A global survey of reef fishes shows that the consequences of biodiversity loss are greater than previously anticipated as ecosystem functioning remained unsaturated with the addition of new species. Additionally, reefs worldwide, particularly those most diverse, are highly vulnerable to human impacts that are widespread and likely to worsen due to ongoing coastal overpopulation.

This paper provides an analysis of the distribution patterns of marine biodiversity and summarizes the major activities of the Census of Marine Life program in the Caribbean region. The coastal Caribbean region is a large marine ecosystem (LME) characterized by coral reefs, mangroves, and seagrasses, but including other environments, such as sandy beaches and rocky shores. These tropical ecosystems incorporate a high diversity of associated flora and fauna, and the nations that border the Caribbean collectively encompass a major global marine biodiversity hot spot. We analyze the state of knowledge of marine biodiversity based on the geographic distribution of georeferenced species records and regional taxonomic lists. A total of 12,046 marine species are reported in this paper for the Caribbean region. These include representatives from 31 animal phyla, two plant phyla, one group of Chromista, and three groups of Protoctista. Sampling effort has been greatest in shallow, nearshore waters, where there is relatively good coverage of species records; offshore and deep environments have been less studied. Additionally, we found that the currently accepted classification of marine ecoregions of the Caribbean did not apply for the benthic distributions of five relatively well known taxonomic groups. Coastal species richness tends to concentrate along the Antillean arc (Cuba to the southernmost Antilles) and the northern coast of South America (Venezuela – Colombia), while no pattern can be observed in the deep sea with the available data. Several factors make it impossible to determine the extent to which these distribution patterns accurately reflect the true situation for marine biodiversity in general: (1) highly localized concentrations of collecting effort and a lack of collecting in many areas and ecosystems, (2) high variability among collecting methods, (3) limited taxonomic expertise for many groups, and (4) differing levels of activity in the study of different taxa.

Summary 1.Patterns of species richness along latitudinal, elevational and depth gradients often exhibit a mid-gradient peak. Similar patterns with a mid-domain peak in richness are produced, as a result of geometric constraints on species distributions, by models that randomize species range size and placement over a bounded gradient. 2. Proponents of these so-called mid-domain models argue that they provide an appropriate null hypothesis for examining species richness patterns along spatial gradients. Furthermore, some claim that because these models seem to explain a large proportion of the large-scale spatial variation in richness, geometric constraints on species distribution are in fact the cause of these patterns. 3.A critical examination of model assumptions reveals that some are unrealistic, conceptually flawed or internally inconsistent. Additionally, tests of mid-domain models have suffered from methodological deficiencies derived from arbitrariness and circularity in the definition of domain boundaries, collapsing two-dimensional (2-D) patterns into a single dimension (1-D), and the use of interpolated ranges, all of which can bias test results in favour of the models. Tests have also been statistically naive by using fairly insensitive measures of deviation between observed and predicted patterns and ignoring the increased probability of Type I error that can result in analyses of spatially autocorrelated data. 4. In spite of this, a review of the empirical evidence indicates that most studies do not show a high degree of concordance between observed and predicted species richness patterns, particularly in 2-D. Additionally, spatial patterns of variation in range size and species turnover do not unequivocally support mid-domain models. Thus, the models do not adequately describe observed species richness gradients and thus fail to explain them. 5. Although mid-domain models have served a useful purpose in drawing attention to the need to clarify the null expectation in the study of species richness gradients, their use appears to be severely limited by difficulties associated with the treatment of ranges, boundary definitions and a lack of clarity regarding the extent to which the observed data should be used to generate the null patterns.

Aim  To assess whether the total richness of the shore‐fish fauna of a discrete biogeographical region can be predicted, and to estimate how long it is likely to take to enumerate that fauna. Location  The Tropical Eastern Pacific (TEP), an isolated biogeographical region with a high level of endemism (72%) among its modestly rich, known fauna of shore fishes (1222 named + 58 known undescribed shallow‐water species). Methods  We used patterns in the long‐term dynamics and accumulation curves of descriptions of new species, which began in 1758, correlates of these patterns, and the body size–frequency distributions of various ecological groups of the fauna to (1) try to predict the total richness of that fauna, (2) estimate how many species might be missing and what biological characteristics they might have, and (3) estimate how long their discovery and description will take to complete. Results  Accumulation curves for the entire fauna, for all TEP endemics or for reef and soft‐bottom species (77.5% of the fauna) are not approaching asymptotes, and their description rates have remained fairly stable over the past century. However, curves for pelagic and multi‐habitat species (22.5% of the fauna) may be nearing asymptotes, perhaps because these species are relatively accessible to collection. These curves clearly indicate that the total TEP fauna is substantially richer than the presently known fauna, but do not allow reliable prediction of its richness. Extrapolations from frequency distributions of the body size of different ecological groups of TEP fishes indicate that the entire fauna is at least 12–15% larger than the currently known fauna. Main conclusions  From recent description trends, undiscovered species will tend to be small, have limited geographic and depth ranges, and live in deeper water. Poorly known, priority areas for taxonomic investigation in the TEP include deeper reef habitats, two isolated island groups, and several continental areas with unusual environments. At current levels of traditional taxonomic activity, the description of known unnamed species will take c.15 years, and assessment of the richness of unknown species, which probably number in the hundreds, will take decades.