Chemical Composition of Ectoprocta (Bryozoa)

Abstract

Published data on the elemental composition of the Ectoprocta (Bryozoa) are supplemented by new chemical analyses of 28 ectoproct samples, distributed among 13 species, for organic matter, CO 2 calcium, magnesium, strontium, barium, phosphorus and iron. The new data, in addition to the 25 fairly complete analyses previously published (distributed among 19 other species) suggest the existence of 3 species groupings that are based on composition and are related to habitat. Group I consists of genera that have more than 50 percent organic matter (dry weight). It includes all species of the entirely freshwater Phylactolaemata and the commonly brackish-water and freshwater Ctenostomata. Group II includes Cheilostomata having from 25 to 50 percent organic matter (dry weight). These genera are bush-like in growth habit and may be anchored to fine-grained sediment bottoms. Genera in Group II contain appreciable amounts of P 2 O 5 (1.0-2.0 percent) and Fe 2 O 3 (0.4-1.0 percent) in the ash. Only calcite has been observed in the mineralized portion of the skeleton of Group II species. Group III includes Cheilostomata and Cyclostomata that have less than 25 percent organic matter. These forms require stable surfaces for colonization. They contain a lesser amount of P 2 O 5 (0.1-0.6 percent) and of Fe 2 O 3 (less than 0.4 percent) than Group II genera. About 15 percent of Group III species have aragonitic skeletons. "Pure" aragonitic hard parts contain about 1.0 percent SrO (1.4 wt. percent SrCO 3 and 0.3 percent MgO (0.6 wt. percent MgCO 3 ) whereas "pure" calcitic skeletons contain less than 0.4 percent SrO (0.6 wt. percent SrCO 3 ) and more than 3.5 percent MgO (7.4 wt. percent MgCO 3 ). Based on the few species analyzed, some additional taxonomic and ecologic generalizations are suggested. Calcitic cheilostomes contain more magnesium than do calcitic cyclostomes. Warm water calcitic species have higher magnesium concentrations than do cold water calcitic species. Specimens from an estuary contain more P 2 O 5 and less strontium than do specimens from areas of normal marine salinity, and specimens from nearshore areas have more iron than do specimens from deeper offshore areas. The order of concentration of elements in ectoprocts relative to the composition of sea water is 10 5 for phosphorus and iron, 10 3 for barium, 10 2 for calcium and strontium, and 10 1 for magnesium. However, the elements that are highly enriched in ectoprocts, especially iron and phosphorus, may be supplied to a considerable extent by sources other than normal sea water, such as food (diatoms in particular), and occluded matter of terrigenous origin. Twenty-eight protein and chitin amino acids were studied in three representative marine ectoproct species: Bugula simplex, a calcitic cheilostome, Parasmittina nitida, an aragonitic cheilostome, and Tubulipora liliacea, a calcitic cyclostome. Similar proportions but widely different amounts (from 0.6 to 11 percent organism dry weight) of amino acids occur in these species. Obvious variations in amino acid proportions relate more directly to degree of calcification and to mineralogy than to species classification. Chitin amino acids recoverable in residues after leaching with acid form less than 2 percent of the total organic content of the organism.