Review: Price, Vincent, Venkatachalam, Bolton, Basson (2006) Concordance between different measures of biodiversity in Indian Ocean macroalgae. Marine Ecology Progress Series, 319:85-91.

Feature Paper: DOWNLOAD * Price, Vincent, Venkatachalam, Bolton, Basson (2006) Concordance between different measures of biodiversity in Indian Ocean macroalgae. Marine Ecology Progress Series, 319:85-91.

Author Abstract: We examine relationships between species richness (S), rarity (R) and average taxonomic distinctness (Δ+) from analysis of a comprehensive dataset for benthic marine algae (including Cyanophyta). This comprises 2894 species from 66 sites across the Indian Ocean. Ranked values for the sites, determined according to the 3 metrics, show significant positive correlation (p ≤ 0.01); Mauritius, India and Aldabra emerge as biodiversity ‘hotspots’, while Indonesia (Nias Island), Maldives (Male Atoll) and the Gulf of Aden are ‘coldspots’. Concordance between metrics was unexpected, given their disparity in robustness to sampling rigour and particularly since Δ+ is conceptually unrelated to S and R. Lack of significant latitudinal correlations was also evident except for Δ+, which increased towards temperate waters in the southern hemisphere. This contrasts with the variable patterns observed with longitude, for which significant correlations (negative, i.e. towards the west) were prevalent only for S (algae overall and separate categories except Phaeophyta), evident for R (Cyanophyta only) and absent for Δ+. Hence, use of one floral category as a surrogate for biodiversity in another is not guaranteed. Aquatic biodiversity patterns are complex, in accordance with recent findings derived mainly from faunal datasets. Relationships between different metrics can depend on both the group(s) selected and the environmental or geographical factor(s) examined. Our study is based on analysis of extensive but low resolution (presence/absence) data (Silva et al. 1996) collected from sites of variable size that were not sampled evenly. We address these constraints, but acknowledge the possibility that some patterns may prove to be artefacts, pending analysis of data from recent and ongoing studies. However, we do not expect this to significantly affect our overall conclusions.
 

Note to Readers: Follow links above for author email, full article text, or the publishing scientific journal. Author notes in my review are in quotes.

Review: Today's paper is the last of this week's survey of marine algae. Like the previous two papers, it looks at taxonomic diversity other than mere species richness, which is most common. This paper looked at 66 sampling locations throughout the Indian Ocean and examined 2894 species of marine algae among five major taxonomic groups. 

The authors examined species richness, rarity (as a function of range size and not abundance), and average taxonomic distinctness. The authors chose rarity because "unlike endemism it is relatively unaffected by spatial scale." The authors ranked values in each metric and determined "hotspots and coldspots of marine algal biodiversity," revealing "Mauritius, India and Aldabra as the sites of highest diversity [with] Indonesia (Nias Island), Maldives (Male Atoll) and the Gulf of Aden as the sites of lowest diversity." Look to the full paper for the complete list of rankings though some obvious disparities (from sampling effort) are apparent, with for example Kuwait and Iraq having widely varying values even though their coastlines are relatively the same and they are geographically adjacent.

The authors also examined latitudinal and longitudinal diversity patterns, noting that "significant negative correlation with longitude was evident for algae as a whole as well as for Cyanophyta, Rhodophyta and Chlorophyta [corresponding] with generally higher values of species richness in regions within 30 to 80ºE, and with lower values further east within 80 to 120ºE. Only Cyanophyta showed significant correlation (negative) with longitude [for rarity]. Average taxonomic distinctness showed significant correlation (negative) with latitude only for Phaeophyta, equating to an increase towards temperate waters in the southern hemisphere while for longitude no significant association was evident."

One problem the authors found was that for algal data, uniform geographical data are seldom available, with many sites at political levels and they had to log-transform site coastline lengths because of large variation. As a result, species richness was "highly sensitive to uneven sampling areas and effort, even though our computations of species richness attempted to standardize for area disparities."

The authors found that all three metrics "showed strong concurrence in terms of ranking sites as biodiversity hotspots and coldspots." Unlike corals and reef fishes, which we examined last week, there was a "virtual absence of significant latitudinal correlation for all 3 metrics, in contrast to the variable patterns observed with longitude, suggesting that relationships between different biodiversity measures in marine floras may not be straightforward."

One significant conclusion (echoed by the previous two papers) is that algae should probably not be grouped together as a whole, as the authors note that "algae and seaweed are ecological and not taxonomic terms," with the wide differences in seaweeds discussed previously this week. The authors did find stronger longitudinal correlations than latitudinal ones though, with the western Indian Ocean perhaps more diverse than the eastern Indian Ocean (the opposite is generally true for fishes and corals, with the exception of a minor peak in diversity in the Red Sea for those groups). 

Hopefully these three papers enlighten a bit more about algae and consider them as a unique and interesting grouping of diverse and unrelated organisms that doesn't always behave like corals and fishes, while sharing the same ecological place in space and time.