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Chapter 15 The Marine Habitat The diversity of marine life The ocean is home to a wide variety of organisms Marine organisms range from microscopic bacteria and algae to the largest animal in the world (blue whale) Number of known marine species: 250,000 Classification of living things Organisms can be classified into one of three domains of life: Archaea Bacteria Eukarya Figure 12-1 Classification of living things Organisms can also be classified into one of five kingdoms: Monera Protoctista Fungi Plantae Animalia Figure 12-1 Classification of living things Taxonomic classification includes the following increasingly specific groupings: Kingdom Phylum (Division for plants) Class Order Family Genus Species Taxonomic classification of selected organisms Category Human Killer whale Giant kelp Kingdom Phylum Subphylum Class Order Family Genus Species Animalia Chordata Vertebrata Mammalia Primates Hominidae Homo sapiens Animalia Chordata Vertebrata Mammalia Cetacea Delphinidae Orcinus orca Protoctista Phaeophyta Phaeophycae Laminariales Lessoniaceae Macrocystis pyrifera Classification of marine organisms Marine organisms can be classified into one of three groups based on habitat and mobility: 1. Plankton (floaters) Phytoplankton (drifting plants and algae) Zooplankton (drifting animals) 2. Nekton (swimmers) 3. Benthos (bottom dwellers) Plankton Plankton (singular plankter) are a diverse group of organisms that live in the water column of large bodies of water and that cannot swim against a current. They provide a crucial source of food to many large aquatic organisms, such as fish and whales. Plankton: Examples Phytoplankton Zooplankton Figure 12-2 Nekton Oceanic nekton comprised animals largely from three clades Vertebrates formed the largest contribution, these animals are supported by either bones or cartilage. Mollusks are animals such as squids and scallops. Crustaceans are animals such as lobsters and crabs. There are organisms whose initial part of their lives were identified as being planktonic but when they grew and increased in body size they become nektonic. A typical example was the medusa of the jellyfish. Nekton: Examples Figure 12-4 Benthos Benthos is the community of organisms which live on, in, or near the seabed, also known as the benthic zone.[1] This community lives in or near marine sedimentary environments, from tidal pools along the foreshore, out to the continental shelf, and then down to the abyssal depths. Many organisms adapted to deep-water pressure cannot survive in the upper parts of the water column. The pressure difference can be very significant. Because light is absorbed before it can reach deep ocean-water, the energy source for deep benthic ecosystems is often organic matter from higher up in the water column which drifts down to the depths. This dead and decaying matter sustains the benthic food chain; most organisms in the benthic zone are scavengers or detritivores. Benthos: Examples Figure 12-5 Marine Ecosystems: • • • • • • • • • • • Open Ocean Coral Reef Kelp Forest Mangrove Forest Deep Ocean Rocky Shore Polar Sea Salt Marsh Estuary Intertidal Zone Photic Zone Ocean Zones The ocean can be divided into zones based on depth (vertically) and distance from land (horizontally) Different zones of the ocean have conditions that support different organisms What is an ecosystem? An ecosystem is a physically distinct area that contains a community of interacting organisms Ocean zones and continental margins Many ocean zones are defined based on continental margins. To help you understand ocean zones, let’s first review continental Margins: Continental Margin: Submerged area of continents. Include: Continental Shelf (flat gradually sloping seafloor) from shoreline to ~ 200m; End of Shelf is called the Shelf Break Continental Slope (steeply sloping seafloor) seaward of shelf break Continental Rise (Moderately sloping seafloor) seaward of slope Ocean zones and continental margins Life cycle of a squid Squid experience benthic, planktonic, and nektonic stages Squid are considered meroplankton (opposite = holoplankton) Figure 12-3 Pelagic and benthic zones One simple ocean zone classification is between the water and the ocean floor The water is referred to as the pelagic zone Organisms that swim through the water column are known as nekton The ocean floor is referred to as the benthic zone Organisms that live here are benthic organisms or benthos Shark: Pelagic (nekton) Crab: Benthic (benthos) Pelagic zone divisions (depth from surface) Epipelagic (0-200m) Mesopelagic (200-1,000m) Bathypelagic (1,000-4,000m) Abyssopelagic (4,000-6,000m Hadalpelagic (6,000-10,000m) Benthic zone divisions (seafloor zones) Supralittoral –shore above high Littoral – the intertidal zone tide (sometimes submerged and sometimes above water) Sublittoral – seafloor of the continental shelf (from low tide to the shelf break) Bathyl – seafloor of the continental slope to the deep ocean bottom Abyssal – deep ocean bottom between the base of the slope and 6,000 m Hadal – the deepest zone, below 6,000m Distribution of species on Earth The land has more species because it has greater environmental variability than the ocean Most ocean species are benthic because of greater environmental variability compared to pelagic environments Figure 12-6 Adaptations of organisms to the marine environment The marine environment presents many challenges to organisms because seawater: Is dense enough to support organisms Has high viscosity Experiences variations in temperature and salinity Contains variable amounts of dissolved gases Has high transparency Has a dramatic change of pressure with depth Marine organisms have various adaptations for the conditions of the marine environment Need for physical support Condition: Seawater is dense enough to support marine organisms Adaptations: Many marine organisms lack rigid skeletons, appendages, or vast root systems Instead, they rely on buoyancy and friction to maintain their position within the water column Seawater’s viscosity controlled by temperature Condition: Seawater’s viscosity (resistance to flow) is strongly affected by temperature Cold water has higher viscosity than warm water, so is more difficult to swim through Warm water has lower viscosity, so organisms tend to sink within the water column Seawater’s viscosity controlled by temperature Adaptations: Many warmwater organisms have ornate appendages to say afloat Many cold-water organisms are streamlined to swim more easily Warm-water copepod Cold-water copepod Figure 12-7 Seawater’s viscosity and adaptations of phytoplankton Condition: Phytoplankton must remain in sunlit surface waters Adaptations: Small size increases surface area to volume ratio Appendages increase frictional resistance Tiny droplet of low density oil increases buoyancy Figure 12-8 Variations in temperature Condition: Coastal water temperatures vary more than the open ocean or at depth Adaptations: Many coastal organisms can withstand a wide temperature range (are eurythermal) Most open ocean and deep-water organisms can withstand only a small temperature range (are stenothermal) Variations in salinity Condition: Coastal environments experience greater salinity variation than the open ocean or at depth Adaptations: Many shallow-water coastal organisms can withstand a wide salinity range (are euryhaline) Most open ocean and deep-water organisms can withstand only a small change in salinity (are stenohaline) Osmosis Condition: Osmosis is the movement of water molecules through a semipermeable membrane from higher to lower concentrations Osmosis removes water from hypotonic organisms Osmosis adds water to hypertonic organisms Figure 12-13 Osmosis Adaptations: Figure 12-14 Dissolved gases: Oxygen Condition: Marine animals need oxygen to survive Adaptations: Many marine animals use gills to extract dissolved oxygen from seawater Marine mammals must breathe air Figure 12-15 Abundance of dissolved oxygen and nutrients with depth Figure 12-20 Seawater’s high transparency Condition: Seawater has high transparency Camouflage Adaptations: Transparency Camouflage Countershading Migration (DSL) Countershading Figure 12-17 The deep scattering layer (DSL) Organisms within the deep scattering layer undertake a daily migration to hide in deep, darker waters during daytime Figure 12B Increase of pressure with depth Condition: Pressure increases rapidly with depth Adaptations: Most marine organisms lack large compressible air pockets inside their bodies Water-filled bodies exert the same amount of pressure as is pushing inward, so marine organisms do not feel the high pressure at depth Divisions of the marine environment Main divisions: Pelagic (open sea) Benthic (sea bottom) Figure 12-19 End of Chapter 12 ESSENTIALS OF OCEANOGRAPHY 7TH EDITION
