Environ Monit Assess (2015) 187:44 DOI 10.1007/s10661-014-4257-9
Monitoring of coastal coral reefs near Dahab (Gulf of Aqaba, Red Sea) indicates local eutrophication as potential cause for change in benthic communities Malik S. Naumann & Vanessa N. Bednarz & Sebastian C. A. Ferse & Wolfgang Niggl & Christian Wild Received: 29 April 2014 / Accepted: 29 December 2014 # Springer International Publishing Switzerland 2015
Abstract Coral reef ecosystems fringing the coastline of Dahab (South Sinai, Egypt) have experienced increasing anthropogenic disturbance as an emergent international tourism destination. Previous reports covering tourism-related impacts on coastal environments, particularly mechanical damage and destructive fishing, have highlighted the vital necessity for regular ecosystem monitoring of coral reefs near Dahab. However, a continuous scientific monitoring programme of permanent survey sites has not been established to date. Thus, this study conducted in situ monitoring surveys to investigate spatio-temporal variability of benthic reef communities and selected reef-associated herbivores along with reef health indicator organisms by revisiting three of the locally most frequented dive sites during expeditions in March 2010, September 2011 and February 2013. In addition, inorganic nutrient concentrations in reef-surrounding waters were determined to evaluate bottom-up effects of key environmental parameters on benthic reef community shifts in relation to grazer-induced top-down control. Findings revealed that from 2010 to 2013, live hard coral cover declined significantly by 12 % at the current-sheltered site Three M. S. Naumann (*) : V. N. Bednarz : S. C. A. Ferse : W. Niggl : C. Wild Coral Reef Ecology Group (CORE), Leibniz Center for Tropical Marine Ecology (ZMT), Fahrenheitstrasse 6, 28359 Bremen, Germany e-mail: [email protected] C. Wild Faculty of Biology and Chemistry, University of Bremen, NW 2 / Leobener Str., 28359 Bremen, Germany
Pools (TP), while showing negative trends for the Blue Hole (BH) and Lighthouse (LH) sites. Hard coral cover decline was significantly and highly correlated to a substantial increase in turf algae cover (up to 57 % at TP) at all sites, replacing hard corals as dominant benthic space occupiers in 2013. These changes were correlated to ambient phosphate and ammonium concentrations that exhibited highest values (0.64±0.07 μmol PO43 − −1 l , 1.05±0.07 μmol NH4+ l−1) at the degraded site TP. While macroalgae appeared to respond to both bottom-up and top-down factors, change in turf algae was consistent with expected indications for bottom-up control. Temporal variability measured in herbivorous reef fish stocks reflected seasonal impacts by local fisheries, with concomitant changes in macroalgal cover. These findings represent the first record of rapid, localised change in benthic reef communities near Dahab, consistent with indications for bottom-up controlled early-stage phase shifts, underlining the necessity for efficient regional wastewater management for coastal facilities. Keywords Top-down and bottom-up control . Inorganic nutrient enrichment . Herbivory . Coral-algal interactions . Tourism . South Sinai . Egypt
Introduction In comparison to many other oceanic regions, where in recent decades tropical coral reef ecosystems have declined significantly due to impacts from an array of global (e.g. ocean warming) and often local (e.g.
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overfishing, eutrophication) stressors, shallow water reefs of the Red Sea may currently be considered comparably intact (Hoegh-Guldberg et al. 2007; Kotb et al. 2008; Wilkinson 2008). Except for the 1998 global mass coral bleaching event, which caused severe damage in reefs of the Southern Red Sea (Wilkinson 2004) and findings of reduced coral calcification in the Central Red Sea due to ocean warming (Cantin et al. 2010), impacts of global climate change until now appear remarkably low. Recently, this even gave rise to the theory of the Gulf of Aqaba in the Northern Red Sea being a potential future refuge for scleractinian corals from threats of global change (Fine et al. 2013). Nevertheless, there is existing evidence for severe Red Sea coral reef degradation, highlighted by a decline of >30 % in living hard coral cover at particular sites, also in the Gulf of Aqaba (Riegl and Velimirov 1991; Jameson et al. 1999; Wilkinson 2004, 2008). Main reasons for this decline during past decades were local impacts of intense coastal development (construction, sewage discharge, solid waste and sedimentation) and direct mechanical damage (coral breakage by divers, snorkelers and shipping activities) associated with an expanding regional tourism industry (Rinkevich 2005; Wilkinson 2008). Tourism was initially introduced along the Egyptian Gulf of Aqaba coastline in the 1970s and experienced exponential growth since the late 1980s, becoming the prime regional source of income (Hawkins and Roberts 1994; PERSGA 2001; Rinkevich 2005). Until the Arab Spring revolution of 2011, tourism represented the major foreign exchange earning sector in Egypt, with coastal tourism as its major subsector reaching two million tourists at the Gulf of Aqaba in 2003 (Cesar 2003; OECD 2006). About 60 % of these visited local reef environments as divers or snorkelers, causing significant ecosystem degradation (SEAM 2004a; Rinkevich 2005; Jobbins 2006). While initial tourism development focussed on the Sharm el-Sheikh area located at the southern end of the Gulf of Aqaba, Dahab became a world-renowned dive destination for an increasing (nonquantified) number of tourist visitors by the late 1990s. Since then, tourism-related activities, especially extensive diving and snorkelling, promoting mechanical damage and sediment resuspension, have been identified as major threats to the coastal reef environments of Dahab. In this area, accepted site sustainability limits (5000–6000 dives a−1) have been exceeded by far, reaching >30,000 dives a−1 for popular dive sites (Hawkins and Roberts 1997; Cesar 2003; Hasler and Ott 2008).
Environ Monit Assess (2015) 187:44
The Dahab reef sites investigated by the present study are located within the Nabq and Abu Galum Managed Resources Protected Area, for which authorities issue fishing permits exclusively to resident Bedouin tribes. However, actual fishing regulations are unenforced and practiced techniques, including destructive net fishing and trampling, are impacting coastal reefs in the Dahab area (Hannak 2008; Samy et al. 2011; Hannak et al. 2011). Eutrophication and pollution of coastal waters may represent another potential, yet underinvestigated, local impact on the reefs near Dahab, resulting from intense construction of on-shore hotel and gastronomic facilities in direct reef vicinity, mostly without connection to the public sewage treatment systems. Information concerning this topic is sparse, except for one previous study reporting that up to 60 % of Dahab residents may not be serviced by the public sewage system due to insufficient infrastructure and maintenance, while poorly treated sewage may be released into the desert from pools of biological oxidation treatment systems (EcoConServ 2005). The same study suggested seepage of untreated sewage from septic tanks operated by remotely located tourism facilities to coastal waters and its use for coastal plant irrigation as potential threats to fringing coral reef environments. Current awareness of potential local stressors and existing evidence for local coral reef degradation emphasise the vital necessity for regular ecosystem monitoring in Dahab to enable detection of rapid reef community shifts and identification of driving factors. However, a continuous scientific monitoring programme of permanent study sites has not been established to date. The few previous studies including reef ecosystem assessments conducted in the Dahab region each have generated snapshots of individual reef sites in time only or have focussed on selected benthic community categories (e.g. hard corals), while the application of different survey techniques unfortunately impedes the comparison of their findings (Ammar et al. 2006; Hasler and Ott 2008; Tilot et al. 2008; Ammar 2009). Indeed, generating quantitative information for the detection of spatio-temporal variability in coral reef communities necessitates reassessments of identical monitoring parameters at permanent study sites by applying identical survey techniques over time (e.g. Sweatman et al. 2008). Thus, the aims of the present study were (1) to establish the first continuous scientific reef ecosystem monitoring of identical survey sites within the Dahab region investigating benthic and reef fish communities
Environ Monit Assess (2015) 187:44
for spatio-temporal variability and (2) to identify relevant bottom-up and top-down factors controlling benthic reef community composition. To this end, three reef sites were surveyed during three expeditions to Dahab from 2010 to 2013 to assess benthic and fish community composition, the occurrence of coral-algae contacts, abundance of herbivorous sea urchins and inorganic nutrient concentrations in reef-surrounding waters.
Materials and methods Study sites Three of the most frequented coral reef dive sites (i.e. ‘Blue Hole’, ‘Lighthouse’ and ‘Three Pools’; Fig. 1) located on the coastline of Dahab (Gulf of Aqaba, Red Sea) were selected for continuous reef ecosystem monitoring and assessed accordingly during three expeditions carried out in March 2010 (winter), September 2011 (autumn) and February 2013 (winter). The study site Lighthouse (LH) is located close to Dahab City Center, while Blue Hole (BH) and Three Pools (TP) both are remotely located ca. 9 km north and south of LH, respectively. All monitored reef sites are situated close to shore (
Monitoring of coastal coral reefs near Dahab (Gulf of Aqaba, Red Sea) indicates local eutrophication as potential cause for change in benthic communities Malik S. Naumann & Vanessa N. Bednarz & Sebastian C. A. Ferse & Wolfgang Niggl & Christian Wild Received: 29 April 2014 / Accepted: 29 December 2014 # Springer International Publishing Switzerland 2015
Abstract Coral reef ecosystems fringing the coastline of Dahab (South Sinai, Egypt) have experienced increasing anthropogenic disturbance as an emergent international tourism destination. Previous reports covering tourism-related impacts on coastal environments, particularly mechanical damage and destructive fishing, have highlighted the vital necessity for regular ecosystem monitoring of coral reefs near Dahab. However, a continuous scientific monitoring programme of permanent survey sites has not been established to date. Thus, this study conducted in situ monitoring surveys to investigate spatio-temporal variability of benthic reef communities and selected reef-associated herbivores along with reef health indicator organisms by revisiting three of the locally most frequented dive sites during expeditions in March 2010, September 2011 and February 2013. In addition, inorganic nutrient concentrations in reef-surrounding waters were determined to evaluate bottom-up effects of key environmental parameters on benthic reef community shifts in relation to grazer-induced top-down control. Findings revealed that from 2010 to 2013, live hard coral cover declined significantly by 12 % at the current-sheltered site Three M. S. Naumann (*) : V. N. Bednarz : S. C. A. Ferse : W. Niggl : C. Wild Coral Reef Ecology Group (CORE), Leibniz Center for Tropical Marine Ecology (ZMT), Fahrenheitstrasse 6, 28359 Bremen, Germany e-mail: [email protected] C. Wild Faculty of Biology and Chemistry, University of Bremen, NW 2 / Leobener Str., 28359 Bremen, Germany
Pools (TP), while showing negative trends for the Blue Hole (BH) and Lighthouse (LH) sites. Hard coral cover decline was significantly and highly correlated to a substantial increase in turf algae cover (up to 57 % at TP) at all sites, replacing hard corals as dominant benthic space occupiers in 2013. These changes were correlated to ambient phosphate and ammonium concentrations that exhibited highest values (0.64±0.07 μmol PO43 − −1 l , 1.05±0.07 μmol NH4+ l−1) at the degraded site TP. While macroalgae appeared to respond to both bottom-up and top-down factors, change in turf algae was consistent with expected indications for bottom-up control. Temporal variability measured in herbivorous reef fish stocks reflected seasonal impacts by local fisheries, with concomitant changes in macroalgal cover. These findings represent the first record of rapid, localised change in benthic reef communities near Dahab, consistent with indications for bottom-up controlled early-stage phase shifts, underlining the necessity for efficient regional wastewater management for coastal facilities. Keywords Top-down and bottom-up control . Inorganic nutrient enrichment . Herbivory . Coral-algal interactions . Tourism . South Sinai . Egypt
Introduction In comparison to many other oceanic regions, where in recent decades tropical coral reef ecosystems have declined significantly due to impacts from an array of global (e.g. ocean warming) and often local (e.g.
44
Page 2 of 14
overfishing, eutrophication) stressors, shallow water reefs of the Red Sea may currently be considered comparably intact (Hoegh-Guldberg et al. 2007; Kotb et al. 2008; Wilkinson 2008). Except for the 1998 global mass coral bleaching event, which caused severe damage in reefs of the Southern Red Sea (Wilkinson 2004) and findings of reduced coral calcification in the Central Red Sea due to ocean warming (Cantin et al. 2010), impacts of global climate change until now appear remarkably low. Recently, this even gave rise to the theory of the Gulf of Aqaba in the Northern Red Sea being a potential future refuge for scleractinian corals from threats of global change (Fine et al. 2013). Nevertheless, there is existing evidence for severe Red Sea coral reef degradation, highlighted by a decline of >30 % in living hard coral cover at particular sites, also in the Gulf of Aqaba (Riegl and Velimirov 1991; Jameson et al. 1999; Wilkinson 2004, 2008). Main reasons for this decline during past decades were local impacts of intense coastal development (construction, sewage discharge, solid waste and sedimentation) and direct mechanical damage (coral breakage by divers, snorkelers and shipping activities) associated with an expanding regional tourism industry (Rinkevich 2005; Wilkinson 2008). Tourism was initially introduced along the Egyptian Gulf of Aqaba coastline in the 1970s and experienced exponential growth since the late 1980s, becoming the prime regional source of income (Hawkins and Roberts 1994; PERSGA 2001; Rinkevich 2005). Until the Arab Spring revolution of 2011, tourism represented the major foreign exchange earning sector in Egypt, with coastal tourism as its major subsector reaching two million tourists at the Gulf of Aqaba in 2003 (Cesar 2003; OECD 2006). About 60 % of these visited local reef environments as divers or snorkelers, causing significant ecosystem degradation (SEAM 2004a; Rinkevich 2005; Jobbins 2006). While initial tourism development focussed on the Sharm el-Sheikh area located at the southern end of the Gulf of Aqaba, Dahab became a world-renowned dive destination for an increasing (nonquantified) number of tourist visitors by the late 1990s. Since then, tourism-related activities, especially extensive diving and snorkelling, promoting mechanical damage and sediment resuspension, have been identified as major threats to the coastal reef environments of Dahab. In this area, accepted site sustainability limits (5000–6000 dives a−1) have been exceeded by far, reaching >30,000 dives a−1 for popular dive sites (Hawkins and Roberts 1997; Cesar 2003; Hasler and Ott 2008).
Environ Monit Assess (2015) 187:44
The Dahab reef sites investigated by the present study are located within the Nabq and Abu Galum Managed Resources Protected Area, for which authorities issue fishing permits exclusively to resident Bedouin tribes. However, actual fishing regulations are unenforced and practiced techniques, including destructive net fishing and trampling, are impacting coastal reefs in the Dahab area (Hannak 2008; Samy et al. 2011; Hannak et al. 2011). Eutrophication and pollution of coastal waters may represent another potential, yet underinvestigated, local impact on the reefs near Dahab, resulting from intense construction of on-shore hotel and gastronomic facilities in direct reef vicinity, mostly without connection to the public sewage treatment systems. Information concerning this topic is sparse, except for one previous study reporting that up to 60 % of Dahab residents may not be serviced by the public sewage system due to insufficient infrastructure and maintenance, while poorly treated sewage may be released into the desert from pools of biological oxidation treatment systems (EcoConServ 2005). The same study suggested seepage of untreated sewage from septic tanks operated by remotely located tourism facilities to coastal waters and its use for coastal plant irrigation as potential threats to fringing coral reef environments. Current awareness of potential local stressors and existing evidence for local coral reef degradation emphasise the vital necessity for regular ecosystem monitoring in Dahab to enable detection of rapid reef community shifts and identification of driving factors. However, a continuous scientific monitoring programme of permanent study sites has not been established to date. The few previous studies including reef ecosystem assessments conducted in the Dahab region each have generated snapshots of individual reef sites in time only or have focussed on selected benthic community categories (e.g. hard corals), while the application of different survey techniques unfortunately impedes the comparison of their findings (Ammar et al. 2006; Hasler and Ott 2008; Tilot et al. 2008; Ammar 2009). Indeed, generating quantitative information for the detection of spatio-temporal variability in coral reef communities necessitates reassessments of identical monitoring parameters at permanent study sites by applying identical survey techniques over time (e.g. Sweatman et al. 2008). Thus, the aims of the present study were (1) to establish the first continuous scientific reef ecosystem monitoring of identical survey sites within the Dahab region investigating benthic and reef fish communities
Environ Monit Assess (2015) 187:44
for spatio-temporal variability and (2) to identify relevant bottom-up and top-down factors controlling benthic reef community composition. To this end, three reef sites were surveyed during three expeditions to Dahab from 2010 to 2013 to assess benthic and fish community composition, the occurrence of coral-algae contacts, abundance of herbivorous sea urchins and inorganic nutrient concentrations in reef-surrounding waters.
Materials and methods Study sites Three of the most frequented coral reef dive sites (i.e. ‘Blue Hole’, ‘Lighthouse’ and ‘Three Pools’; Fig. 1) located on the coastline of Dahab (Gulf of Aqaba, Red Sea) were selected for continuous reef ecosystem monitoring and assessed accordingly during three expeditions carried out in March 2010 (winter), September 2011 (autumn) and February 2013 (winter). The study site Lighthouse (LH) is located close to Dahab City Center, while Blue Hole (BH) and Three Pools (TP) both are remotely located ca. 9 km north and south of LH, respectively. All monitored reef sites are situated close to shore (
