Importance of sieve size in deep-sea macrobenthic studies

Abstract

The deep-sea is well known for high benthic biodiversity despite being a low-food environment. However, most deep-sea organisms are very small in size as an adaptation to food limitation. Macrofauna are generally considered to be organisms larger than 0.5 mm and smaller than 3 cm. However, the smaller body size in the deep sea has led to the use of mesh sizes ranging between 0.25 and 0.5 mm to collect macrofauna, 0.3 and 0.5 mm being the most commonly used mesh sizes for deep-sea sampling. In this study, we tested the effectiveness of sieves of two different mesh sizes (0.3 and 0.5 mm) in assessing macrofaunal diversity, density and biomass. A total of 66 species were obtained with the smaller mesh, while the larger mesh retained only 40 macrofaunal species. Thus, use of larger mesh resulted in the loss of 39% species over the smaller mesh (p=0.0001). However, both sieves yielded high densities of organisms, high species diversity and steep rarefaction curves for nematodes and polychaetes. Using the larger mesh resulted in a significant loss in biomass of 90% and 78% for polychaetes and nematodes, respectively. Vertically in the sediment, faunal density was sampled more effectively with the smaller mesh sieve. Our results show a significant reduction in the number of species, organism density, and biomass of macrofauna with use of a 0.5 mm mesh rather than a 0.3 mm mesh and that a sieve of lower mesh size is more suitable for evaluation of deep-sea macrofauna.

Keywords:

• Abyssal
• biomass
• density
• diversity
• macrofauna
• mesh size

Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory, University of Copenhagen, Denmark

Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory, University of Copenhagen, Denmark

Acknowledgements

The authors acknowledge the Ministry of Earth Sciences, Government of India for financial support for the project on Polymetallic Nodule–Environment Impact Assessment of Nodule Mining, under which the current work was carried out. We thank the Director, National Institute of Oceanography, for providing the necessary facilities. The first author would like to thank CSIR for the fellowship provided for carrying out her PhD work. We would like to thank Dr Jürgen Guerrero Kommritz from the Zoologiscehs Museum Hamburg, Germany, for his help in the identification of tanaids. We are thankful to Dr Rahul Sharma, project leader, PMN-EIA, for providing valuable comments on the manuscript. We acknowledge the Plymouth Marine Laboratory and the DARWIN worldwide Pollution-Monitoring Programme for providing training in nematode identification and PRIMER software package. We also acknowledge three anonymous reviewers for providing useful and stimulating discussion on the manuscript. This is contribution no. 4373 of NIO, Goa.

Notes

Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory, University of Copenhagen, Denmark