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Horizontal and vertical distribution patterns in Macoma balthica natural variation and the effect of manipulated densities

Boer, M.K. de (1997) Horizontal and vertical distribution patterns in Macoma balthica natural variation and the effect of manipulated densities. Master's Thesis / Essay, Biology.

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The patch nature of environments combined with the behaviour of species determines the spatial arrangement of individuals. This spatial heterogeneity is functional within ecosystems and spatial structuring is therefore an important component of ecosystems. In this study the spatial distribution of Macorna baithica was determined in the field and combined with two density experiments on the spatial arrangement of individuals. The spatial distribution and abundance of Macoma baithica was studied for two lengthclasses at an intertidal area of Richel in the western Wadden Sea. The depth distribution observed in the field displays a U-shaped relation with length. The preferred size class (_ 18 mm) for Knots, the main predator of Macoma baithica, was buried deepest. Macoma's _ 12.5 mm were found to exhibit a contagious distribution on a scale of 6 to 1100 metre radius. This in contrast to Macoma's < 12.5 mm, which showed a random distribution with a slight tendency towards a contagious distribution. The differences in distribution between the two lengthclasses might be attributed to a strategy of timely shifts during the first year of their lives. Dry and wet habitat sampled cores only showed a difference (not significant) in density at the largest sample size investigated. In the field experiment on Richel there was a strong trend that density influenced depth distribution of Macoma baithica _ 12.5 mm. The factors length, AFDMSiPhOn, DMsheIl and AFDMmt have an effect on the depth distribution in the field experiment on Richel. In the IBN experiment contagious distributed Macoma's were buried significantly shallower than regular distributed Macoma's, a phenomenon which might be explained by the occurrence of intraspecific competition over food or other favourable conditions. Risk of predation is influenced by the foraging strategy of the predator and may also contribute to this phenomenon. Furthermore a relation was found between burying depth and total horizontal movement, which negatively correlated with each other. With increasing density the total horizontal movement increased significantly.

Item Type: Thesis (Master's Thesis / Essay)
Degree programme: Biology
Thesis type: Master's Thesis / Essay
Language: English
Date Deposited: 15 Feb 2018 07:45
Last Modified: 15 Feb 2018 07:45

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