A critique of traditional approaches to seaweed distribution in light of the development of vicariance biogeography
An overview of the primary approaches to seaweed biogeography is provided in light of the development of vicariance biogeography. Each approach is discussed with particular regard to the extent to which the methods and objectives are compatible with vicariance. Ecological biogeography is considered an offshoot of ecology and physiology and is more appropriate in determining current distributions of organisms and aspects of physiological ecology rather than the speciation history of monophyletic groups. The R/P quotient of Feldmann and distribution of algal life-forms do not fall within the aegis of vicariance and are considered useful only in a descriptive sense. The examination of seaweed spans propounded by Pielou is considered flawed because of the lack of dependence on monophyletic groups. The floristic school of analysis of many seaweed biogeographers is analagous to the panbiogeography of Croizat, and provides the basis for the more concrete phylogenetic hypotheses that are the basis for vicariance analysis. The latter is considered the best methodology for studying the relationship between patterns of cladogenesis and the distribution of constituent taxa.
Geographical variation in the distributions of macroalgae in estuaries
Assemblages of macroalgal species present in the upper reaches of estuaries were compared using published species lists for the North Atlantic, covering a north-south gradient in Europe from Iceland to northern Spain, and in North America between the St. Lawrence and Virginia. Patterns were sought using cluster analysis and ordination. Three groupings of estuaries were noted: Icelandic, mainland European and American. There was a slight trend of increase in the ratio of red to brown algae with decreasing latitude in Europe, though not as marked as for open coastal algae. This might be associated with the effect of temperature on salinity tolerance. Despite this biogeographic trend, some of the commonest species appear to be widely spread through estuaries, possibly including southern Atlantic and Pacific locations. Confirmation of the trends suggested requires further data from southern European estuaries.
A Floristic and Ecological Survey. The Benthic Macro-Algae of Rehoboth Bay, Delaware
The benthic macroscopic algae of Rehoboth Bay, Delaware, were studied over a 14-month period in 1969—1970. The objcctives of the survey were to describe, qualitatively and quantitatively, the bay's poorly-known macro-algae Community and to corrdate patterns of distribution and seasonal change with environmental parameters. The average depth of the bay, which covets more than 35 square kilometers, is 1.9 meters. Tidal amplitude within the bay is about 30 cm, Seasonal water temperatures ranged from freezing to 29.6 C. During the study salinity averaged 27.8%0l ranged from 20.1% to 30,6/00ϊ and was rarely less than 24%. Fifty-nine taxa of Rhodophyta, Chlorophyta and Phaeophyta were recorded. Agardhidla ttnera^ Graci/aria verrucosa and U ha lactitea were found year-round throughout the bay. Three distinct aggregations of algae were apparent, even though most of the algal Community \vas unattached. The Gr&cilaria aggregation consisted mainly of Gracilaria verrucosa and several species of smaller algae were generally mixed with Gracilaria. *T\\tAgardhtella aggregation was characterized by large quantities of Agardhiella tenera with few other species in the sampies. The V ha aggregation was characterized by quantitatively small sampies which mcluded many species; Uha laciuca constituted the major portion of the sample wet volume. Spatial distribution of the three aggregations was closely correlated with sediment distribution which suggests that \vater movements play a role in maintaining a pattern of distribution which is determined by other factors, Salinity and temperature did not appear to be critical limiting factors in geographical distribution, although light may have been. The seasonal distribution of algae was typical of northern temperate waters. The Phaeophyta were nearly absein during the summer months, but increased in number of species and individuals during the colder months. Total Standing crop was greatest during the summer and least during the winter. Maximum Standing crop was more ciosely correlated to the temperature maximum than to the surface light energy maximum.