Patterns of species diversity and endemism in comparable temperate brown algal floras

Abstract

Brown algal species diversity is compared in 100 km sections of the coastlines of four warm temperate regions: southern Australia, California, southwestern Africa, north-central Chile. The highest diversity (over 140 species per section) is found in southern Australia. California has a reasonable diversity (around 70 species per section), and both southern Australia and California have high regional endemism. Sections of north-central Chile and southwestern Africa have similar patterns, with low diversity (< 30 species per 100 km section), low endemism, few or no fucoids, and up to 25% of the brown algal flora are environmentally tolerant species of Scytosiphonales. Species turnover between contiguous sections of coast is generally related to relative change in temperature regime. Thus the high diversity of southern Australia is due to high species diversity within the 100 km sections, with little turnover, except for a rapid reduction in eastern Victoria likely to be related to lack of rocky substatum. It is hypothesized that low diversity and endemism in Chile and southwestern Africa can be explained by the occurrence of major environmental perturbations (upwelling and El Niño effects) in these regions, producing variable inter-annual temperature conditions that select out tolerant species from the local floras.