26 . SMITHSONIAN CONTRIBUTIONS TO THE MARINE SCIENCES 



FIGURE 20. Sections of C. compactian from nearby stations in northern Labrador, 

 off Nain, over a single year of growth, showing two summer bands (arrows) of 

 dense interfilament calcification separated by a wide band of winter cells having 

 little interfilament calcite. (A) Etched wall of a Hiatella cavity, 9-1 1 m depth at Jenks 

 Island. (B) Vertical fracture of a plant from Baker Island, 12-14 m depth. These 

 yearly bands are not of the same age; B shows a year with 20% more year growth 

 than A, as arrows indicate. 



has been shown (discussed further below), they can continue to 

 grow and calcify for at least part of a sunless winter. (Laboratory 

 studies underway also show repairs to damage of the perithal- 

 lium with growth in total darkness; Adey et al., unpublished). 



Moreover, in Labrador and the high Arctic, where clath- 

 rostromes lie 10-30 m deep under several meters of sea ice and 

 snow for 6-10 months of the year, winter calcification driven 

 directly by photosynthetic CO, removal seems unlikely. The 

 pattern of inner-wall calcification remains seasonally constant, 

 changing only in cell length and requiring only additional radi- 

 ally placed integral crystals of the same form. As suggested by 

 Adey (1998), inner-wall crystals in corallines are likely nucleated 



on organic templates and metabolically emplaced by ion pumps 

 in cell membranes. If so, rather than being diffusely distributed 

 over the length of the meristem cell and into upper perithallial 

 cells, these carbonate additions occur in a plane in the meristem 

 (i.e., a ring around the "middle" of each cell). On the other hand, 

 interfilament calcite formation in northern waters, strongly tied 

 to summer tissues, could result from precipitation as a result of 

 photosynthetic CO, removal by the epithallium. This remains to 

 be determined in laboratory studies. 



Clathromorphum spp., along with many coralline genera, 

 not only have a considerable ability to turn calcification on and 

 off (for example, in conceptacle formation) but are also broadly 



