Ecology lecture 3 slides

Aquatic Biomes and Species Interactions

Overview of Aquatic Biomes

Aquatic biomes are defined as ecosystems located in water, which can significantly vary in salinity, temperature, and light availability. The primary aquatic biomes include:

• Freshwater: Characterized by low salinity levels, it includes ecosystems such as lakes, rivers, ponds, and streams. Freshwater habitats are crucial for many species, providing essential resources such as drinking water, breeding grounds, and nutrient cycling.

• Estuaries: Featuring brackish water, estuaries occur at the interface where freshwater rivers meet the ocean. These environments support high biodiversity and are vital for species such as migratory fish, shellfish, and birds, while serving as nurseries for many marine organisms.

• Marine: High salinity environments constitute marine biomes, which include vast oceans and diverse habitats such as coral reefs, open ocean waters, and coastal regions. Marine ecosystems are characterized by their complex food webs, various stratification, and the importance of both light and nutrients in supporting life.

Depth in the Ocean

The depth of ocean water is crucial as it influences light penetration, temperature gradients, and the overall ecological interactions occurring within the aquatic environment.

• Mesopelagic Zone: Often referred to as the twilight zone, this area (200-1000 meters deep) allows for limited light penetration, enabling a unique community of organisms that include smaller fish and invertebrates.

Zonation in Aquatic Habitats

Aquatic ecosystems exhibit various zones, each marked by distinct physical characteristics and biological communities:

• Benthic Zone: The bottom region of a body of water, encompassing sediments and all associated organisms. This zone is crucial for nutrient cycling and the habitat for numerous species.

• Pelagic Zone: The open water column situated above the benthic zone, supporting diverse life forms that rely on the ability to swim or float.

• Photic vs. Aphotic: The photic zone is the upper layer of water where sunlight penetrates, facilitating photosynthesis, while the aphotic zone lacks light, resulting in distinct ecological dynamics.

• Intertidal, Neritic, Oceanic Zones: These zones are categorized based on their distance from the shore, with the intertidal zone experiencing periodic exposure to air, while the neritic zone is rich in various nutrients due to upwelling, and the oceanic zone refers to the open sea.

Stratification in Lakes

Lakes can exhibit various stratified zones that impact aquatic life and water chemistry:

• Littoral Zone: A shallow area near the shoreline that supports diverse plant and animal life, often characterized by abundant sunlight and warm waters.

• Photic Zone: This upper layer allows sunlight penetration, enabling photosynthesis and supporting primary production.

• Limnetic Zone: The open waters of a lake that are too deep for rooted plants but rich in phytoplankton and zooplankton.

• Benthic Zone: Comprising the bottom habitats that can host a range of organisms, including decomposers that play a pivotal role in nutrient recycling.

• Aphotic Zone: Characterized by its depth where light fails to reach, this zone is home to specially adapted organisms that depend on detritus and other food sources.

Lake Temperature and Oxygen Levels

Understanding the thermal dynamics is key to aquatic habitats:

• Thermocline: An area of rapid temperature change within water layers that can influence oxygen distribution and biological activity.

• Summer Stratification: Lakes can develop layered temperatures during summer, with a warm, oxygen-rich top layer and a cooler, oxygen-poor bottom layer.

• Mixing during turnover: Seasonal changes, particularly in spring and fall, can cause turnover, allowing nutrients from the bottom to re-enter the photic zone, stimulating productivity.

Open Ocean and Nutrient Levels

The open ocean is characterized by nutrient gradients that impact biological productivity:

• Stratification Patterns: The depth influences temperature and nutrient levels in the water, significantly affecting marine life.

• Nutrient Categories:

  • Eutrophic: These waters are rich in nutrients, leading to high productivity and often resulting in algal blooms that can deplete oxygen levels.

  • Oligotrophic: Low in nutrients and productivity, oligotrophic waters are typically clear and support unique biological communities adapted to low-nutrient conditions.

Marine Habitats

Shallow water marine habitats encompass a wide variety, including:

• Kelp Forests: These underwater forests provide critical habitat for numerous species and serve as an important resource for coastal communities.

• Coral Reefs: Renowned for their biodiversity, coral reefs support countless marine organisms and are vital for coastal protection and fisheries.

• Intertidal Zones: Areas that experience periodic exposure to air and are inhabited by a range of organisms adapted to extreme conditions.

Interspecific Interactions

Interspecific interactions between species can shape community dynamics:

• Competition: Interaction that is detrimental to both species involved as they vie for limited resources.

• Mutualism: A beneficial interaction where both species gain advantages, such as pollination by insects for flowering plants.

• Predation/Herbivory: Where one species benefits at the expense of another; predators capture prey, while herbivores feed on plants.

• Parasitism: A relationship where one species benefits while harming the host, such as ticks on mammals.

• Commensalism: An interaction where one species benefits and the other is neither helped nor harmed.

Rocky Intertidal Zone

Classification of the rocky intertidal zone includes numerous organisms:

• Splash Zone: Organisms here must tolerate desiccation (drying out) and extreme conditions.

• High, Mid, Low Intertidal Zones: Support diverse organisms such as snails, barnacles, mussels, and sea stars, each adapted to their specific environment.

Competition in Rocky Intertidal

Space limitation in the intertidal leads to significant competition:

• Resource Limitation: The physical space available for organisms is limited, intensifying competition for attachment surfaces and resources.

• Effects of Competition: Such competition can lead to lower reproductive rates and higher mortality, ultimately influencing population dynamics.

Barnacle Biology and Competition

The life cycle and spatial dynamics of barnacles illustrate competition clearly:

• Life Cycle: Adult barnacles are sessile and attach to rocks, while their larvae are planktonic and free-swimming.

• Spatial Dynamics: The distribution of barnacle species, such as Chthamalus (higher up) compared to Balanus (lower down), reflects their adaptability to environmental conditions.

Removal Experiments in Intertidal Zones

Investigating intertidal dynamics through removal experiments demonstrates resource competition:

• Experiment 1: Removal of Balanus indicated that Chthamalus could settle and thrive in previously competitive spaces.

• Experiment 2: In contrast, removing Chthamalus allowed Balanus a chance to settle, highlighting the interplay between species.

Ecological Niche and Competition

Understanding the concepts of ecological niches clarifies competition outcomes:

• Fundamental Niche: The range of environmental conditions in which a species can survive without competitors.

• Realized Niche: The range actually occupied when competition and other biotic interactions are present.

• Competitive Exclusion Principle: This principle suggests that two species competing for identical resources cannot coexist indefinitely; one will outcompete the other.

Coral Reef Dynamics

The environment of coral reefs is delicately balanced:

• Conditions: Found in warm, shallow waters, these reefs remain nutrient-poor yet boast high biodiversity, demonstrating complex ecological interactions.

• Coral Polyps and Zooxanthellae Symbiosis: Coral polyps depend on the symbiotic algae (zooxanthellae) for nourishment and, in return, provide the algae with a protected environment and the compounds necessary for photosynthesis.

Evolution and Survival of Coral Polyps

The mutualism between coral polyps and zooxanthellae illustrates co-evolution:

• Mutual Benefits: Zooxanthellae provide essential carbohydrates derived from photosynthesis; in turn, polyps offer a safe habitat and nutrients for algal growth.

  Symbiosis and mutualism are not the same. Symbiosis is a form of mutualism.

Coral Reef Declines and Competition

Coral reefs face numerous threats leading to declines:

• Changing Face of Reefs: Coral cover is dramatically decreasing, impacted by increased competition with macroalgae due to nutrient loading.

• Factors of Change: Overfishing, disease outbreaks, nutrient run-off, and climate change collectively threaten reefs, necessitating urgent conservation measures.

Key Points and Management Strategies

Enhancing community resilience in aquatic ecosystems relies on understanding complex interactions:

• Complex Interactions: Interspecific competition, herbivory, and mutualism all contribute to community dynamics and resilience. Environment: abiotic and biotic. Mechanism: effects on birth, death and growth rates.

• Conservation Efforts: Established marine protected areas, strategies for managing nutrient inputs, and actions to combat climate change are paramount for preserving aquatic ecosystems.

• critical points: redundancy and resilence.