Bees in Europe -- and pollinator research in Greece

There are 1,965 bee species in Europe (~20,000 species on Earth).  Bee species diversity in Europe is partially due to its Mediterranean areas which provide excellent conditions for many bees, and mapping of bee diversity in Europe (figure 1) shows a general increase towards the Mediterranean areas.  ~400 of Europe's bee species are endemic to Europe.  Many of these are associated with mountains and other high elevation habitats, the Canary Islands, Mediterranean islands, and the Mediterranean peninsulas of Spain, Italy, and Greece.

While collecting pollen and nectar, pollen attaches to the insect's body.  The result is that bees transfer pollen grains from flower to flower.  In this way, they help plants sexually reproduce.  Some plants can only be pollinated by certain species.  Therefore, the loss of bee diversity can lead to loss of plant diversity.  A recent European regional assessment has reported the status of all 1,965 European bee species.  The geographic range of this assessment extends from Iceland in the west to the Ural Mountains in the east, and from Franz Josef Land in the north to the Mediterranean in the south.  The Canary Islands, Madeira, and the Azores were also included.

9.2% of bee species are considered threatened at the European level, though this proportion is uncertain due to the high number of species for which there is insufficient data.  For 56.7% of the bee species in Europe, there was not enough data to evaluate the risk of extinction; these species were classified as data-deficient.  The honey bee (Apis mellifera) has been evaluated as data-deficient on the European Red List.  This species is native throughout Europe (except Iceland, the Faeroe Islands, northern Scandinavia, and the Azores), but it is not known whether the species still has self-sustaining wild populations in Europe.

Compared to all other European wild bees, bumblebees are the best-studied group.  According to the European Red List, 23.6% of bumblebee species are threatened with extinction, and populations are decreasing for 45.6% of bumblebee species.  Land-use changes resulting in loss of natural environment is a serious threat to many bumblebees in Europe.  The amount of habitat for the critically endangered bee species Bombus cullumanus has been greatly diminished, resulting in an 80% population loss, in the last decade.  A primary cause of this has been farming practices that involve removing clovers, the main food source for B. cullumanus.  This bee species was previously widespread, but now only exists in a few locations across Europe.  Additionally, Bombus fragrans (the largest bumblebee species in Europe, and red-listed as endangered) is also seriously threatened by intense agricultural land-use, as this is destroying areas of its native habitat in the steppes of Ukraine and Russia.  Rising temperatures and extended periods of drought are also responsible for major changes in bumblebee habitat.  For example, Bombus hyperboreus (the second largest bumblebee species in Europe, and red-listed as vulnerable) is strictly limited to Scandinavian tundra and the extreme north of Russia.  Continued climate change is likely to dramatically reduce B. hyperboreus's habitat and lead to population losses.

The geographic distribution of bee species richness in Europe is shown in figure 1.  The relatively low bee diversity observed on the Balkan Peninsula, north of Greece, is most likely the result of the relatively low amount of research and sampling effort conducted in this region.

Figure 1:  Geographical distribution of bee species richness in Europe.


The geographic distribution of bee species endemism in Europe is shown in figure 2.  There is a high number of endemic bee species in southern Europe.  Similar to the species richness map, the relatively low bee endemism observed in large areas of the Balkan Peninsula is most likely the result of the relatively low amount of research and sampling effort conducted in this region.  Many southern-European bee species also occur in neighboring areas of Asia and north Africa.  Though these species are endemic to these biogeographic regions, they are not represented in figure 2.

Figure 2:  Geographical distribution of bee species endemism in Europe.


The expansion- and intensification of agriculture is a major threat to bees in Europe.  Associated with this is the loss of natural habitat, widespread use of insecticides and herbicides, and livestock farming (resulting in grazing regimes that are damaging to grasslands and fragile ecosystems).  Additionally, the increased frequency of fire in Mediterranean ecosystems, immediately followed by grazing on these post-fire plant communities, decreases bee diversity in these fragile ecosystems.

Urban- and commercial development is another major threat to bees in Europe.  Tourism in coastal regions has led to increases in local populations and number of hotels.  It is estimated that by 2020 there will be ~350 million tourists visiting the Mediterranean coastal region.  Along the mainland Mediterranean coasts of Spain, France, and Italy, 75-80% of the coastal sand dunes have been destroyed by tourism, urbanization, and industry.  Sand dune ecosystems in Greece and Portugal are also under urbanization pressure.  These threatened ecosystems are home to bee species such as Osmia balearica and Osmia uncicornis.  In alpine regions of Europe, a large amount of natural habitat has been converted to ski areas or has been destroyed for other tourism-related infrastructure development.  Red-listed alpine bees such as Bombus brodmannicus are threatened by skiing-related development.  An additional threat related to urban development, sea walls in low-lying coastal areas heavily impact coastal habitats, especially saltmarshes.  This directly impacts specialized endemic bee species such as Colletes halophilus.

Numerous projects, both restoration practice- and scientific research-based, currently address various threats to pollinators, though our knowledge on pollinator diversity, population dynamics, and threats remains limited.  And as mentioned above, there is insufficient data for many, if not most, pollinator species and populations.  The POL-AEGIS project represents a pioneer effort to fill gaps of knowledge.  This project focuses on a wide range of the Aegean archipelago, and the project spans from january 2012 to september 2015.  The aims of the project are to assess pollinator diversity (ecological and genetic) and investigate the causes of pollinator diversity loss.  Here, bees are not the only pollinators studied, and this allows for a more holistic approach to understanding the status of the region's pollinator communities.  Successful achievement of the aims of this project are expected to increase pollination studies and help in creating a regional Red List of pollinators.  Diversity assessments are conducted on 8 islands of the Aegean archipelago (figure 3), individually selected to collectively cover a wide geographical- and climatic gradient within the Aegean Sea and the Sea of Crete.

Figure 3:  Overview of the project's fieldwork areas shown for different work topics.


Of all 33 European countries, Greece has the highest density of honey bee hives, and beekeeping in Greece is increasing.  So far no study has addressed the question of whether solitary bee diversity is affected by competition from honey bees.  Part of the POL-AEGIS project is to examine the effect of hive density on the foraging efficiency, reproduction, diversity, and pollination effectiveness of wild bees.  The project also examines how plant-pollinator networks are infuenced by various grazing intensities, and this will result in valuable knowledge regarding pollinator conservation in Mediterranean regions with livestock, as well as allow for pasture management recommendations.  A third aim within the POL-AEGIS project is to examine the impacts of fire on pollinator diversity, pollination services, and plant-pollinator networks.  This part of the research will be conducted in areas that were heavily burnt within the last few years in Greece.  The results are expected to provide new knowledge for making post-fire management recommendations.

The POL-AEGIS project will communicate its results in scientific articles, books, conference presentations, websites, and Greek popular science journals (e.g. Melissokomiki Epitheorisi -- Apicultural Review), and the project uses a scientific approach alongside community outreach.  Researchers have the large task of systematic collection of pollinators throughout a very fragmented region, and this is taking place at an unprecedented scale.  The results will be valuable for society at several levels.  Locally, bee-friendly management will allow farmers to improve crop quality, help beekeepers to practice balanced apiculture, and provide a more holistic view of nature for wildlife conservationists and land managers.  Regionally, the results of the POL-AEGIS project will provide baseline data useful for future monitoring and sustainable pollinator conservation.

LINK to Nieto et al.'s 2014 article, prepared by IUCN (International Union for Conservation of Nature), and published by the European Commission.
LINK to Petanidou et al.'s 2013 article in Journal of Apicultural Research.

Giant clams -- and restoration in the Philippines

Giant clams are the largest bivalve molluscs, and they live in the warm seas of the Indo-Pacific region.  There are ten known species of giant clam.  The dorsal body wall, or mantle, of all giant clam species is a habitat for a symbiotic photosynthetic algae (Gymnodinium microadriaticum), and during the day, a giant clam opens its shell and extends its mantle tissues so the symbiotic algae can receive sunlight needed for photosynthesis.  Therefore, giant clams are only found in relatively shallow and clear waters, including those associated with coral reefs; the deepest known giant clam occurrence is 20 meters.  Giant clams are filter feeders on particulate organic matter, and the metabolic products of their symbiotic algae provide them with an additional source of nutrition.

Depending on the species, a giant clam reaches maturity after 4 to 9 years.  They reproduce sexually and produce both eggs and sperm, and they cannot self-fertilize.  Through chemical signalling, many individuals synchronize the release of sperm and eggs into the water (broadcast spawning), and this helps ensure fertilization.  Spawning seems to occur during incoming tides; spawning is intense for 30 minutes to two-and-a-half hours, with contractions occurring every 2 to 3 minutes.

A fertilized eggs floats in the sea for about 12 hours until hatching into a planktonic larva.  It then begins to produce a calcium carbonate shell, and soon develops a "foot" which is used to move on the substrate.  Larvae can also swim to find suitable habitat.  Giant clam larvae do not host symbiotic algae, and rely completely on filter feeding.  After about one week, the giant clam settles on the substrate, though frequently changing locations during the first weeks.  The largest giant clam, Tridacna gigas, can grow to weigh over 200 kg, measure 120 cm in length, and has an average lifespan in the wild of 100 years or more.

The distribution of giant clams (figure 1) spans from south- and east Africa to the east Pacific beyond French Polynesia (between 30°E and 120°W), and from Japan to Australia (between 36°N and 30°S).  Tridacna maxima has the widest distribution, and the greatest species diversity of giant clams is observed in the central Indo-Pacific.  Seven species can be found in southeast Asia, but many populations are declining dramatically, and there are cases of local extinctions.  Local extinctions of giant clam species have been reported in areas of the Philippines, Indonesia, Micronesia, Malaysia, and Singapore.  Giant clams can be found throughout Oceania (Australasia, Melanasia, Micronesia, and Polynesia).  While abundance of giant clams in Oceania has been declining, there are areas in Oceania with unusually high abundances, including the Ashmore, Cartier, and Mermaid reefs of Australia.

Figure 1:  Distribution of giant clams.  Blue triangles represent non-scientist observations where species is unknown.


Their numbers have been greatly reduced due to overharvesting and loss of habitat, and giant clams are also seriously affected by increasing sedimentation and pollution.  Furthermore, increasing sea surface temperatures leads to the loss of symbiotic algae.  Eight species of giant clam are red listed as conservation-dependent or vulnerable; another species, Tridacna costata, was only recently discovered and is therefore not yet listed, though "critically endangered" is the proposed appropriate category.

A number of countries including Tonga, Palau, Fiji, Soloman Islands, and Cook Islands, have attempted to restore giant clam populations through local aquaculture- and restocking programs.  The Marine Science Institute (MSI) at the University of the Philippines has a long and successful record of rearing cultured giant clams to restore populations.  The restocking of giant clams in the Philippines began in 1987 as interest grew among private and public sectors for establishing giant clam ocean nurseries.  A collaborative research program for culturing bivalves was organized, the MSI being one of the participants in the program.  Key objectives of the restocking program were to establish broodstocks and develop culturing techniques, with the aims of mass-production for restocking and creating livelihoods around giant clam farming.

Field surveys around the Philippines indicated that the 3 largest giant clam species were rare.  In fact, only 2 wild sub-adult Tridacna gigas, and no Hippopus porcellanus, were found.  Restocking started slowly, as only a limited number of giant clams were available to place in the wild, and restored populations initially suffered heavy losses due to poaching and illegal fishing.  Eventually, individuals and groups teamed up to protect giant clams, and marine protected areas became regarded as suitable sites for restocking giant clams.

Scuba divers collected gametes (sperm and eggs) in plastic bags and took them to the boat where gametes of different individuals were mixed, thereby fertilizing the eggs.  Hatchery-raised giant clams were released as juveniles throughout the Philippines, and stewards were trained to monitor the survival and growth of restocked clams.  Giant clams have been restocked at more than 40 sites (figure 2) spread over more than 20 coastal provinces of the Philippines.  The northern region (Luzon) has received the greatest number, as it is close to MSIs hatchery.  The Hundred Islands National Park in the north has been another region of focus due to a special project funded by the Philippine Tourism Authority.

This giant clam restoration initiative has increased collaborator interest in protecting- and culturing giant clams, and improvements in practices and methods have provided valuable lessons to the restoration practitioners involved.  One important lesson learned is that restoring giant clam populations must include the strong commitment of local communities.

LINK to Othman et al.'s 2010 article in The Raffles Bulletin of Zoology.
LINK to Gomez and Mingoa-Licuanan's 2006 article in Fisheries Research.