Marine Life and Ocean Ecosystems: A Comprehensive Study
Marine Life and Ocean Ecosystems
Benthic Organisms
Epifauna: Organisms living on the surface of the ocean floor, such as corals, mussels, sea stars, sea urchins, and sponges.
Epibenthos: Organisms that live in association with the seafloor but swim up into the water column, such as carpet sharks, shrimp, and rays.
Hard Bottoms: Animals adapted to live on the top of rocks.
Infauna: Organisms that live burrowed into the ocean floor, such as clams and polychaetes. They use tubes for food and oxygen supply.
Soft Bottoms: Animals adapted to live in the sediment; primarily infauna.
Environmental Factors Affecting Marine Life
Currents: The survival of plankton is affected by where the currents carry them. Food supply varies as changing circulation patterns lead to higher or lower nutrient concentrations.
Temperature: Affects photosynthesis and mixing of the water column.
Water Column Productivity: Synthesis of organic matter from inorganic substances, mainly by photosynthesis. Requires light, nutrients, and other elements. Limiting factors include NO3 and PO4. Others include Ca, Si, and CO3. Productivity can also be limited by grazing (heterotrophs).
Six Main Groups of Benthic Organisms
1. Sponges (Porifera): Lack internal organs. Specialized cells with different roles. Filter feeders.
2. Cnidarians: Simple organisms with some internal organs, such as corals, sea anemones, and hydrozoans. Predators that eat whatever reaches their tentacles. Corals form CaCO3 substrates and exist as colonies of polyps with symbiotic zooxanthellae algae. They require temperatures between 18-30°C, normal salinity, sunlight, and strong waves.
3. Sea Worms (Polychaetes): Segmented, varying in size and shape. Includes filter feeders, detritus feeders, scavengers, and carnivores.
4. Molluscs (Bivalves, Gastropods, Cephalopods): Bivalves are filter feeders or deposit feeders. Gastropods are algae scrapers and predators of sessile organisms. Cephalopods are predators of fish and other cephalopods.
5. Crustaceans: The most diverse group of marine animals, including large true crabs, lobsters, shrimps, and insect-sized isopods and amphipods. One group, barnacles, is sessile.
6. Echinoderms: Sea stars are predators of sessile organisms. Brittle stars (ophiuroids) are deposit feeders and filter feeders. Sea urchins are grazers and deposit feeders. Sea cucumbers are deposit feeders and filter feeders.
Intertidal Zones
The rocky shoreline is divided into splash, high tide, mid-tide, and low tide zones.
- Spray Zone: Above the spring high tide line but occasionally wet from wave spray and storms.
- High Tide Zone: Submerged only during the highest high tides.
- Middle Tide Zone: Alternately submerged by all high tides and exposed during low tides.
- Low Tide Zone: Usually submerged but dry during the lowest tides.
Animal Adaptations to Intertidal Zones
- Desiccation: Ability to seek shelter, shells that can be closed, thick “skin” to prevent drying out.
- Strong Wave Energy: Strong holdfasts or other attachment mechanisms, hard structures (shells).
- Predators: Firm attachment to the rocky substrate, stinging cells, camouflage, ability to break off (and regrow) body parts.
- Difficult Reproduction: Release of a large number of eggs and sperm in synchrony, often tied to the spring high tide.
- Rapid changes in temperature, pH, salinity, and O2 cause shells to be able to maintain internal environment.
Feeding Styles of Sediment Dwellers
- Suspension Feeding: Animal buried in sediment but has a special structure to filter food (plankton) from the overlying water column (e.g., clam).
- Deposit Feeding: Process organic material coating the sediments (e.g., worms and benthic crustaceans).
- Carnivorous Feeding: Prey on infaunal species (e.g., sand star).
Muddy/sandy environments typically support smaller organisms like crabs, worms (polychaetes), bivalves, and microalgae. They rarely support macroalgal species because there is not enough substrate for these species to attach, and often the water is too turbid and sedimentation rates are too high.
Deep Ocean Floor Characteristics
Vast area, stable environment, dark, cold (~4°C), homogeneous, constant salinity, high O2 content, high pressure, and usually slow bottom currents.
Fish Morphology and Locomotion
| Shape | Adaptation |
|---|---|
| Streamlined | Fast swimmers (e.g., tuna) |
| Flattened from top to bottom | Bottom dwellers (e.g., sea moth) |
| Flattened sideways | Bottom dwellers (e.g., flounder) |
| Eel-like | Live in vegetation (e.g., eel) |
| Triangular, round | Slow swimmers |
| Fin | Function |
|---|---|
| Dorsal | Helps to stabilize |
| Pectoral | Balance, steer, brake |
| Pelvic | Balance, steer, brake |
| Anal | Stabilize |
| Tail | Provide power for movement |
| Predator | Specialized teeth for grasping and chewing |
| Nibbler | Take small bites |
| Food Strainer | Strain food floating in currents |
| Food Sucker | Draw food through the mouth like a vacuum |
| Parasite | Attach to another fish and live off its juices |
Fish Habitats
1. Marine Fish
- Pelagic Fish: Live up in the water column, away from the bottom.
- Demersal Fish: Live on or buried in the water bottom.
- Neritic Fish: Live in the water column that lies over the shelf.
- Oceanic Fish: Live in the waters beyond the shelf break.
- Deep-Sea Fish: Live in the deepest parts of the ocean.
2. Freshwater Fish
- Rheophilic: Prefer continuous current.
- Limnophilic: Prefer calm water.
- Both can be pelagic, demersal, or in between.
3. Brackish Water Fish
Derived from sea and freshwater. Some migrate between the two.
Ocean Chemistry
What are the sources of elements in seawater?
Land, formation of hydrothermal vents, volcanic input, and rivers.
How did carbonate or bicarbonate decrease from 12% in river water to 1% in oceans?
Because animals use them to form calcium carbonate shells (e.g., coccolithophores, fish bones, oysters, cephalopods, pteropods, corals).
What is residence time?
The amount of time the elements stay in a specific reservoir (atmosphere, ocean, ice, etc.) before they are consumed by organisms or transferred into other reservoirs.
Example: Carbonate was a minor component in rivers and became a major component in the ocean (used by organisms).
Why is the ocean not getting saltier?
Because the amount of salt input equals the amount of salt output.
Example: Formation of ice (ocean becomes saltier) and melting of ice (ocean becomes less salty).
Ocean Dynamics
Ekman Spiral: The spiraling pattern described by changes in water direction and speed with depth.
Ekman Transport: The net transport of water by wind-induced motion.
Mechanical Wave: A disturbance created by a vibrating object that travels through a medium from one location to another, transporting energy as it moves.
Tides: The rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon and the Sun and the rotation of the Earth.
Water circulation is induced by density variation of water. Air circulation is induced by variability of air density. Wind friction with water current.
Coriolis force changes the direction of the wind and the current.
Waves are different based on the initiating force.
Tide is one kind of wave.
H2O + CO2 → H2CO3 → H+ + HCO3-.
Pycnocline Layer: The boundary zone between the surface water and deep water layers where a sharp density gradient exists.