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Effects of territorial damselfish on cryptic bioeroding organisms on dead Acropora formosa
Stockholm University, Faculty of Science, Department of Zoology.
Stockholm University, Faculty of Science, Department of Zoology.
2005 (English)In: Journal of Experimental Marine Biology and Ecology, ISSN 0022-0981, E-ISSN 1879-1697, Vol. 327, no 1, 91-102 p.Article in journal (Refereed) Published
Abstract [en]

Many damselfishes exclude other grazers from their territories and “farm” filamentous algae within their territories. In this study the indirect effect of damselfish territories on faunal composition and abundance of internal bioeroders of dead Acropora formosa (Dana, 1846) was investigated in territories of two damselfish species, Stegastes nigricans (Lacepède, 1802) and Plectroglyphidodon lacrymatus (Quoy and Gaimard, 1825). S. nigricans tends to be more protective and defend their territories more aggressively than P. lacrymatus. Newly killed branches of A. formosa were placed inside and outside damselfish territories, for 1 or 2 years, at a coral reef near Zanzibar, Tanzania. As predicted, the coral branches became covered with more filamentous algae in the S. nigricans territories than in the controls, with intermediate levels in the P. lacrymatus territories. Among the internal bioeroding fauna, polychaetes were by far the most common group. In total, there were significantly more borers in the first year than the second, which was mainly due to a high abundance of sabellids. Furthermore, sabellids were significantly more abundant in control areas and in the P. lacrymatus territories compared to the S. nigricans territories. However, many other genera showed the opposite pattern, with more polychaetes in the fish territories compared to the controls. There was also a clear difference in assemblage structure between S. nigricans territories and controls. Thus, we found strong effects of whether a piece of coral was placed inside or outside a damselfish territory on the abundance of many of the bioeroding taxa. We discuss multiple reasons for these indirect effects of the territories, including that deposit feeding bioeroders may benefit from the dense algal turf found inside the territories whereas suspension feeding bioeroders may benefit from substrate with less filamentous algae found outside territories. Considering our results in the context of the large areas of coral reefs that typically are defended as territories by damselfishes, these fish are likely to have a considerable impact on the boring community of a coral reef.

Place, publisher, year, edition, pages
2005. Vol. 327, no 1, 91-102 p.
Keyword [en]
Acropora formosa, Bioeroding organisms, Coral reef, Damselfish
National Category
Biological Sciences
Identifiers
URN: urn:nbn:se:su:diva-22925DOI: 10.1016/j.jembe.2005.06.012OAI: oai:DiVA.org:su-22925DiVA: diva2:189748
Available from: 2004-04-28 Created: 2004-04-28 Last updated: 2011-05-31Bibliographically approved
In thesis
1. Benthic cryptofauna and internal bioeroders on coral reefs
Open this publication in new window or tab >>Benthic cryptofauna and internal bioeroders on coral reefs
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The cryptofauna of coral reefs may act as a food source for fish, while being grazers or predators themselves, and hence constitute an important group in the coral reef food web. In addition, the actively eroding taxa of the cryptofauna contribute to the decomposition and recirculation of calcium carbonate and are consequently essential for the rebuilding new coral. However, when coral reefs are disturbed, changes in these functions may severely affect the reef ecosystem. In this thesis correlations and causal effects of environmental factors on benthic cryptofauna and bioerosion of corals were investigated at several coral reefs off the west coast of Zanzibar (Unguja), Tanzania.

An aim in the first paper was to investigate effects of elevated nutrient levels on bioerosion and bioeroding fauna. Yet, the study found no difference in abundance of the total eroding fauna with distance to a major sewage outlet. However, the faunal composition differed along the gradient, with some deposit feeders being more numerous near the outlet and some suspension feeders being more numerous further away. In a comparison of three coral taxa, as well as coral rubble, the total boring fauna did not differ significantly in abundance or erosion.

Internal bioerosion generally increases with time, and the second paper focused on the succession of bioeroders at two experimental sites. There was more total internal erosion at one of the sites, and some eroding taxa were common at one site while rarely found at the other. While some taxa followed an expected successional pattern, others did not. Within taxa, number of individuals was uncorrelated to the extent of erosion, suggesting that it is a result of increased growth rate and low recruitment of new individuals.

The last two papers deal with the influence of fish grazing of algae on the bioeroding and non-eroding cryptofauna, respectively. The bioeroding community showed a complex response to varying grazing pressure, varied within and outside damselfish territories, with some taxa, usually suspension feeders, being more abundant in highly grazed areas outside damselfish territories while deposit feeders were more abundant within territories. Further, with a high grazing pressure, the non-boring cryptofauna decreased in abundance compared to areas protected from grazing. However, this was not true for all taxa. Comparing the abundance of taxa at the surface of the coral with taxa in the coral holes and cavities, none of these correlated in numbers.

Place, publisher, year, edition, pages
Stockholm: Zoologiska institutionen, 2004. 43 p.
Keyword
bioerosion, cryptofauna, coral, invertebrates, damselfish
National Category
Ecology
Identifiers
urn:nbn:se:su:diva-127 (URN)91-7265-889-4 (ISBN)
Public defence
2004-05-19, sal G, Arrheniuslaboratorierna, Svante Arrhenius väg 14-18, Stockholm, 10:00
Opponent
Supervisors
Available from: 2004-04-28 Created: 2004-04-28Bibliographically approved

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