Fig 1.
Schematic representation of ventilation and bio-irrigation in the blind-ended burrow of the lugworm, Arenicola marina.
Lugworms ventilate intermittently oxic overlying water into their burrows to survive anoxic conditions. The flow of water passes over the gills of the worm and is subsequently forced (or bioirrigated) into the surrounding sediment. Porewater advection changes the sediment biogeochemistry dramatically. The extent and the scale of this effect depend on the ventilation activity of the animal and the distribution pattern of the irrigated water.
Fig 2.
Schematic drawing of PET/CT scanner.
The bucket containing sediment and lugworms is positioned on a table that can be moved accurately from the CT to the PET compartment of the scanner (Modified from [15]).
Fig 3.
3D visualization and quantification of water movement between overlying water and the sediment compartments.
Left pictures: The location of radioactivity within the reference region of interest (ROIref) is framed in blue and the sediment ROI (ROIsed) is framed in green on a 3D picture (front and side view) obtained from the PET scanner after 59 minutes. The temporal change in the radioactivity within each ROI is shown on the scatter plots (colors of symbols correspond to the colors of frames). Arrows indicate the timing of pictures to the left. Front (25 cm) x Side (15 cm).
Fig 4.
Construction of 3D images showing bioirrigating lugworm in sediment.
A series of 2D cross-sections were assembled by computer to create full 3D images of the object (CT) and water injected with tracer (PET). Finally the co-registered 3D images are combined to form the resulting picture after 37 min. Artificial colors are used to highlights different components. The bucket was 25 cm in diameter.
Table 1.
Lugworm body weight and burrow dimensions as measured from the CT images.
Fig 5.
Images of the temporal change in radial bioirrigation.
Left panel: Front and side view of a sediment compartment at different times showing the two cross sections (1: near the feeding pocket; 2: along the burrow shaft) of the burrow. The dashed lines indicate the sediment water interface. Right panel: Development of the bioirrigated area at cross section 1 and 2 after 17, 33 and 52 min (from top to bottom). The circles indicate the burrow circumference. Note the different scales in the two panels.
Fig 6.
Ventilation pattern of lugworm number 3 (see Table 1) with pumping (P), reverse ejection (E) and maintenance (M) periods.
The dotted line represents the zero baseline. The initial resting phase is probably due to a stress response after bucket movement.
Table 2.
Lugworm ventilation parameters based on the combined results from PET and CT imaging.
Fig 7.
3D visualization of lugworm, Arenicola marina, movements within the sediment.
Front and side images of 18F injected lugworm, Arenicola marina. The worms were injected with (A) 150 μl and (B) 50 μl of 18F solution and placed at the surface. PET pictures acquired every minute show the burial behavior and speed of the lugworms. The dashed lines indicate the sediment water interface. Front (25 cm) x Side (15 cm).