3.2.2b Intertidal invertebrate species

Description

A quantitative pilot study of the composition of the benthic community of macro- invertebrates on intertidal rocky platforms was undertaken to provide detailed information on variation in biodiversity along the length of the Ningaloo Marine Park and determine the appropriate design of a monitoring protocol powerful enough to determine predefined levels of change. These general overall aims were in the context of the Ningaloo Marine Park Draft Management Plan of 2004, which set out a vision of maintaining the ecological values in the Park, and protecting it from adverse human impacts.

Aims

• Identify the species diversity of key flora and fauna in selected representative habitats
• Determine the abundance, size composition and distribution of these key species
• Establish how the current abundances of targeted and non-targeted species (subtidal and intertidal) compare with the natural abundances of these species in the Ningaloo Marine Park.

Methods

• Sample rocky intertidal platforms attached to shore in and out of sanctuary zones in the six major geographical regions of the Ningaloo Marine Park.
• Sample entire community of macroinvertebrates living on the intertidal platforms within the marine park using replicate 1m2 quadrats at each site.

Outcomes

• This study provides a start to an inventory of invertebrates on intertidal platforms at Ningaloo Marine Park, and some insights for the design of sampling schemes to detect differences among places and changes over time.
• Of 289 species found in our samples, only 3 species may be restricted to Ningaloo Reef, 127 species were gastropods, and 92 species were represented by single individuals. All of 15 of 30 the carefully identified species with known distributions also occur outside the Park, many extending to other states.
• Cowries (Cypraea cauputserpentis and C. moneta) provided a case study for detecting differences outside and inside Jurabi Sanctuary Zone. Their overall scarceness and variable abundance meant that detecting a twofold difference between inside and outside the zone, even with 4 replicate sites in each condition, would have very low statistical power, or require impossibly large number of replicate sites.
• An intensive study of small giant clams, Tridacna maxima, at 20 sites substituted space for time in the absence of long-term studies. Our interpretations indicated variability in recruitment and mortality, including failures of cohorts to recruit and catastrophic events of mortality. Spatial and temporal variability in the composition of the assemblages of invertebrates was similar to that of the individual species; spatial variability predominated over temporal variation, and demonstrated that the assemblages had different membership according to the region of the Park. The sites in Sanctuary Zones represent much of the variation in composition of the macroinvertebrates on rocky platforms.