Zebra mussel

Type Description

"The shells of D. polymorpha larvae are transparent and their internal organs are visible. In adults, the ventral part is concave or flat, with a ridge forming on the sharp edges of the shell (Koç, 2009). In a study conducted in Lake Eğirdir, the average length of adult mussels was recorded as 14.4 mm (Bayhan, 1996). It is noted that the lengths of adult mussels vary between 6-45 mm and they live for 2-3 years in temperate zones (ZMIS, 2001).

Eggs: The eggs of zebra mussels are spherical and white. The eggs are released into the water through the water intake tube of the adult females (Wang and Denson, 1995).

D-shaped Larva: The D-shaped larva is the first free-swimming larval stage resulting from the metamorphosis of the trochophore larva. During this stage, D-shaped shells are formed from secretions of the shell glands. The hinge area where the shells meet is flat, and the free edges are rounded. The shells are transparent and of equal size (Altınyar et al., 2001).

Veliger Larva: The D-shaped larva transforms into a veliger larva, which is the first larval stage with a visible and colored shell. The transformation involves swelling and widening of the section near the hinge, forming a beak-like structure that covers the hinge. The veliger larva is typically shaped like an oyster rather than a triangular mussel. During this stage, the larvae increase in size and use the velum, a ciliated swimming-feeding organ, to move and feed (Nichols and Black, 1993).

Pediveliger Larva: The pediveliger larva is formed when the veliger larva develops a foot. The pediveliger larva uses both the velum and its foot to move in a circular pattern, a characteristic behavior for this stage. This is the last free-swimming larval stage in open water. The pediveliger later attaches itself to settlement substrates using its foot and settles into its environment using byssal threads (Nichols, 1996).

Settlement Stage: During this stage, which closely resembles fish eggs, the larva lacks a velum. The settled larva, which started to produce byssal threads in the pediveliger larval stage and settled into its environment, has lip-like palp organs around the mouth and no ciliated swimming-feeding organ (Altınyar et al., 2001).

Young Mussel Stage: Following the metamorphosis during the settlement stage, the mussel changes its shape from the typical oyster-like shape of larval stages to a triangular or mussel-like shape, entering the young mussel (juvenile) stage (Altınyar et al., 2001). When juveniles reach sexual maturity, they are called adults. It is accepted that juveniles, whose lengths reach 8-9 mm, reach sexual maturity and transition to the adult stage (ZMIS, 2001).

Adult Stage: Zebra mussels, as their name suggests, have bands on their shells, ranging from light to dark colors. The patterns created by these bands are highly variable in terms of both color and shape, reflecting the meaning of the species name ""polymorpha,"" which means ""many forms."" The colors of the bands can range from black to brown, with some individuals having very faint bands, while others may have shells that are entirely light brown to black (Altınyar et al., 2001).

One typical feature of adult zebra mussels, as in other species of the Dreissenidae family, is the presence of numerous strong byssal threads that emerge from the base. These attachment structures allow them to live on a variety of substrates, providing the ability to live above, rather than inside, the attachment substrate in contrast to many other mussel species (e.g., Unionidae family species) (Koç, 2009)."

Habitat

"The main environmental factors affecting mussel life include the physical and chemical properties of water (water temperature, pH, dissolved oxygen, calcium level, salinity), suitability of attachment and settlement sites, and water velocity (Neumann and Jenner, 1992).

When the larvae begin to transition to the young mussel stage, they search for a suitable surface and attach themselves to the bottom. They adhere to hard surfaces using fibers called ""byssus."" It is also known that they can attach to plants (Benson and Raikow, 2007). The density of attachment varies from hundreds of individuals per square meter to millions (Neumann and Jenner, 1992). After attaching, zebra mussels begin to erode the surface and disrupt its integrity. They remain in the same place where they attach for 3-9 years. If there is no suitable hard surface for attachment, they cluster together and attach to each other. They can also attach to macrophytes in highly alluvial and turbulent periods (Benson and Raikow, 2007; Koç, 2009).

Some zebra mussel populations in Europe have been found at river mouths, where their continuity is linked to tidal fluctuations (Benson and Raikow, 2007). The ability of mussels to adapt to oxygen-deprived conditions is limited. In an oxygen-deprived environment, they can survive for 24 hours in an environment where osmotic and ionic balance is disrupted at 20°C. Therefore, the habitat of zebra mussels is limited to the littoral zones of eutrophic waters, above the thermocline layer (Neumann and Jenner, 1992; Koç, 2009).

Dreissena can survive outside water for several days in cold and humid conditions (Benson and Raikow, 2007). Zebra mussels originated from the lakes of southeastern Russia and spread along waterways. They have been transported by ships to Northwest Russia, Central and Western Europe, Scandinavia, England, Ireland, and North America.

Natural distribution areas of the species: Drainage basins of the Black Sea and Caspian Sea and related estuaries, coastal waters, freshwater lakes, reservoirs, and rivers. The spread of D. polymorpha in Europe has been ongoing since the 18th century. It spread to all major drainage basins in Europe in the late 18th and early 19th centuries due to the construction of canal systems (Benson and Raikow, 2007; Koç, 2009).

D. polymorpha was first identified in England in 1824 and later spread to Denmark, Sweden, Finland, Ireland, Italy, and other European countries (Altınyar et al., 2001).

In North America, the mussel was found in Lake St. Clair in the Great Lakes region in 1988, and it spread to all lakes in the basin and reached the Mississippi River, reaching the Mississippi Delta in the south (Altınyar et al., 2001).

Records of Dreissena species in Turkey date back to ancient times. The presence of fossils in Neogene layers in Yapıldak area in Çanakkale proves that it is a native species (Geldiay and Bilgin, 1973). According to Geldiay and Bilgin (1973), the places where D. polymorpha is found in Turkey are Lake Eğirdir, Lake Kovada, Lake Beyşehir, and Lake Sapanca. Since 1997, the mussel species causing problems in the Atatürk Dam and HEPP has also been identified as D. polymorpha.

Places where D. polymorpha has been identified in Turkey include Lake Terkos, Lake Sapanca, Lake Akgöl, Lake Taşkısığı, Lake Acarlar, Lake Poyrazlar, Lake Eğirdir, Lake Kovada, Lake Beyşehir, Lake Bafa, and İkizcetepeler, Lake Hirfanlı, Lake Kesikköprü, Lake Kapulukaya, Lake Gazibey, Lake Keban, Lake Karakaya, Lake Atatürk, Lake Birecik, Lake Karkamış, Lake Gölköy, Lake Seyhan, Lake Çatalan, Lake Aslantaş, and Lake Derbent (Altınyar et al., 2001) and Karacaören I and II dam lakes (Gülle, 2005; Koç, 2009)."

Reproductive Information

"The reproductive cycle of zebra mussels shows significant variations in Europe, Russia, and North America. These variations cannot be fully explained by environmental factors alone. Individuals living in different regions adapt to different environments by extending or shortening their larval periods and changing their spawning times. For example, the time from fertilization to the formation of a young mussel can vary from 8 days to 240 days (Nichols, 1996; Koç, 2009).

Dreissenids are separate sexes, and fertilization occurs in the water column (Benson and Raikow, 2007). In immature individuals, the testis is seen as a distinct black stripe along the edge of the internal organs. Spermatogenesis occurs in late spring. The rate of maturation of spermatozoa increases in summer. By the end of June and mid-August, the testes are completely filled with mature spermatozoa. After the end of August, spermatozoa are not observed (Garton and Haag, 1993; Koç, 2009).

In female mussels, gametogenesis occurs similarly to males. In early spring, there are immature eggs. The development of follicles and eggs continues throughout the spring and summer. By mid-July, the ovarian follicles are filled with eggs. The eggs are mature, freely arranged, and attached to the base membrane of the follicle. Studies have shown that there are no eggs in the ovaries of samples collected after the end of August (Garton and Haag, 1993; Koç, 2009).

The average lifespan of zebra mussels is estimated to be 3-5 years. In some exceptional cases, mussels up to 10 years old have been found. Females with a shell length of 16 mm can produce 0.5 million eggs, while females with a length of 24 mm can produce 1.6 million eggs (Neumann and Jenner, 1992).

In a study conducted in Lake Eğirdir, veliger larvae were found in April at a water temperature of 13°C. Field studies concluded that spawning was most intense in July and August. Veliger larvae were observed in plankton samples until October. From September onwards, it was observed that many mature individuals in the population died. This event was thought to be a result of spawning. Young individuals dominated the population in October and November (Bayhan, 1996)."

Lifecycle

"This species' planktonic developmental stage depends on water temperature and food availability. This period, which lasts 3-5 weeks, can reach a size of up to 220 μm (Neumann and Jenner, 1992).

1st size class: 1.0-12.9 mm (0 years old),
2nd size class: 13.0-17.9 mm (1-year-old and older mussels),
3rd size class: Larger than 17.9 mm (older mussels) (Jantz and Neumann, 1998).

Trochophore Larval Stage: The trochophore larva is the first of the mussel's free-swimming stages, but it is not considered a free-swimming larva (veliger) because it lacks a shell and a ciliated swimming-feeding organ (velum), and its nutrition depends on nutrients from the egg (yolk). The trochophore larva moves with its cilia (Altınyar et al., 2001; Koç, 2009).

Veliger Larval Stages: The term ""veliger"" is used for the larval stages of bivalve mussels. The main difference from the trochophore larva is the presence of a ciliated swimming-feeding organ (velum) and a shell. This period is divided into three separate stages based on their structural characteristics: D-shaped, glochidial, and pediveliger. Before settling, the veliger larva spends 8-10 days in the water column, dispersing over long distances with the current (Füreder and Pöckl, 2007; Koç, 2009).

Attachment Phase: The attachment phase is a period in which the mussel, through the metamorphosis of its pediveliger larvae, attaches to the substrate with numerous attachment threads, which is very different from other life stages. The transition of free-swimming larvae to settled stages (plantigrade and juvenile) occurs on natural and artificial hard surfaces in the water. Young individuals attach to watercraft or fishing equipment. It is estimated that veliger larvae traveled more than 306 km in the Illinois River in North America before being noticed. The total number of mussels attached in the river in one year is estimated to be 1.94-2.13 x 10^14 (Füreder and Pöckl, 2007; Koç, 2009)."

Nutrition Information

"The main food sources of the zebra mussel are phytoplankton and zooplankton. Dreissena primarily reduces phytoplankton. It also filters out bacteria, zebra mussel veligers, microzooplankton, and other suspended matter from the water column. Veliger larvae are not as effective as sessile adults in filtration. The grazing rate of benthic adults is 103 times higher than that of veliger larvae. While zebra mussels can ingest microzooplankton such as veligers and rotifers, they cannot consume mesozooplankton. They can filter particles smaller than 1 μm but also filter larger particles. Therefore, bacteria are their most important food source. They are about 90% more effective at filtering than other mussels and oysters because they can filter very small particles. The filtration rate can vary depending on factors such as the size of the mussel, phytoplankton abundance, temperature, and suspended matter (Benson and Raikow, 2007; Koç, 2009).

In a study conducted in Lake Eğirdir, the most abundant algal species found in the mussels' stomach contents were recorded as Cocconeis pediculus, Cymbella affinis, Cymbella cymbiformis, Cymbella entricosa, and Rhoicosphenia curvata. Additionally, Amphora ovalis, Cocconeis placentula, Cymatopleura elliptica, Cymbella cistula, Denticula elegans, Denticula tenuis, Gomphonema intricatum, Gomphonema olivaceum, Gomphonema parvalum, Navicula, and Synedra ulna were also identified in the stomach contents (Bayhan, 1996).

It has been determined that the zebra mussel is a filter feeder that feeds on small algae and invertebrates, bacteria, detritus, and organic matter, with the size of the nutrients utilized by the mussel ranging from 1-35 μ. It has been noted that turbidity negatively affects the feeding of mussels, with filtration capacity decreasing as turbidity increases (Claudi and Mackie, 1994; ZMIS, 2001; Koç, 2009).

For the zebra mussel, Nannochloropsis limnetica and Cryptomonas erosa are high-quality foods containing polyunsaturated fatty acids (PUFAs). Organisms with limited PUFAs, such as Scenedesmus obliquus and Aphanothece sp. (cyanobacterium), are considered low-quality food sources for mussels (Wacker and Elert, 2003)."

General Impact Information

"To be successful in a new habitat, an organism must make adjustments in its way of life by showing seasonal adaptations and specializations (Garton and Haag, 1993). The invasion of non-native species has had the most common and harmful anthropogenic effects on the world's ecosystems. The arrival of dreissenids in the lakes and rivers of North America is a well-known example of this (Zhu et al., 2006).

Clogging in Filtration Systems:
It has been observed that Dreissena mussels proliferate excessively in the cage nets of trout farms in lakes and in the ropes attached to them, causing problems in cleaning the nets for fishermen (Öktener, 2004).
Zebra mussel issues are experienced in the Atatürk, Birecik, and Karkamış Dams and HEPPs in the lower basin of the Euphrates Basin.
• Damages in dam suction pipe closure beams, shaft seals, and trash grills,
• Effects on drinking water facilities: water pipelines, valves, and taps, as well as housing water installations,
• Effects on irrigation water facilities: water intake structures and covers,
• Effects on fisheries production stations and fish farms: dredging systems and cages,
• Effects on aquatic products: they can attach to crayfish (Astacus leptodactylus), Potamogeton pectinatus, P. perfoliatus, Myriophyllum spicatum, Chara, and crabs (Altınyar et al., 2001, Koç, 2009).

In the United States and Canada, it has been reported that the damage caused by zebra mussels in water conveyance facilities amounts to hundreds of millions of dollars, the damage in power plants between 1993-1999 is 3.2 billion dollars, the annual damage in industrial facilities and workplaces is 5 billion dollars, and the annual damage to power stations is 375,000 dollars per station (Altınyar et al., 2001).

Fouling on Watercraft:
Fouling prevents the operation of screening machines and commercial boats. It can cause overheating and damage to boat engines by settling in the cooling systems. Intense fouling occurs in transportation buoys, and many of them become unusable (Altınyar et al., 2001; Koç, 2009).

Disruption in the Food Chain:
Following an invasion that results in large populations, the zebra mussel causes significant reductions in phytoplankton biomass. When zebra mussels invaded Lake Erie in the year, it caused an 82% decrease in Diatom abundance, a 100% change in turbidity and Secchi disk visibility, and a 90% decrease in algal abundance. Measurements at the sampling station in Saginaw Bay showed a 60% decrease in chlorophyll-a. After the invasion of zebra mussels in the Hudson River, phytoplankton biomass decreased by 85% (Benson and Raikow, 2007; Koç, 2009).

The increase in light transmittance due to the decrease in turbidity positively affects the development of aquatic macrophytes. As light transmittance increases, water temperature will also increase. The decrease in phytoplankton causes a decrease in dissolved oxygen. As a result, macrophytes fill this gap because they are also a source of dissolved oxygen. However, there will be a gap between the decrease in phytoplankton biomass and the increase in macrophyte abundance. As the UV-B filtering effect of dissolved oxygen is eliminated, the filtered light will reach deeper into the water column. Natural mussel populations have decreased significantly after the invasion of zebra mussels in the Great Lakes, Hudson River, and Mississippi River (Benson and Raikow, 2007; Koç, 2009).

Changes in the food chain will also affect fish. Increased competition will lead to a reduction in zooplankton biomass, resulting in a decrease in planktivorous fish biomass. Fish larvae feeding on microzooplankton will be more exposed to the negative effects of zebra mussel invasion. Benthic-feeding fish can benefit from the increase in macrophytes, unlike planktivorous fish. Changes in the feeding habits of pelagic fish may also occur. Furthermore, the proliferation of macrophytes can change the habitat of fish. Experiments have shown that zebra mussels negatively affect the development of fish larvae due to food chain interactions (Benson and Raikow, 2007; Koç, 2009).

According to Karatayev et al. (2003), the invasion of zebra mussels has led to an increase in benthic-feeding fish populations. Altınyar et al. (2001) stated that zebra mussels have caused an increase in the number and quantity of benthic fish species. This characteristic is one of the economic benefits of the species.

By attaching to oysters, the zebra mussel hinders the operation of the oyster's valve, compresses its siphon, shares its food, restricts its movement, and empties its metabolic waste onto it. It has been reported that oysters have completely disappeared from Lake St. Clair today (Benson and Raikow, 2007). In the Great Lakes region, many known bird species are seen as predators of zebra mussels. While this may be a new food source for these predators, it is also possible that it may negatively affect fish and birds by increasing their toxins. Some researchers have a very negative view of the effects of zebra mussels. For example, the zebra mussel will disrupt both benthic and pelagic food chains, change turbidity, alter dominant phytoplankton and zooplankton species, and ultimately disrupt balances (Benson and Raikow, 2007; Koç, 2009)."

General Management Information

"Painting with Anti-Adhesive Paints: Paints or coatings containing zinc or copper prevent the attachment of zebra mussels. It is reported that, except in ecologically very necessary situations, it should not be applied (ZMIS, 2001; Koç, 2009).
Mechanical Filtration: Excessive filtration with sieves with an opening of 40 μ can be an applicable method in cooling systems with limited flow (Bobat et al., 2002; Koç, 2009).

Mechanical Cleaning: It has been reported in studies that zebra mussels can be effectively removed mechanically with wire brushes, scrapers, or other physical methods (ZMIS, 2001; Koç, 2009).

High-Pressure Water Jet Cleaning: This method can be effectively used in areas where water is drained. After cleaning, the mussels must be removed from their location (Altınyar et al., 2001; Koç, 2009).

Extremely Low-Frequency Electromagnetism (ELF-EM): In studies on the effect of extremely low-frequency electromagnetism (ELF-EM) on living organisms, it has been found that the method affects the binding and transport of ions, including calcium, in cells and tissues (Altınyar et al., 2001; Koç, 2009).

Heat Treatments: It is recorded that all mussels, including those in clusters, die after staying at -10 °C for 4 hours (Altınyar et al., 2001; Koç, 2009).

Freezing or Drying: Effective combat can be achieved by exposing mussels to air temperatures below freezing point as a result of water level decreases in winter with zebra mussel infestations (Altınyar et al., 2001; Koç, 2009).

High-Speed Flows: Water flow rates higher than 1.5 m/s prevent mussels from attaching (Altınyar et al., 2001; Koç, 2009)."

General Pathway Information

"The expansion of Dreissena species' distribution areas is widely accepted to be mainly due to maritime transportation and the discharge of ballast water from ships into non-infested areas. Other factors facilitating their spread include water plants carried by boats, water currents, and migratory waterfowl (ZMIS, 2001).

Gravel brought by a commercial cargo ship from the northern coast of the Black Sea served as a carrier that brought zebra mussels to North America. Through passive migration during the larval stage, they spread to a wide drainage area. Dreissena can survive outside water for several days in cold and humid environments (Benson and Raikow, 2007)."

Notes

"The main reason for the rapid local spread of zebra mussels is their females' ability to produce 1 million eggs in one breeding season. Additionally, during the larval stage, they can be in the plankton for several weeks and can move more than 300 km with the currents. Another reason is their ability to attach to a wide variety of hard surfaces with byssal threads and their biomass can exceed 10 kg per m2 (Astanei et al., 2005).

Information about the natural enemies of zebra mussels is provided below:

Predators: Some of the fish species that feed on zebra mussels include Esox lucius (Pike), Barbus capito pectoralis (Barbel), Tinca tinca (Tench), Stizostedion lucioperca (Zander), Oncorhynchus mykiss (Rainbow Trout), Carasobarbus luteus (Bream), Atherina boyeri (Topmouth gudgeon), Cyprinus carpio (Common carp) (Altınyar et al., 2001). Zebra mussels also serve as a valuable food source for waterfowl. It has been noted that in aquatic areas where zebra mussels settle, there is an increase in waterfowl populations; in addition, there are changes in the distribution areas, wintering places, migration times, and routes of waterfowl (Altınyar et al., 2001). Examples of birds known as predators of zebra mussels include Fulica atra (Coot), Aythya fuligula (Tufted duck), A. ferina (Pochard) (Burla and Ribi, 1988). According to initial determinations of the 10 predators found in different classes of mussels in Eurasia and North America, in our country, there are 3 species, namely Astacus leptodactylus (Crab), Yengeç (The sample taken from Kesikköprü could not be diagnosed), and Rattus norvegicus (Norway rat) (Altınyar et al., 2001; Koç, 2009).

Parasites: Zebra mussels are the first intermediate host of Bucephalus polymorphus, a parasite in zander fish (Yıldırım et al., 1996). In studies conducted on adult and juvenile mussels living in Kesikköprü Dam Lake, Aspidisca sp, Spirostomum sp, Pinnularia nobilis, Capsellira sp, Difflugia sp., and Chromadora canadensi were determined as parasitic organisms in the mantle cavity of mussels (Elibol et al., 2003). Pseudomonas fluorescens damages the digestive system of zebra mussels (Gu and Mitchell, 2002).

Competing Organisms: Competing organisms are defined as organisms that compete with mussels for settlement sites, food, and oxygen, hindering their development or causing their death. Spongilla lacustris (L.), a species of the competing sponge genus Spongilla identified in Eurasia, was also identified in Kesikköprü Dam Lake (Elibol et al., 2003)."

References