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An oldie but a goodie

The unseen value of an historical shell collection. 

Alone, a single shell might share a small glimpse into the world that created it. In their hundreds, or even thousands however, shells can become powerful storytellers about the land, the environment, and the changes they’ve experienced along their journey through time. In this blog by Ben Mortensen, Collection Technician, Drier Collection, we explore what we can learn from a special collection of almost century-old shells, and what they mean for environmental research today.

An oldie but a goodie

The Drier Collection:

An oldie but a goodie

The Drier Collection is a large assortment of predominantly New Zealand molluscan shells, collected between 1926 and 1930. The shells were collected from all over New Zealand, including from Rangitāhua/Kermadec Islands, Manawatāwhi/Three Kings Islands, the Chatham Islands and the sub-Antarctic Islands. Most of them are marine molluscs, but there are also a number of freshwater molluscs and land snails. The collection was assembled by Dr Ezra Newton Drier, a Canadian, who had emigrated to New Zealand in 1916 to practice medicine. He later became an avid shell collector, most likely as a result of becoming a member of the Auckland Museum Institute and meeting conchologist A.W.B. Powell (Blom 2023).

Although these old shell collections can and often do make for impressive display material, their true value lies not in their display potential, but in the data that they hold. Historical shell collections can provide a rich source of historical baseline data, and provided it is accurate and analysed correctly, it can be used to make significant contributions to scientific research and conservation. The data from these older shell collections is typically in the form of old handwritten labels or collection log books, and this information first needs to be accurately captured and digitised. With the staggering rates of biodiversity loss that the planet is currently faced with, the need to record and maintain collection data has never been more vital. By digitising and aggregating the data you can transform how scientific research is conducted and consequently enhance the overall efficiency of biodiversity conservation and environmental management. All the specimen records and data from the Drier Collection are now freely available through Auckland Museum’s Collections Online, as well as international data aggregation portals, such as the Global Biodiversity Information Facility (GBIF).

Buccinulum (Euthrena) robustum, MA72029, © Auckland Museum, CC BY 

Eudoxochiton nobilis

One of the main applications for historical baseline data is to help assess changes in species abundances over time. Analysing species declines in particular, has become an increasingly important component of conservation research. Knowing which species are at risk and where means that suitable environmental management policies can be put in place to help protect vulnerable species. The Drier Collection now dates back more than 90 years and can provide some invaluable historical baseline data for New Zealand Mollusca for that time. For instance, the collection contains some unusually large lots, sometimes consisting of hundreds or even thousands of specimens. These large lots can give an indication of large past population numbers, and when compared to current population data can be used to help demonstrate that certain species are now becoming rare or even locally extinct in certain areas. Two specific examples from the collection of populations that may have experienced declines based on these comparative observations, are the Kākahi/New Zealand freshwater mussel (Echyridella menziesii) collected from Lake Taupo and Lake Rotoiti, and the Takai/Ostrich foot shell (Struthiolaria papulosa) collected from Cheltenham Beach, Auckland.

The population decline of the New Zealand freshwater mussel is already well known and has been attributed to loss of habitat associated with river modification, eutrophication, and other types of pollution, and also possibly through the loss of the host fish on which their life cycle depends (McDowall 2002). The decline of this species is of particular concern due to the important ecosystem service it provides. In lakes with dense mussel populations, their filter feeding activity significantly reduces algae and sediment suspended in the water column and thus improves water quality. The historical data from the Drier Collection, i.e., the several large specimen lots (250+) collected from Lake Taupo and Lake Rotoiti, appears to reinforce the science on the decline of this species, and reiterates the importance of having data that helps to document such declines. It is a similar situation for the ostrich foot shells collected from Cheltenham Beach. A large collection lot containing 611 specimens suggests that there was once a large healthy population there. However, this species is no longer found in these numbers at this location, if at all. Although the actual reason for this particular population decline is as yet unknown, having data that shows evidence of a decline can then prompt new research to be done to find out why.

 
Large specimens of Eudoxochiton nobilis, a species of chiton collected from Muriwai, Auckland.

Climate change is one of the major drivers behind the changing population dynamics and biodiversity loss in the marine environment. The rising sea and air temperatures are expected to push the geographic ranges of many marine species poleward (Helmuth et al. 2002, Sorte et al. 2011). Through the use of historical data sets, examples of these range shifts have already been observed in a number of different intertidal species (Barry et al. 1995, Sagarin et al. 1999). In much the same way, the historical data from the Drier Collection could potentially be analysed alongside historical climate data so that comparisons can be made between past and present to help give a better understanding of how the changing climate may be affecting New Zealand’s molluscan populations.

The collection information is not the only source of data that these shells have. The actual physical specimens themselves can also provide a wealth of valuable information and be extremely useful for answering questions concerning population declines. For instance, because molluscs can record environmental conditions within their shells as they grow through the incorporation of molecular isotopes (McConnaughey & Gillikan 2008), having access to well curated historical collection material allows for analysis to be done on the shells themselves in order to determine whether or not the population declines may be the result of environmental changes. Having physical access to the historical collection material also means that size comparisons can be made between species from different time periods. One particular observation made from the Drier Collection, are the notable size differences of a species of chiton (Eudoxochiton nobilis), collected from Muriwai Beach on Auckland's west coast. The specimens from the Drier Collection appear to be significantly larger than those collected from there more recently. It has been suggested that intraspecific size differences between animals from different locations could be due to the differential energy costs associated with the different locations (Sebens 2002). This could also be true for animals from the same location from different time periods if the environmental conditions of that location have changed over time. Molecular isotope analysis could again be done on the specimens themselves to determine whether or not the size differences observed in these chitons could be the result of environmental changes and the differential energy costs associated with them.

Part of a large lot of ostrich foot shells (Struthiolaria vermis) collected from Cheltenham Beach, Auckland. In total, the lot contained 611 specimens.

Due to the raft of environmental changes that the planet is presently undergoing, it has become increasingly imperative that we improve our understanding of our marine ecosystems so we can put in place effective legislation to help protect ocean biodiversity. Collectively, historical data sets such as the Drier Collection, when digitised, aggregated, and made freely available, can lead to new and important insights about things such as changes in population numbers, specimen size and species movements which have taken place in New Zealand over time. These insights can then be used to help inform important decisions about concerns such as the future direction of conservation research and conservation policy. 

References

Barry, J.P., C.H. Baxter, R.D. Sagarin and S.E. Gillman 1995. Climate related, long term faunal changes in a California rocky intertidal community. Science 267, 672 - 675.

Blom, W.M. 2023. Dr Ezra Newton Drier (1871-1942) and his collection of New Zealand Mollusca. Records of the Auckland Museum. Vol. 57: 17-30.

Helmuth, B., C.D. Harley, P.M. Halpin, M. O'Donnell, G.E. Hofmann, C.A. Blanchette 2002. Climate change and latitudinal patterns of intertidal thermal stress. Science. 298(5595):1015-7. doi: 10.1126/science.1076814. PMID: 12411702

McConnaughey, T & D. Gillikin 2008. Carbon isotopes in mollusk shell carbonates. Geo-Marine Letters. 28. 287-299. https://doi.org/10.1007/s00367-008-0116-4

McDowall, R.M. 2002. Decline of the kākahi – identifying cause and effect. Water and Atmosphere 10(4): 8-9.

Sagarin, R.D., J.P. Barry, S.E. Gilman, C.H. Baxter 1999. Climate-related change in an intertidal community over short and long time scales. Ecol. Monogr. 69: 465 - 490.

Sebens, K.P. 2002. Energetic Constraints, Size Gradients, and Size Limits in Benthic Marine Invertebrates, Integrative and Comparative Biology, Volume 42, Issue 4, Pages 853–861, https://doi.org/10.1093/icb/42.4.853

Sorte, C.J.B., S.J. Jones, L.P. Miller 2011. Geographic variation in temperature tolerance as an indicator of potential population responses to climate change, Journal of Experimental Marine Biology and Ecology, Volume 400, Issues 1–2, Pages 209-217, ISSN 0022-0981. https://doi.org/10.1016/j.jembe.2011.02.009