51. The impact of green macroalgal mats on benthic invertebrates and overwintering wading birds.
- Author
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Thornton, Ann and Thornton, Ann
- Abstract
A consequence of increased nutrient levels within an estuarine ecosystem is the development of green macroalgal blooms or ‘mats’. These mats can cover extensive areas of estuarine intertidal habitats and have biomass >1 kg m-2 (wet weight). One of the key metrics for assessment of the ecological condition status of estuarine features in Europe is the extent and biomass of macroalgal mats. The aim of this research is to establish whether the development of green macroalgal mats affects feeding relationships between invertebrate assemblages and overwintering migratory wading birds in Poole Harbour - a temperate estuarine ecosystem on the south coast of England. Poole Harbour is designated for its populations of overwintering migratory wading birds. As such, any decline in wading bird numbers as a result of nutrient enrichment affecting their food supply or altering feeding behaviour, would result in sanctions under current legislation. This field research consisted of three main objectives: 1) Measuring the biomass and extent of the macroalgal mat within Poole Harbour. 2) Analysing any changes to the benthic invertebrate community under varying macroalgal mat densities. 3) Observing and recording the behaviour and feeding success of key wading bird species; in particular how they responded to changes in prey availability and varying levels of macroalgal mat coverage. Samples of macroalgal mat were taken monthly or bi-monthly on mudflats at four locations around the harbour over two years and wet weight biomass was recorded. Wading bird invertebrate prey availability was measured using benthic core samples taken at upper, mid, and lower shore levels at three key sites. Invertebrate size- classes were recorded and converted into available energy (kJ m-2) according to the preferred diet of each of the five wading bird species studied. Observations of wading bird behaviour were recorded over two overwintering periods (September – March). Digital video recordings were take