a rapid biodiversity assessment methodology tested on intertidal rocky shores
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AQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS
Aquatic Conserv: Mar. Freshw. Ecosyst. 20: 452463 (2010)
Published online 30 March 2010 in Wiley InterScience(www.interscience.wiley.com). DOI: 10.1002/aqc.1111
A rapid biodiversity assessment methodology tested on intertidalrocky shores
TIMOTHY D. OHARAa,, PRUE F. E. ADDISONa, RUTH GAZZARDa, TRUDY L. COSTAb
and JACQUELINE B. POCKLINGTONb
aMuseum Victoria, GPO Box 666, Melbourne 3001, AustraliabZoology Department, University of Melbourne, Melbourne 3010, Australia
1. Conservation managers require biodiversity assessment tools to estimate the impact of human activities onbiodiversity and to prioritize resources for habitat protection or restoration. Large-scale programs have beendeveloped for freshwater ecosystems which grade sites by comparing measured versus expected species richness.These models have been applied successfully to habitats that suffer from systemic pressures, such as poor waterquality. However, pressures in other habitats, such as rocky intertidal shores, are known to induce more subtlechanges in community composition.2. This paper tests a biodiversity assessment methodology that uses the ANOSIM R statistic to quantify the
biological dissimilarity between a site being assessed and a series of reference sites selected on the basis of theirsimilar environmental prole. Sites with high R values for assemblage composition have an anomalousassemblage for their environmental prole and are potentially disturbed.3. This methodology successfully identied moderate to heavily perturbed sites in a pilot study on 65 rocky
intertidal sites in south-eastern Australia. In general, measures based on percentage cover (ora and sessileinvertebrates) were more sensitive than abundance (fauna). Copyright r 2010 John Wiley & Sons, Ltd.
Received 19 August 2009; Revised 23 December 2009; Accepted 27 January 2010
KEY WORDS: biodiversity assessment; ecosystem health; intertidal; invertebrates; algae; dissimilarity; multivariate; ANOSIM
Coastal marine habitats are affected by various humanactivities including habitat destruction and changedhydrology (e.g. for sea walls, boat ramps, marinas, etc.);water pollution (e.g. nutrients, toxins, salinity, temperature);
trampling or displacement by visitors; direct harvesting oforganisms for food, bait, aquaria or curiosity; introducedspecies; and climate change (Suchanek, 1994; OHara, 2002).
In response, marine managers frequently request standardizedbiodiversity assessment indices of site condition for state ofenvironment reporting and to guide the allocation of scarce
management resources (Bailey et al., 2004). This information isoften required at large spatial scales on a limited budget.Typically managers want to rank site condition across the
entire jurisdiction of their agency.For example, the Natural Heritage Trust of the Australian
Government commissioned Museum Victoria to develop and
test a biodiversity assessment methodology to rank thecondition of at least 60 rocky intertidal sites across 1100 km
of coastline in the State of Victoria in temperate south-easternAustralia. This posed a number of methodological challengesthat would be typical of meso-scale projects in coastal
environments. First, there were no consistent quantitativemeasurements of environmental stressors across the study area.Monitoring of pollutants or nutrient enrichment was spatiallyconcentrated around a few sewerage outfalls and popular
beaches (OHara, unpubl. data). Measurement of recreationaluse was sporadic at best (Addison et al., 2008). Second, thebiological assemblages were potentially inuenced by the range
of strong environmental (e.g. temperature, primary production,wave exposure, geology) and biogeographical gradients thatwere known to occur across the study area (OHara, 2000;
OHara and Poore, 2000; Underwood and Chapman, 2007).Third, the intertidal assemblages were likely to be characterizedby high spatial and temporal variability in species abundance,
*Correspondence to: Timothy D. OHara, Museum Victoria, GPO Box 666, Melbourne 3001, Australia. E-mail: email@example.com
Copyright r 2010 John Wiley & Sons, Ltd.
particularly at small (o1m) and regional (110 km) scales(Archambault and Bourget, 1996; Underwood and Chapman,1998; Fraschetti et al., 2005).
Consequently, without direct measurement of stressors, sitecondition had to be assessed solely from the composition and/or abundance of the fauna and ora, assuming that a change
will occur in the ecosystem in response to exposure to stressors(Bailey et al., 2004; Pinedo et al., 2007). However, the variationinduced by human stressors had to be distinguished from the
high environmental variability. The lack of stressormeasurements precluded partitioning environmental andimpact factors across a multivariate regression frameworksuch as distance-based linear modelling (McArdle and
Anderson, 2001). Moreover, pilot data suggested that asingle comprehensive multivariate analysis of all sites wouldbe unlikely to derive identiable groups of sites with an
affected assemblage because of the presence of many strongenvironmental gradients across the large study area.
An alternative potential methodology was the reference
condition approach (RCA) developed for freshwater systemsthat uses sites as the basic sampling unit, factors outenvironmental variation through the careful selection of
reference (control) sites, and measures the difference inbiological assemblage composition between test and referencesites as the basis for a preliminary assessment of site condition(Bailey et al., 2004). The RCA forms the basis for large-scale
programs to monitor freshwater systems in various countries,including RIVPACS in the United Kingdom (Wright, 1995;Clarke et al., 2003), AUSRIVAS in Australia (Simpson and
Norris, 2000) and BEAST in Canada (Reynoldson et al., 1995).However, there were potential problems in applying these
freshwater methodologies to coastal systems. Existing RCA
implementations develop an expected taxon list for a test sitebased on taxa found at the matching reference sites andcompute an observed over expected taxa (O/E) ratio for the
test site, which is used as an index of site condition. Not onlydoes this probabilistic presence/absence approach requirespecies-rich systems (Marchant et al., 1997), it also assumesthat environmental degradation will cause a loss of taxa at a
site (or at least the loss of the ability to detect them). However,on rocky shores, impacts such as trampling or harvesting areknown experimentally to induce subtle species-specic
responses in abundance rather than result in local extinction(Keough and Quinn, 1998, 2000). Models based on abundanceare likely to be more sensitive than models based on
presenceabsence (Hewitt et al., 2005). Moreover, atmoderately polluted sites, nutrient enrichment can cause anincrease in species richness (Pearson and Rosenberg, 1978;Bishop et al., 2002). These difculties can be avoided by using
a multivariate measure of the difference in assemblagesbetween a test site and a selected group of reference sites.One solution is to use the residuals from a PCA analysis or
multivariate regression as the basis of an index of disturbance(e.g. the CDI method, see Flaten et al., 2007). However,residuals reect model error in addition to natural variability
and human disturbance. PCA in particular is rarelyappropriate for the non-linearities and zero-inated datacommon in ecological studies (Clarke and Warwick, 2001).
Consequently it was decided to test a novel methodologythat used the non-parametric ANOSIM R statistic (Clarke,1993) to quantify the overall difference in assemblagecomposition between a test site and a series of reference
sites, which were quantitatively selected on the basis of theirsimilar environmental prole. ANOSIM R is based onsimilarity coefcients which can utilize abundance or
presence/absence data and make no assumption about thedirection of the assemblage change. Although ANOSIM R wasdeveloped as a test statistic to calculate the signicance level of
multivariate differences between groups (Clarke, 1993), it is auseful comparative measure in its own right because it isderived from ranked rather than absolute similarity measures
and then scaled to lie between 1 and 1 (Clarke and Warwick,2001; Anderson et al., 2008). For example, comparativeANOSIM R measures are used to optimally split groups ofsamples in the linkage-tree procedure (Clarke et al., 2008).
Here we systematically calculate ANOSIM R values betweeneach site and its group of selected reference sites with a similarenvironmental prole, using these values to rank sites with
anomalous assemblages for further investigation.This biodiversity assessment methodology, hereafter called
MAVRIC (monitoring and assessment of Victorias rocky
intertidal coastline), was tested on both macro-invertebratefaunal and oral assemblages from 65 rocky intertidal sites insouth-eastern Australia, one of the largest intertidal surveys
conducted in the southern hemisphere. Sites ranged from beingputatively affected by sewage pollution (adjacent to outfalls) ortrampling (popular recreational sites) to relatively inaccessiblesites with no identied site-specic human impacts.
The MAVRIC biodiversity assessment methodology
The MAVRIC biodiversity assessment procedure has two basicsteps: (1) selection of a set of reference sites for comparisonwith a test site on the basis of their shared environmental
characteristics (termed nearest-neighbour sites after Linkeet al., 2004); and (2) calculation