Statoblast

Abstract: 1. The hypothesis that nutrient enrichment will affect bryozoan abundance was tested using two complementary investigations; a field-based method determining bryozoan abundance in 20 rivers of different nutrient concentrations by deploying statoblast (dormant propagule) traps and an experimental laboratory microcosm study measuring bryozoan growth and mortality. These two methods confirmed independently that increased nutrient concentrations in water promote increases in the biomass of freshwater bryozoans. 2. Statoblasts of the genus Plumatella were recorded in all rivers, regardless of nutrient concentrations, demonstrating that freshwater bryozoans are widespread. Concentrations of Plumatella statoblasts were high in rivers with high nutrient concentrations relative to those with low to moderate nutrient concentrations. Regression analyses indicated that phosphorus concentrations, in particular, significantly influenced statoblast concentrations. 3. Concentrations of Lophopus crystallinus statoblasts were also higher in sites characterised by high nutrient concentrations. Logistic regression analysis revealed that the presence of L. crystallinus statoblasts was significantly associated with decreasing altitude and increasing phosphorus concentrations. This apparently rare species was found in nine rivers (out of 20), seven of which were new sites for L. crystallinus. 4. Growth rates of Fredericella sultana in laboratory microcosms increased with increasing nutrient concentration and high mortality rates were associated with low nutrient concentrations. 5. Our results indicate that bryozoans respond to increasing nutrient concentrations by increased growth, resulting in higher biomasses in enriched waters. We also found that an important component of bryozoan diets can derive from food items lacking chlorophyll a. Finally, bryozoans may be used as independent proxies for inferring trophic conditions, a feature that may be especially valuable in reconstructing historical environments by assessing the abundance of statoblasts in sediment cores.

Abstract: BUSHNELL, J. H. & RAO, K. S. 1974. Dormant or quiescent stages and structures among the Ectoprocta: physical and chemical factors affecting viability and germination of statoblasts. Trans. Amer. Micros. Soc., 93: 524-543. In the Gymnolaemata dormancy or quiescence is restricted to hibernacula, stolonic sections, or to cells of the cystid wall of certain cheilostomes, which remain alive for extended periods in the winter in the absence of feeding polypides. New aspects of the fine structure of statoblasts of the Phylactolaemata are discussed and illustrated, using the first scanning electron microscope for statoblasts. Surface details of the capsule and annulus and the fibrous nature of the tubercles of Plumatella fruticosa are included. The architecture of the suture zone of statoblasts of three species is found to be notably different. The medial rib of this zone is seen to be continuous or discontinuous, and lateral ribs vary in terms of design and orientation. Statoblasts demonstrate both obligate and facultative dormancy. Statoblast production and number of generations of statoblast produced colonies in one season varies among species. Exogenous factors, including light, temperature, and water chemistry relate in different degrees to induction of dormancy and germination. In the same context possible endogenous factors are discussed. Tolerances of statoblasts to extremes of temperature and desiccation are reviewed. Statoblasts of certain species of Plumatella are viable after exposure to sewage pollution, to high levels of heavy metals and toxins, and to pesticides and herbicides including toxaphene and 2, 4-D butyl ester.

Abstract: Changes in host phenotype are often attributed to manipulation that enables parasites to complete trophic transmission cycles. We characterized changes in host phenotype in a colonial host–endoparasite system that lacks trophic transmission (the freshwater bryozoan Fredericella sultana and myxozoan parasite Tetracapsuloides bryosalmonae). We show that parasitism exerts opposing phenotypic effects at the colony and module levels. Thus, overt infection (the development of infectious spores in the host body cavity) was linked to a reduction in colony size and growth rate, while colony modules exhibited a form of gigantism. Larger modules may support larger parasite sacs and increase metabolite availability to the parasite. Host metabolic rates were lower in overtly infected relative to uninfected hosts that were not investing in propagule production. This suggests a role for direct resource competition and active parasite manipulation (castration) in driving the expression of the infected phenotype. The malformed offspring (statoblasts) of infected colonies had greatly reduced hatching success. Coupled with the severe reduction in statoblast production this suggests that vertical transmission is rare in overtly infected modules. We show that although the parasite can occasionally infect statoblasts during overt infections, no infections were detected in the surviving mature offspring, suggesting that during overt infections, horizontal transmission incurs a trade-off with vertical transmission.