Unimodal relationship between biomass and species richness of deep-sea nematodes: implications for the link between productivity and diversity

Abstract

Describing large-scale patterns of biological diversity is a first step towards understanding the mechanisms that generate and maintain diversity. The highly diverse deep-sea floor is the largest ecosystem on Earth, but the productivity−diversity relationship in this biome is not well characterized. We investigated this relationship by using biomass of nematodes as a proxy for productivity (particulate organic carbon flux to the seabed). We used sample data collected from the New Zealand and Antarctic regions and combined these with published data from around the globe for broader analyses. There was a significant unimodal relationship between nematode biomass and diversity, i.e. expected number of species, ES(51) both within the New Zealand region and across ocean basins. This relationship remained significant after accounting for the effects of both water depth and nematode abundance. These findings support earlier suggestions of a unimodal productivity−diversity relationship in the deep sea that were based on other proxies (e.g. water depth, modelled particulate organic carbon flux). We argue that the 'productivity context' is of primary importance when determining the strength and nature of the relationship between other environmental factors and diversity. Studies that include either or both extremes of the productivity scale are likely to find that productivity is the main factor limiting deep-sea diversity, whereas those focusing on the intermediate productivity range are more likely to find that other factors (e.g. disturbance, habitat heterogeneity) play a role.KEY WORDS: Southwest Pacific · Kaikoura Canyon · Ross Sea · Southern Ocean · Nematodes · Macroecology · Biomass Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 454: [53][54][55][56][57][58][59][60][61][62][63][64] 2012 ships are also common (Mittelbach et al. 2001, Witman et al. 2008. A number of underlying mechanisms have been proposed to explain productivity− diversity relationships, although there is much debate about their relative contributions (Rosenzweig 1992, Waide et al. 1999, Gross & Cardinale 2007. As the number of individuals increases with productivity, diversity may increase through higher proportions of rare (Preston 1962) and specialist species (Evans et al. 2006), lowered extinction rates and/or higher speciation rates (Rex 1973, Wright 1983. Negative productivity−diversity relationships may result from increased rates of competitive exclusion (Grime 1973, Rosenzweig & Abramsky 1993, temporal variability in productivity (Chown & Gaston 1999) or environmental stress (e.g. hypoxia, Levin & Gage 1998). A combination of these mechanisms, operating to increase and decrease diversity, might be responsible for the unimodal productivity−diversity relationship often observed.Most of our knowledge of productivity−diversity relationships has been gained from terrestrial and shallow aquatic habitats (e.g. Mittelbach et al. 2001). Such relationships, however, have not been well char...

3. Ecology of free-living marine nematodes

“…3.3 ; data available in Leduc et al 2012). The shape of this relation is conceptually unimodal; sites with extremely low abundances are represented by few species, and an increment in abundance entails an increase in the number of coexisting species ( Figs.…”

Diverse foraging strategies by a marine top predator: Sperm whales exploit pelagic and demersal habitats in the Kaikōura submarine canyon

“…1), has been described as the most productive non-chemosynthetic habitat recorded to date in the deep sea . It harbours exceptional biomass of infaunal and epifaunal invertebrates, including nematodes, and also benthic-feeding fish Leduc et al 2012). Furthermore, the presence of many top-predators targeting mesopelagic prey (e.g., Benoit-Bird et al 2004, Boren et al 2006 suggests that the area hosts a highly productive pelagic system.…”

“…It is therefore essential to better understand what sustains the diet of sperm whales and the environmental features which drive their distribution. Given the extreme benthic biomass of the Kaikōura Canyon (De , Leduc et al 2012, and that demersal fish are known to constitute an important part of the diet of sperm whales in the region (Gaskin & Cawthorn 1967), we hypothesise that sperm whales at Kaikōura are likely to forage extensively near the seafloor.…”

Unravelling the environmental drivers of deep-sea nematode biodiversity and its relation with carbon mineralisation along a longitudinal primary productivity gradient

“…Deep-sea diversity has been documented to vary positively (Glover et al, 2002; Published by Copernicus Publications on behalf of the European Geosciences Union. Lambshead et al, 2000Lambshead et al, , 2002, negatively (Gooday et al, 2012) or unimodally (Leduc et al, 2012a;McClain et al, 2012;Tittensor et al, 2011) with productivity for different taxa and geographic regions. These differences in diversityproductivity trends may be related to the differential productivity ranges considered (Rex and Etter, 2010).…”