Ocean Studies Introduction to Oceanography American Meteorological Society

1. Ocean StudiesIntroduction to OceanographyAmerican Meteorological Society Chapter 9 Marine Ecosystems

2. Case in Point • Blooms of phytoplankton, microscopic algae, occur widely in surface ocean waters. • Sometimes a bloom of a single species occurs and can cause serious harm to the environment, the demise of marine organisms, economic losses, and human health problems, including illness and death. • Amnesic shellfish poisoning is one of the many possible consequences of harmful algal blooms (HABs) or red tides. • Red tides are becoming more frequent worldwide. • Blooms of toxic algae have been blamed for fish kills and the deaths of marine mammals around the world.

3. A second type of harmful algal bloom, known as a high biomass bloom, depletes the supply of dissolved oxygen in seawater. Harmful algal blooms develop in the waters of almost every coastal state of the U.S. Case in Point

4. Marine Ecosystems • Driving Question: • What are the basic components and structure of marine ecosystems and what is their source of energy?

5. Marine Ecosystems • In this chapter, we examine: • How interactions among the biosphere, atmosphere, and ocean govern the distribution and abundance of life in the ocean • The components of marine ecosystems including producers, consumers, and decomposers • The processes operating within marine ecosystems including energy supply for growth and reproduction, factors influencing biological production in the ocean, the role of nutrients and trace elements as limiting factors, and the importance of microbes in marine ecosystems • The physical and biological processes governing the flux of carbon into and out of the ocean over a range of time scales

6. Requirements for Marine Life • One major difference between life in the ocean and life on land is the much greater space and variety of marine habitats. • In addition to water and energy, marine life forms require nutrients and trace elements in sufficient quantities. • According to the law of the minimum, the growth and well being of an organism is limited by the essential resource that is in lowest supply relative to what is required.

7. Structure of Marine Ecosystems • An ecosystem is a fundamental subdivision of the Earth system in which communities of organisms interact with one another and with the physical conditions and chemical substances of their habitats. • All ecosystems have both living (biotic) and nonliving (abiotic) components plus energy sources. • Biotic components include producers, consumers, and decomposers whereas abiotic components constitute their physical and chemical environment.

8. Structure of Marine Ecosystems • PRODUCERS • Photosynthesizing organisms • Plants, algae, and some bacteria • Floating, microscopic unicellular algae, photosynthetic bacteria, and other groups of organisms capable of photosynthesis are responsible for more than 99% of biological production in the photic zone. • referred to as phytoplankton • diatoms, coccolithophorids, dinoflagellates, and bacteria • The smallest and probably the most numerous of phytoplanktonic organisms are certain groups of bacteria.

9. Structure of Marine Ecosystems • PRODUCERS • Diatoms are a diverse group of protista (or protoctista) having properties of both plants and animals. • Coccolithophorids are a single-cell photosynthesizing organism covered with tiny calcium carbonate plates. • Appear to thrive in nutrient-poor waters, forming large blooms that turn surface waters greenish blue as viewed from space

10. Structure of Marine Ecosystems A large red tide formed by the dinoflagellate Noctiluca. Coccolithophorid bloom in the Bering Sea off Alaska

11. Structure of Marine Ecosystems • PRODUCERS • Dinoflagellates have two flagella (thread-like structures) and no solid covering so that they are not preserved in marine sediment deposits. • some species form red tides • The smallest and probably the most numerous of phytoplanktonic organisms are certain groups of bacteria. • lack internal cellular structure such as nuclei, chloroplasts and mitochondria

12. PRODUCERS Scientists have discovered extraordinary ecosystems in the deep ocean in which chemical energy, rather than sunlight, drives the basic biological processes referred to as chemosynthesis The total amount of carbon converted from carbon dioxide into organic matter is known as primary production referred to as carbon fixing Structure of Marine Ecosystems Cyanobacteria are the most abundant photosynthetic organisms in the ocean

13. Structure of Marine Ecosystems • CONSUMERS • Single-cell and multi-cellular consumers that drift passively with ocean currents or are weak swimmers are referred to collectively as zooplankton. • include bacteria and dinoflagellates as small as 2 micrometers • most zooplanktonic organisms are suspension or filter feeders

14. Structure of Marine Ecosystems • CONSUMERS • Most ubiquitous members of the zooplankton are copepods, a diverse group of tiny crustaceans covered with an exoskeleton • Include both herbivorous and carnivorous species • Play an important intermediate role in marine food chains, feeding on phytoplankton and, in turn, being eaten by larval and juvenile fish • Larger members of the zooplankton community include euphausiids and other shrimp-like crustaceans called krill. • Zooplankton is the main food source for larger consumers in the sea.

15. Structure of Marine Ecosystems Euphausiids (krill) occur in large swarms in the Southern Ocean and feed on algae on the under surface of sea ice Copepods are tiny crustaceans that are an important food source for juvenile fish and shellfish.

16. Structure of Marine Ecosystems • DECOMPOSERS • Consumers that feed on dead organic matter, either on the ocean bottom or in the water column • Break down organic matter and recycle nutrients back into the ecosystem

17. TROPHIC STRUCTURE OF ECOSYSTEMS Complex of linked food chains is described as a food web Each feeding position occupied by an organism within a food web is called a trophic level. Energy is transferred from lower trophic levels to higher trophic levels. Structure of Marine Ecosystems

18. Structure of Marine Ecosystems • TROPHIC STRUCTURE OF ECOSYSTEMS • Ecological efficiency is defined as the fraction of the total energy available at one trophic level that is transformed into work or some other usable form of energy at the next higher trophic level. • Varies depending on types of organisms and ecosystems • A complex food web with diverse food sources tends to be more stable and less vulnerable to environmental change than is a simple ecosystem.

19. BIOACCUMULATION Some persistent toxins move from one trophic level to the next, building in concentration along the way as one organism consumes another. Process of continually increasing concentration within a food web is called bioaccumulation Consequence of the ecological inefficiencies that prevail between trophic levels—the biomass declines at each successively higher level but the toxins remain Structure of Marine Ecosystems Field studies in the freshwater ecosystem of Saginaw Bay, Lake Huron, MI found bioaccumulation of PCBs in successively higher trophic levels

20. Ecosystem Processes • ENERGY FOR GROWTH AND REPRODUCTION • Photosynthesis converts solar energy into chemical energy. • Because solar radiation is essential for photosynthesis, this process occurs only during daylight and primarily in relatively shallow waters. • Most sunlight is absorbed very near the ocean’s surface; typically 80% is absorbed in the upper 10 m (33 ft) of water. • The depth to which sunlight penetrates ocean water depends on the clarity of the water.

21. Ecosystem Processes • ENERGY FOR GROWTH AND REPRODUCTION • Energy-releasing chemical reactions can occur in the ocean without sunlight. • Many microbes synthesize organic matter, obtaining energy from chemical reactions fueled by energy-rich substances, such as hydrocarbons (petroleum or methane gas), hydrogen sulfide, and various metals. • discharged in the waters of hydrothermal vents

22. Ecosystem Processes • PRODUCTION IN THE PHOTIC ZONE • Net production: the amount of organic matter produced during photosynthesis that exceeds the amount consumed via cellular respiration • confined to surface sun-lit waters • The total amount of carbon fixed into organic matter through photosynthesis in a given unit of time is the gross primary production. • No net primary production occurs below the compensation depth—usually the ocean depth where the light level diminishes to about 1% of what it is at the surface. • Primary production using recycled nutrients is called regenerated production.

23. Ecosystem Processes • PRODUCTION IN THE PHOTIC ZONE • Primary production requires sunlight, nutrients, and phytoplankton (above the compensation depth) and varies with both location and season. • Primary production is very low in much of the tropical ocean due to a lack of nutrients.

24. Ecosystem Processes • PRODUCTION IN THE PHOTIC ZONE • At temperate latitudes, production varies with the season. • In winter, sunlight is weak and surface waters become more dense and sink. • In spring, more intense solar heating reestablishes the pycnocline and stratification, halting the deep mixing of autotrophs. • Conditions are favorable for a dramatic increase in phytoplankton populations, an event known as the spring bloom. • Explosive growth of zooplankton populations that graze on the phytoplankton • In polar regions sunlight limits production although ocean stratification is generally absent and nutrients are abundant.

25. This satellite image shows the spring bloom around Arctic Canada in May 2003. Areas of high chlorophyll concentration are shown in red, orange, and yellow whereas areas of lower production are in shades of green and blue.

26. Ecosystem Processes • NUTRIENTS AND TRACE ELEMENTS AS LIMITING FACTORS • Some areas of the ocean have sufficient nitrogen, phosphorus, and sunlight but still have low levels of production. • These areas are often in the middle of ocean basins, far from land, and are known as HNLC regions (for high nutrients, low chlorophyll). • This condition might arise from the lack of some element that usually occurs in trace quantities. • iron is often a limiting trace metal in marine ecosystems • HNLC regions of the ocean may be so distant from terrestrial sources of wind-borne iron particles that input of iron-rich dust is insufficient to make these areas productive.

27. Ecosystem Processes • MICROBIAL MARINE ECOSYSTEMS • Microbes, single-celled organisms including bacteria, apparently dominate life in the ocean along with viruses and a group of organisms known as archaea. • Microbes act as both producers and consumers. • Contribute enormously to global oceanic primary production and are especially important in open ocean waters

28. Ecosystem Processes SeaWiFS image of marine biological production during 2007. Areas of relatively high production are shown in red, orange, and yellow whereas areas of relatively low production are in shades of green and blue.

29. Ecosystem Processes • MICROBIAL MARINE ECOSYSTEMS • The ocean is home to three major groups of microbes: bacteria, archaea, and viruses. • Archaea and bacteria together form the class of organisms called prokaryotes. • All prokaryotes are unicellular • Essentially no internal cellular structure • Eleven different types of microbes (nine bacteria and two archaea) dominate life in the ocean in numbers and probably in mass. • Many different types of unicellular eukaryotes of very small sizes also inhabit the ocean. • collectively known as protozoa • include ciliates and dinoflagellates

30. Ecosystem Processes • MICROBIAL MARINE ECOSYSTEMS • Bacteria and archaea are significant consumers in marine food webs. • Can directly absorb and digest dissolved organic carbon (DOC) that cannot be used as food by larger organisms • Bacteria and archaea are food sources for the smallest heterotrophs, including dinoflagellates and ciliates. • The organic carbon they consume seldom reaches the rest of the marine food web, but is recycled within a semi-separate food web, the so-called microbial loop that operates parallel to the larger food web.

31. Ecosystem Processes A simple microbial loop linked to a schematic marine food chain

32. Ocean’s Role in the Global Carbon Cycle • The ocean—primarily the deep ocean—is the most significant reservoir of carbon in the Earth system. • Holds about 50 times the amount of carbon dioxide contained in the atmosphere and about 20 times the amount of carbon stored in the biosphere • Two different sets of processes, biological and physical, govern the cycling of carbon into and out of the ocean.

33. Ocean’s Role in the Global Carbon Cycle • PHYSICAL PUMP • An important process controlling the ocean subcycle of the global carbon cycle • Primarily physical in nature and is known as the physical pump or solubility pump • Acts in concert with ocean heat transport and heat loss to the atmosphere to convey carbon to the deep ocean where it may be sequestered for millennia

34. Ocean’s Role in the Global Carbon Cycle • PHYSICAL PUMP • Situated above Antarctic Bottom Water (AABW) is a large water mass that encircles the entire Southern Ocean: Circumpolar Deep Water • Produced by mixing of AABW with the overlying deep waters of the Atlantic and Pacific Ocean basins • Circumpolar Deep Water circulates slowly throughout the ocean on a time scale of 1000 years • Gradually warms and diffuses upward into the surface layer where CO2 is released (outgassed) to the atmosphere because carbon dioxide is less soluble in warmer water

35. Ocean’s Role in the Global Carbon Cycle • BIOLOGICAL PUMP • The downward transport of particulate organic carbon Biological processes that control the distribution of carbon in the ocean constitute the biological pump.

36. Ocean’s Role in the Global Carbon Cycle • BIOLOGICAL PUMP • Eighty percent of primary production in the ocean takes place in the photic zone of the open ocean and roughly equals the amount of organic matter produced by all land plants annually. • In the photic zone, phytoplankton and other photosynthetic organisms convert inorganic carbon into organic carbon and organisms grow and reproduce rapidly. • Particulate organic carbon (POC): carbon contained in marine snow plus the carbon in the sinking bodies of zooplankton and other marine animals • POC may be eaten by zooplankton or decomposed by bacteria or other microbes and converted back to dissolved inorganic carbon.

37. Ocean’s Role in the Global Carbon Cycle • BIOLOGICAL PUMP • Particles of organic matter that settle to the sea floor and are not recycled by bottom-dwelling organisms are buried in sediment deposits, removing the carbon they contain from the water and the biosphere for perhaps millions of years. • Another way in which organic carbon is recycled in the ocean is by re-mineralization, by being converted back to soluble inorganic forms. • Cycling of carbon into and out of the ocean is a key player in Earth’s climate system. • Carbon dioxide fluxes at the interface between the ocean and atmosphere vary greatly from one region of the ocean to another.

38. Ecosystem Observations and Models • Studies of the oceanic carbon sub-cycle on various temporal and spatial scales rely on data obtained remotely by satellite-borne instruments. • NASA’s Sea-viewing Wide Field-of-View Sensor (SeaWiFS): maps ocean color (the distribution of photosynthetic pigments and particularly chlorophyll-a, the most significant photosynthetic pigment in marine algae). • Advanced Very High-Resolution Radiometer (AVHRR) sensor onboard NOAA’s polar-orbiting satellites measures sea surface temperatures on a global scale. • For information on ocean properties at depths below the range of satellite sensors, ocean scientists rely on in situ observations taken at specific locations over a lengthy period, spanning years, decades, or longer.

39. Ecosystem Observations and Models • These time series data permit scientists to construct numerical models ranging in complexity from those applicable to a single location, to three-dimensional models of the global ocean. • The principal goals of these models are to identify processes and explain observations, combine many types of data to improve estimates of biogeochemical fluxes, and improve predictability of future ocean states. • Another major goal of ocean modelers is to produce coupled models that integrate biogeochemical and physical processes. • Biogeochemical aspects of ocean modeling are essential and data are being collected, processes are being studied, and the gap between physical modeling and biogeochemical modeling is closing.

40. Conclusions • Marine ecosystems are composed of producers, consumers, and decomposers and their energy is supplied via photosynthesis or chemosynthesis. • Persistent toxic chemicals may enter marine food webs and bioaccumulate, threatening the well being of organisms (including humans) feeding at higher trophic levels. • Primary production in the ocean’s photic zone varies spatially and temporally because of seasonal changes in sunlight, weather, fluctuations in nutrient supply, the availability of trace elements, stratification of ocean waters, and upwelling.