Seaweed Flora Research Articles

A reassessment of Northern Atlantic seaweed biogeography

Abstract On the basis of 25 seaweed floras of both the North Atlantic Ocean and the Mediterranean Sea mutual similarity dendrograms have been obtained for whole floras as well as for major taxonomic groups. Nine biogeographical regions were recognized: Tropical Western Atlantic Region, Warm Western Atlantic Region, Cold Western Atlantic Region, Arctic Atlantic Region, Cold Eastern Atlantic Region, Warm Eastern Atlantic Region, Subtropical Eastern Atlantic Region, Tropical Eastern Atlantic Region, Mediterranean Region. With some minor differences the pattern in the various taxonomic groups is very similar. Statistical relationships have been sought between species numbers and several geographical features (latitude, longitude, average February seawater temperature, average August seawater temperature, tidal height and coastal length). For the whole flora (including the Rhodophyta), tidal height appears to be inversely related to species numbers, and average seawater temperature in August and February is di...

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.

The influence of upwelling on South African west coast seaweeds

Upwelling from the Benguela Current system on the South African west coast has produced a seaweed flora distinct from that in the region east of Cape Agulhas. The origins of the major red algal component of the West Coast flora appear to be in temperate and polar regions of the southern Pacific Ocean, whereas the South and East Coast floras are more closely related to the floras of the tropical Indian Ocean and of South and West Australia. Although the West Coast flora has a high degree of endemism, recent evidence suggests that events since the initiation of the Benguela system < 12 million years ago have been crucial in its formation. Evidence on the effects of upwelling on growth and physiology suggests that rapid irregular fluctuations in temperature and nutrients on the West Coast have little effect on the strongly seasonal patterns of development, which are probably brought about by aspects of the light regime. Variations in light intensity in the sublittoral caused by upwelling or downwelling conditions appear to have relatively minor effects on seaweed production. Little is known of the effects of high concentrations of available nutrients in upwelled water, although the kelp Ecklonia maxima appears to have evolved both morphologically and physiologically to the West Coast conditions.

World-wide Relationships between Red Seaweed Floras: A Multivariate Approach

World-wide Relationships between Red Seaweed Floras: A Multivariate Approach

New Zealand seaweed flora and its relationships∗∗

Abstract The New Zealand botanical region includes New Zealand's three main islands and the Kermadec, Chatham, Solander, Snares, Bounty, Antipodes, Auckland, Campbell, and Macquarie Islands as well as other minor islands within this region. A short resumé of the history and present knowledge of the seaweed flora is given. Important ocean currents are illustrated. The seaweed (benthic marine algal) flora consists of: Chlorophyceae, 37 genera (3% endemic), 165 species (38 endemic), 3% undescribed (estimate); Phaeophyceae, 75 genera (7% endemic), 146 species (34% endemic), 6% undescribed; Rhodophyceae, 176 genera (4% endemic), 524 species (47% endemic), 7% undescribed. The floristic relationships between the islands within the region are expressed in terms of percentage of marine algal species each island has that is common with other islands (Table 2). The more important distributions of species are given. The external relationships of this region indicate a cosmopolitan, a circumpolar, and an Australasian element. Species shared with South America or Japan, and introductions within recent times, are discussed.

The distribution of seaweed floras in the tropical and subtropical Atlantic Ocean: a quantitative approach

Records of nearly 1500 species of marine algae present in over 80 countries, states, and islands of the tropical and subtropical Atlantic were analyzed to ascertain the relationships between their floras. Association analysis was unsatisfactory, cluster analysis was better, but, of the classificatory methods, indicator species analysis was best. However, the most meaningful results were obtained by ordination using reciprocal averaging. This method demonstrates that after the separation of the marine flora of South-West Africa (Namibia), two clearly defined groupings representing the eastern Atlantic and the western Atlantic are apparent. On the western side, the floras, apart from that of Uruguay, are a relatively close-knit group, except that the northern coast of the Gulf of Mexico together with the southern Atlantic States of the U.S.A. are distinct from the southern Gulf of Mexico and Caribbean groups. On the eastern side of the Atlantic the floras are less closely related. A well-marked tropical group extends from Gambia to Cameroun but does not include the Gulf of Guinea islands which form another group with Angola. This latter group is transitional to the colder water floras lying northwards of Senegal and south of Angola.

The marine flora of the Cap Blanc peninsula: its distribution and affinities

The shores of the Cap Blanc peninsula, along which runs the border between Mauritania and Western Sahara (former Spanish Sahara), were studied in November 1975. Littoral zonation is described and an annotated list is presented of the 188 species of algae now known from Mauritania and Western Sahara together with a further 23 species identified only to genus. In this present study 88 species of algae (excluding Cyanophyceae) were determined resulting in an increase of 67% and 37% respectively for the previously known marine floras of Western Sahara and Mauritania. Of 97 marine algae known from specific localities on the Cap Blanc peninsula, only 21 are common to both its eastern and western sides. Several tropical species reach their northern limit on the eastern side of the peninsula and many warm-temperate species reach their southernmost limit on the western side. Thus the Cap Blanc peninsula appears to represent a boundary between the warm temperate seaweed flora of North West Africa and the subtropical transition flora of Mauritania and Senegal to the south.

Contrasts between the benthic communities of subtidal hard substrata at Marcus and Malgas islands: a case of alternative stable states?

The fauna and flora of two sublittoral communities situated in close proximity on the west coast of South Africa are described and shown to be radically different, despite the fact that both experience similar physical conditions. One of these communities, at Marcus Island, has prolific beds of the black mussel Choromytilus meridionalis (35 954 g wet weight·m−2) accompanied by a large number of other species, notably sea urchins, holothurians, brittle stars, whelks and barnacles. In contrast, the other site, Malgas Island, is dominated by a large population of rock lobsters Jasus lalandii together with a dense seaweed flora (3 866 and 4 402 g wet weight·m−2 respectively). The numbers of species are similar at both sites (102 at Malgas Island and 107 at Marcus Island) but only 34 per cent are common to both localities. Although preliminary research indicates that the two sites have fairly similar physical conditions and bottom topography, they maintained their contrasting communities for the whole research period (1983–1986) and have probably done so for at least nine years, suggesting that they represent two stable alternative states of the same ecosystem. In the absence of rock lobsters at Marcus Island, wave action and inter/intraspecific competition are the main forces structuring the benthic community. Stability is maintained here by the resilience and rapid recovery of the mussel population after disturbance by storms. Where rock lobsters are abundant, as at Malgas Island, intense predation pressure is the main force controlling the structure of the benthos, and it is continually maintained because the rock lobsters are resistant to the effect of storms. Therefore, the presence or absence of high densities of rock lobsters is fundamental to the maintenance of these two contrasting communities.