Assessing long-term changes in chironomid assemblages linked to past fluctuations in Leach’s Storm-Petrel populations on islands in the Western Atlantic Ocean
Nutrient loading is an important factor that can indirectly deplete dissolved oxygen concentrations in lakes. In environments where seabirds nest and breed, guano is a prominent source of nutrients that can eutrophy waterbodies. Such external nutrient inputs may deplete bottom-water oxygen, resulting in shifts in bottom-water invertebrate communities that are sensitive to changes in oxygen. Chironomidae (non-biting midges) can be used as paleolimnological indicators to infer changes in past oxygen conditions due to their sensitivity to oxygen concentration, excellent preservation in sediments and abundance. I assessed the long-term changes in subfossil chironomid assemblages linked to reconstructed changes in the seabird colony size of the Leach’s Storm-Petrel in ponds located off the Canadian East coast on Baccalieu Island, Newfoundland, and Grand Colombier Island, Saint Pierre and Miquelon, France, to qualitatively reconstruct past changes in dissolved oxygen conditions, and thereby indirectly infer changes in colony size. Ornithological surveys indicate declines in the Leach’s Storm-Petrel colony in Newfoundland since the 1980s, whereas the colony in Saint Pierre and Miquelon is believed to be stable or increasing, albeit based on limited observational data. Using dated sediment cores from seabird-impacted lakes, I isolated chironomid head capsules, taxonomically identified them to the genus level, and determined their abundance and diversity. Using the chironomid assemblages, I qualitatively inferred lake oxygen conditions over the past ~1700 and ~5700 years on Baccalieu Island and Grand Colombier Island, respectively. Furthermore, I investigated if the timing of changes in chironomid-inferred oxygen coincided with known occurrences of seabird-derived inputs in the lakes’ catchments, as determined by surveys and other paleolimnological proxies. The chironomid data provides novel information on past oxygen levels in the lakes. In both sites, chironomid assemblages indirectly tracked past changes in the storm-petrel colony size, and their more recent declines. These data, alongside several paleolimnological proxies, will be used to determine the long-term natural variability and dynamics of Leach’s Storm-Petrel populations. This research provides data required to implement informed conservation and management strategies. Moreover, understanding the background conditions and responses of lakes to nutrient loading provides insights on the effects and tolerance of lakes to disturbance.