prelim 2

primary production

process by which organisms convert light/chemical energy into organic matter

Why is it important to understand primary production?

forms the base of marine food webs, allowing us to understand the variability of all marine organisms (ecosystem function)

biogeochemistry

understanding how life in the ocean affects global elemental cycles

Global carbon cycle

photosynthesis consumes CO2 gas —> respiration by all organisms produces CO2

What explains the difference between photosynthesis and respiration by all of the organisms?

what sinks to the ocean floor

Global oxygen cycle

Photosynthesis produces oxygen, and half of global photosynthesis takes place in the ocean

plankton

small organisms that drift with ocean currents

phytoplankton

small cells (often single cells) that contain chlorophyll and drift with ocean currents

photosynthesis + formula

chemical reaction using H2O and CO2 and sunlight to form glucose and oxygen —> glucose is the energy source for subsequent metabolic reactions

6CO2 + 6H2O + Light Energy —> C6H12O6 + 6O2

What does the magnitude of primary production depend on?

availability of sunlight and essential plant nutrients (required for construction of complex molecules)

respiration

reactions to construct new complex molecules and provide metabolic needs that consume oxygen and produce CO2 (opposite of photosynthesis)

net primary production

difference between the amount of CO2 consumed by cell during photosynthesis and CO2 exported from cell during respiration (equal to net change in carbon)

3 groups of phytoplankton

1. diatoms (need silica)

2. flagellates (mobile)

3. photosynthetic bacteria

compensation light level

light intensity where net primary production is 0

What happens at light levels below the compensation light level?

phytoplankton cells do not have sufficient light to photosynthesize —> respiration exceeds photosynthesis

What are the three different levels of compensation light intensity for phytoplankton?

1. light limited (low light)

2. light saturated (optimal light)

3. photoinhibited (high light)

compensation depth

depth at which ambient light intensity (natural environment light) is equal to the compensation light intensity

4 Phytoplankton Nutrients of Interest to Oceanographers

Nitrogen, phosphorus, silica (for diatoms), iron

How does nutrient concentration affect the dominant size of phytoplankton cells?

dependent on surface area to volume ratio: small phytoplankton grow better at lower nutrient concentrations, larger ones in higher nutrient concentrations

What is the Main Source of Nitrogen, Phosphorous and Silica to the

Surface Ocean?

vertical mixing/upwelling of nutrient-rich deep water to the surface

When global warming enhances the surface temperatures, what happens to ocean primary production?

warmer surface —> shallower thermocline/harder to vertically mix —> less nutrients coming up from cold waters —> less production

What is the main source of Iron input to the surface ocean?

Dust blowing off continents (so limited in Southern Ocean)

How do iron inputs to the ocean influence nutrient limitation?

More iron —> phytoplankton do more nitrogen fixation (using nitrogen gas as nutrient) —> extra nitrogen but limited phosphorus

What compounds most often limit growth?

nitrogen most often, iron in areas with low iron input, phosphorus in areas with high iron input

Why are nutrient levels and primary production low in subtropical gyres?

Convergence of Ekman layer forms a mound of warm low-nutrient water —> downward flow, making it hard for nutrients to move upwards

What causes equatorial upwelling and why is it important for ocean productivity?

trade winds push water westward, making thermocline deeper in west —> Ekman divergence near equator pulls surface water away and allows deep water to upwell especially in eastern equitorial Pacific and Atlantic (high production)

What is tidal mixing and where does it occur?

mixes water column from bottom to top (bottom nutrient-rich water —> top), occurring in shallow continental shelf areas season-round

What is coastal upwelling and when does it occur?

upwelling from wind and Ekman offshore transport that is seasonally variable (e.g. wind blows towards south, moving Ekman layer offshore, leading to upwelling on coast)

What is the seasonal phytoplankton bloom in the North Atlantic?

spring brings high light + high nutrients leftover from winter nutrient upwelling —> optimal productivity

What is the Critical Depth Theory, and how does it explain when phytoplankton blooms occur?

As mixing depth increases, phytoplankton spend more time below the compensation depth (in the dark) —> when cells mix below the critical depth (net zero carbon), they lose too much carbon

How do seasonal changes in the mixing depth affect NPP over the course of a day?

Winter: mixing below critical depth b/c deeper thermocline, so daily NPP negative

Summer: mixing above critical depth b/c shallower thermocline, so daily NPP positive

Two seasonal blooms

1. Deep Winter Mixing: nutrients brought to surface

2. Springtime stratification: shoaling mixing above critical depth

Oceanic NPP is about what percentage of Global NPP?

46%

Why does the open ocean contribute most of the NPP despite low intensities compared to coastal regions?

open ocean is so vast —> dominates total ocean NPP

Pelagic

the water column environment (organisms living in the open ocean)

Benthic

the seafloor environment, including coral reefs

Nekton

able to swim against ocean currents (e.g. fish)

autotrophs

group of organisms whose energy/carbon for growth comes from non-organic sources, e.g. phytoplankton with sunlight and CO2

heterotrophs

group of organisms whose energy/carbon for growth comes from previously formed organic carbon material, e.g. zooplankton consume phytoplankton

trophic level

nutritional feeding levels within a food chain/web

How do we decide if an Organism is Autotrophic or Heterotrophic?

if it contains chlorophyll, it is an autotroph

What is the general rule of thumb for the preferred prey size?

1/10 the consumer size, so an organism’s prey will be 1/10 its size and its predators will be 10x its size

exploitation efficiency

efficiency with which a consumer population can find and ingest all prey in the environment

gross product efficiency

biochemical efficiency of converting ingested prey into consumer biomass

What determines the efficiency of carbon or energy transfer from one trophic level to another?

trophic transfer efficiency = exploitation efficiency x gross product efficiency

Diel Vertical Migration

avoiding detection by separation in time: zooplankton go to the surface of the ocean at night to feed while avoiding visual predators like small fish, then go to the safety of the deep darkness in the day

grazer

marine organisms that eat algae and other plant material

What happens to exploitation efficiency when Spring Blooms in the Temperate North Atlantic Region?

exploitation efficiency is very low: much of phytoplankton in early spring is not found by grazers and instead sinks into the deep ocean as dead phytoplankton cells

What happens to exploitation efficiency in Tropical Environments?

exploitation efficiency is very high: small grazers are active and consume phytoplankton

What do exploitation and gross product efficiency range between?

exploitation: 10 to 90%

gross product: 20 to 60%

Food Chain Length of Open Ocean Versus Coastal Upwelling Regions

Low nutrient open ocean: small phytoplankton —> 7 trophic levels to harvestable fish (smaller means a smaller organism eats it, then a smaller organism eats that one, there’s more intermediary steps), so big overall loss

High nutrient coastal upwelling: large phytoplankton —> 2 trophic levels to fish, so small overall loss

oligotrophic

pelagic environment (water column) with low nutrient concentrations (e.g. vast subtropical gyres)

eutrophic

pelagic environment (water column) with high nutrient concentrations (e.g. coastal upwelling zones)

What did the traditional 1970s marine food chain model include and overlook?

Included: medium-large phytoplankton eaten by medium-large zooplankton

Overlooked: heterotrophic/autotrophic bacteria and heterotrophic flagellates

What did the Use of Epifluorescent Microscopy and Fluorescent DNA Stains reveal?

increased estimates of bacterial abundance in the ocean + allowed easy distinction between autotrophic/heterotrophic flagellate cells

Microbial Loop

term coined by Azam et al. in a 1983 scientific publication that described the role microbes play in the marine carbon cycle

What is Prochlorococcus and how was it discovered?

a new type of very small autotroph present in high abundance oligotrophic regions, which was discovered using analytical flow cytometry

Why is Prochlorococcus so important in the global ocean ecosystem?

They are the smallest phytoplankton cells and have the growth advantage in the low-nutrient open ocean, so they are the main contributor to primary production (25%+)

How do phytoplankton size and ecosystem type affect the efficiency of the biological carbon pump?

Large phytoplankton → large grazers → large fecal pellets that sink easily → efficient carbon pump (common in eutrophic waters)

Small phytoplankton → small grazers → fecal matter too tiny to sink → carbon is recycled by microbes → inefficient carbon pump (common in oligotrophic waters)

vertical zonation

pattern of species forming distinct horizontal bands at specific heights in the intertidal zone (e.g. x species at x height)

How are species arranged in the intertidal zone?

arranged within relatively narrow vertical ranges

What sets the upper limit to species distributions?

physical stresses, e.g. temperature and food availability

What sets the lower limit to species distributions?

biological interactions: competition for space and predation

Why do gray barnalces settle higher than rock barnacles in the intertidal?

they can tolerate drying better

Intermediate Disturbance Hypothesis

disturbance (e.g. log damage) maximizes species diversity by periodically removing competitively dominant species, allowing less competitive species to re-establish themselves

How does Pisaster starfish predation affect intertidal diversity?

Pisaster predates mussels and prevents them from dominating, leading to higher species diversity in a rocky intertidal community

keystone species

species that have effects on their communities that are proportionately much greater than their abundance would suggest (e.g. Pisaster starfish)

What happens to kelp forests when sea otters are removed?

Sea otters eat sea urchins —> removal increases sea urchins that overgraze kelp —> low kelp

What happens to kelp forests when sunflower starfish are removed?

Sunflower starfish eat sea urchins —> removal increases sea urchins that overgraze kelp —> low kelp

What percentage of kelp has been lost in parts of the Northern California coast?

95%

zooxanthellae

algal symbionts (microscopic algae living in other organisms) in coral tissue —> provide 60-90% of coral nutrition through photosynthesis

What are the four natural limits to coral growth?

1. temperature

2. sunlight

3. competition for space

4. predation

What are the stages of coral reef formation?

1. new island forms (e.g. ocean-ocean) —> fringing reef develops near shore

2. island sinks slowly —> coral grows upwards and forms barrier reef

3. island fully submerges —> coral atoll

drowned coral reefs

coral that eventually stops growing because it became submerged in deep waters, often b/c island sinks too fast or sea level rises too fast

Who do corals compete with for space?

other corals and macroalgae

What does the Crown of Thorns starfish do to corals?

very important predator of corals, primary cause of coral mortality in some cases

What does overfishing result in?

less fish that feed on algae —> algae grows unchecked and smothers corals

How does rising CO2 affect ocean chemistry and corals?

More CO2 —> higher acidity, which slows calcium carbonate precipitation and leads to coral dissolution

Coral Bleaching

zooxanthellae gives coral its beautiful colors —> bleaching occurs when corals expel their zooxanthellae due to environmental stress, which is either regained if small stress or results in coral death

What effect does El Nino have on coral reefs?

Corals bleach when water rises 1 C above normal levels, so El Nino’s increased global temperatures caused mass coral bleaching (especially Great Barrier Reef)

Expected Scenario for Coral Reef Survival With 1.5ºC Versus 2.0ºC Global Warming

IPCC Report (Oct 2018):

1. Coral reefs decline by 70-90% in a 1.5C world

2. Virtually all coral reefs lost in a 2C world

Pakicetus

a hoofed-mammal that is classified as the earliest whale (~53 million years ago after the dinosaurs)

What special feature indicates a whale/cetacean species?

shape of the ear bone

When and how did baleen whales diverge from toothed whales?

Baleen whales = large filter-feeders that first appeared ~35 million years ago (diverged b/c of environmental changes)

Pacific Humpback Migration relative to seasons

summer: feeding at high latitudes with lots of biological productivity

winter: making calves at low altitudes, which are warm but have low food

Odontocetes + purpose of their sounds

toothed whales that produce rapid bursts of clicks/whistles, with single clicks for echolocation and collections of clicks for close communication

Mysticetes

baleen (filter-feeding) whales that make long, low-frequency sounds known as whale song

What are the main purposes of baleen whale (mysticete) vocalizations?

• Sexual selection: complex songs during mating season

• May aid navigation, but no sign of true echolocation

Three sources of human sound in the ocean

1. naval operations (SONAR)

2. commercial shipping

3. oil exploration (seismic surveys)

How is whale vocalization visualized?

spectrograms with time on x-axis and frequency on y-axis + loudness denoted by brightness of color

PCB

Polychlorinated Biphenyls, which are man-made chemicals formerly used in industrial products

Why are PCBs dangerous for orca whales?

Bioaccumulates in the fat of top predators (e.g. orcas) and can be passed from mother to calf —> half of orcas may be lost in 30-50 years

What did the International Convention for the Regulation of Whaling (ICRW) achieve?

established the International Whaling Commission (IWC) to make decisions on quota levels of whales —> they ceased all commercial whaling in 1985

Polar Water Molecule

oxygen is highly electronegative —> water molecule is highly polar

Why is water known as the universal solvent?

has the highest dissolving power of any substance b/c polar water molecules separate ions (e.g. NaCl —> Na and Cl)

Hydrogen Bond

electrostatic attraction between partial positive and partial negative charges on adjacent polar molecules

What two opposing forces determine the structure of water in its three phases?

H-bond energy (weak bond energy that does not change strength) and thermal energy (breaks adjacent molecules, increases with increasing temperature)

Solid Ice characteristics

Low temperature limit (< 0 C)

E_thermal < E_hbond

Liquid water characteristics

Intermediate temps (0 - 100 C)

E_thermal = E_hbond

Water vapor characteristics

High temperature limit (> 100 C)

E_thermal > E_hbond