24 . SMITHSONIAN CONTRIBUTIONS TO THE MARINE SCIENCES 



FIGURE 18. Shallow-water habitat (3-5 m), with young (estimated 60 years old), 

 mound-forming plants of C. compactum in NE Newfoundland. Some plants are 

 strongly faceted (right arrow); others are more dome-shaped without facets (top arrow). 

 Several plants are fusing and with time will develop clathrostromes. The branching red 

 coralline is Lithothamnion glaciale (left arrow). Image by Alok Mallick. 



rate as a function of temperature fully explains differences in 

 both mean yearly thickness and conceptacle maturity time for 

 C. compactum from the Gulf of Maine to Labrador and for C. 

 nereostratum in the North Pacific. Since detailed temporal con- 

 ceptacle development data are not available for C. nereostratum, 

 approximate temperature-growth curves are presented, but con- 

 ceptacle development is not included on the graph. On the basis 

 of a comparison with Gulf of Maine data, conceptacle matura- 

 tion of C. nereostratum in the North Pacific should be similar 

 to, but a little slower than, that of C. compactum in the Gulf of 

 Maine. Field data from the Aleutian Islands are inadequate to 

 fully verify this hypothesis. 



Wall Structure and Calcification 



As demonstrated by Adey (1965) for C. compactum and 

 by Lebednik (1976) for C. nereostratum, all perithallial growth 

 and calcification in Clathromorphum occurs in the primary 

 meristem. Herein growth and calcification are shown to occur 

 along a narrow horizontal plane through the meristem (Figures 

 17, 24). With no bridging calcification (perithallium to epithal- 

 lium), a fracture plane can be easily induced. Although a sec- 

 ondary meristem can form within broken-out conceptacles or 

 on damaged surfaces (in the uppermost perithallium), the pri- 

 mary meristem produces most of the calcified tissue. As shown 

 in Figures 16A,B, 17B,D, and 24B and unlike other genera of 



corallines (Adey et al., 2005), the interfilament calcite crystals in 

 Clathromorphum are larger and more irregular than the inner- 

 wall crystals; the latter are short, prismatic, very fine, and ori- 

 ented radially. The interfilament crystals are oriented vertically 

 or diagonally and tend to be deltoid in shape. The thickness of 

 the radial, inner-wall crystals remains largely unchanged season- 

 ally, whereas interfilament calcification is thick in summer and 

 absent or thin and irregular in winter. This pattern also occurs 

 in the naturally etched surfaces of bivalve-bored cavities, where 

 the layers form ridges in the summer and grooves in the winter 

 (Figures 19, 20). 



In decalcified sections (Figure 8E), epithallial filaments, 

 lacking cell fusions, often disaggregate. In perithallial tissues, the 

 filaments are mostly cohesive because of the fusions organically 

 linking adjacent filaments. Nevertheless, between the fusions and 

 in the cells below the meristem where fusions are lacking, fila- 

 ments can locally disaggregate since there is no common inter- 

 filament wall. In the perithallium, inner calcified cell walls are 

 organically framed, whereas the space between the filaments is 

 apparently devoid of organic material and may or may not be 

 filled with carbonate, depending on the season. It has been widely 

 accepted that calcification in corallines is "simple" precipitation 

 resulting from removal of CO, during photosynthesis, with or- 

 ganic nucleation centers specifying calcite rather than aragonite 

 (Ries, 2010; however, see Adey, 1998). This is highly unlikely in 

 Clathromorphum species of Arctic and Subarctic seas because as 



