Importance and sustainability of endangered communities of bee pollinators in the machair, a changing coastal ecosystem

The machair is a unique environment localised in Western Scotland and North-west Ireland, characterised by low-level coastal grasslands usually fronted by a higher dune ridge. The machair is highly subsidised by marine resources and often connects to a wide range of freshwater bodies. Thus, machair plays an important dual role as both buffer and link between ocean and freshwater catchment systems. In addition, due to sandy soils providing relatively good agricultural potential, machair has been used extensively for arable agriculture(1).

A varied wildlife inhabits the machair, with some species of flora and fauna of high conservation priority. Of particular interest is a fascinating group of insect pollinators (bumblebees and solitary bees) that now largely depend on the machair wildflowers for their survival in the British Isles. Notably, the charismatic Great Yellow bumblebee has seriously declined in the UK and can now be found only in western and northern fringes of Scotland. These bees provide fundamental pollination services to many machair wildflowers, and therefore their survival and health is key for the preservation of the machair itself. Salt-tolerant plants (like those growing in the machair) typically accumulate high levels of sodium in their tissues and are particularly attractive and beneficial for bumblebees that normally struggle, as do all other pollinators, to gain enough sodium from their diet(2). It is possible that machair flowers provide higher sodium rewards to their bumblebee pollinators and this reinforces the complex reciprocal mutualism linking these two types of organisms.

This PhD project will investigate the complex relationship linking bumblebees and the machair from a landscape ecology and insect physiology perspective, and use this understanding to predict how future climate change and human management might impact this fragile ecosystem. The student will start their research by looking at historic data to infer how plant and pollinator communities of the machair have changed over time in different areas, and link this to recent information on nectar and pollen production by different species (OBJECTIVE 1). Some preliminary evidence suggests that insect-pollinated plants have decreased overall in the machair (with some extraordinary exceptions), while wind-pollinated plants have become more prevalent(3). The next step will be to characterise the levels of sodium and other nutrients that naturally occur in machair plants, and then test in the lab how some key plant species respond to varying levels of sodium in the environment (OBJECTIVE 2). The student will then characterise the adaptation of bumblebee pollinators to the machair, by looking at their foraging preference and their response at the molecular and physiological levels to plants reared under different sodium regimes in a common garden setup (OBJECTIVE 3). Finally, the student will combine historical, observational and experimental data from previous objectives to predict how changing environmental conditions (for example increasing sea incursions caused by climate change) will affect sodium levels in the machair and, as a consequence, the communities of local bee pollinators (OBJECTIVE 4).

(1)Angus Ocean and Coastal Management (2018)
(2)Mitchell Science of The Total Environment (2020)
(3)Lewis Oikos (2014)