Analysis of seaweed distributions in North Carolina waters indicates a basic difference between the shallow and deep water assemblages. The deep water flora is composed of 190 species, primarily taxa also occurring in the tropics and 110 of the deep water species do not have ranges
which extend any further north. The shallow water flora also includes 190 species. They live in more variable environmental conditions and include a larger number of species (78) which are known to both the north and south than does the deep water flora (45 species). Thirty two species from
shallow water and only seven from deep water find conditions in North Carolina suitable for growth and development but do not occur further south. Earlier observations concerning the importance of North Carolina's waters as a boundary region between southern and northern floras have been strengthened
and the recent view of the region between Cape Cod and Cape Canaveral as a broad transition region between a northern flora and a southern flora is also documented. The North Carolina segment of that region is shown to be a coastline where the transition is especially significant with respect
to total number of species and to the northern limitation of tropical elements. The Virginia-Maryland coast has only 105 species compared to North Carolina's 289 and is chiefly significant as a region in which 30 northern, temperate taxa reach their southern limits of distribution. The South
Carolina coast has only 95 species reported and is not important as either a northern or southern limit of seaweed distribution.
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