- Title
- Environmental impacts of habitat fragmentation and heavy metal contamination on estuarine seagrass communities
- Creator
- Rappe, Rohani Ambo
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2007
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- Seagrasses are generally known for their significant role in marine and estuarine ecosystems. The growth in human population along the coastal regions, where the seagrass live, makes them very vulnerable to the human-induced disturbances. Large-scale seagrass decline has been reported worldwide due to this problem. There is an evident need to monitor seagrass population to predict future changes and to protect coastal ecosystems from further degradation. The decline of seagrass beds results in their fragmentation and appearance of smaller patches of seagrass isolated from each other, The first goal of this thesis is to study how fragmentation of seagrass beds influence their role in the ecosystem. This study focused on how fragment size and its distance from the main bed influence abundance of mobile epifauna associated with seagrass. Artificial seagrass units were constructed to mimic the seagrass fragmentation at a small scale. The result from this experiment suggested neither fragment size nor on-patch location (edge vs middle) adequately account for variation in the abundance of seagrass-associated epifauna. The distance from large beds of seagrass was important, however. Fragments placed far away from the natural seagrass were colonized to a grater degree than the fragments placed near seagrass beds. Large fragments were also colonized more than the small ones at the furthest distance from natural beds. Thus, fragmentation does not necessary lead to decease in epifaunal abundances. The small isolated patches may serve as refuge sites of the marine organisms. The second part of the thesis specifically deals with the effect of heavy metal contamination on seagrass and associated fauna. Despite the well-publicised issue of metal contamination of highly urbanised estuaries and its effect on seagrasses, this is the first study that assessed the contamination effect on the seagrass community using a range of bioindicators and biomarkers in order to obtain an integral picture of the contamination effect. It was found the seagrass, Zostera capricorni accumulated high concentration of heavy metals and provide a good correlation between the concentration in their tissues and in the sediment. Moreover, there was no evidence of impact on the seagrass biomass, shoot and leaf density. Thus, this seagrass can be used as a good bioindicator because of the above reasons, and also they are sedentary and abundant in the polluted site, which makes them easily available for sampling. The abundance of epifaunal organisms associated with the seagrass was used as a bioindicator at the community level. Only gastropods decreased in abundance in the contaminated site in spring (when the number of seagrass fauna generally higher), and this might potentially be a good bioindicator in this system. Shell dimension and fluctuating asymmetry were used as biomarkers for this purpose. It was found that a bivalve associated with seedgrass, the ark cockle Anadara trapezia, in the polluted location (Cockle Baby) showed distinct morphological characters compared to the ones in unpolluted locations. The cockles were bigger, heavier and had bigger shell-height/shell-length ratios, but appeared much less abundant, which is contradicted with historically high abundance of this species in this location (Cockle Bay). Moreover, the cockles exhibited higher shell asymmetry compared to the ones in unpolluted locations. Leaf dimensions and leaf asymetry of seagrasses,
and Halophila ovalis, were also employed as biomarkers. The results revealed that there was no significant difference in leaf asymmetry of seagrass from polluted and unpolluted locations. The effect of heavy metal might have been surpassed by other factors such as nutrients, which were also high in the polluted area. Interestingly, the leaves of seagrass in the polluted location compared to unpolluted ones were longer and wider indicating that there was a possibility that the detrimental effect of heavy metals on seagrass was compensated by favourable effects of elevated nutrients. Laboratory studies were conducted to determine whether heavy metals themselves affected seagrasses. The results revealed that heavy metals exposure affected the growth of seagrass, and lead to increase in fluctuating asymmetry. Thus, leaf dimensions, shell dimensions and fluctuating asymmetry of seagrass and seagrass associated fauna were sensitive to metal pollution and they might be suitable to indicated contamination in seagrass system. - Subject
- seagrass; marine ecosystems; fluctuating asymmetry; estuarine ecosystems; artificial seagrass; heavy metal pollution; Zostera capricorni; Anadara trapezia; bioindicators; biomarkers; bivalves
- Identifier
- http://hdl.handle.net/1959.13/1312589
- Identifier
- uon:22437
- Rights
- Copyright 2007 Rohani Ambo Rappe
- Language
- eng
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| View Details Download | ATTACHMENT01 | Thesis | 144 MB | Adobe Acrobat PDF | View Details Download | ||
| View Details Download | ATTACHMENT02 | Abstract | 8 MB | Adobe Acrobat PDF | View Details Download |