, microscopy data suggest thatH. pacificaorganelles do not experience the same rearrangement and integration asTeleaulax amphioxeia's. We measuredM. rubrum's functional response, quantified the magnitude and duration of growth benefits, and estimated kleptoplastid photosynthetic rates. Our results suggest that a lack of discrimination betweenH. pacificaand the preferred preyT. amphioxeia(perhaps due to similarities in cryptophyte size and swimming behavior) may result inH. pacificaingestion Thus, while blue‐green cryptophytes may represent a negligible prey source in natural environments, they may helpM. rubrumsurvive whenTeleaulaxare unavailable. Furthermore, these results represent a useful tool for manipulatingM. rubrum's cell biology and photophysiology.
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- PAR ID:
- 10556701
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Journal of Eukaryotic Microbiology
- Volume:
- 72
- Issue:
- 2
- ISSN:
- 1066-5234
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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