Monitoring of coastal coral reefs near Dahab (Gulf of Aqaba, Red Sea) indicates local eutrophication as potential cause for change in benthic communities

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 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 PO4 (3-) l(-1), 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.

Recolonization of Marginal Coral Reef Flats in Response to Recent Sea‐Level Rise

“…High rates of sedimentation and low light levels negatively affect coral survival rates (Rogers, ). The combined effects of anthropogenic sedimentation and nutrient enrichment can severely inhibit coral recruitment and settlement, slow coral recovery, reduce resilience, and eventually induce declines in coral coverage and species richness (Abelson et al, ; Birrell et al, ; Naumann et al, ; Nava & Tamírez‐Herrera, ; Wielgus et al, ; Yeemin et al, ).…”

New insights into carbon acquisition and exchanges within the coral–dinoflagellate symbiosis under NH 4 + and NO 3 − supply

“…On the other hand, many inshore fringing reefs experience increased sedimentation and nutrient levels in response to fertilizer use and land clearing [10]. Consequently, at certain periods of the year, inorganic nitrogen and phosphorus concentrations can be much higher [16][17][18][19] than the usual levels measured on reefs (less than 0.5 mM for nitrogen [20][21][22], less than 0.1 mM for phosphate [23][24][25]). Furthermore, the geomorphology and the different sources and types of pollution, will also change the abundance of nitrogen sources (nitrate versus ammonium) and the N : P ratios of coastal ecosystems [26,27].…”

Using Landsat Data to Assess the Status of Coral Reefs Cover along the Red Sea Coast, Egypt

“…Naumann at al. studied the effect of nutrient on coral reefs near Dahab (Gulf of Aqaba, Red Sea) for 3 years monitoring coral reef cover and water measurement for ammonia, phosphate and nitrates and he found that the live hard coral cover declined significantly through these 3 years about 12 % and increased of algal cover at this sites about 57% [40]. The study shows that ammonia, nitrate, nitrate, total phosphorus, silicate and phosphate concentration recorded the highest concentration from 2010 to 2012 while the total nitrogen concentration showed the highest concentration from 1998 to 2000 and 2012.…”