International Journal of Aquaculture, 2024, Vol.14, No.1, 1-8 http://www.aquapublisher.com/index.php/ija 3 1.2 Role of symbiotic algae in hard coral tissues Symbiotic algae, typically belonging to the genus Zooxanthellae, are single-celled algae that closely associate with hard corals. These algae reside within the tissues of hard corals, imparting brown or golden pigments to the coral's transparent tissues, hence often referred to as "brown algae." Photosynthetic symbiotic algae convert sunlight into energy through photosynthesis, and then transport organic carbon and nutrients to the hard coral, providing the necessary resources for growth and survival (Hazraty-Kari et al., 2022). This symbiotic relationship plays a crucial role for hard corals. Symbiotic algae contribute approximately 90% of the energy through photosynthesis, enabling hard corals to grow rapidly and construct their robust skeletons. Additionally, the symbiotic algae provide the necessary organic substances for hard corals, including glucose, amino acids, and fatty acids. Hard corals also offer a suitable habitat for symbiotic algae in this relationship, as well as protection from suspended sediments and predators. 1.3 Mutual dependency between symbiotic algae and corals The relationship between hard corals and symbiotic algae is one of mutual dependency, where they cooperate to maintain the stability of the entire coral reef ecosystem. However, this relationship is delicate and highly sensitive to environmental changes. Hard corals obtain most of their energy from symbiotic algae, but adverse environmental conditions such as elevated sea temperatures, deteriorating water quality, or storms may harm the symbiotic algae. In such cases, hard corals may expel the symbiotic algae, leading to a phenomenon known as coral bleaching. Coral bleaching poses a severe threat to the hard coral ecosystem as it causes the loss of a substantial energy supply for hard corals (Wu et al., 2022). If this phenomenon persists for an extended period, hard corals may eventually die, negatively impacting the entire coral reef ecosystem. This makes the interdependence between hard corals and symbiotic algae more significant and underscores its significance as a core issue in the face of climate change threats to tropical hard coral reefs. The close mutual dependency between hard corals and symbiotic algae is a key factor in the success of tropical coral reef ecosystems. Symbiotic algae provide energy and organic matter to hard corals, enabling their growth and reproduction, while hard corals offer a suitable habitat and protection for symbiotic algae. However, this relationship faces numerous threats, particularly environmental changes resulting from climate change. 2 Impact of Climate Change on the Relationship between Tropical Hard Corals and Symbiotic Algae Tropical hard coral reefs are among the world's most vulnerable ecosystems, playing a crucial role in the Earth's ecosystems. However, the threats of climate change have had severe impacts on these valuable ecosystems. Among them, the relationship between hard corals and symbiotic algae is particularly fragile, drawing significant attention to the interaction between tropical hard corals and climate change. 2.1 Effects of elevated sea temperatures on corals One of the most significant impacts of climate change is the rise in sea temperatures. Tropical hard corals are highly sensitive to temperature changes and exist within a relatively narrow temperature range. When sea temperatures increase, hard corals face a series of challenges. Firstly, high temperatures can cause damage to the symbiotic algae within the coral, leading to coral bleaching (Pang et al., 2021). Coral bleaching (Figure 2) is a severe phenomenon as it disrupts the stable relationship between corals and symbiotic algae, causing hard corals to lose the majority of their energy supply. Furthermore, elevated temperatures accelerate the metabolic rate of hard corals, increasing their demand for more energy. If hard corals cannot acquire sufficient energy, they may cease growth or even start to dissolve, ultimately leading to the decline of coral reefs. Therefore, the rise in sea temperatures poses a severe threat, not only is it harmful to hard corals themselves, but also has adverse effects on the entire coral reef ecosystem.
RkJQdWJsaXNoZXIy MjQ4ODYzNA==