5.1 Biodiversity
In preceding sections, we have seen the main characteristics of the Mediterranean Sea and which are the most important factors that impact marine life and habitats. In this section we’ll explore the concept of marine conservation, its implication and tools, but in order to do that we need to do a step back and understand what we care to conserve: the biodiversity, and the function and services the ecosystems provide.
The term biodiversity has become a common expression in science, media and government lexicon on a global scale over the last 20 years (Fig.1_Ses5.1_Biodiversity Hall, American Museum of Natural History, New York_Wikimedia Commons).
Biodiversity or biological diversity is the variety of life, in all of its manifestations. A longer and more formal definition is given in Article 2 of the international Convention on Biological Diversity (1992 Rio Earth Summit), which states that “Biological diversity means the variability among living organisms from all sources including, inter alia, terrestrial, marine and other aquatic ecosystems and the ecological complexes of which they are part; this includes diversity within species, between species and of ecosystems” (Fig.2_Ses5.1_Biodiversity cloud). It encompasses the variety of species (both plant and animal) but also the variety of genes within those species and the variety of ecosystems in which the species reside. So that biodiversity can be divided for convenience in three groups: genetic diversity, organismal diversity and ecological diversity.
The Earth is predominantly blue ocean but the is not yet an adequate understanding about the biodiversity of many marine habitats. The total area of seabed explored by humans represents an infinitesimal fraction of the total. Emblematic are the data collected by the Census of Marine Life (CML) over the past 10 years (www.coml.org). The CML was a global network of researchers, nearly 3000, in more than 80 nations engaged in a 10-year scientific initiative to assess and explain the diversity, distribution, and abundance of life in the oceans. Their results indicate that there are approximately 250’000 marine (non-microbial) species formally describe in the scientific literature with as many as another 750’000 species not described.They also estimate that there may be more than a billion types of microbes living in the oceans!
Another example is the marvellous underwater life of the tropical coral reefs (Fig.3_Ses5.1_Tropical coral reef_Wikimedia commons) where hundreds of epibenthic invertebrates’ species are known, but many other species are un-described, and probably even more remain undiscovered.
Biodiversity is not evenly distributed; rather it varies greatly across the globe, from tropical to temperate areas, as well as within regions. The Mediterranean Sea is one of the main eco-regions of the planet and due to its high biodiversity it is among the most important ecosystems in the world. It is considered a “biodiversity hotspot” (sensu (Myers et al. 2000): an area where exceptional concentrations of endemic species are undergoing exceptional loss of habitats.
The Mediterranean natural environment is a combination of geomorphological and climatic factors. Its biological diversity is mainly due to the adaptation of many species to the hot and dry summers (e.g. Astroides calycularis, Fig.4_Ses5.1_Astroides calycularis_Eva Turicchia) and to the mild winters that characterize temperate climate. The high primary productivity, due to the movements of cold water masses in the basin, also contributes to its high biodiversity: the wind and the currents put the nutrients back into the water column making them available for the planktonic organisms, the first link in the food chain.
Biodiversity is the result of 3.5 billion years of evolution and it changes every day. The total biomass is constant but it is the contribution of the species that changes across the years. Conservation of biodiversity is one of the major focuses of recent conservation efforts.
Myers N, Mittermeier RA, Mittermeier CG, da Fonseca GAB, Kent J (2000) Biodiversity hotspots for conservation priorities. Nature 403:853
5.1.1 The main objectives of the Convention of Biological Diversity.
The Convention on Biological Diversity (CBD), known informally as the Biodiversity Convention, is a multilateral treaty. The Convention is the first agreement to address all aspects of biological diversity: species, ecosystems and genetic resources. It is indeed the first time that genetic diversity is specifically covered in a binding global treaty that was signed in 1993.
The objectives of the Convention on Biological Diversity are expressed in its article 1: the conservation of biological diversity, the sustainable use of its components, and the fair and equitable sharing of the benefits arising out of the utilization of genetic resources, including by appropriate access to genetic resources, transfer of relevant technologies and funding. Another important point of the Convention is the recognition that all humanity has interest in ensuring the conservation of biological diversity, including poor nations, women and indigenous people, and that it needs to be addressed by coordinated international action. The second article of the Convention of Biological Diversity talks about the variety of species but also the variety of genes within those species. In particular the Article 2 gives us the definition of biological diversity which says that “Biological diversity means the variability among living organisms from all sources including, inter alia, terrestrial, marine and other aquatic ecosystems and the ecological complexes of which they are part; this includes diversity within species, between species and of ecosystems”. So, this treaty besides giving us an encompassing definition of biodiversity, teaches us how be a good human being.
5.1.2 The definitionof genetic diversity.
Genetic diversity is one of the biodiversity groups, along with the organismal diversity and ecological diversity. In particular, genetic diversity, is the total number of genetic characteristics in the genetic makeup of a species. It is distinguished from genetic variability, which describes the tendency of genetic characteristics to vary.
The genetic diversity is mainly due to the mutations that lead to the formation of new alleles. The recombination remixes the alleles by creating new allelic combinations in successive generations. Mutation can take place in every moment of the life of an organism but they will be transmitted only if they interest the cells of the germinal line or the gametes. This process takes place during meiosis in two ways: following the third law of Mendel, the maternal and paternal chromosomes contained in a meiocyte are divided into the gametes in equal portions, or through the crossing-over, the phenomenon by which a paternal chromatid exchanges parts of the chromosome with the maternal one.
This variation is also given by the action of the environment on the organism which can lead to changes that will be transmitted to the following generations. The variation is usually distinguished in continuous and discontinuous variation. The discontinuous variation is linked to characters for which there is a finite and limited number of phenotypes. The continuous variation concerns those characters with a very high number of phenotypes. Scientists have counted more than 100 million variations, but the high rate of endangered species can lower this value a lot.
5.1.4 Ecological diversity: an explanation.
First of all, you should know that biodiversity comprehends different varieties of nature's aspects, and one of its branches is ecology.
To give you an idea of what it could possibly be, let's have a look at the word's etymology. The word "Ecology" comes from the Greek word "oikos" (house) so if you think about that, it deals with the natural habitats (both terrestrial and aquatic) of all living organisms.
The term diversity can also be divided into more precise measures: by itself, "diversity" can be a little bit vague. We can talk about species richness, for instance, which is essentially the number of species in a given area and also about species evenness.
The more it is looked at, the less clearly defined it appears to be, and viewing it from different angles can lead to different perceptions of what is involved. The problem has been exacerbated by the fact that ecologists have devised a huge range of indices and models for measuring diversity. Perhaps as a result of these, diversity has a knack of eluding definition and in one instance S.H. Hurlbert even went so far as to define it as a ‘non-concept’. Even though it may be hard to comprehend it at first, we can still try to classify it. We have different kind of ecology interpreted in terms of habitat, the main ones being oceans, seas, deserts, savannas, wetlands, forests, grasslands etc.
Ecological diversity maintains Earth natural state because of the photosynthesis that purifies the air and some marine plants that purify the water; some plants are also used for medical purposes.
Because of how important the variety of ecosystems are, we should take care of the environment and nature around us. Ecological diversity is, in fact, in danger: just think that a lot of species are in extinction because of the climatic change, deforestation and so on.
To prevent ever more terrible situations some environmental non-governmental organizations,such as WWF and Greenpeace, have been founded.
5.1.5 Define the concept of habitat and name at least 3 different marine habitats.
In ecology, a habitat is the natural environment of an organism; a place that is natural for its life and growth, and that is characterized by both physical and biological features.
The main marine habitats are:
-Littoral zone: the part of a sea or lake or river which is close to the shore.
-Intertidal zone: the area that is above water and underwater at high tide.
-Estuaries: an area where seawater mixes with freshwater.
-Kelp forests: underwater areas with a big density of kelp.
-Coral reefs: underwater ecosystem characterized by corals, colonies of coral polyps .
-Ocean banks:part of a seabed,Ocean banks may be of volcanic nature.
In general marine habitats can be divided into coastal and open ocean .
Coast habitats are found in the part that is from as far as the tide comes in on the shoreline out to the edge of the continental shelf. Marine life is found in coastal habitats, even though the shelf area occupies only seven percent of the ocean zone.
Open ocean habitats are in the centre of the oceans, these are, in descending order by area, the Pacific, Atlantic, Indian, Southern (Antarctic), and Arctic Oceans, beyond the edge of the continental shelf.
Marine habitats can be very different from each other, they are influenced by many factors, one of them the water temperature.
Tropical water has coral reefs full of tiny, colourful fish while waters in the polar regions have many species that have adapted to water that can be colder than the temperature that water normally freezes, such places support many newly discovered marina microorganisms and other lifeforms that have adapted to the conditions.
5.1.6 Define endemic species and provide an example for the Mediterranean Sea.
Endemic species are plants and animals that exist and live in only one specific geographical area.
The word endemic is from New Latin endēmicus, from Greek ενδήμος, endēmos, "native".
Some species can be endemic to large or small areas: some are endemic to a particular continent (for example the armadillo is endemic to America), some to a part of a continent and others to a single island. Endemism is more common in some regions than in others for example in areas that have unusual environmental characteristics or areas that are isolated in some way so that the species have difficulties spreading to other areas, such as Hawaiian Islands, Australia and the southern tip of Africa. In less isolated regions, like Europe and North America, there aren't many endemic species.
Physical, climatic, and biological factors can contribute to endemism.
Endemics can easily become endangered or extinct if their restricted habitat changes.
In the Mediterranean Sea we find around 25000 species of plants. More than half of them are endemic species. There are almost 2000 endemic species of animals too.
An example of an endemic specie in the Mediterranean Sea is the Arcipenser naccari (Adriatic sturgeon), a little fish that lives in the Adriatic Sea. We can only find it there. It eats aquatic invertebrates, amphipods, gastropods and annelids. During its life it mainly frequents river estuaries. The scientific name was given in honour of Fortunato Luigi Naccari, the first one that discovered the existence of the species.
5.1.7 Why the Mediterranaean Sea can be considered a "biodiversity hotspot"?
Firstly, to know why the Mediterranean Sea can be considered a biodiversity hotspot we have to look at what is a biodiversity hotspot.
So, what's a biodiversity hotspot?
A biodiversity hotspot is a biogeographic region that is both a significant reserve of biodiversity and is threatened with destruction.
To be qualified as a biodiversity hotspot, a region must meet two rigorous criteria which are:
1. It must have at least 1,500 vascular plants found nowhere else on Earth (known as "endemic" species). This means that a hotspot is unique and irreplaceable.
2. It must have lost 70% or more of its original natural vegetation.
Around the world, 36 areas are qualified as hotspots. They represent just 2.3% of Earth’s land surface, but they support more than half of the world’s plant species as endemics and nearly 43% of bird, mammal, reptile and amphibian species as endemics.
The Mediterranean Sea can be considered as a biodiversity hotspot as its flora consists of 15,000 to 25,000 species,
60% of which are unique to the region. About one third of the Mediterranean fauna is endemic.
There are 1,912 species of amphibians, birds, cartilaginous fish, endemic freshwater fish, crabs and crayfish, mammals, dragonflies and reptiles that have been determined to live in the Mediterranean region. About 19% of these species are threatened with extinction: 5% critically endangered, 7% endangered and 7% vulnerable.
About 16 irreplaceable species are already extinct, including some endemics such as
the Hula Painted Frog Discoglossus nigriventer, the Canary Islands Oystercatcher Haematopus meadewaldoi and the Sardinian Pika Prolagus sardus.
5.1.8 The Astroidescalycularisand its charcateristics.
Astroides calycularis is a colonial coral consisting of a group of polyps, each of which sits in a stony cup known as a calyx. The colonies have a diameter between 25 and 30 cm while they are approximatively 10 cm high. The colour of these organisms ranges from deep yellow to orange and are therefore very beautiful and able to adorn the marine depths. Each polyp has about thirty very short tentacles surrounding its mouth. The colony grows by asexual reproduction. Deep-water colonies are bush-shaped, the calices are circular, while shallow-water colonies tend to be ellipsoid in shape, their calyces are polygonal.
During the Pleistocene (Ice Age) Astroides calycularis had a wider distribution than it does now and could be found living all over the western Mediterranean Sea. Nowadays it is native to the part of the western Mediterranean Sea that is south of Sardinia and is also present in the Atlantic Ocean near the Strait of Gibraltar. Where it is present it contributes to the "life" of the coralline environment as a "builder" and generally contributes to the "growth" of the submerged cliffs thanks to the deposition of its carbonate skeletons. Astroides Calycularis is found on rocks and walls, under overhangs and in submarine caves at depths down to about 40-50 m, as such it is particularly adaptable and does not suffer too much changes in brightness or other chemical-physical parameters. Astroides calycularis is nocturnal, the polyps remaining retracted back into their calices during the day. When expanded at night, they feed on zooplankton, small fish and perhaps bacteria. Its colonies are unisexual, males liberate sperm into the sea and fertilisation takes place in the coelenteron (gastric cavity) of the female. The eggs have yolks, and the embryos are brooded in the coelenteron until they are liberated into the water column as planula larvae.
It has suffered a gradual progressive decline and is considered a species at risk of extinction. Recent studies have high
5.1.9 A definition of primary production and its connection to biodiversity.
The primary production is the production of organic compounds form the CO2 present in the atmosphere or in water, which occurs mainly through photosynthetic processes or, to a lesser extent, chemosynthetic ones. All life on Earth is directly or indirectly dependent on primary production. The organisms responsible for primary production, called primary or autotrophic producers, are at the base of the food chain. In terrestrial environments they are mainly plants, while in aquatic environments the seaweed play preponderant role. We can divide primary production into terrestrial and oceanic, but we will focus more on the oceanic one. In the oceans almost all the primary production is due to the seaweed and the vascular plants make only a small contribution. The term "seaweed" includes different types of organisms, from single floating cell to multicellular organisms that live attached to the substrate. This group includes photoautotrophic organisms belonging to different Phyla: prokaryotic bacteria and three categories of eukaryotes (green seaweed, brown seaweed and red seaweed). Vascular plants are represented by marine phanerogams such as Posidonia Oceanica. Initially many researchers believed that the relationship between species richness and net primary productivity could be visualized as a hump-shaped or modal curve, with richness first rising and then declining with increasing productivity. However, subsequent theoretical and empirical research, including meta-analyses, seriously diminished acceptance of the modal pattern as a canonical relationship. Research in recent decades has shown that biodiversity promotes ecosystem functions, including primary productivity.