The Microbial World

Introduction We begin our survey of ocean life with the smallest of marine organisms, the bacteria and archea. Both groups contain members which are capable of photosynthesis and are known as primary producers. These primary producers are responsible for directly or indirectly feeding most marine organisms.

From the largest… Whale shark, Rhincodon typus

To the smallest… Octopus larvae

Prokaryotes The first organisms we will consider will be the prokaryotes. Prokaryotes are the smallest, simplest (and oldest) organisms around. Unlike other animals we will study, prokaryotes lack a nucleus. Two main categories of prokaryotes are Archea and Bacteria

Other shapes include rods, rings and spirals. Marine bacteria take on many shapes, including spheres such as Thiomargarita namibiensis, a benthic bacteria which can be seen with the naked eye. Other shapes include rods, rings and spirals. Some may form into large calcium containing mounds (stromatolites). Still others break down organics and cycle nutrients. Stromatolites, Exuma Cays, B.I

Life and Death Perhaps one of the most interesting evolutions of bacteria concerns the development of bioluminescence and toxins (tetrodotoxin). Whether used as a flashlight fish’s trick for attracting prey, or giving a good buzz to your fugu sushi, bacteria occupy some amazing niches in the marine world!

Cyanobacteria: Red Tide Planktonic species, such as cyanobacteria (which can cause red tides), often multiply very rapidly. They contain red pigments! Red tides (Karenia brevis)- can be caused by dinoflagellates too (photo).

Archaea: Extreme Conditions Archaea are similar to bacteria, but they are able to tolerate conditions most other bacteria wouldn’t be caught dead around... okay, maybe they would be caught dead here! Some are able to tolerate temperatures near hydrothermal vents (176°F, 80°C).

Prokaryotic Metabolism

How do you eat?? Many bacteria (autotrophs) are perfectly capable of feeding themselves, making their own organic compounds by photo- or chemosynthesis. Bacterial photosynthesis can be different than that found in plants (i.e. you might produce S instead of O2). Some autotrophs which produce methane as products are being used to meet our energy needs.

Bacteria which utilize other sources of carbon (organics) to exist are known as heterotrophs. Many heterotrophs are involved in decay processes and some even exist in anoxic (no O2) conditions. Still others are actively fixing nitrogen from gas to molecules which other animals can use as food during primary production.

Unicellular Algae Being composed of one cell isn’t an evolutionary dead end. Algae, Diatoms, Dinoflagellates, and Radiolarans all have been around for millions of years (if not billions). Being eukaryotic, unicellular organisms such as these use a variety of methods to eat, metabolize, and reproduce. As a group these organisms are known as Protist!

Diatoms contain many organelles that enable them to exist under potentially harsh conditions. Most diatoms consist of strikingly delicate outer shells of SiO2 (frustules) which provide limited protection and light penetration.

Diatoms reproduce asexually (cell division) and sexually (auxospore), depending on external conditions.

located within the groove and the other Dinoflagellates exhibit two flagella which permit movement. Theca One flagella is located within the groove and the other is located at the lower end (not visible). Groove Dinoflagellate, Gonyaulax polyedra

Slilicoflagellates are characterized by star-shaped internal skeletons Slilicoflagellates are characterized by star-shaped internal skeletons. Some may be used for aging marine sediments.

Still others, like these Coccolithophorids, are surrounded by shells of calcium carbonate (CaCO3) and are responsible for significant primary production! Umbilicosphaera sibogae

Some eukaryotes are more like animals than like plants! In fact, having a single cell is about the only thing that these critters have in common with other eukaryotes we have observed. Foraminiferans and radiolarans utilize specialized pseudopodia (spine-like projections) to capture food.

The outer shell, or test, is made of CaCO3 and serves as a protective structure.

Ciliates are protozoans which utilize cilia for feeding and in some cases locomotion.

Bahia Fosforescente, Puerto Rico At night this bay is illuminated by Pyrodinium bahamense, a phosphorescent dinoflagellate.