Rapid relative increase of crustose coralline algae following herbivore exclusion in a reef of El Salvador

Xochitl E Elías Ilosvay; Johanna Segovia; Sebastian Ferse; Walter Ernesto Elias; Christian Wild

doi:10.7717/peerj.10696

Rapid relative increase of crustose coralline algae following herbivore exclusion in a reef of El Salvador

PeerJ. 2021 Feb 11:9:e10696. doi: 10.7717/peerj.10696. eCollection 2021.

Authors

Xochitl E Elías Ilosvay¹, Johanna Segovia², Sebastian Ferse^{1

3}, Walter Ernesto Elias⁴, Christian Wild¹

Affiliations

¹ Faculty of Biology and Chemistry, Marine Ecology Department, University of Bremen, Bremen, Deutschland.
² Universidad Francisco Gavidia, San Salvador, El Salvador.
³ Department of Ecology, Leibniz Centre for Tropical Marine Research (ZMT), Bremen, Germany.
⁴ Unaffiliated, Antiguo Cuscatlán, La Libertad, El Salvador.

Abstract

The Eastern Tropical Pacific (ETP) is one of the most isolated and least studied regions in the world. This particularly applies to the coast of El Salvador, where the only reef between Guatemala and Nicaragua, called Los Cóbanos reef, is located. There is very little published information about the reef's biodiversity, and to our knowledge, no research on its ecology and responses to anthropogenic impacts, such as overfishing, has been conducted. The present study, therefore, described the benthic community of Los Cóbanos reef, El Salvador, using the Line-Point-Intercept-Transect method and investigated changes in the benthic community following the exclusion of piscine macroherbivores over a period of seven weeks. Results showed high benthic algae cover (up to 98%), dominated by turf and green algae, and low coral cover (0-4%). Porites lobata was the only hermatypic coral species found during the surveys. Surprisingly, crustose coralline algae (CCA) showed a remarkable total cover increase by 58%, while turf algae cover decreased by 82%, in experimental plots after seven weeks of piscine macroherbivore exclusion. These findings apparently contradict the results of most previous similar studies. While it was not possible to ascertain the exact mechanisms leading to these drastic community changes, the most likely explanation is grazing on turf by small grazing macroherbivores that had access to the cages during the experiment and clearing of CCA initially covered by epiphytes and sediments. A higher CCA cover would promote the succesful settlement by corals and prevent further erosion of the reef framework. Therefore it is crucial to better understand algal dynamics, herbivory, and implications of overfishing at Los Cóbanos to avoid further reef deterioration. This could be achieved through video surveys of the fish community, night-time observations of the macroinvertebrate community, exclusion experiments that also keep out herbivorous macroinvertebrates, and/or experimental assessments of turf algae/CCA interactions.

Keywords: Benthic community structure; Eastern Tropical Pacific; Exclusion experiment; Herbivore.

Grants and funding

The fieldwork of this study was funded by the Kellner und Stoll Stiftung, Bremen. Xochitl E Elías Ilosvay Master’s studies were financed by the German Academic Exchange Service (DAAD). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.