The aims of this thesis were to document the pattern of distribution of the apparently rare marine algal species endemic to southern Australia, test the validity of the apparent rarity and seek causes of the patterns. A review of the concepts and causes of rarity with special reference to the marine macroalgae of temperate Australia is preceded by a brief background to macroalgal taxonomy, growth patterns, reproduction and ecology.
One hundred and forty-two species met the selected rarity criterion of occurring at five or fewer localities, as data-based in the Australian Virtual Herbarium. Seventy-one rare species were of broad range (>500 km), forty-five of narrow range (50–500 km), and twenty-six of restricted range (<50 km). The characteristics common to > 60% of rare macroalgae were that of small size and of filamentous or coarsely-branched habit. Of the three major taxonomic groups (Divisions Chlorophyta, Heterokontophyta and Rhodophyta) rare species within the Heterokontophyta (brown algae) were proportionally under-represented. Recognised rare species are discussed in terms of taxonomic affiliation, range, form and function, and co-occurrence of species in localised areas.
Six ‘centers of rarity’, areas with high proportions of rare species, were identified. These were Rottnest I WA, King George Sound WA, Eucla WA, Fowlers Bay SA, Port Phillip Bay VIC and D’Entrecasteaux Channel TAS. Using the random forest procedure, analyses indicated that there are particular environments and distinct environmental extremes that favour high proportions of rare species. Associations were found between high proportions of rare species and extremes of sand substratum, nitrate, phosphate, and chlorophyll-a. Overall, the analyses suggested that rare species are predominantly associated with low-nutrient environments and sandy substrata, whereas highly productive waters appear to be bereft of rare species.
The potential association of rare species with rare environments was tested. Fifteen environmental domains were identified, and Port Phillip Bay VIC and south-east Tasmania emerged as areas particularly favourable for rare species. However, the spatial extent of domains was not related to the mean proportion of threatened species within them. Other possible explanations for concentrations of rare species or high proportions of rare species, are associations with habitat complexity, or associations with escape routes along glacial drainage pathways during sea level change. Such conditions pertain to the areas with the highest concentrations of rare species.
A field program of target-searching for rare species was undertaken to elucidate rare species distributions. Results from underwater visual census surveys (UVC) supported the patterns of rare species found in historical herbarium records. A total of 489 macroalgal species were recorded collectively from 111 UVC surveys. Sixteen rare species were observed, representing ~11% of the 142 rare species. Notable range-extensions are reported for 7 rare species, and specific life history phases are newly recorded for 2 rare species.
A novel find that comprises a new family and probable new order, Entwisleia bella gen. et sp. nov. (F. Entwisleiaceae fam. nov.), was described upon a suite of morphological features that distinguish it from other known taxa. Planned genetic analyses will elucidate the ordinal classification of the new taxon and contribute to the formal proposal of the species.
Fifty rare marine macroalgae have been recorded from sites within sanctuary (no-take) zones of existing marine protected areas. A general paucity of adequate abundance and seasonality data thwarts confirmation of occurrence and/or persistence of these species within sanctuary zones, and therefore they cannot be firmly considered as adequately safeguarded.