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. 2014 Oct 22;9(10):e111043.
doi: 10.1371/journal.pone.0111043. eCollection 2014.

Hydrostatic pressure and temperature effects on the membranes of a seasonally migrating marine copepod

David W Pond  1 , Geraint A Tarling  2 , Daniel J Mayor  3
Affiliations

Hydrostatic pressure and temperature effects on the membranes of a seasonally migrating marine copepod

David W Pond et al. PLoS One. .

Abstract

Marine planktonic copepods of the order Calanoida are central to the ecology and productivity of high latitude ecosystems, representing the interface between primary producers and fish. These animals typically undertake a seasonal vertical migration into the deep sea, where they remain dormant for periods of between three and nine months. Descending copepods are subject to low temperatures and increased hydrostatic pressures. Nothing is known about how these organisms adapt their membranes to these environmental stressors. We collected copepods (Calanoides acutus) from the Southern Ocean at depth horizons ranging from surface waters down to 1000 m. Temperature and/or pressure both had significant, additive effects on the overall composition of the membrane phospholipid fatty acids (PLFAs) in C. acutus. The most prominent constituent of the PLFAs, the polyunsaturated fatty acid docosahexanoic acid [DHA - 22:6(n-3)], was affected by a significant interaction between temperature and pressure. This moiety increased with pressure, with the rate of increase being greater at colder temperatures. We suggest that DHA is key to the physiological adaptations of vertically migrating zooplankton, most likely because the biophysical properties of this compound are suited to maintaining membrane order in the cold, high pressure conditions that persist in the deep sea. As copepods cannot synthesise DHA and do not feed during dormancy, sufficient DHA must be accumulated through ingestion before migration is initiated. Climate-driven changes in the timing and abundance of the flagellated microplankton that supply DHA to copepods have major implications for the capacity of these animals to undertake their seasonal life cycle successfully.

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Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1
Figure 1. Calanoides acutus, a marine copepod that descends into the deep sea to overwinter in a state of dormancy.
The large oil sac occupying the abdomen is thought to provide energy storage and aid buoyancy control. Body length 3 mm.
Figure 2
Figure 2. Map indicating locations of the four study sites in the Southern Ocean.
(APF = Antarctic Polar Front, SACCF = Southern Antarctic Circumpolar Current Front, SBACC = Southern Boundary of the Antarctic Circumpolar Current).
Figure 3
Figure 3. Profiles of temperature at the four biological sampling stations in the Scotia Sea (Jan–Feb 2008).
Horizontal lines depict the sampling intervals of the Bongo net (0–400 m) and the MOCNESS multinet (375–1000 m).
Figure 4
Figure 4. Redundancy analysis distance triplot of the phospholipid fatty acid data from 85 individual C. acutus (‘sites’) using 20 fatty acids (‘species’).
The effects of depth and temperature are plotted as vectors (solid- and dashed lines respectively). Symbols and colours denote Station identity, with the overall effect of each Station being represented by filled symbols. The primary and secondary sets of axes relate to the sites and species loadings respectively.
Figure 5
Figure 5. Model-predicted effects of depth and temperature on the percentage composition of (a) 22:6(n-3), (b) 16:0 and (c) 18:0 in the phospholipid fatty acids of C. acutus.
Data points are presented for guidance only.
Figure 6
Figure 6. Model-predicted effects of temperature on the percentage composition of 20:5(n-3) in the phospholipid fatty acids of C. acutus.
Data points are presented for guidance only.
See this image and copyright information in PMC

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Grants and funding

The authors thank the officers and crew of the RRS James Clark Ross for their assistance and professionalism whilst at sea. This research was supported by grants from the Marine Alliance for Science and Technology for Scotland (MASTS) and the NERC (NE/J007803/1). The research is also a contribution to the ECOSYSTEMS programme of the British Antarctic Survey. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
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