Marine ecosystems and their substantial biodiversity are threatened all over the world (NRC 1995). The world’s coastal zones and shallow seas are impacted directly and indirectly by increasing pressure to supply natural resources and space to meet human needs and the negative impacts of the resulting poor land-use practices. Multiple and cumulative threats have already caused the loss of both species and genetically unique stocks of organisms and have undermined the functioning of many marine systems. Conservationists, and the non-governmental organizations they represent, are concerned that unless we change our attitudes towards the use of the seas, the marine biodiversity crisis will worsen. The ocean is home to millions of species and the health of the oceans is strongly dependent upon marine biodiversity. Climate change due to human activity has a direct impact on marine species by altering their abundance, diversity, and distribution. Their feeding, development, and breeding, as well as the relationships between species, are also affected. At present, the major perceived threats to marine biodiversity include the effects of climate change, ocean acidification, invasive species, overfishing, and other extractive activities, pollution and marine debris, habitat degradation, fragmentation and loss, human population expansion, tourism, and the impact of a wide range of human activities in the coastal zone (Harley et al. 2006; Occhipinti-Ambrogi and Charles 2007; Molnar et al. 2008; Zakaria et al. 2016; Zakaria et al. 2018a). In general, ecosystem components mainly affect the chemical and biochemical composition, distribution, and diversity of water organism communities (El-Naggar et al. 2017).
The Red Sea has a unique geographic location which makes its ecosystem is highly sensitive to temperature and salinity, which is reflected in the distribution, biodiversity and overall nutritional aspects of aquatic communities (Mona et al., 2019). Many studies cited that the aquatic communities, composition, distribution, and biodiversity, are strongly affected by variations in environmental and nutritional conditions (Farag et al., 2019; Mansour et al., 2020). In the current study, the data of physicochemical parameters showed little variations in water temperature, overall nine stations. Desalination stations (Helnan and Morgana) were recorded the highest salinity values, due to the brine discharges, which were negatively reflected on the average of abundance (15.56 ind./m2) of macro-benthos-invertebrate in the Gulf of Aqaba. In the same line, tourism stations (Canyon and Blue Hole, which showed the lowest DO) were recorded the lowest average of abundance (13.63 ind./m2). On the other hand, the protected stations (Solar Lake and El-Sokhna, which showed the highest DO) were presented the highest average of abundance (22.75 ind./m2). These obtained data illustrated that the anthropogenic activities (tourism and desalination) are strongly affect ecosystem components (DO and salinity), as well as the abundance and biodiversity of macro-benthos-invertebrates in the Gulf of Aqaba.
The results of this study reveal there have been severe reductions in the macro-benthos-invertebrate diversity in the Gulf of Aqaba, where a total of 53 species were recorded during the study period. The increase in anthropogenic activities along the Gulf of Aqaba has played a significant role in the decline, absence, and even extinction of some species. Mona et al. (2019) confirmed that human activities are the major reason for these changes in biodiversity and that these activities can cause habitat destruction if they continue and not resolved or reduced. Human activities on the Aqaba Gulf have also led to the degradation of various natural habitats. These practices create changes in the environment that species must then adapt to; some species can adapt, while others cannot.
According to the results obtained in this study, the abundance and diversity of macro-benthos invertebrates increase toward the north of the Gulf and the lowest values were recorded in Dahab. This may be due to land use increases more in the south than in the north of the Gulf and because Dahab city is considered the most affected by tourism, fishing activities and flooding. On the other hand, due to the absence of human activities, the results revealed that the protected sites, like Solar Lake and El-Sokhn, have a higher abundance and diversity more than the others. On the contrary, Blue Hole has the lowest abundance and diversity because it is considered one of the world’s most attractive sites for diving and snorkeling, as well as other tourism services. El-Naggar et al. (2017) decided that intense tourism in Blue Hole can lead to biodiversity degradation and ecosystem damage.
As for the distribution of micro-benthos among surveyed zones, the intertidal zone is the lowest in both abundance and diversity criteria; this is because the zone is the most directly affected by tourism, fishing activities and flooding, in addition to it being the first recipient of coastal impacts. For this reason, the species tend to escape to the other safer zones. On the other hand, the increase of abundance and diversity in the back reef zone may be due to the fact that its contains many microhabitats that can increase diversity; however, the abundance is low because it is also impacted by tourism, fishing, and other activities. In this context, the reef flat zone is safer than the back reef zone, and it is also usually used as a resting place for many species that escape the reef crest and back reef zone. Farrag et al. (2019) cited that any disturbance occurring in the natural habitats of species strongly affects their presence and stability, thus affecting biodiversity. Accordingly, Costanza et al. (1971) stated that when the ecological impacts caused by habitat disturbance are coupled with general environmental degradation, such as eutrophication, toxic pollution, or global climate change, the capacity of marine ecosystems to support sustainable biodiversity is reduced. Even more importantly, when essential habitat is lost, as in the use of shores for coastal development, the critical threshold levels inevitably decrease (Dayton 2000). Ultimately, the paradox is that marine ecosystems are increasingly less able to support demand, even as demand continues to increase.
The results showed that there was a higher percentage of similarity between sites that are subject to similar human impacts, where the highest similarity percentage was between the Morgana and Helnan sites, which are affected by the presence of water desalination plants for both Taba and Nuweiba cites, respectively. There is also a high percentage of similarity between the Solar Lake and El-Sohkn sites, which are considered to be the most protected sites and have little or no impacts. The similarity was also high between the Canyon and Blue Hole sites, which are both affected by heavy activities of tourism, and between the lagoon and Hobieq sites, which are heavily affected by fishing activities. Astoundingly, the different types of influence create variation in the community structure. Therefore, the direct or indirect actions by humans have resulted in a decrease in biodiversity. The Convention of Biological Diversity states that there are both indirect and direct human drivers to biodiversity loss. Some of the indirect human drivers are demographic, economic, sociopolitical, scientific and technological, and cultural and religious factors. Some of the direct human drivers are changes in local land use and land cover, species introductions or removals, external inputs, harvesting, air and water pollution, and climate change (Vihervaara et al. 2010).
Based on the results of this study, tourism is the human activity that has the greatest influence on marine ecosystems. PCA analysis confirmed this finding. This can be attributed to the fact that the tourism beneficiaries are unable to deal with the environment and marine life. Tourism has become one of the largest economic activities in the world and the rapid growth of the industry has produced more infrastructure, increased pollution, and created adverse impacts on biodiversity. In the same context, the sites exposed to floods are significantly lower in biodiversity, even though there are species that can adapt to this natural phenomenon and that are increasing in abundances, such as the high abundance of the snails Coralliophila violacea and Cellana eucosmia. Accordingly, Nicholls (2002) confirmed that coastal flooding can result in a wide variety of socio-economic and environmental impacts on different spatial and temporal scales. Flooding can destroy coastal habitats and can erode dune systems.
It is clear from the present results that fishing activities have severe effects on biodiversity and habitat stability in the study area. Uncontrolled fishing practices dramatically affect biological communities by causing cascading effects down food webs that decrease diversity or productivity. Overfishing or unregulated fishing, which removes certain species or ages, have led to these effects because many of these species may be naturally rare or unevenly distributed. Due to its high nutritional value and easy access—as well as its popularity as a food source for fishermen and the local community of Bedouin—Tridacna spp. was decreased to its lowest abundance at sites that are directly affected by human activities, especially fishing. Courchamp et al. (2006) stated that overexploitation through fishing activities can lead to resource depletion and put a number of threatened and endangered species at risk for extinction. The exponential growth of the human population experienced in the last several decades has led to the overexploitation of marine living resources to meet the growing demand for food. For example, overfishing is by far the biggest threat for species listed as endangered or vulnerable to extinction, with species extinction being caused primarily by habitat loss, degradation, and fragmentation (Noss et al. 1995). In addition, over-collection of commercial mollusks reduces the number of certain species or may even result in the complete disappearance of other species from the area (Gössling et al. 2004). Anthropogenic activities (especially the salts as results of desalination processes) strongly affects the concentration of nutrient, nitrification, in the marine ecosystem (especially N and P), which considered an important key for plankton nutritional value and communities (El-Naggar et al. 2019; Zakaria & El-Naggar 2019), which is reflected on aquatic food webs (El-Damhougy et al. 2019; Zakaria et al. 2018b). Finally, the integration of remote sensing technique with macro-benthic-invertebrate distribution data revealed that anthropogenic activities affect the presence and absence of species, and influence the dominance status of species in the stations.