Seabirds as monitors of mercury contamination in the Portuguese Atlantic

Monteiro, Luis Rocha (1996) Seabirds as monitors of mercury contamination in the Portuguese Atlantic. PhD thesis, University of Glasgow.

Abstract

The past and present status, ecology and conservation of the Azores seabirds were analysed. Historical population trends inferred from 16th and 17th century chronicles indicate dramatic declines for most species. Current community structure and functioning were reviewed and updated to provide a framework for their use as monitors of mercury in the marine environment. Ecological segregation among Procellariiformes involves partitioning between epipelagic and mesopelagic food resources. A review of mercury in seabirds was undertaken. Mercury dynamics and factors causing inter- and intra-specific variations in mercury concentrations are discussed. Methodological considerations relating to the use of seabird tissues as monitors for mercury are discussed and recent studies on geographical and temporal changes are summarised. The breeding biology of Madeiran storm petrel Oceanodroma castro in the Azores was studied. Two dimorphic and temporally segregated populations (hot and cool seasons) breed annually and sympatrically on Graciosa island. The hot season birds are 10% smaller in egg and body mass but are longer-winged and longer-tailed than cool season birds. The two groups were readily separated by discriminant analysis, with over 85% of the individuals being correctly assigned to the population they belong. Possible ecological constraints and adaptations promoting divergence are discussed. These populations may represent a case of sympatric speciation with time as the isolating mechanism. The moult phenology of adult Cory's Shearwater Calonectris diomedea borealis overlaps a great extent with the breeding season. Primary renewal starts five weeks after peak hatching and seven weeks before peak fledging. Such an overlap of wing moult and breeding has never before been described in a pelagic and highly migratory seabird such as the Cory's Shearwater. Intra-specific variations of mercury concentrations in tissues of seabirds from the Portuguese Atlantic were analysed, providing a baseline 'noise' for their use as monitors. Examination of relationships between mercury concentrations in blood and plumage of adults and chicks provided validation of current models for mercury dynamics in birds and elucidation of most intra-specific patterns of variation in mercury concentrations. Moult emerged as the main explanation for variations of mercury concentrations in contour feathers and blood of adults. In chicks, mercury concentrations in plumage and blood decline dramatically with age. This growth dilution effect results from highly transient blood concentrations due to an imbalance between mercury dietary intake and co-accumulation in developing plumage and growing internal tissues. Linear relationships between mercury concentrations in blood and growing feathers were found in chicks and adults. The slopes of such relationships were consistent over a wide range of concentrations and indicate a standard feather: blood partition coefficient of about 3. Mercury concentrations in short-lived fish of low trophic levels were investigated in relation to their vertical distribution. Concentrations were positively correlated with median daytime depth, increasing by four-fold from epipelagic (300m). This confirmed enhanced bioaccumulation of mercury in marine mesopelagic environments due to methylmercury production in sub-thermocline low oxygen seawater. The relationship between mercury in diet and seabird body burdens of mercury was investigated. Seabirds specialised on mesopelagic prey show mercury burdens about four-fold higher than those feeding predominantly on epipeiagic prey. Ecological segregation in seabird communities resulted in many parts of the world into feeding specialisation on pelagic or mesopelagic organisms, and thus seabirds may be used for monitoring mercury contamination within and between vertical compartments of marine ecosystems. (Abstract shortened by ProQuest.).

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Additional Information: Supported by funding from the Junta Nacional de Investigaçâo Cientffica (JNICT, Portugal) post-graduate grant (BD/2289/92-IG) and a research contract with JNICT (STRDB/C/MAR/228/92).
• Keywords: Ecology, Biogeochemistry, Environmental health.
• Colleges/Schools: College of Medical Veterinary and Life Sciences
• Supervisor's Name: Furness, Dr. Robert
• Date of Award: 1996
• Depositing User: Enlighten Team
• Unique ID: glathesis:1996-71672
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 17 May 2019 09:31
• Last Modified: 27 Oct 2021 13:54
• URI: https://theses.gla.ac.uk/id/eprint/71672

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