Diana L. Steller

Environmental factors influencing distribution and morphology of rhodoliths in Bahía Concepción, B.C.S., México

Abstract Aerial and SCUBA diving observations revealed numerous, dense concentrations of free living, branched, nongeniculate coralline algae (rhodoliths) at depths of 3–12 m in Bahia Concepcion, B.C.S., Mexico. Plants were up to 10 cm in size, and commonly occurred at high densities forming a near continuous layer overlying a mixture of calcareous fragments and sediment. In contrast to other geographic regions, rhodolith shape remained spherical along depth-related gradients of water motion and sedimentation. Branch density and size, however, generally decreased with increasing depth. Surveys, as well as transplant and movement experiments, suggested that broad scale (east vs. west shore) and depth distribution of rhodolith beds within the bay are controlled by water motion and sedimentation. Additional experimental and taxonomic studies are needed to understand the smaller scale distribution patterns, and among and within bed variation in plant size and branch density. Such studies will allow a more rigorous interpretation of paleoenvironments based on the morphology of fossil rhodoliths.

The Healthy Heart: Lessons from Nature's Elite Athletes.

The incidence of cardiovascular disease in humans is more than three times that of many wild and domestic mammals despite nearly identical heart morphologies and responses to exercise. A survey of mammalian species from 0.002-kg shrews to 43,000-kg whales shows that the human heart is more dog-like than cat-like and that neither body size nor longevity accounts for the relative vulnerability to cardiovascular disease. Rather, a major difference is daily activity patterns, which may underlie the comparatively healthy hearts of wild mammals.