Marine environmental resource managers and consultants require comprehensive, accurate and current data on the status of marine biodiversity in order to fully evaluate resource consent applications that involve development, impact or encroachment within the marine environment, and for identifying areas of coast appropriate for conservation. The role and efficacy of existing global, national and regional marine biodiversity databases in delivering these types of data are evaluated. Consultation with environmental consultants revealed that none regularly, if ever used any existing marine biodiversity database during their routine consulting activities. Moreover, no existing biodiversity database had appropriate data-mining tools, although each was determined to provide information of value to resource managers and environmental consultants operating at national and regional scales; none was deemed to provide the sort of information required to manage marine resources at a local scale. To achieve the objectives of this research programme, resource managers, data users and data compilers were consulted to determine their ideal data and database requirements. Existing biodiversity data sets that included New Zealand marine biodiversity then were searched or procured, and these data and that of a novel data set of species occurring at 296 intertidal and 25 fringe-saline (effectively freshwater) sites within and proximal to the Hauraki Gulf Marine Park (from Mimiwhangata Bay in the north to Tauranga Harbour in the south) were compared with species inventories from environmental consultants operating in this region. Biodiversity data from the 296 saline, comprising presence/absence data for 713 taxa recorded from the survey region were analysed in detail. Significantly different species assemblages were identified amongst these 296 sites, five intertidal habitats being recognised, each with characteristic species assemblages: marine-hard shores, marine-soft shores, brackish-hard shores, brackish-soft shores, and mangrove shores. Species richness and diversity were consistently higher in marine habitats, and greatest on hard substrata. Most sites host unique assemblages of species. A novel index of species richness is proposed, and although the spatial distribution of richness isn’t particularly revealing, as obvious patterns in the distribution of richness are not apparent, this index has value in that the richness of any shore can be compared and contrasted with that of others throughout the region. Augmenting this richness index is a novel index of species rarity. Based on the frequency of occurrence of taxa on shores throughout the survey region, very rare through to ubiquitous taxa are recognised to routinely occur on almost all shores, regardless of the total species richness. Moreover, very rare to uncommon taxa often comprise a disproportionately high percentage of the total species occurring on any given intertidal shore, in any habitat. Accordingly, alarm bells should ring for reviewers of resource consent applications wherein environmental consultants state that an area subject to development ‘hosts no rare, unique or otherwise remarkable species or ecology.’ Two applications of these novel biodiversity data are demonstrated: the relationship between species richness and regional council consented activities is described, with a negative correlation reported for the intensity of disturbance (using the number of consented activities as a proxy for disturbance) and species richness on marine hard shores; and an appraisal of four selection criteria for marine reserves (naturalness, representativeness, uniqueness and complementarities), wherein the intertidal fauna and flora of no existing or proposed marine reserve appears to be natural, unique or representative, and effort seems to have been spent duplicating certain assemblages of species in reserve networks. The former is intuitively obvious, but the latter is alarming, and the ramifications of it far reaching in terms of conservation of the marine environment. Protocols for conducting biodiversity surveys must be established and implemented to elevate the standards of environmental consultants, resulting value judgements on the composition of species, and the likely and actual effects of these developments on the marine environment to ensure that statements made in reports are based on current data rather than perceptions and client expectations. It is possible that resource consents have been issued based on spurious appraisals of the immediate and cumulative effect of discharge on the environment, or of the relative rarity (or appreciation of this) of species that occur within it. Prior to development of the novel Monalisa data set, no existing database or data set existed that provided the information routinely required by managers and consultants to make informed judgements that affect coastal development throughout the survey region. Recommendations for additional research to build on findings detailed herein are made.