Exploring the growth of deep-sea bivalves in areas of potential sea-floor mining

Exploring the growth of deep-sea bivalves in areas of potential sea-floor mining

 

Supervisors: Dr Crispin Little (School of Earth and Environment), Dr Adrian Glover (Life Sciences, Natural History Museum, London) and Dr Clare Woulds (Geography)

 

Project Partners: Dr Dan Jones (National Oceanography Centre), Dr Thomas Dahlgren (University of Gothenburg, Sweden) and Dr Jon Copley (School of Ocean and Earth Science, Southampton)

Contact email: earctsl@leeds.ac.uk

 

The area of seabed beyond the continental shelves makes up one of the largest of the Earth’s ecosystems. However, the deep-sea benthos is very poorly understood, in large part because the relative inaccessibility of the environment. What is known is that deep-sea communities are diverse, heterogeneous in their composition and contain both generalist and specialist organisms, such as those living in particularly challenging locations, like hydrothermal vents. The life histories of most deep-sea animals are enigmatic. For example, knowledge of growth rates for most species is lacking, as is the extent to which these rates might be influenced by distant external factors, such as photic zone productivity and tidal effects. These life history questions are not esoteric because the deep-sea environment is being increasingly impacted by human activities, both indirectly through changes in the climate system, and directly through current and planned exploitation of marine resources (e.g., Glover et al. 2018). For example, in the past several years the UK Government has acted as the Sponsoring State to an International Seabed Authority authorised commercial exploration licence for polymetallic nodules over 118,000 square kilometres of the central Pacific abyssal seafloor, and the first machines for commercial mining of nodules are now being tested. Further, deep-sea fisheries are expanding the range and depth of their operations, as is the hydrocarbons industry.

 

All these commercial operations will increasingly impact the deep-sea environment, and questions about the duration of post-mining ecological recovery or the extent of potential set-aside areas are hampered by a general lack of data about deep-sea animals (Jones et al. 2017; Van Dover et al. 2017). Studying growth rates of most these animals will be difficult, as traditional methods used in shallow waters, such as mark and recapture, or aquarium studies are not technologically feasible. However, shell-forming deep-sea animals, principally molluscs, are amenable to growth studies, because the shell is an archive of past growth (Figure 1), and can also be preserved into the fossil record, unlike the soft parts of an animal. The study of the growth of shells – sclerochronology – has been widely applied to bivalve molluscs, and has proven to be useful to elucidate many aspects of the biology and ecology of individual animals, including determining the age and growth rate, seasonal temperature extremes, and times of food scarcity or annual reproduction cycles. Further, shell geochemical data (stable carbon and oxygen isotopes, trace and minor element ratios) can also provide proxy information for environmental and physiological conditions during the life of the animal (e.g. Lartaud et al. 2010; Richardson 2001). So far, sclerochronological techniques have been largely confined to shallow water bivalves (e.g. oysters and scallops), and there have been few studies on deep-sea species. These few studies have shown both fast (e.g. Nedoncelle et al. 2013 and Schöne et al. 2005 for hydrothermal vent mussels) and very slow (centuries) growth rates (e.g., Wisshak et al. 2009 for deep-sea oysters) for deep sea bivalves, indicating the need for further study to better understand the variation in this fundamental aspect of biology of these animals

 

Figure 1: Growth lines in deep-sea hydrothermal vent mussel shells revealed in SEM (top) and using Mutvei’s solution (bottom). Both images from Nedoncelle et al. (2013).

Aims and objectives:

The project will provide essential new information about the growth of bivalves (and potentially corals and gastropods) from a wide variety of deep-sea environmental settings, including:

• Hydrothermal vents and polymetallic nodule fields, targeted for imminent commercial exploitation.
• Deep-sea sedimented sites that may be affected by future climate-induced warming.

 

Established sclerochronological imaging and geochemical techniques (see reference list) will be used to analyse a wide range of bivalves from existing museum and personal collections. Fossil shells from similar palaeoenvironments may also be investigated. However, the small, fragile shells of many deep sea bivalves (Figures 2 and 3) will necessitate the modification of some existing methodologies, with the potential to develop new approaches, as appropriate. Mathematical processing (e.g. spectral analysis) of analytical results will be an essential component of the research, therefore applicants require strong mathematical skills, as well as a background in a relevant discipline.

Figure 2: Bivalve Bathyarca sp. from the Clarion-Clipperton Zone, central Pacific.

Figure 3: Bivalve Yoldiella sp. from the Clarion-Clipperton Zone, central Pacific.

 

Potential for high impact outcome

The project address several aspects of NERC societal challenges, including ‘benefiting from natural resources’ because the deep-sea is currently being targeted as an area for minerals exploitation, and ‘managing environmental change’ as the potential effects of deep-sea mining are currently poorly understood, with much of the necessary base line information still lacking. Further, increasing evidence shows that even the deep-sea is not immune from anthropogenic climate change effects. While sclerochronology has been widely used for shallow water molluscs, the application of the technique to deep-sea species is in its infancy, partly because of the difficulty in obtaining specimens, so the research is likely to yield impactful science. Outcomes from this research are likely to be relevant to government policy on regulation of the so-called ‘blue economy’.

Training

The student will work within the Earth Surface Science Institute (ESSI) under the supervision of Dr Crispin Little (palaeo@leeds research group) and Dr Adrian Glover (Life Sciences, Natural History Museum, London), with additional support from Dr Clare Woulds (Geography).  Project partners Dr Dan Jones (National Oceanography Centre), Dr Thomas Dahlgren (University of Gothenburg, Sweden) and Dr Jon Copley (School of Ocean and Earth Science, Southampton) will provide relevant specimens for study, expertise in deep-sea ecology and sclerochronological analysis. As a member of research groups at the University of Leeds and the Natural History Museum the student will have access to a broad spectrum of relevant expertise, which will be supplemented by an extensive range of research and personal development workshops delivered by the University of Leeds, from numerical modelling, through to managing your degree, and preparing for your viva (http://www.emeskillstraining.leeds.ac.uk/). The student may also be able to take part in an international research cruise Probable cruise to the Clarion-Clipperton Zone in February 2024.

 

References

Glover, A. G., Wiklund, H., Chen, C., & Dahlgren, T. G. (2018). Point of view: managing a sustainable deep-sea ‘blue economy’requires knowledge of what actually lives there. Elife, 7, e41319.

Jones, D.O., Kaiser, S., Sweetman, A.K., Smith, C.R., Menot, L., Vink, A., Trueblood, D., Greinert, J., Billett, D.S., Arbizu, P.M. and Radziejewska, T., 2017. Biological responses to disturbance from simulated deep-sea polymetallic nodule mining. PLoS One, 12(2), p.e0171750.

Nedoncelle, K., Lartaud, F., de Rafelis, M., Boulila, S.,Le Bris N. (2013) A new method for high-resolution bivalve growth rate studies in hydrothermal environments. Mar. Biol. 160:1427–1439.

Richardson, C.A. (2001) Molluscs as archive of environmental change. Oceanogr. Mar. Biol. 39:103–164.

Schöne, B.R., Giere, O. (2005) Growth increments and stable isotope variation in shells of the deep-sea hydrothermal vent bivalve mollusk Bathymodiolus brevior from the North Fiji Basin, Pacific Ocean. Deep Sea Res. Part I 52:1896–1910.

Schöne, B.R., Dunca, E., Fiebig, J., Pfeiffer, M. (2005) Mutvei’s solution: an ideal agent for resolving microgrowth structures of biogenic carbonates. Palaeogeogr. Palaeoclimatol. Palaeoecol. 228:149–166.

Van Dover, C.L., Ardron, J.A., Escobar, E., Gianni, M., Gjerde, K.M., Jaeckel, A., Jones, D.O.B., Levin, L.A., Niner, H.J., Pendleton, L. and Smith, C.R., 2017. Biodiversity loss from deep-sea mining. Nature Geoscience, 10(7), pp.464-465.

Wisshak, M., López Correa, M., Gofas, S., Salas, C., Taviani, M., Jakobsen, J., Freiwald, A. (2009) Shell architecture, element composition, and stable isotope signature of the giant deep-sea oyster Neopycnodonte zibrowii sp. n. from the NE Atlantic Deep-Sea Research Part I: Oceanographic Res. Pap.56: 374-407.