Appunti Fundamentals of Marine Biology

Fundamentals of marine biology

Oral test and exam dates

Oral test regarding both lessons and tutorials. Date of exams: 1/2/22, 28/2/22, 22/4/22.

Introduction

Marine biology is the study of organisms that live in the sea (all water that has some degree of salinity, e.g., estuaries). In the ocean, there’s an incredible variety of organisms. It’s important to know the differences and similarities between different ecosystems. It’s difficult to define what is actually marine biology, because it includes many disciplines different from among them. Marine biology is different, but related, from biological oceanography (from the perspective of the ocean). The main elements are:

• Functional biology (function of the organisms Ex. Adaptation of a kelp forest)
• Ecology (interactions)
• Biodiversity (How many species? How did they evolve, arise?)

There are many reasons why it is important to study the ocean (see slide). We have just scratched the surface of the understanding of marine environment. The ocean is full of resources, like fish, molecules (bioactive compounds, used in everyday life), raw materials. It is also important for tourism (21 million dollars every year).

Historical background

Humans started to learn about the ocean when they first saw it. Archaeologists have found many fossil shells back from the Stone Age: this means humans used to use material coming from the sea. They used them for more than food (necklace, weapons…).

Fun fact: In ancient Egypt, there were signals saying not to eat pufferfish.

Ancient Pacific islanders were expert mariners; they also produced maps (a way to transfer knowledge). Phoenicians were the first Western navigators, using astronomical knowledge. Ancient Greeks had an extensive knowledge of marine life, quite precise at reproducing fish. Herodotus mapped the world, inventing the term Atlantic (back then, they knew just one continent, see map). Aristotle is considered the first marine biologist, describing vertebrates and invertebrates, and knowing that cetaceans were mammals. Other people, like Arabs, Vikings (probably reached North America, way before Columbus), and Chinese (Ming dynasty), had a similar story with the ocean.

During the Renaissance period, we have many expeditions, like the one of Magellan and the one of James Cook. During the 19th century, some expeditions were completely dedicated to scientific research. Examples include James Clark Ross and John Ross, Edward Forbes, and Charles Darwin—voyage with HMS Beagle.

The first purely scientific expedition was made by C. W. Thompson, voyage on HMS Challenger. (4717 new species discovered, new parameters for the ocean, proof that life exists in deep sea). This expedition laid the foundations of modern marine science.

In order to study marine biology, it’s required to have a base on the shore permanent marine laboratory in France, Italy, England, and the US.

During World War II, the SONAR was developed as a weapon. This allowed for better characterization of the bathymetry of the sea floor. They also understood that some animals can use a similar system (like some mammals, e.g., Beluga).

In the 50’s, the first scuba was developed by Emile Gagnan and Jacques Cousteau. Scuba diving is sometimes not enough, so submarines to discover the deep sea were invented. The first one was called the Bathysphere. Modern ships are equipped with the latest equipment for scientific research. Many other instruments used are ROV, AUV (not connected to remote, free to move), buoy. Animals also can be used for research, used as AUV (recording sensors). Also, satellites are important for the study of marine biology (ex. Currents, chlorophyll concentrations) just like drones.

Scientific method

The scientific method depends on observation (fundamental unit of the method). Induction is the accumulation of observations to make a generalization. Prediction is made by using logic and premise. This inference, based on logical associations of conclusions with facts and premises, is a deduction. Both induction and deduction lead to making a statement that might be true and that must be testable, a hypothesis. Sometimes experimentation is required to test our hypothesis. The experiment has to be controlled in order to prevent a variable from influencing. Control groups are very important. Statistics are largely used in analysis.

World Oceans

Earth is a water planet. Close to the continents, the depth of the ocean is a few hundred meters deep (except from Antarctica where it is 1000m deep). The Oceans are classified in 4 main basins:

• Pacific Ocean: the oldest (called like this after the break of Pangea, but way older, f.k.a. Panthalassic, born 750 mya) and the largest and deepest. From the Bering Sea to the Southern Ocean 15500 km, it is currently shrinking, cm every year. It contains 20-30000 islands (Micronesia, Melanesia, Polynesia).
• Atlantic Ocean: the deepest point is shallower than the one in Pacific Ocean. Second largest, born with the Pangea break. Currently expanding.
• Indian Ocean: second youngest, third largest and shallower than Atlantic Ocean. Contains only 1500/2000 islands, it’s the warmest ocean.
• Arctic Ocean: the smallest ocean, shallowest and less salty. Partially to almost completely covered by ice. Salinity and T vary seasonally.
• Southern Ocean: is the youngest one, fourth largest and least island containing. Salinity is currently decreasing. Seasonal variation.

They are all actually connected. There are also many marginal seas, like the Mediterranean; they border continents, semi-isolated from open ocean by island arc or land ridge. It is a not universal definition and in geopolitics, they correspond to territorial water. They have different characteristics.

The structure of the ocean floor

Planet Earth originated 4.5 billion years ago. After the big bang, particles started to collide and form. The early Earth was a very hot environment, the material started to settle according to density. Material started to cool down and solidify forming the crust. Three different layers can be identified:

• Centre core can be divided into inner core (which is solid and hotter) and outer core (which is fluid and colder than inner).
• Mantle can be also divided into lower and upper. The mantle is solid but behaves as a fluid (a viscous one). Upper mantle can be divided into asthenosphere and lithosphere.
• Crust is divided between oceanic crust (made of basalt) and continental crust (made of granite).

Francis Bacon noted that the Eastern coast and Western coast of the Atlantic fit together. A. Wegner in 1912 proposed the hypothesis of continental drift (at first it was not accepted because he didn’t say how they move and the cause of movement). In the 50’s and 60’s, scientists proposed a cause, plate tectonics. The use of sonar allowed the discovery of mid-ocean ridge systems (transform faults).

There is also a system of deep depression called trenches. Geological activity is concentrated around mid-ocean ridge and trenches. Volcanoes are associated with trenches. Crust around the mid-ocean ridge is much younger than the other crust. This is because there happens the formation of new crust.

Magnetic field of our planet periodically changes direction (small amount of time geologically speaking). When magma comes out of the middle ocean ridge, it freezes so magnetic particles contained inside this rock show what was the direction of magnetic field when they froze. This can be considered as a proof of the continuous forming of new rocks.

Pieces of oceanic crust are separating at the mid-ocean ridges, creating cracks in the crust called rifts. When a rift occurs, it releases some of the pressure on the underlying mantle. This allows hot mantle material to melt and rise up through the rift. The ascending magma pushes up the oceanic crust around the rift to form the mid-ocean ridge. When it reaches the earth’s surface, it cools and solidifies to form new oceanic crust. The entire process is called sea-floor spreading, and the ridges are called spreading centers.

Lithosphere is formed by crust and the uppermost part of the mantle. It can be divided into lithospheric plates. Every year Pacific is shrinking, Atlantic is expanding. Trenches are where crust is destroyed. Trenches can be formed in different ways, based on which types of plates are colliding.

• Continental and oceanic—it forms an area where the geological activity is huge, like in Andes.
• Two oceanic plates—there can be formation of an island made from a volcano.
• Sometimes two plates can cause no destruction. This is called a shear boundary (ex. San Andreas, in California).

The cause of movement can be convection heat from the Earth’s core causes the movement of the mantle. But this is just one of the causes. The main accepted hypothesis is that oceanic lithosphere cools as it ages, becoming denser. It sinks into the mantle, forming a trench. The movement of lithosphere is dominated by plate tectonics. The ocean floor can be divided into continental margins (submerged parts of the continent can be divided into continental shelf, shelf break, continental slope, continental rise) and deep-sea floor.

Continental shelf: makes up about 8% of the ocean surface. Is composed of continental crust. In the past it was outside the water, it can present canyons caused by the past presence of rivers. It is a gentle slope. The width can be quite variable. It ends with a shelf break that occurs at depths of 120 / 200 meters.

Continental slope begins at the shelf break.

Continental rise is the place where we have accumulation of sediments in a zone called deep-sea fan.

We may have both active and passive margins.

• Active ex. South America. Formation of a trench between an oceanic plate and a continental plate. On the coastline, these processes give active margins steep, rocky shorelines, narrow continental shelves, and steep continental slopes.
• Passive: no trenches. Geological activity is much lower. It is not a boundary between two plates. They typically have flat coastal plains, wide shelves, relatively gradual continental slopes. Because there are no tectonic processes to remove it, sediment accumulates at the base of the continental slope: passive margins therefore usually have a thick continental rise.

Deep ocean basins are a part of the deep sea floor. The deep sea floor is not homogeneous. Many structures can be found, like trenches, volcanic islands (sea mounts), guyots…

The Middle oceanic ridge is a particular structure. It is formed of a central rift valley. Water is able to enter the fracture and arrives at the mantle, it heats up and causes the formation of hydrothermal vents when it comes out. Then it cools down, releasing all of the minerals, leading to the formation of the black smokers.

Other types of vents were discovered but the water coming out is cooler, they are near the ridge but not on the ridge and chimneys are formed by carbonate. Many organisms can live near these chimneys, like many polychaetes.

History of the Earth

• 200 million years ago, all the continents were joined in a supercontinent Pangea. Antarctica was approximately the same place it is today. The sea was called Panthalassa. Tethis sea was the richest in life part of the ocean.
• 180 million years ago, a new rift appeared: birth of North Atlantic Ocean. Pangea is now divided into Laurasia and Gondwana.
• 135 million years ago, the birth of the Southern Atlantic Ocean. Formation of a single mid ocean Atlantic ridge. Later North America, Greenland, and Europe separated. India continued to move North until it collided with Asia forming the Himalayas.

This knowledge is important when working with organisms. Fossils of some organisms can be found both in Africa and America, this because these two were once united.

Sediments are an important type of proof, information. They can be:

• Lithogenous, derived from the chemical breakdown of continental rocks (weathering).
• Biogenous, are shells of marine organisms like diatoms, radiolarians, foraminifers, and coccolithophorids. Calcareous ooze—skeletons made by CaCO₃ (coccolithophorids) and siliceous ooze—skeletons made of SiO₂ (Radiolarians).

Pteropods (shell made of aragonite)—animal that can contribute to biogenous sediment. Biogenous sediment is called microfossils—each particle corresponds to the remain of a dead animal/organism. We can obtain from them information about the climate of the past. A method used to date microfossils is carbon dating. It is also possible to say the temperature of the water by measuring ratios of Mg to Ca, or Sr to Ca. (Mg is incorporated into Ca and this reaction is endothermic so heat is needed to have this process. If this process happened, we know that the temperature was higher. Instead, Sr to Ca happens in the other way so we have this process when the temperature was low) or different isotopes of O₂.

Chemical and physical properties of seawater

Water has a high specific heat, just like the heat of vaporization and the highest latent heat of melting (high because of hydrogen bonds). It is a universal solvent, good at dissolving salts. Some of the solids dissolved derive from weathering, others come from Earth’s interior, others are released in the atmosphere by volcanoes.

Salinity: grams of dissolved inorganic solids per thousands grams of seawater (parts per thousand - ‰) Generally measured as practical salinity unit (psu or S): electrical conductivity of the seawater relative to a standard KCl solution at 1 atm and 15°C. psu is nearly identical to ‰. Even if we have variations of salinity, we have ions that are present with the same proportions (Rule of constant proportions).

Residence time: avg time that a unit of weight of a substance spends in the ocean before being lost to sediments or continents. Categories are: major elements, minor elements, and trace elements. Estimate salinity can be measured as chlorinity or conductivity. Average salinity is 35‰. This data can change in different portions of the sea (ex. Red sea and Baltic sea). Latitudinal variation in the balance of evaporation and precipitation causes salinity maxima at 30° N and S, and minima at the equator and higher latitudes.

Temperature is very variable according to latitude and depth. Closed to the poles and variations are less. Temperature is very important because with salinity it influences density, which is correlated to currents and movements of organisms.

There are gases dissolved in the ocean, like O₂, CO₂, and N₂. Gases dissolve better in cold and less salty water. The amount of these gases is also influenced by biological activities. Bottom waters are generally oxygenated by mixing with other shallow waters. In some water bodies, the supply of organic matter outstrips the role played by mixing waters. The vertical structure of the water column influences local oxygen concentration.

Another important parameter is that it is transparent. Water can travel along water column. Transparency is strongly affected by materials suspended and by plankton. Much of the light is absorbed or scattered.

Pressure changes dramatically with depth. Water is much heavier than air. 1 atm every 10 m. Many species are not adapted to abrupt changes of pressure. The fish in the picture have the internal organ expanded, after it was fished and took on the surface too rapidly: gas tends to expand when the pressure decreases abruptly. Some organisms are able to adapt to this type of changes, like sperm whales.

Life in the seawater

Seawater has several properties: the main ones to consider when we want to understand the effect on organisms are temperature, salinity, oxygen, light, density, and viscosity. These last two influence the general pattern of the ocean. Organisms have adapted to different conditions.

• Temperature: affects latitudinal distribution of most marine species. Organisms can be divided into homeotherms (regulate body temperature) and polikilotherms (not able to do it). There are fish able to regulate their body temperature, like fast swimming fishes (tuna). We can also divide them into stenotherms (can face little thermal variation so their position in the water column is quite limited) and eurytherms. Some animals living in cold areas can slow down their metabolism. In other organisms, temperature influences the sex of newborns.
• Salinity: changes in salinity may occur seasonally. Organisms must control the chemical composition of their body. Many of them can expel salt or may use diffusion. We can divide organisms between osmoregulators and osmoconformers. Stenohaline can face little salinity variation while Euryhaline can face large salinity variation. The most variations in salinity can be found at the pole, after the melting of ice.
• Oxygen: the level of O₂ is quite variable in the water column and according to latitude. Missing of the currents influences the presences of the oxygen. We can divide organisms into five categories: Obligate aerobes, facultative anaerobes, microaerophiles, aerotolerant anaerobes, obligate anaerobes.
• Light: solar energy is the main source of heat in the ocean and fundamental for photosynthesis. Most of the photosynthesis occurs in the first few meters of the ocean. The deep sea instead may live thanks to production (?). In the deep sea, many organisms can produce light by themselves.
• Density influences the movement of the water, like viscosity, so the movement of organisms. Primary effects are the primary results on the organisms (ex. Water velocity and turbulence), Secondary effects influence food, oxygen, and nutrients. Physical properties of water are different from the ones of atmosphere: density (ρ) = mass per unit volume (salts make seawater denser than the freshwater); dynamic viscosity (η) = measure the stickiness between the layers of the fluids; kinematic viscosity (ν) = stickiness under the influence of gravity.

In any fluid, there are two basic forces: viscous forces (keep the fluid together) and inertial forces (tendency of a moving object to continue moving when no force is applied to it). Reynolds number (Re) measure the relative importance of inertial and viscous effects of a fluid and on objects in a fluid. If the Re>> inertial forces dominate, if Re << objects do not move unless we apply a force. Velocity can be measured following two approaches: object fixed to the bottom in a moving fluid...