Change search
ReferencesLink to record
Permanent link

Direct link
Differences between fish and sea urchin herbivory – effects onmacroalgal abundance and influence on status of an EastAfrican coral reef
Stockholm University, Faculty of Science, Department of Systems Ecology.
Stockholm University, Faculty of Science, Department of Systems Ecology.
(Marine Programs, Wildlife Conservation Society, Bronx, NY)
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Macroalgal removal by herbivores is a key mechanism influencing recovery potential ofcorals after a disturbance event in a reef ecosystem. Both fish and sea urchins are usuallyconsidered important herbivores maintaining a healthy reef, but grazing mechanisms andefficiency differ between them. This study was conducted in a Kenyan coral reef lagoon,using two sites with different herbivore community compositions as a model system. Theherbivore community at the first site is dominated by fish, whereas sea urchins dominatein the second site. Temporal variation of macroalgal distribution, biomass and communitycomposition was investigated at five occasions during a nine months period. The studyillustrates the influence that different herbivore community compositions may have oncoral reef status. Despite an almost 4 times higher estimated total herbivore consumptionwithin the fish-dominated park, macroalgal biomass was found to be up to 10 timeshigher than in the sea urchin-dominated unprotected site. Thus, sea urchins may notconsume as much algal biomass per individual, but seem to have a higher algal clearancecapacity in comparison to herbivorous fish. Such disparity between consumption andactual algal biomass removal could be the result of inter- and intraspecific differences ingrazing mechanisms as well as grazing behavior between grazer types in the two sites.Despite the higher macroalgal biomass, the fish dominated site has over time experienceda higher coral recovery, possibly resulting from a higher structural complexity,heterogeneous macroalgal distribution and the composition of the herbivore community.The results suggest that the fish dominated community does not ensure low algalbiomass, but may still increase the potential for coral recovery. The urchin dominatedcommunity on the other hand resulted in low macroalgal biomass, but may have a longerroute to recovery after disturbance

Keyword [en]
Ecosystem change; Macroalgae; Herbivory; Fish; Sea Urchins; Coral Reefs
National Category
Biological Sciences
URN: urn:nbn:se:su:diva-48279OAI: diva2:374816
Available from: 2010-12-06 Created: 2010-12-06 Last updated: 2010-12-16Bibliographically approved
In thesis
1. Macroalgal community dynamics on coral reefs: Implications for management
Open this publication in new window or tab >>Macroalgal community dynamics on coral reefs: Implications for management
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Although rather inconspicuous on healthy coral reefs, macroalgae form the basis of coral food webs. Today, macroalgae are generally increasing and many reefs undergo transitions from coral to macroalgal dominance resulting from e.g. enhanced nutrient loading or increased fishing.

This thesis aims to investigate the relative importance of top-down and bottom-up regulation, and different herbivore types, on macroalgal distribution, fecundity and community composition on coral reefs. Papers I and II indicate that macroalgal abundance in a coral reef system is largely governed by top-down regulation through grazing by herbivores, while bottom-up regulation through enhanced nutrient availability rather influence algal species composition. Paper II also shows that these regulating effects are not as evident in an area with relatively strong water motion, suggesting that impacts of anthropogenic disturbance may be site-specific. Paper III shows that herbivory is an important factor influencing macroalgal growth and subsequent reproduction. Furthermore, Paper IV and V conclude that efficiency in removing macroalgal biomass is dependent on the type of dominant herbivore, where sea urchins seem to be more effective than fish. Paper IV indicates a seasonal variation in macroalgal biomass and distribution in a small geographic scale but with relatively high temporal resolution. Paper V on the other hand shows these same effects, but with a focus on geographic variation, including a large part of the East African region, as well as between year temporal variations in Kenya. Together, results from the two latter studies indicate that herbivory by fish may not be able to prevent a macroalgal bloom in a degraded system where substrate availability for algal colonization is high, but that it may still facilitate coral recovery over time. Thus, a large algal biomass may not necessarily indicate a reef beyond the possibility of recovery.

Place, publisher, year, edition, pages
Stockholm: Department of Systems Ecology, Stockholm University, 2011. 46 p.
Macroalgae, Coral Reefs, Herbivory, Nutrients, Ecosystem change, Fish, Sea Urchins, East Africa
National Category
Biological Sciences
Research subject
Marine Ecotoxicology
urn:nbn:se:su:diva-48281 (URN)978-91-7447-200-4 (ISBN)
Public defence
2011-01-28, Nordenskiöldsalen, Geovetenskapens hus, Svante Arrhenius väg 12, Stockholm, 13:00 (English)

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Accepted. Paper 4: Manuscript. Paper 5: Manuscript.

Available from: 2011-01-03 Created: 2010-12-06 Last updated: 2013-12-09Bibliographically approved

Open Access in DiVA

No full text

Search in DiVA

By author/editor
Mörk, ErikLilliesköld Sjöö, Gustaf
By organisation
Department of Systems Ecology
Biological Sciences

Search outside of DiVA

GoogleGoogle Scholar
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

Total: 34 hits
ReferencesLink to record
Permanent link

Direct link