Posidonia and other seagrasses are one of the most important marine ecosystems on Earth. Many dare to categorize them as the jungles of the sea, for its high biodiversity. It is what we are going to see in this article, especially focusing on the Posidonia oceanica‘s meadows!
WHAT ARE MARINE PHANEROGAMS?
The seagrasses are plants that colonized coastal marine environments, being present in all oceans and seas, except the Antarctic. There are about 66 species.
All have a similar pattern: a horizontal underground rhizome (a thick buried stalk), from which are born the roots and vertical ramifications from where emerge leaves.
Throughout evolution, they have acquired the necessary adaptations to live in an environment with a high concentration of salts. They have the ability to perform underwater pollination by little flowers, in addition to reproduce asexually.
As we have already mentioned, we will focus on Posidonia oceanica, an endemic species of the Mediterranean Sea. It has the typical structure mentioned above, but among its peculiarities there are leaves of 0.5 cm wide and one meter long, grouped in bundles of 4-8 leaves.
Posidonia oceanica’s meadow (Picture: Manu Sanfélix).
In just one square meter can be 10,000 leaves. As a result, the particles that fall to the bottom are trapped and form what is known as “matte”, a very compacted substrate that rises slowly (10-18 cm/century), which acts as a barrier against the waves, favouring the formation of beaches. Do you want to know why we are losing beaches?
Did you know that on the island of Formentera (Balearic Islands, Spain) there have been found an individual of Posidonia older than 100,000 years?
BIODIVERSITY IN POSIDONIA MEADOWS
Posidonia meadows and other seagrasses are ecosystems with high biodiversity. In addition to the organisms living permanently, others reproduce, put the lay or refuge there. There have been described about 1,000 species in them.
Despite the high associated biodiversity, only few species are able to feed on the plant. Examples include salema progies (Sarpa salpa), the green turtle (Chelonia mydas), some sea urchins such as Paracentrotus lividus … all with symbiotic bacteria in the digestive tract.
There are many algae and animals that live attached to the leaves or rhizomes, called epiphytes. Examples include the hidrozoa Aglaophenia harpago and the bryozoan Lichenopora radiata. But undoubtedly the most characteristic epiphyte animal on Posidonia is Electra posidoniae. This bryozoan form a narrow structure above the plant’s leaves.
Hidrozoa Aglaophenia harpago above Posidonia oceanica (Picture: Peter Jonas).Briozoa Lichenopora radiata (Picture: Javier Murcia).Briozoa Electra posidoniae (Picture: Jordi Regàs, CIB).
Logically, there are also animals moving on the leaves. These are small animals that feed on epiphytes, such as crustaceans, gastropods (snails and slugs); polychaete, flatworms, nematodes and echinoderms. Examples are the nudibranch Diaphorodoris papillata and the crustacean Idotea hectica.
Nudibranch Diaphorodoris papillata (Picture: CIB).Crustacean Idotea hectica (Picture: David Luquet).
One of the most characteristic animals of the Posidonia oceanica is the nobel pen shell (Pinna nobilis), the biggest Mediterranean mollusc, which can grow to a meter and lives with part of the body buried in sand.
Nobel pen shell (Pinna nobilis) (Picture: Maite Vázquez)
Among the echinoderms, it is considered that the starfish Asterina pancerii is the only strictly linked to the meadow, although sea urchins such as Paracentrotus lividus can become very abundant.
Other animals that roam freely in the meadow are fishes. The painted comber (Serranus scriba) is the most common; but the most unique is Opeatogenys gracilis, green in order to camouflage itself in the leaves. Other that camouflage really good are the fishes from the genus Syngnathus, such as S. typhle and S. acus.
As we have seen, Posidonia meadows are areas with high biodiversity of animal and plant species. So, it is home to many species at different stages of their life cycle.
But its importance goes further. Due to its growth through underground rhizomes, Posidonia retains the sand and, century after century, forms a natural barrier that provides protection for the coast, allowing the formation and gives stability to beaches, dunes and coastal forests.
Finally, a lot of organic matter is dispersed by currents and waves to other ecosystems.
REFERENCES
Ballesteros, E & Llobet, T (2015). Fauna i flora de la mar Mediterrpania. Ed. Brau
Departament de Medi Ambient, Generalitat de Catalunya (2002). Biodiversidad y medio marino. Mediterrània viva. Editorial Anthias SL.
Minguell, J (2008). Flora i fauna del Mediterrani.
Ruiz, JM; Guillén, JE; Ramos Segura, A & Otero MM (Eds) (2015). Altas de las praderas marinas de España. IEO/IEL/UICN. Murcia-Alicante-Málaga. 681 pp.
Triptych: Las praderas de Posidonia en peligro. Parc Natural del Montgrí, les Illes Medes i el Baix Ter.
Did you know that in the Mediterranean Sea habitually lives 8 species of cetaceans, among dolphins and whales; in addition to other visitor and spontaneous species, such as the killer whale? In this post, a new version of “Cetaceans in the Catalan coast“, the first post published in this blog, I will give more information about the cetaceans that live in this small sea.
INTRODUCTION
Cetaceans originated 50 million years ago in the ancient Tethys Sea, from terrestrial mammals. Approximately, there are 80 living species in the world, but only 8 of them live habitually in the Mediterranean and other species are present only in some seasons or sporadically.
HABITUAL CETACEANS OF THE MEDITERRANEAN SEA
STRIPED DOLPHIN
Striped dolphin (Stenella coeruleoalba) is a cetacean with a black or bluish grey colouration in the back and white in the ventral part. There is a black line from the eye to the anal region through each side, and another one from the eye to the pectoral fin. Mediterranean striped dolphins are slightly smaller than their neighbours from the Atlantic, and achieve a maximum length of 2.2 m.
They may live in big groups, till hundreds of individuals. Anyway, in the observations that I have done in the Mediterranean, groups included from 5 to 50 animals. They are very acrobatics and they can jump 7 meters above the sea surface.
Striped dolphins are common in both Mediterranean basins, specially in the open sea, being so many abundant in Ligurian Sea, Gulf of Lion, Alboran Sea (between Andalucía, Spain, and Morocco) and the Balearic Sea (between the Iberian Peninsula and the Balearic Islands).
This is the most abundant species in the Mediterranean (about 117,000 animals in the western basin), but they are in a vulnerable status of conservation due to the affection by morbillivirus, pollutants such as organochlorine compounds and fishing devices.
BOTTLENOSE DOLPHIN
Bottlenose dolphins (Tursiops truncatus) maybe are the most known for the population because they are the protagonist of some movies and they are the most common cetacean in captivity.
Their robust body is grey, clearer in the sides and white in the abdomen. Bottlenose dolphins are 4 m long.
Their groups, integrated by females and offspring or young males, range from 2 to 10 animals. They live in all the coasts of the Mediterranean Sea.
Their conservation status in the Mediterranean is vulnerable. It is though that their population is about 10,000 animals. Competence with commercial fisheries, bycatch and water pollution are among their threats.
SHORT-BEAKED COMMON DOLPHIN
Short-beaked common dolphin (Delphinus delphis) is easily recognisable for the colouration of its body: dorsal region is dark and sides are cream-coloured or yellow, and constitute a V in the half of the body. Like striped dolphins, they are also small animals (2-2.5 m).
Short-beaked common dolphin (Delphinus delphis) (Picture: JKMelville, Creative Commons).
They live in numerous groups in open waters, from 10 to 200 animals, but sometimes groups of several thousands have been seen.
They enjoy with boats:
Despite their name, it is difficult to observe them because they are endangered in the Mediterranean. In the last 40 years, their population have been reduced by half. There are several reasons: lack of preys due to competence with fishers, bycatch, habitat degradation, sound pollution and high concentrations of pollutants.
FIN WHALE
Fin whale (Balaenoptera physalus) is the biggest whale in the Mediterranean and the second one in the world.
Fin whale (Balaenoptera physalus) (Picture: Circe)
Fin whale’s head is V-shaped, wide and flatten. It is dark grey in the back and white in the abdomen, but asymmetric in the jaws: left side is dark grey and right side is white. Dorsal fin is short and placed in the last third of the body. In the moment of diving, caudal fin is not shown out of the water. Blow may be 8 meters height and narrow. Their maximum length is 24 m.
They are usually seen alone or in small groups (normally mother and calf) in open waters. In the Mediterranean, they are most frequently sighted between Balearic Islands and Ionian Sea, being specially abundant in the Gulf of Lion.
According to IUCN, it is a vulnerable species in the Mediterranean, but it is endangered worldwide. The Mediterranean population includes 5,000 adults. They are victims of strikes with ships, high DDT concentrations, acoustic pollution due to seismic surveys and bycatch.
Have you seen this fin whale rescue from Fuerteventura?
SPERM WHALE
Sperm whales (Physeter macrocephalus) are the biggest toothed whales and one of the biggest cetaceans in the Mediterranean.
Sperm whale (Physeter macrocephalus) (Picture: Gabriel Barathieu, Creative Commons).
Sperm whales have a rounded or triangular hump instead of a dorsal fin, which is followed by six exaggerated “knuckles”. An important clue for its identification is the blow: it is a bushy blow directed low, left and forwards. Head, which is square, represent 1/3 of the total length of the body. It is dark or grey, with the lower part of the mouth white. To dive, they show the caudal fin out of the water. They may be 20 long.
Their groups are composed by females and their offspring, other groups of young males and adult males are solitary. The number of animals per group ranges from 10 to 15, but smaller groups also exist. They are usually seen in oceanic waters of all the Mediterranean.
It is an endangered species in the Mediterranean due to they are accidentally captured in fishing nets, by strikes with vessels and the annoyance provoked by marine traffic. It is estimated that live some thousands in the Mediterranean.
Have you seen this video of a sperm whales that “adopt” a deformed cetacean?
RISSO’S DOLPHIN
Risso’s dolphin (Grampus griseus) is grey when is born, but becomes paler with age for the presence of scars that do not disappear. They might measure 4 m.
Generally, they live in groups of 3-50, despite sometimes groups of some thousands have been spotted. In the Mediterranean, it is widely distributed in open waters, being more abundant in the western basin, where they prefer continental slope and submarine canyons.
Their status of conservation is unknown, but bycatch and acoustic and chemical pollution affect them.
LONG-FINNED PILOT WHALE
Long-finned pilot whale (Globicephala melas) is the biggest dolphin species in the Mediterranean, since it may achieve 6 m. Black in general, this pilot whale has a anchor-shaped ventral patch. Its flippers measure one fifth of the length.
Long-finned pilot whale (Globicephala melas) (Picture: Wikiwand).
Their groups range from 10 to 60 animals, but also several thousands. Groups include several generations of females with their calves. In the Mediterranean, it is abundant in the western basin, specially in the Strait of Gibraltar and Alboran Sea.
There is deficient data to evaluate its status of conservation. Anyway, it is known that are threatened by bycatch, strikes and acoustic and chemical pollution.
CUVIER’S BEAKED WHALE
Cuvier’s beaked whales (Ziphius cavirostris) are dark grey or brown, paler in the head. Their head is bulky, and the beak is not much marked. They may be 7 m long.
They usually live in groups of 2-7 individuals or alone, in deep oceanic waters.
It is difficult to observe them due to the little activity in surface, reason that can explain why there are not enough information to evaluate their conservation status. It is known that are specially sensible to acoustic pollution, both military activities or seismic surveys. Moreover, the ingestion of plastic and bycatch also affect them.
KILLER WHALES IN THE MEDITERRANEAN?
Killer whales (Orcinus orca) are one of the most fascinating cetaceans. They live in polar and tropical waters, from the coast to open sea.
Killer whale (Orcinus orca) (Picture: Jose J. Díaz)
In the Mediterranean, however, they are only considered residents in the Strait of Gibraltar, with a size population of 32 whales. Their presence in the Strait, it is believed that is linked to the presence of bluefin tuna, their food.
Their status of conservation is unknown, but direct death by fishers, reduction of their preys, annoyances and habitat degradation are among the causes of their reduction.
IUCN (2012). Marine Mammals and Sea Turtles of the Mediterranean and Black Seas. Gland, Switzerland and Malaga, Spain: IUCN
Kinze, CC (2002). Mamíferos marinos del Atlántico y del Mediterráneo. Ed. Omega
Lleonart, J (2012). Els mamífers marins i els seus noms. Terminàlia, 5, 7-25
Notarbartolo di Sciara G. (compilers and editors) (2006). The status and distribution of cetaceans in the Black Sea and Mediterranean Sea. IUCN Centre for Mediterranean Cooperation, Malaga, Spain.
Some month ago, we talked about starfishes and we said that there are some animals, which are also echinoderms, with which they can be easily confused. Well, in this post we will talk about these animals: the brittle stars. We are going to explain their features to distinguish them from starfishes and we are going to expose some Mediterranean species.
THE BRITTLE STARS
The brittle stars or ophiuroids are a class of echinoderms with more than 2,000 living species, which live in all types of seafloor.
What features do you have to pay attention to differentiate a brittle star from a starfish? Brittle stars have five arms, which are thin and sharply originate from the central disk. This feature is key to not confuse them with starfishes. Another characteristic you have to observe to differentiate brittle stars from starfishes is in the bottom (oral side) of the animal: the ambulacral grooves are closed and covered by plates. Furthermore, tube feet don’t have suckers because they are more involved in locomotion than in feeding. In fact, their arms are constituted by articulated ossicles (called vertebrae) that allow their displacement.
Having the arms so thin, where are their organs? The mouth is in the lower part of the body and is surrounded by plates acting as jaws. They have no anus, so products that are not digested are expelled through the mouth. All organs are located in the central disc. They use bursae to breathe, which are bags in which water enters and leaves. In addition, the reproductive organs are connected to these bags, so that they expel gametes with water (although some species incubate their offspring). Most species have separate males and females.
Where can you observe brittle stars? Brittle stars normally live in rocky seafloor with low or without light, usually hidden in cracks, where they feed on suspension particles, but some of them are carnivorous and one species can catch fishes by using their arms as a cage.
SOME EXAMPLES FROM THE MEDITERRANEAN SEA
In the Mediterranean Sea, we can find about 34 brittle star species. Six of them are endemic and other 2 species are exotic. Here, we will explain 5 of them.
SMOOTH BRITTLE STAR (Ophioderma longicauda)
It is the largest species. It comprises a pentagon-shaped central disc (about 3 cm of diameter) with arms, which are a bit bony and are 15 cm long. It has a brown colour on the dorsal side and is lighter in the ventral side and arms. They can be find till 50-70 meters deep under rocks, in holes and cracks; but the young individuals can hide between seaweed. They feed on worms and bivalves, mainly during the night.
Common brittle stars have the whole body covered with long spines, which can take a variable colour (usually brown and grey tonalities). They can measure up to 12 cm. It is the most abundant in both hard and soft bottoms, up to 100 meters deep. It feeds on particles with the ambulacral system. Did you know that they can live about 10 years? A curiosity: if you take one of these brittle stars and let it fall to the bottom, it sinks with open arms, allowing you to distinguish it from the following species.
Common brittle star (Ophiothrix fragilis) (Picture: Animal Base).
BLACK BRITTLE STAR (Ophiocomina nigra)
Although it is similar to the previous species, it can be distinguished from the common brittle star by the fact that in this species the spines are only in the arms, are shorter and are laterally arranged. It also has a brown to black colour, while arms are lighter than the disk (measuring up to 2.5 cm in diameter). It lives in shallow, rocky and sandy areas. To differentiate it from the common brittle star, if you catch one of them and you let the brittle star to drop, the ophiurid sinks with arms folded upwards.
Black brittle star (Ophiocomina nigra) (Picture: Segrest Farms)
AMPHIURA CHIAJEI
It is a small brittle star, with his body normally buried in the mud, so that only shows the arms abroad, which are very long and are used to collect debris. Its color is orange red. It is usually found between 10 and 200 meters deep.
This brittle star can not be confused with any other: it has its entire body covered with granules and has a considerable size. It is of uniform grey colour. They live in deep rocky substrates, sedimentary continental shelf and over gorgonian between 50 and 200 meters deep.
Coll M, Piroddi C, Steenbeek J, Kaschner K, Ben Rais Lasram F, et al. (2010) The Biodiversity of the Mediterranean Sea: Estimates, Patterns, and Threats. PLoS ONE 5(8): e11842. doi:10.1371/journal.pone.0011842
Hichman, Roberts,Larson, l’Anson & Eisenhour (2006). Principios integrales de Zoología. Ed. McGraw Hill (13 ed).
Martin P (1999). Claves para la clasificación de la fauna marina. Ed. Omega
Riedl R (1986). Fauna y flora del Mar Mediterráneo. Ed. Omega
Vàzquez, J & Maluquer-Margalef, J (coord.) (2014). Guia pràctica per conèixer la natura de Catalunya. IPCENA. Lleida. 576 p.
The Mediterranean Sea is a “sea in the middle of the land” (Mare medi terraneum, in Latin). Do you know how many species live in this small sea? Do you know which is the average and maximum depth? These and more questions are answered in this post and are going to show you the magnificence of this sea.
HOW MANY SPECIES LIVE IN THE MEDITERRANEAN SEA?
Approximately 17,000 species have been reported to occur in the Mediterranean Sea. Did you think that they were more or less than 17,000? Of these, 26% are marine microbes (microorganisms), but it might be higher if we consider the very limited data available. If we just consider the animals, most of them are crustaceans (13.2%) and molluscs (12.4%), while vertebrates represent a small part (4.1%). Plants represent only a 5% of the amount of species. It’s important to highlight the presence of about 1,200 algae species, but authors have included them in the microbes and plants, despite they are not true plants.
Percentage of species in each group (Picture: Marc Arenas Camps).
These 17,000 species represent a 6.4% of the global species. Is this a lot or a little? If one considers that the Mediterranean Sea is only a 0.82% in surface area and 0.32% in volume as compared to the world oceans, draw conclusions yourself. It means that less than a 1% of the surface area of ocean have more than a 6% of the marine species!
The average of the total endemics is about 20%. It means that 20% of the species in the Mediterranean Sea can be found only in the Mediterranean. Some examples are the famous seagrass Posidonia oceanica, the emblematic Mediterranean monk seal (Monachus monachus), and the seaweed Rissoella verruculosa.
Posidonia oceanica is a very important species in the Mediterranean, which constitutes an ecosystem by itself (Picture: For Divers).
For all these reasons, the Mediterranean Sea is considered a hot spot of biodiversity, explained by paleogeographic and ecological reasons. From a paleogeographic point of view, its high species richness is due to both its long evolutionary history and the diversity pump from the Atlantic Ocean. In addition, from an ecological view, its species richness is due to the present-day variety of climatic and hydrologic situations, leading to the occurrence of temperate and subtropical species.
In this numbers, we have to add an additional 600 metazoan species. Who are they? The Mediterranean biodiversity is influenced by the introduction of 600 new species, which represent a 3.3% of the total estimates. In fact, this number is continuously increasing. Molluscs (33%), arthropods (18%) and chordates (17%) are the groups with more alien species. A well-known and toxic example is the blowfish.
IS THE MEDITERRANEAN SEA A DEEP SEA?
The Mediterranean sea is the deepest enclosed sea on Earth. It has an average depth of 1,460 m and a maximum of 5,267 m. The deepest part of the sea is placed on the Matapan trench, in Greece. We can compare the average and the maximum depth in other enclosed seas to give some evidence: Baltic Sea ( 55 and 421 m respectively), North Sea (94 and 660 m), Black Sea (1,240 and 2,245 m) and Red Sea (491 and 3,040 m).
What happens when we compare the Mediterranean Sea with the Earth’s oceans? In my opinion, the “sea between the land” don’t stay behind, but let’s see the numbers (average and maximum depth): Pacific Ocean (4,001 and 11,034 m), Atlantic Ocean (3,605 and 8,605 m), Indian Ocean (3,854 and 7,455 m), Southern Ocean (4,500 and 7,235 m) and Arctic Ocean (1,430 and 5,625 m).
DID YOU KNOW THAT THE MEDITERRANEAN SEA BECAME NEARLY DESICCATED?
About 6 million years ago, towards the end of the Miocene, the Mediterranean Sea was isolated from the rest of the world ocean. Because of the Mediterranean sea has a negative water balance, it is that evaporation is higher than the entrance of water, it become almost desiccated and, probably, was transformed into a series of large evaporitic lakes during the salinity crisis at the Messinian Stage.
Mediterranean geography during the salinity crisis in the Messinian stage (Picture: Paubahi, Creative Commons).
Probably, the landscape during the salinity crisis should have looked like the nowadays Dead Sea. This salinity crisis should have driven deep water fauna to extinction, but some of the shallow-water biota may have survived.
Probably, the landscape during the salinity crisis should have looked like the present Dead Sea (Picture: AtlasTours.Net).
OPEN OCEAN REPRESENTS 80% OF THE TOTAL MEDITERRANEAN WATERS
The continental shelves of the Mediterranean are narrow and crossed by submarine canyons, so open sea represents a large area. In fact, 80% of the total Mediterranean waters are open ocean and can be classified as deep sea. An unusual characteristic is the high homothermy from 300-500 m to the seafloor (there is an homogeneous temperature of 12.8 – 13.5ºC in the western Mediterranean and 13.5 – 15.5ºC in the eastern Mediterranean).
REFERENCES
Ballesteros E & Llobet T (2015). Fauna i flora de la mar Mediterrània. Ed. Brau
Bianchi CN & Morri C (2000). Marine Biodiversity of the Mediterranean Sea: Situation, Problems and Prospects for Future Research. Marine Pollution Bulletin. Vol. 40, No. 5, pp. 367-376
Coll M, Piroddi C, Steenbeek J, Kaschner K, Ben Rais Lasram F, et al. (2010) The Biodiversity of the Mediterranean Sea: Estimates, Patterns, and Threats. PLoS ONE 5(8): e11842. doi:10.1371/journal.pone.0011842
Hofrichter R (2004). El mar Mediterráneo. Fauna, Flora y Ecología: Guía sistemática y de identificación. Ed. Omega
Hofrichter R (2004). El mar Mediterráneo. Fauna, Flora y Ecología: Parte general. Ed. Omega
Hutchinson S & Hawkins LE (2005). Océanos. Biblioteca virtual. Scyla Editores
Since some time ago, newspapers are talking and warning about the arrival of the blowfish in the Mediterranean. This post expects to describe these famous animals and explain which the danger is for humans.
HOW IS THE BLOWFISH OF THE MEDITERRANEAN?
Blowfishes are a group present in the Mediterranean because they have accessed through the Suez Canal, so blowfishes are an exotic species. The species in the Mediterranean is the silver-cheeked toadfish (Lagocephalus sceleratus). Quickly, they established in the Eastern Mediterranean, but recently they have been found in the Adriatic sea (east of Italy). In this article published in the Mediterranean Marine Science, you may find a map with the concrete places (we cannot publish here for copyright). The silver-cheeked toadfish is native to tropical waters of the Pacific and Indian oceans, including Red Sea, where lives in muddy and sandy sea bottoms close to coral reefs between 10 and 180 m deep. They feed on a wide variety of animals and plants thanks to its powerful beak.
Their colouration is greenish with dark spots above, silver band from mouth to caudal fin and white belly. They can be distinguished from other blowfishes of similar colouration for their symmetric tail. The spines of the fins, moreover, are all soft. Their body is not covered by scales, but some small spines in the belly and in the dorsal part of the body. With two big teeth in each jaw, they constitute some kind of beak. When they feel in danger, they absorb water in a lateral cavity in the stomach to swell the body. The biggest animals can measure more than one metre long, but in average, they measure 40 cm.
Like other fish with a powerful jaws and big enough, the blowfish can produce a deep injury. Some species of blowfish can be specially aggressive. Most of the accidents are produced when manipulating alive animals.
However, this fish is poisonous and, in fact, it has caused some human deaths due to the presence of the toxin tetrodotoxin, which is 1,200 times more poisonous than cyanide. This toxin can paralyse the muscles, so it stops breathing and produce death by suffocation. It is known that with 0.009 mg for each kg of body weight is lethal. To give an example, a person with 70 kg who ingest 0.63 mg of the toxin may die (yes, in mg!). Most curious is the fact that the toxin is not produced by theirselves, but bacteria that ingest through food.
Nader M., Indary S., Boustany L., 2012. FAO EastMed The Puffer Fish Lagocephalus sceleratus (Gmelin, 1789) in the Eastern Mediterranean. GCP/INT/041/EC – GRE – ITA/TD-10
A team of researchers of several Italian organizations has published on May 2015 its findings about the responses of cetaceans in high sea waters to summer maritime traffic in the Western Mediterranean Sea. This post is a summary of this study.
INTRODUCTION
Nowadays, cetaceans have to face several threats, like the loss of their habitat, depletion of resources, interaction with fisheries and chemical and acoustic pollution, among others. In the case of ship transport, it can cause long-term changes in distribution, short-term changes in behaviour or direct physical injuries (e. g. collisions).
The Mediterranean Sea is one of the world’s busiest waterways. Moreover, shipping traffic is growing together with the concern of its impacts on fauna. In addition, we have to have in consideration that summer month are the busiest in naval traffic, especially due to the increase on cruise ships and passenger ferries.
The goal of this study was to outcome if the intensity of traffic in high sea waters was statistically different between presence and absence of cetacean sightings.
STUDY AREA AND DATA COLLECTION
Because of most of the Mediterranean cetaceans are mainly pelagic and there is a lack of information in these areas, the research had been conducted along six transects within shipping routes that connects Italy, France and Spain in high sea waters (placed in Ligurian-Provençal basin, the northern and central Tyrrhenian Sea and the Sardinian and Balearic Seas).
The transects were surveyed from June to September between 2009 and 2013 using ferries as observation platforms. During this period, more than 95,000 km were surveyed and the presence of eight cetacean species was recorded.
Introductory online course on cetaceans. Now, 40% off, till 30th June. Available only in Spanish.More info here.Click the picture to access to the coupon.
CETACEANS AND MARITIME TRAFFIC
In locations with cetacean sightings, the number of vessels was 20% lower than the number of vessels in the absence of sightings. In the case of the three most frequently sighted species; fin whale (Balaenoptera physalus), striped dolphin (Stenella coeruleoalba) and sperm whale (Physeter macrocephalus); this difference was, respectively, 18%, 20% and 2%. Concerning other species, in the case of Cuvier’s beaked whale (Ziphius cavirostris) the difference was 29% and in the Risso’s dolphin (Grampus griseus) was 43%. It was found that for bottlenose dolphins (Tursiops truncatus) the difference was insignificant. Finally, for common dolphin (Delphinus delphis) and for pilot whale (Globicephala melas) any conclusion can be given.
Nevertheless, despite the number of ships recorded during cetacean sightings was lower in all areas, the percentage difference range from 11 to 49% among areas.
So, in high sea areas during summer, where cetaceans were seen, there were a significantly lower abundance of ships. Some explanations can be given: animals could tend to avoid more impacted zones with small displacements by seeking areas with fewer vessels, could change their distribution to occupy low traffic areas or could increase diving activity where intense traffic occurs. The intensity of the response of cetaceans to the intensity of traffic has important differences among areas and species. So, there are several factors that affects this percentage difference, like specific ecological needs and local environmental conditions.
In the case of fin whale, where marine traffic is intense, the presence of fin whales is generally lower, with the exception occurring in the central part of the Ligurian Sea. The explanation could be that this region is ecologically favourable in summer since it is a feeding ground for this species and these whales are present for feeding reasons. Therefore, there is a coexistence between traffic and fin whales.
Fin whale (Balaenoptera physalus) (Picture from Circe)
Another example is striped dolphin. Due to its high mobility, this dolphin can avoid the presence of vessels and this could be the reason why there is a negative response between this species and ship presence.
Striped dolphin (Stenella coeruleoalba) (Picture from Marc Arenas Camps)
About sperm whale and Cuvier’s beaked whale, there were no difference in both species in the Ligurian Sea and the reason probably is that sperm and Cuvier’s beaked whale have their feeding grounds in this basin and, moreover, the slopes and submarine canyons are confined in specific areas. However, differences are observed in other areas.
Finally, bottlenose dolphin did not show any response to traffic. Probably, because it is a coastal species, it is more used to sharing its typical habitat with maritime traffic.
All you need is Biology 
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