Life in the Ocean

• All living things grow, metabolize, react to the external environment and reproduce

– Organisms need energy and ingredients• Energy: the ability to do work

– Metabolism: process by which organisms gain energy from the external environment.

• The ingredients: Biomolecules– Carbohydrates, Proteins, Lipids, Nucleic

Acids

Photosynthesis and Respiration

Nutrients

• Materials needed to make biomolecules.– Raw materials are nutrients, and they include

minerals, vitamins, and other inorganic compounds• Nitrogen and Phosphorus are usually the most important

nutrients in the marine environment.• Often called limiting nutrients because without them they

limit productivity.– Nitrate (NO3-1), the most important form of nitrogen, is used

in making proteins and nucleic acids

– Phosphate (PO4-3), the most important form of phosphorus, is used in making phospholipids, ATP and DNA.

Primary Production

• Sugars produced by photosynthesis are raw material for the other organic compounds, such as lipids, proteins and nucleic acids.

– When autotrophs produce more organic matter than they use, there is an overall gain in organic matter.

– This net increase is called primary production, and it is this primary production that supplies all the heterotrophs, i.e. animals, with food.

Challenges of Life in the Ocean

• Lack of substrate– They are at constant risk of sinking– They are constantly being thrashed around

by mixing.

Challenges of Life in the Ocean

• Transparency of seawater– Adequate light for photosynthesis only exists

in the upper part of the ocean, in a region known as the euphotic zone,

• ranges from 10-200m in depth.• The euphotic depth is the depth at which light

levels are 1% of surface light, which is considered to be when light becomes limiting for photosynthesis.

Challenges of Life in the Ocean

• Lack of Nutrients– Most of the nutrients in the ocean are below

the euphotic zone.• Where there is enough light, there often aren’t

enough nutrients for primary production

Temp, O2, Nitrate Profiles

Global Nitrate Profiles

Global Primary Productivity

Phytoplankton

• Phytoplankton (plant-wanderer) are the primary producers in the open ocean

– They range in size from 1 - 100m (there are 1000 m in a mm)

– The smaller you are, the less you sink.– When you are that small, you can be thrown around by

breaking waves and it doesn’t affect you at all.– When you’re that small you have a higher surface-to-volume

(S/V) ratio, which increases your ability to pick up nutrients, which may be in very low concentrations. » The larger the organism, the smaller the S/V ratio, the

smaller the organism, the larger the S/V ratio.– Being that small you tend to reproduce quickly, so that your

numbers can increase rapidly under the right circumstances.» During a phytoplankton bloom, some cells will divide as

much as 3 times per day.

It’s Good to be Small

• The smaller you are, the less you sink.

• When you are that small, you can be thrown around by breaking waves and it doesn’t affect you at all.

• When you’re that small you have a higher surface-to-volume (S/V) ratio, which increases your ability to pick up nutrients, which may be in very low concentrations.

Phytoplankton Reproduce Exponentially

• Being that small you tend to reproduce quickly, so that your numbers can increase rapidly under the right circumstances.– During a phytoplankton bloom, some cells

will divide as much as 3 times per day.

Plankton• Greek for Wanderer or Drifter• Organisms that can’t swim against a

current• Usually small

– Picoplankton: 0.2-2 μm– Netplankton: >20 μm

• Types– Phytoplankton– Zooplankton– Protists

Phytoplankton

• Greek for Plant Drifter

• Vary in size from 1-100 μm

• Grow very fast– Cells divide as much as 3 times/day

• Make own food but need – Light, Nitrogen, Phosphorus

• Examples– Diatoms, Dinoflagellates

Dinoflagellates

Diatoms

Zooplankton

• Animal Wanderer

• Holoplankton: plankton their entire lives– Ex: Copepods

• Meroplankton: planktonic part of their lives– Ex: Fish, crabs, lobster, barnacles

• Need to eat other things

• Examples– Copepods, Protozoans, Pteropods, Jellies

Copepods

Protozoans

Pteropods

Jellies