The influence of productivity on abyssal foraminiferal biodiversity

Gooday, Andrew J., Bett, Brian J., Jones, Daniel O.B. and Kitazato, Hiroshi (2012) The influence of productivity on abyssal foraminiferal biodiversity. Marine Biodiversity, 42 (4), 415-431. (doi:10.1007/s12526-012-0121-8).

Abstract

The quantity and quality of organic matter reaching the deep-sea floor is believed to exert a strong control on benthic foraminiferal assemblages, including the diversity and density of populations and the distribution patterns of species. In addition, some species seem to be associated with strong seasonality in primary productivity. We test relationships between diversity and mean annual productivity based on carefully selected datasets (>63-?m sieve fraction including soft-shelled taxa) from the NE Atlantic, Weddell Sea, and Equatorial and North Pacific. We used (1) ‘live’ (Rose Bengal stained) foraminiferal density, (2) mean annual surface productivity and (3) estimated organic carbon flux to the seafloor as proxies for food supply to the benthos. A suite of species richness, diversity and dominance measures all decreased significantly with increasing density, whereas species density showed a significant increase. In contrast, none of the relationships between these measures and primary productivity or its seasonality were significant. Only the Margalef and Brillouin indices exhibited a significant decrease with increasing values of carbon flux to the sea floor. When sites from the NE Atlantic were treated separately, significant relationships (?ve) emerged between flux and all diversity measures, and between foraminiferal densities and most (8 of 9) diversity measures. For the equatorial Pacific, however, these relationships were mostly (16 of 18) not significant. Size fractioned (>150-?m and >63-?m fraction including phytodetritus) data from the NE Atlantic samples yielded significant correlations (?ve) between several diversity measures and foraminiferal densities, but many fewer when related to estimated carbon flux to the seafloor. We also considered published datasets from the Arctic (Wollenburg and Mackensen Mar Micropaleontol 34: 153–185, 1998) and North Atlantic (Corliss et al. Deep-Sea Res 56: 835–841, 2009) Oceans. Diversity values (Fisher ? index based on ‘live’ counts) from seasonally and permanently ice-covered areas (depth range, 94–4,427 m) in the Arctic were significantly correlated (+ve) with estimated flux. Correlations were also significant for sites below permanent ice cover (1,051–4,427 m) and for those >4,000 m. Positive correlations between foraminiferal density and diversity were significant for the whole dataset and for sites with permanent ice cover, but not for the deep sites. Analysis of unstained calcareous foraminifera of Holocene age from the N Atlantic (2,118–4,673 m water depth) revealed significant relationships between diversity and seasonality, but not with flux. Additional analyses of ‘seasonal’ and ‘non-seasonal’ N Atlantic sites with a comparable range of estimated flux values (2–4 g C m?2 year?1) revealed that diversity increased with increasing flux and density in both cases, with significantly lower diversity at the seasonal compared to the non-seasonal sites. The contradictions between our data (?ve relationship between food availability and diversity) and those of Wollenburg and Corliss (+ve relationship) are difficult to explain and underline the need for further studies employing consistent methods to analyse ‘entire live’ assemblages across productivity gradients.

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