3_Coastal_habitatsa

Coastal Habitats

Chapter 3 is crucial for upcoming tests; review thoroughly as some questions will not be covered in lectures. Understanding coastal habitats is essential for appreciating the biodiversity and ecological functions unique to these areas, especially in the context of the United Arab Emirates (UAE).

Objectives

• Introduce special marine coastal ecosystems, with a particular focus on UAE coastal ecosystems.

• Explain how physical factors such as temperature, sunlight, nutrient availability, and salinity influence the functioning and distribution of marine coastal ecosystems.

Mangroves

Definition

Mangroves are a unique group of trees and shrubs that grow in intertidal zones of tropical and subtropical climates, where saltwater and land meet. These ecosystems are characterized by their specialized adaptations to saline and waterlogged conditions.

Growing Conditions

Mangroves flourish in environments that are typically harsh and unsuitable for most tree species: their growth is supported by saline waters, waterlogged anoxic soils, and strong wave action, particularly during storm surges, which makes them ecologically significant and resilient.

Distribution

Mangroves are predominantly found along the Gulf and east coast of the UAE, indicative of their adaptive capacity to various local conditions. They cannot survive in environments with minimum sea surface temperatures below approximately 19-20°C, as freezing conditions are detrimental to their growth and survival.

Adaptations

• Saltwater Adaptations: Mangroves have evolved several mechanisms to exclude salt at their roots, excrete excess salt through their leaves, concentrate salts in older leaves or bark, and store salts in vacuoles away from metabolically active cells, showcasing their remarkable resilience.

• Waterlogged Sediment Adaptations: They possess specialized structures called pneumatophores, which facilitate oxygen transport to their roots in anaerobic conditions. Some species rely on anaerobic respiration for energy, which contributes to their slower growth rates.

• Stability Against Waves and Storms: Prop roots are critical for anchoring mangroves in shifting sediments and offer resistance against strong wave forces, highlighting their structural adaptations that ensure ecosystem stability.

Importance of Mangroves

Mangroves serve various ecological and economic functions:

• They act as vital nurseries for juvenile fish and crustaceans, providing complex habitats that serve both as refuge and a food source.

• Approximately 75% of juvenile fish in tropical regions depend on mangroves for their habitat during early life stages.

• Their root systems offer attachment sites for algae and commercially important invertebrates like oysters, contributing to local fisheries.

• Mangroves help stabilize shorelines by dampening wave energy and supporting the habitats of deposit feeders, preventing coastal erosion.

• Mangrove leaves constitute a primary food source for detritivores, enriching the food web.

• They play a crucial role in carbon sequestration, being approximately 45-55 times more effective than terrestrial forests due to sediment coverage that inhibits decay and carbon release.

• Culturally, mangroves are significant for coastal protection and property safeguarding, prompting planting initiatives aimed at reaching targets such as planting 100 million mangroves by 2030 to combat sea-level rise.

Mangrove Species in UAE

Native mangrove species include Avicennia marina, which is the most prevalent in the region. Historically, Rhizophora mucronata was also present, although it is now extinct in the UAE and undergoing reintroduction efforts despite remaining scarce.

Associated Ecosystems and Species

Mangroves host a wide array of species, including algae, barnacles, oysters, and various crabs, which provide diverse niches that support significant biological interactions. Noteworthy species include juvenile fish, Portunid crabs, and the Khor Kalba kingfisher, all of which illustrate the biodiversity supported by mangrove ecosystems.

Threats to Mangroves

Coastal development projects, oil spills, and pollution pose significant threats to mangrove populations. Given their ecological importance, ongoing preservation efforts are crucial as plantation initiatives strive to enhance coverage that has been historically reduced.

Seagrasses

Definition

Seagrasses are flowering plants known as angiosperms, distinct from algae, that thrive underwater in shallow, light-rich marine environments. They play vital roles in coastal ecology, facilitating many marine processes.

Adaptations

• Rhizomes: These underground stems provide anchoring and nutrient absorption, allowing seagrasses to thrive despite shifting sediment conditions.

• Photosynthetic Shoots: The leaves absorb sunlight and nutrients for growth and reproduction, maximizing their ability to adapt to changing environments.

Importance of Seagrasses

Seagrasses are crucial for ecosystem health:

• They prevent coastal erosion and trap sediment, stabilizing shorelines and maintaining habitat integrity.

• Create nutrient-rich environments that support various deposit feeders.

• Provide essential refuge for diverse marine species, including commercially valuable fish stocks, contributing to local fisheries.

• Facilitate diverse marine life by offering attachment sites for filter feeders and other organisms.

• They are significant in nutrient cycling, facilitating high productivity that converts organic matter into food, thereby supporting complex food webs.

• Seagrasses also serve as a direct food source for species such as dugongs and green sea turtles, highlighting their role in marine food chains.

• Importantly, they capture 25-35 times more carbon per square meter than terrestrial forests, making them effective carbon sinks in the marine environment.

Seagrasses in the UAE

Seagrasses are extensive in the shallow waters of the Gulf, particularly in western Abu Dhabi, which hosts the largest continuous seagrass bed spanning approximately 5,500 km². The three native species include Halodule uninervis, Halophila ovalis, and Halophila stipulacea, with H. uninervis being the most prevalent in these waters.

Threats to Seagrasses

Seagrass ecosystems face numerous threats, including coastal development that leads to increased sedimentation which limits light access, dramatically affecting seagrass survival. Additionally, the influx of excess nutrients can result in harmful algal blooms that further diminish light availability.

Coral Reefs

Definition

Corals are marine invertebrates that form symbiotic relationships with zooxanthellae algae, which dwell within their tissues. These algae provide essential nutrients to corals through photosynthesis, while corals offer shelter and access to nutrients.

Importance of Coral Reefs

Coral reefs are among the most biodiverse ecosystems on the planet:

• They are extremely productive and provide habitats supporting a wide variety of marine life, even in nutrient-poor conditions.

• Coral reefs are vital for fisheries, tourism, and coastal protection, demonstrating their economic and ecological significance.

• Over 25% of marine species inhabit coral reef ecosystems, which cover less than 1% of the ocean floor, illustrating their importance in global marine biodiversity.

Threats to Coral Reefs

Coral reefs face severe threats from climate change, particularly temperature extremes that cause coral bleaching, especially during warmer months. Additionally, increased sedimentation from coastal activities hinders photosynthesis and may lead to the smothering of corals, stressing the need for conservation efforts.

Kelp Forests

Definition

Kelp forests are underwater ecosystems formed by kelp, a type of brown algae that thrives in nutrient-rich, cooler waters. Some kelp species can grow over 30 meters in length, creating complex underwater habitats.

Importance

Kelp forests provide essential habitat and food for a vast array of marine organisms, playing critical roles in maintaining coastal ecosystem health:

• They support keystone species such as sea otters, which help regulate urchin populations, thereby contributing to the overall balance of the ecosystem.

Salt Marshes

Definition

Salt marshes are coastal wetlands found in intertidal regions, often merging with estuaries, characterized by salt-resistant plants that can tolerate saline conditions.

Importance

These ecosystems are highly productive and valuable:

• They serve as critical habitats for a variety of animal species.

• Salt marshes prevent coastal erosion by trapping sediments and have an excellent capacity for carbon sequestration, demonstrating their role in mitigating climate change impacts.