Marine diversity: the paradigms in patterns of species richness examined

Abstract

SUMMARY:The two central paradigms of marine diversity are that there is a latitudinal cline of increasing species richness from poles to tropics and that species richness increases with depth to a maximum around 2,000 m and thereafter decreases. However, these paradigms were based on data collected in the late 1950's and early 1960's. Here I show that the 1960's data, are not representative and thus the paradigms need re-examination. New data from coastal areas in the northern hemisphere record species richness as high as the highest recorded in the deep-sea. Whilst this suggests that the cline of increasing diversity from shallow to deep-sea does not exist, however, the database for the deep sea is not sufficient to draw such a conclusion. The basic problem with the data from the 1960s is that samples were taken on ecological scales and yet they are used to answer evolutionary questions. The questions that such data were to answer were why do the tropics have higher species richness than polar regions or why do deep-sea sediments have more species than coastal sediments? Evolutionary questions need data from much larger spatial areas. Recently, data representative of large scales have been collected from coastal areas in the northern hemisphere and show that there is a cline of increasing species richness from the Arctic to the tropics, but there does not yet seem to be a similar cline in the southern hemisphere. A number of hypotheses have been proposed for the observed patterns in biodiversity. In terrestrial ecology the energy-productivity hypothesis has gained wide acceptance as an explanation for the latitudinal gradient. Here I examine this and other hypotheses critically. Finally an analysis of research priorities is made. Assessment is urgently needed of the spatial scales and dynamics of species richness from point samples to assemblages, habitats and landscapes, especially in coastal areas and in the tropics, where the threats to biodiversity are greatest. New technologies are available, such as side-scan sonar, acoustics, and under-water digital video cameras but as yet have been relatively little used. Conservation of marine biodiversity must be based on sound theory, yet marine diversity studies lag well behind those of terrestrial habitats.

Soft bottom species richness and diversity as a function of depth and iceberg scour in Arctic glacial Kongsfjorden (Svalbard)

“…Species-accumulation curves (sensu Gray 2001;Fig. 2) show that the Wve replicates sampled were suYcient to include >90% of the soft-sediment species as they already level at 3-4 cores.…”

“…Marine species diversity in the northern hemisphere generally declines from low to high latitudes (Thorson 1957;Brattegard and Holthe 1997;Roy et al 1998;Gray 2001). However, environmental and biotope complexity may favour biodiversity on small scale.…”

Intra- and interspecific differences in palatability of Arctic macroalgae from Kongsfjorden (Spitsbergen) for two benthic sympatric invertebrates

“…Therefore, it seems that the low number of herbivores in Arctic waters is more related to factors such as food quality or physical properties of macroalgae that may influence mesoherbivore diversity and population structure. It has been suggested that the relatively young evolutionary history of the Arctic Ocean (Dayton et al, 1994) contributes to a generally low biodiversity due to a relatively short period for adaptation and speciation (Gray, 2001). Another aspect could be the principal inefficiency of macroalgae as nutritional source (Hessen, 1992;Sterner and Hessen, 1994) (e.g.…”

A high local species richness and biodiversity within high-latitude calcareous aggregates of tube-building polychaetes

“…Many hypotheses have been put forward to explain the observed patterns but few causal relationships have been identified (Pianka 1966;Gaston 2000;Hillebrand 2004;Jablonski et al 2006;Harrison and Cornell 2007;Buckley et al 2010). These patterns also exist in the marine benthos (Sanders 1968;Roy et al 1998;Gray 2001;Witman et al 2004), with diversity culminating on tropical coral reefs. Exceptions are however found within some taxa (Hillebrand 2004;Krug et al 2007) and at some high latitude biodiversity hotspots like those created by deep coldwater coral reefs (Jensen and Fredriksen 1992;Freiwald et al 2004).…”