Metazoan Detritivores and Underwater Decomposition Processes of Detached Sublittoral Macrophytes

Bedford, Alan Peter (1986) Metazoan Detritivores and Underwater Decomposition Processes of Detached Sublittoral Macrophytes. PhD thesis, University of Glasgow.

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Abstract

A great deal of attention has been paid to the importance of marine angiosperm litter to coastal marine ecosystems, its decomposition and the role played by associated metazoans in this process. In the Clyde Sea area, autumn storms result in large quantities of kelp being detached. This kelp forms large accumulations on the sea bed in certain;areas. This project sought to examine the involvement of metazoans in the decomposition of this algal material. The fauna associated with sea-bed accumulations of decomposing Laminaria saccharina has been studied by year-round SCUBA diving at two sites in the Clyde Sea Area. Seasonal changes in the densities of 6k species were recorded. The Laminaria carries with it to the sea-bed a large part of its normal fauna. Additional species settle onto the weed from the plankton whilst others migrate onto it from the surrounding sea-bed. Peak densities of associated species were recorded in autumn. Three species were selected for detailed investigation in the laboratory concerning their importance in the decomposition process. These were the polychaete Platynereis dumerilii, the echinoid Psammechinus miliaris and the amphipod Gammarus locusta. The roles of both Platynereis and Psammechinus were examined by comparing their responses (behavioural choice, growth rates, absorption efficiencies of both carbon and protein, gut retention times and faecal output) to fresh and rotting kelp. Platynereis builds its parchment tubes preferentially on the fresh weed and feeds at the mouth of this tube. It grows faster on this diet. Platynereis is a detritivore which exploits the substratum directly. Psammechinus, although showing a behavioural preference for the rotting weed, grows equally well on either diet once it has reached a particular size. Substratum digestion is of paramount importance for Psammechinus when feeding on either diet. Gammarus locusta's responses to the two diets (examined by comparing survival and growth rates in juveniles, fecundity, fertility and breeding behaviour in adults) illustrated the importance of the rotting weed (with its associated micro-organisms) to this organism. The relative importance of interactive cropping by these three detritivores was studied by in situ containment of different species combinations. The presence of Gammarus with Psammechinus resulted in less weed being lost than when Psammechinus was isolated. This is because Gammarus selectively crops rotting weed, retarding frond disintegration by microbes. Platynereis retards microbial colonization of frond tissues ruptured during its feeding by repeated cropping of the same region. These results reflect the situation found in the field with the complete detached weed fauna present. Litter bag experiments in situ showed that , except during the summer, weed is lost from sea-bed accumulations at a faster rate when macrofaunal animals are excluded. Macrofaunal cropping prevents the weed from decomposing very rapidly. Macroalgal decay thus differs profoundly from that of vascular plants. The ecological consequences of this difference are discussed.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Biological oceanography
Date of Award: 1986
Depositing User: Enlighten Team
Unique ID: glathesis:1986-77452
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 14 Jan 2020 11:53
Last Modified: 14 Jan 2020 11:53
URI: http://theses.gla.ac.uk/id/eprint/77452

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