Subtidal macroalgal richness, diversity and turnover, at multiple spatial scales, along the southwestern Australian coastline

Abstract

Spatial variability in the structure of subtidal macroalgal assemblages in southwest Australia was examined at multiple spatial scales using a three-factor hierarchal design. Spatial extents ranged from metres (between quadrats) to many hundreds of kilometres (between regions), and the study encompassed >2000 km of temperate coastline. In addition, the influence of taxonomic resolution, from species level data through to class level, on spatial patterns was investigated to assess the potential evolutionary timescales of the pattern and for developing cost effective regionally applicable surrogates for biodiversity monitoring. Almost 300 species were identified from 14 sites, representing considerable biodiversity and a significant subset of the total benthic macroalgal diversity in the region (~1000 species). Multivariate variability was significant at all spatial scales examined, but most prominent at smallest spatial scales, regardless of taxonomic resolution. Assemblage and species turnover was pronounced at scales of metres to hundreds of metres. Generally, small scale patchiness was a ubiquitous pattern for all individual taxa examined, regardless of taxonomic resolution, while variability at the scale of 10s km was less important. Even so, differences in spatial variability between taxa were observed, and ecological and historical reasons for such differences are proposed. Taxonomic aggregation to family level had minimal effect on spatial patterns, but aggregation to order level led to changes in some aspects of patterns of assemblage structure. The unique and speciose macroalgal assemblages on subtidal reefs in southwest Australia are shaped by a complex array of historical and contemporary processes that act at multiple spatial (and temporal) scales. Understanding the relative importance of these processes requires that further manipulative and correlative work is conducted across a range of ecologically-important spatial scales.

Latitudinal gradients in macroalgal biodiversity in the Southwest Atlantic between 36 and 55°S

“…In the marine environments of the Northern Hemisphere, species richness also increases from the Arctic to the tropics (e.g. Roy et al, 1998Roy et al, , 2000, but there does not seem to be a similar cline in the Southern Hemisphere (Clarke, 1992), as biodiversity is high in Australia (Crame, 2000;Smale et al, 2011) and also at higher latitudes (Gray, 1997). A long history of geographical isolation may account for the relatively high species richness of Antarctica (Gray, 2001).…”

Structure and temporal dynamic of tropical turf forming macroalgal assemblages of the western coast of Mexico

“…Among the most important physical factors are sedimentation (Airoldi & Virgilio, 1998;Balata et al, 2011), wave patterns (Díez et al, 2003;Wernberg & Connell, 2008;Smale et al, 2011), tides (Metaxas & Scheibling, 1993), and water movement (Cheroske et al, 2000).…”

Seaweeds in Two Oceans: Beta-Diversity

“…With the exception of the some Australian studies (Smale et al, 2010(Smale et al, , 2011Waters et al, 2010;Leaper et al, 2011;Wernberg et al, 2013), one in Europe (Tuya et al, 2012) and another two in the northwest Indian Ocean/Red Sea region (Schils and Wilson, 2006;Issa et al, 2016), studies of this scale and The partitioning represents the contribution of turnover and nestedness-resultant processes. Mean ± SD values are presented for the whole South African coast, as well as for each of the four bioregions.…”

“…This points to habitat and/or environmental heterogeneity and neutral processes such as dispersal limitation, stochastic influences or habitat heterogeneity as the main structuring agents of communities within the region. Indeed, habitat heterogeneity generated through stochastic influences such as patchiness due to storms denuding portions of kelp beds (which is the dominant habitat type along the west coast) is well-known in kelp forests (Smale et al, 2011). Furthermore, the prevalence of two kinds of assembly processes to either side of the Cape Peninsula (17), coinciding with the point where a region of low α-diversity (BMP) transitions into a region of higher α-diversity (the Benguela-Agulhas Transition Zone, B-ATZ), suggests that the answer to our question is probably that some historical event was responsible for that disjunction, and that this barrier is still maintained today due to limited mixing between the Agulhas and Benguela Currents (although some of the sections along the west coast between 16/17 and 10 certainly have a reasonable probability of sharing species with sections at the western-most side of the AMP, e.g., 23, 24; see more on the B-ATZ, below).…”

“…Rather, we suggest that the unknown influence is more likely to be neutral influences (Hubbell, 2001) manifesting at a reasonably broad scale. These may include stochastic events (e.g., Smale et al, 2011) or biotic processes caused by differences in species demography, dispersal or the influence of grazers, etc. Such processes are usually finer scaled, but, having said that, the entire west coast region that makes up the BMP is dominated by nestedness-resultant β-diversity, which is also symptomatic of neutral assembly processes.…”