A study analyzes the barriers in the gene flow among marine species in the Mediterranean

Populations close or delimited by seven Mediterranean fronts have been specially studied: the Gibraltar Strait, the Almeria-Oran Front, the Ibiza Channel, the Balearic Front, Sicily Channel, the Otranto Channel, and the southern margin of the Aegean Sea.
Populations close or delimited by seven Mediterranean fronts have been specially studied: the Gibraltar Strait, the Almeria-Oran Front, the Ibiza Channel, the Balearic Front, Sicily Channel, the Otranto Channel, and the southern margin of the Aegean Sea.
Research
(01/06/2017)

The fronts, oceanographic discontinuities that are delimited by marine currents, affect the genetic separation of organisms in the different areas of the Mediterranean, albeit not homogeneously. From a conservation point of view, fronts should be considered frontiers that set independent management units, like regions. In order to protect the Mediterranean, protected areas should be established within all those management units creating a network of connected areas. Therefore all populations would have a connectivity to guarantee their survival. Otherwise, the future of isolated populations is their mid-term disappearance, due an increase of kinship.

These are some of the conclusions of a study published in the journal PLOS ONE and carried out by scientists from the Biodiversity Research Institute (IRBio) and the Centre for Advanced Studies of Blanes (CEAB-CSIC). The experts have analysed the genetic differentiation among populations  of fish, crustaceans and molluscs in the Mediterranean.
 

Populations close or delimited by seven Mediterranean fronts have been specially studied: the Gibraltar Strait, the Almeria-Oran Front, the Ibiza Channel, the Balearic Front, Sicily Channel, the Otranto Channel, and the southern margin of the Aegean Sea.
Populations close or delimited by seven Mediterranean fronts have been specially studied: the Gibraltar Strait, the Almeria-Oran Front, the Ibiza Channel, the Balearic Front, Sicily Channel, the Otranto Channel, and the southern margin of the Aegean Sea.
Research
01/06/2017

The fronts, oceanographic discontinuities that are delimited by marine currents, affect the genetic separation of organisms in the different areas of the Mediterranean, albeit not homogeneously. From a conservation point of view, fronts should be considered frontiers that set independent management units, like regions. In order to protect the Mediterranean, protected areas should be established within all those management units creating a network of connected areas. Therefore all populations would have a connectivity to guarantee their survival. Otherwise, the future of isolated populations is their mid-term disappearance, due an increase of kinship.

These are some of the conclusions of a study published in the journal PLOS ONE and carried out by scientists from the Biodiversity Research Institute (IRBio) and the Centre for Advanced Studies of Blanes (CEAB-CSIC). The experts have analysed the genetic differentiation among populations  of fish, crustaceans and molluscs in the Mediterranean.
 

 

The study reviewed studies on population from previous years regarding the Mediterranean. It has been focused on 70 species that enable the proper analysis of marine fronts. Most of them are fish (the 41% of the studied taxonomic group), but also molluscs (13%) and crustaceans (21%). Populations close or delimited by seven Mediterranean fronts have been specially studied: the Gibraltar Strait, the Almeria-Oran Front, the Ibiza Channel, the Balearic Front, Sicily Channel, the Otranto Channel, and the southern margin of the Aegean Sea.

Fronts are oceanographic discontinuities created when currents or watter masses with different density meet, which makes their merge more difficult. Therefore they act as barriers to populations of organisms and are frontiers that animals cannot cross. But this is not always the case and it does not affect all animals in the same way. According to Marta Pascual, from the Faculty of Biology of the UB and IRBio, and Enrique Macpherson, from CEAB, authors of the study, “The larval phase is when a population spreads the most, since this is the moment when they have more possibilities of crossing a front”. The longer the larval phase, the higher the possibility of crossing the front.

Oceanic front as a barrier for gene flow

In the study, scientists have stated that species with a higher mobility and longer larval phases, have less genetic differences in different areas. This is, according to the authors, due the possibility of being transported by the currents, which makes them to spread easily. Therefore, populations of an area feed from species from other areas, which results in less genetic differences between closer populations. But the frequency of genetic differences increases when it comes to populations that are separated by an oceanographic front.

Species with lower mobility and shorter larval phases use to have a big genetic difference  among populations, since they have a lower possibility of being transported by the current. However, the genetic differences are practically the same whether populations are separated by a front or not.

Therefore, sponge and coral populations separated by a few kilometres are quite isolated between them, regardless of the fronts, since their larvae live for a few hours or days in plankton. However, fish and crustaceans, with a larvae life of several weeks and less genetic differenciation between populations, are affected by the presence of these oceanographic fronts.

This is the first study to analyse the genetic distribution of species in all the Mediterranean oceanographic discontinuities and it aims to determine the impact of the fronts and biological characteristics of species to set an efficient network of reserves that allows preserving the marine biodiversity.