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.
The possible significance of long-range dispersal for the biogeography of seaweeds
Indirect evidence of the existence of long-distance dispersal of seaweeds is provided by the fact that mid-oceanic islands of volcanic origin are inhabited by well-developed seaweed floras which could reach these islands only overseas from continental donor areas. For instance, the flora of Tristan da Cunha (S. Atlantic Ocean) was established by long-distance dispersal in less than 1 million years (the approximate age of the island); the seaweed flora of the Faeroes (N. Atlantic Ocean) could be constituted in less than 10,000 years (the end of the Pleistocene ice cover of these islands). There is no evidence for either supporting or discounting the possible role of planktonic stages of seaweeds (spores, propagules, zygotes) in the long-distance dispersal of seaweeds. There is, however, some evidence of long-distance dispersal as floating plants, or as plants attached to floating objects (including floating algae). There are a few examples of “artificial” long-range dispersal by man (possibly on ship hulls, oysters, in ballast water). Long-range dispersal of seaweeds does exist, but it is an exception rather than the rule. If it were the rule, the world’s seaweed floras would show similar latitudinal gradients in species composition in the oceans and on both hemispheres. This is, however, not the case.
Neohalosacciocolax aleutica gen. et sp. nov. (Rhodophyta), parasitic on Halosaccion minjaii I. K. Lee from the North Pacific
Neohalosacciocolax aleutica gen. et sp. nov., a red alga parasitic on Halosaccion minjaii I. K. Lee, is described from the Aleutian Islands. The parasite is characterized by the development of elongate paraphyses amongst the tetrasporangia, penetration of the host tissue forming pit-connections with the host cells, and formation of cushions in the central cavity as well as on the outer surface of the host. The tetrasporangium bears a stalk cell, and two spermatangia are developed subterminally on a mother cell. Female reproductive organs or cystocarps are not known. Considering the characters of the reproductive organs, it is proposed that the new genus Neohalosacciocolax be referred to the family Palmariaceae.