Fundamentals of Marine Biology

Marine biology

Introduction

Marine biology: study of organisms that live in the sea, all waters that have some degree of salinity. 75% of our planet is covered by water, so it is fundamental to understand this huge environment. This shows a lot of diversity in terms of ecosystem. Try to understand how different organisms adapt to live in this ecosystem. Marine biology is a diverse subject and nearly all disciplines of biology are represented. Marine biology (focusing on the perspective of the organism) is closely related to oceanography, which has different branches such as biological oceanography = from the perspective of the ocean. No real differences.

Main elements in marine biology

• Reproduction
• Locomotion
• Feeding

- Functional biology deals with

• Ecology, interaction of organisms with their physical and biological environment
• Biodiversity, how many species and how they evolve and interact with each other?

Why study marine biology?

• To date, scientists have scratched only the surface of the understanding of the marine environment
• Life has arisen in the sea: studying marine life provides clues about early life on Earth
• Many products come from the sea including food, molecules, raw materials
• The oceans help regulate climate and are highly affected by climate change
• The marine environment has a huge economic value, provides recreation, and supports tourism worldwide
• Some organisms harm humans and human activities directly or indirectly
• The oceans are overexploited, and several marine systems are facing serious issues

Marine life helps determine the very nature of our planet! Pure science, we just know the surface of the marine environment, the knowledge is increasing, but there is a lot we know nothing about. The ocean is fundamental for our planet and for us. Life has arisen in the sea: studying marine life provides clues about early life on Earth. Many products come from the sea, including food, molecules, and raw materials. The ocean helps to regulate our climate.

The 2030 Agenda for Sustainable Development

The 2030 Agenda for Sustainable Development, adopted by all United Nations Member States in 2015, provides a shared blueprint for peace and prosperity for people and the planet, now and into the future. At its heart are the 17 Sustainable Development Goals (SDGs), which are an urgent call for action by all countries in a global partnership. They recognize that ending poverty and other deprivations must go hand-in-hand with strategies that improve health and education, reduce inequality, and spur economic growth all while tackling climate change and working to preserve our oceans and forests. The 17 sustainable goals in the 2030 agenda for sustainable development. For us, the important number is 14: life below water. Strong need to carry out research, important to transfer marine knowledge and technology.

The world's oceans and the current situation

The world’s oceans and seas continue to struggle against increased acidification, eutrophication, and plastic pollution.

Historical background

Humans probably started learning about marine life from the first time they saw the ocean. Archaeologists have found piles of shells dating back to the middle Stone Age. Ancient harpoons and simple hooks have also been found.

Knowledge of the marine environments expanded as people gained skills in navigation. Ancient Pacific Islanders were expert mariners, using winds, waves, and currents to navigate over vast distances and had detailed knowledge of marine life. They produced maps made with shells and sticks to pass on information on their navigations. The Phoenicians were the first Western navigators. By 2000 BCE, they were sailing using astronomical knowledge around the Mediterranean Sea, Red Sea, eastern Atlantic Ocean, Black Sea, and Indian Ocean. Ancient Greeks also had extensive knowledge of the nearshore organisms of the Mediterranean Sea.

Herodotus (450 BCE) mapped the known world: a single ocean surrounding three continents. He invented the word ‘Atlantic’ to describe Western waters.

Aristotle (384-327 BCE) is considered by many as the first marine biologist, due to many important observations he made during his studies. For instance, he described several invertebrate and fish species, understood that cetaceans are mammals, that gills are the respiratory apparatus of fishes, and that marine vertebrates can be oviparous or viviparous.

Several other ancient naturalists brought important improvements in ocean knowledge, such as Hipparchus or Ptolemy (a detailed map including Europe, Asia, and Africa and the coordinates of several localities - 150 CE). Subsequently, Arabs inherited the knowledge of Greeks, Romans, and Phoenicians and dominated the seas, especially thanks to their knowledge of monsoons. Later, Vikings were incredible mariners and around 1000 sailed the Atlantic, probably reaching North America. The Ming Chinese dynasty were expert sailors and, thanks to their advanced technologies, were trading with Africa around 1400.

During the Renaissance period, in Europe, several exploratory expeditions reached Africa, Asia, and Americas. For instance, in 1519, Magellan left Spain for the first circumnavigation of the world, collecting information about different oceans. During this period, several technological advances and new instruments allowed a better comprehension of the ocean environment.

James Cook was one of the first explorers to conduct scientific explorations and host naturalists onboard. Between 1768 and 1779 he conducted three main voyages and explored almost all oceans. During his trips, he gathered information on ocean depth, temperature, currents, and winds and collected several plants and animals.

During the 19th century, some expeditions were completely dedicated to the scientific exploration of oceans. For instance, James Clark Ross and his uncle John Ross explored the Antarctic and Arctic oceans, respectively, and measured the seafloor up to 7000 m deep, also collecting organisms. Edward Forbes dredged the seafloor in the Mediterranean and Atlantic, discovering new species and discussing the influence of depth and temperature on marine life. He also made a first attempt to recognize different regions based on the depth, flora, and fauna.

One of the foremost ‘shipboard naturalists’ was Charles Darwin. He is best remembered for his evolutionary theories, but he also made important contributions to marine biology. During the voyage of HMS Beagle (1831-36), he made detailed observations of all aspects of the natural world, including oceans. For example, he explained the formation of atoll reefs, he studied plankton, and he spent 8 years working on barnacles.

Charles Wyville Thompson led the voyage of HMS Challenger (1872-76), the first purely scientific expedition. He also published one of the first oceanography textbooks (The Depths of the Sea). The Challenger was equipped with labs, dredges, and other sampling instruments and explored all the oceans, collecting information and samples of water, sediments, animals, and plants. It took 20 years and 50 volumes to publish all the results, including:

• 4717 new species discovered and described
• First maps of ocean temperature, depth, currents, sediments
• Proof of existence of life in the depths
• Measurements of several parameters in the water column (up to more than 8000 m deep)

The Challenger expedition, together with other voyages, laid the foundations of modern marine science. To study alive marine organisms and to understand their biology, naturalists began to work also from the shores. Eventually, biologists set up permanent laboratories to keep organisms over long periods. The first outpost was established in France, in 1859: Concarneau Marine Biology Station, followed by some others. For example:

• France (Roscoff - 1872, Banyuls - 1872, Villefranche-sur-Mer - 1882)
• Italy (Stazione Zoologica di Napoli Anton Dohrn - 1872, Stazione Zoologica di Trieste - 1875)
• England (Laboratory of the Marine Biological Society in Plymouth - 1879)
• US (Woods Hole Marine Laboratory)

During World War II, the SONAR (Sound Navigation Ranging) was developed for submarine warfare. This allowed for better characterization of the bathymetry of sea floors and to discover other sources of sound (animals). Learning about these animals became a matter of national security and several marine labs underwent rapid growth (especially in the US).

In the 50s, the first SCUBA (Self-Contained Underwater Breathing Apparatus) was developed by Emile Gagnan and Jacques Cousteau, allowing scientists to observe marine life directly underwater. SCUBA diving has subsequently greatly improved, now allowing divers to descend up to more than 300 m deep. Scientific diving is now widely used in several fields of marine biology. Both conventional and technical diving allow the direct collection of organisms, their observation in the natural environment, and the study of their ecology.

In order to reach the very depths of the ocean, in 1934 the first scientific submarine (the Bathysphere) was used by William Beebe to explore the sea floor off the coast of Bermuda (up to 922 m deep). This record was maintained until 1960, when the bathyscaphe Trieste, built by Auguste and Jean Picard, descended to the depth of 10916 m in the Mariana Trench. Another famous deep-sea submarine, Alvin, under the direction of Robert Ballard, explored several sea floors starting from 1964, allowing for example a better comprehension of the marine life of hydrothermal vents.

In the early days of marine biology and oceanography, ships were originally built for other uses and then converted to ‘scientific vessels’ (e.g., the Challenger). Modern ships are equipped with the latest equipment for navigation, sampling, and studying the organisms that are collected. Today many universities and other institutions operate research vessels. Additionally, a variety of other crafts are now widely used to study sea floors and marine life.

Remote sensing is widely used for both large-scale and local-scale studies. For instance, satellites can be used to measure chlorophyll concentration, surface temperature, currents, etc. Unmanned aerial vehicles can be useful for small-scale surveys.

The scientific method

Marine biology, like all sciences, depends upon a generalized scheme of observation and inference of the natural world: the scientific method. The scientific method depends on observation, induction, deduction, and prediction. Scientific conclusions must be based on observations rather than on preexisting ideas. Observations are the fundamental unit of scientific progress. Induction is the accumulation of specific observations to make a generalization.

By contrast, one can take some premises and use logic to make a prediction. This inference, based on logical associations of conclusions with facts and premises, is a deduction. This method of inference starts with general premises and uses a logical pattern of reasoning to draw some specific conclusions. Both induction and deduction lead to making a statement that might be true and that must be testable, a hypothesis. It must be possible to disprove a hypothesis before the hypothesis can be considered scientific, and in general, no scientific hypothesis can be absolutely proved true: there are no absolute truths!

In most cases, the conditions needed to test a hypothesis do not occur naturally and experimentation is required. In any natural situation, there would be countless factors (variables) that could influence the hypotheses to test. To prevent a variable from affecting an experiment there are two options: 1) to keep the variable from changing and 2) to ensure that any change is identical for all groups→ controlled experiment. A scientific theory is a hypothesis that has passed so many tests that it is generally accepted as true.

Eg: one barnacle species only in the high shore. Use of general principles to attempt to explain the observation: starfish predation, which occurs only in the lower shore, prevents barnacles from surviving. Starfish has a sluggish movement and has no time to reach the high shore. How to test: cages to prevent predation but allowing barnacles to function normally. No effect of caging on high shores and low shores: compare caging with controls.

Experiment:

• Cage on the lower shore
• Cage on the high shore (ctrl 1)
• Follow open areas in both levels (ctrl 2)
• Cage with no sides (ctrl 3)
• Cage with no roof (ctrl 4)

Study statistics.

World oceans

Earth is a water planet. Close to the continents: a few hundred meters deep (continental shelf), with the exception of Antarctica (up to 1,000 m deep). Half of the Earth's surface is covered by oceans nearly 4,000 m deep. The greatest depth is about 11,000 m, in the Mariana Trench. The oceans are classified in five/four main basins:

• Pacific Ocean
• Atlantic Ocean
• Indian Ocean
• Arctic (+ Southern Ocean)

Several shallow seas are connected or marginal to the main basins.

Pacific Ocean

Born 750 mya. Even if it is generally called the Panthalassic Ocean until the breakup of Pangea (200 ma). Largest (155,557,000 km² - mean: 4,188m). From the Bearing Sea to the Southern Ocean: 15,500 km and from Indonesia to Colombia: 19,800 km. Currently shrinking by 2.5 cm/year. 20-30,000 islands (divided in Micronesia, Melanesia, Polynesia). SST: -1,4°C to ~30° C Salinity: 32-37 ppt.

Atlantic Ocean

The break-up of Pangea generated the Central Atlantic 170-200 ma. The opening of the Northern and Southern Atlantic occurred later. Second largest (76,762,000 km² - 15.1% of Earth’s surface) Max depth: 8,605 m (Puerto Rico Trench) - mean: 3,736 m. Several large marginal seas. Currently expanding ~2.5 cm/year. SST: -2°C to ~29° C Salinity: 33-37 ppt.

Indian Ocean

Second youngest of the main oceans: many active spreading ridges. Third largest (68,556,000 km² - 13% of Earth’s surface) Max depth: 8,047 m (Diamantina Trench) - mean: 3,872 m. Second least-islands-containing ocean: only 1,500-2,000 islands. Warmest ocean (30+ °C) Salinity: 32-37 ppt.

Arctic Ocean

Smallest, shallowest, less salty ocean. Partially to almost completely covered by sea ice. Smallest (14,056,000 km² - 2.8% of Earth’s surface) Max depth: 5,608 m (Molloy Deep) - mean: 1,330 m. SST close to sea water freezing point. Salinity and temperature vary seasonally.

Southern Ocean

Youngest ocean (~30 ma). Fourth largest (20,327,000 km² - 4% of Earth’s surface) Max depth: 7,236 m (South Sandwich Trench) - mean: 4-5,000 m. Least-islands-containing ocean. SST: -2 to 10 °C. Salinity is currently decreasing.

Marginal seas

Marginal sea: sea bordering continents, semi-isolated from the open ocean by island arc or land ridge. In geopolitics, a marginal sea corresponds to a territorial water. Sources differ over which seas are considered marginal. There is no ultimate decision. Many marginal seas have unique oceanographic characteristics due to restricted connections and usually shallow waters.

Structure of the ocean floor

Geological processes shape the Earth: the planet Earth originated about 4.5 ba by a dust start to collide, big bang. This led to the formation of the solar system. The internal structure of the earth reflects the planet’s early beginnings. – Three layers: Core (inner and outer) – Mantle (lower and upper) Crust (oceanic and continental). The oceanic is composed of basalt, is denser and younger than the continental that is thicker, composed of granite. Chemical and physical composition and characteristics of the crust differ greatly between the oceans and the continents. The oceanic crust is denser, thinner, younger than the continental crust.

Francis Bacon (1620) noted that the E and W coasts of the Atlantic fit together. Alfred Wegner (1912) proposed the first detailed hypothesis of continental drift: all the continents had once been joined in a single supercontinent (Pangea) and the Panthalassa is the Ocean. He did not understand how continents move. In the 50s and 60s, scientists concluded that the continents drift was real, as part of plate tectonics. This process involves the entire surface of our planet. This happens on the whole planet.

After WWII, the use of sonar allowed the discovery of the mid-ocean ridge system. At regular intervals, the mid-ocean ridge is displaced to one side or the other by cracks or transform faults. Occasionally the submarine mountains of the ridge break the surface to form islands. There is also a system of deep depressions in the sea floor, called trenches. The geological activity is concentrated around the mid-ocean ridge. Earthquakes are clustered at the ridge, and volcanoes are associated with trenches. Sea-floor rock at the ridge is very young and gets progressively older moving away from the ridge. At the ridge crest, there is little if any sediment. Sediments get thicker at greater distance from the ridge. The deepest sediment gets older away from the ridge.

The earth’s magnetic field periodically reverses direction (in avg every 700 k.a.). Basalts come out from the ridges and solidify in different magnetization. Rocks contain magnetic particles that are ‘frozen’ and maintained in their orientation when the rock cools. Sea-floor rocks have patterns of magnetic bands (or magnetic anomalies), that run parallel to the mid-ocean ridge.

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: crust + uppermost part of the mantle (about 100 km thick) Lithospheric plates: oceanic crust, continental crust, or both Asthenosphere: dense, plastic layer of the upper mantle on which the lithosphere floats.