Artificial reefs as a means of improving the state of aquatic ecosystems: tendencies for organization, experience of the Black Sea countries
B.G. Aleksandrov, Odessa Branch Institute of Biology of the Southern Seas NAS Ukraine, 2012 (with abbreviations)
Artificial reefs (ARs) take their beginning from coral reefs, rows formed by ridges of calcareous skeletons of coral colonies in the shallow waters of tropical seas having a high productivity and biological diversity. This effect is connected with the high specific surface of hard substrate suitable for the development of fouling communities, giving shelters to numerous invertebrates and fish, which raise their productivity and chances for survival.
The additional marginal effect takes place when intensity of physical-chemical and bio¬logical interactions greatly grows on the boundary of water-hard surface of ARs. The most significant value of ARs for human economic activity is in attraction of food fish and making them widely used. ARs have a wide spectrum of beneficial aspects and can be used: 1) for attraction and concentration of invertebrates, as well as commercial fish; 2) as an artificial substrate for egg deposits, attaching of larvae and other fry; 3) for creation of shelters for fish fry and other organisms (especially in places of cultivation); 4) for creation of optimal conditions for the formation of a stable highly productive biocoenose, a type of “refugium” for conservation of species, the existence of which is threatened by changing environmental conditions of habitats as seabed, siltation, hypoxia etc.; 5) as biofilters for clearing waters for pollutants.
As ARs can be sited on the seabed and in the water column and can have any form and dimensions, as well as be made of different materials, ARs may be defined as anthropogenic substrates making positive forms of the relief in the water column with the aim of creating a combination of abiotic and biotic characteristics differing from the background environ¬mental conditions. Taking in consideration that hydrotechnical structures, including ARs can have a biologically negative, neutral or positive influence on the aquatic ecosystem (Zaitsev, Yatsenko, 1983), only biopositive constructions will be considered in this overview.
Interrelation of artificial reefs and the aquatic ecosystem. The intensity and scale of interrelation with any physical body including a hard artificial substrate with the eco¬system of the water body is determined by its dimensions. The question of optimal dimen¬sions and shape of the ARs was considered only from the point of fish attraction. Comparing reefs of different sizes, it was shown that the AR is an attractive shelter for fish when its area is of 2,000-5,700 m3 (Rounsefell, 1972; Ogawa et al., 1977). A greater effect can be achieved, if hierarchical structural components of different sizes will be used in the ARs, creating not separate structures, but reef complexes. The minimal size of an element of the AR construc¬tions is 100-250 m3, a separate reef – 800-1,000 m3, groups of reef – 8,000-10,000 m3, reef complex – 80,000 – 100,000 m3 (Ogawa, 1982; Grove, Sonu, 1983).
Experimentally, it was shown that for successful fouling it is necessary to have cavities, holes and interstitial spaces in the AR providing good shelter for the organisms. Their size correlates with the animal size. A mathematical model has been drawn up for the qualitative assessment of the inner and outer AR structure for the purpose of receiving maximum fish productivity (Williams, Barker, 1997). As a result of natural observation, it has been estab¬lished that the height of reefs depends on the water depth. Usually this ratio of height to depth is 0.1. More recent studies (Khaylov et al., 1994) have shown a possibility of managing plant fouling communities through the structure of the physical substrate. Quantitative ratios between the phytomass and indices of the AR geometric shape have been obtained with the decrease in dimensions of the elements of reef constructions by a range of magnitude of 0.2 to 12 cm3. The intensity of their interaction with water flow raises 3 fold. A proper in¬stallation of the AR in relation to dominating current flow is more important than the struc¬ture and design of the reef itself (Ogawa, 1982).
Describing the symphysiological ties of the ARs fouling communities, not only fish, but also planktonic organisms are involved. The reef functions not only as a natural biofilter helping to reduce the concentration of pelagic organisms due to the activity of invertebrate biofilters, but it helps in ameliorating zooplankton during the breeding period of the fouling organisms with larval development stages. The biotope heterogeneity of the hard substrate due to “projections” causes plankton aggregations. Visual underwater observations show that dense aggregations of copepods (>2000 ind./dm3) occur near the projections exceed¬ing average abundance (Shadrin, 1990) which explains the attractiveness of the reefs for fish. For establishing the biotechnological basis for ARs it is necessary to study: 1) the relation of the indices of the structure and functioning of plankton and the area of hard surfaces in the water; 2) how the geometry of the reef structure determines the character of plankton distribution, feeding conditions and security of fish fry; 3) how transformations take place in the periphyton-benthos-plankton system (Shadrin, 1990).
Experience in construction of artificial reefs in the Black Sea. The first AR in the Black Sea was established along the northern Caucasus coast, Bolshoi Utrish Cape in 1972, if we do not take into consideration hydrotechnical constructions for protecting the coast from degradation. This reef of nets with rocks of average 8 m3 size was built for evaluating the prospects of applying similar constructions for ecological and fisheries ame¬lioration (Pupyshev, 1986). In 1976 – 1977 the first experimental car tires reef was built here (Darkov, Machek, 1978). Experimentally, it was proved that the reef is a habitat and breeding ground for many Black Sea species of fish. Car tires were used in many types of constructions. In 1980 1,000 tires were placed on an area of 4,500 m2 in the Dniester Liman (Goncharov, 1981).The reef made up of 160 car tires with a complicated multilayer rectangular construction (5 x 5 x 2 m) was constructed in 1985 (Fig. 5.1) at a 3.5 – 4.0 m depth at Cape Severniy, Odessa Gulf (author of AR is Yu.D. Verba – project director, senior engineer of Odessa Antilandslide Management).
Wide scale use of car tires was reached in the Sea of Azov. In the 1984 – 1987 period more than 13,000 car tires were installed in Obitochniy Bay and the Biryuchiy Island bar at an area of 469,500 m2 (Fig. 5.2). A semi industrial AR of a linear plane type for rearing gobies was used. The increase in food zoobenthos in the reef fouling and successful breeding of gobies allowed raising the commercial stock of gobies up to 67 tons (Izergin, 1990).
Besides car tires, special concrete structures were used like tetrapods (“stabilopods”) of 4.5 t weights and 2 – 25 m height for constructing reefs of any dimensions. These types were used for building modern piers with biopositive properties in the port of Constanta and Varna in 1980 (Fig.5.3). Within 5 years after the building of breakwater piers in Constanta, the average biomass of the fouling on the surface reached 26.6 kgxirr2 with animal-filtrators dominating (Gomoiu, 1989). Special reefs made of tetrapods were built on the Romanian coast for protecting coastal parts designated for aquaculture protection against pollution and for reaching the trophic base and the successful production of mussels. Similar construc¬tions were established in 1982 for protecting the beach area of Mamaia against wave action and for improving the ecological state of the impoverished biocoenosis of the sandy bottom for this part of the Romanian coast (Gomoiu, 1986) When comparing the fouling on the reef with the sandy sediment community located in the same area at the same depth, it was reg-istered that the biomass of mollusks on ARs was 28 fold, of crustaceans – 7.4 fold higher than that of bottom settlements (Gomoiu, 1989).
In 1982 shore line AR was built on the area 50,000 m2 to the west from entrance into Grygor’evsky liman, north western part of the Black Sea. This hydrotechnical construction was created for protection of collapsing abrasive shore subject to the landslides, by surpluses of the heterogeneous soils received when building Odessa Priportovy plant. Sea shore part for 1 km was formed there by the blocks of Pontic limestone. Creation of reef promoted increase of biomass of green seaweed 10 times and increase of species of marine invertebrates 3 times. It increased the number of filter feeding animals (mussels and barnacles) for 1-2 orders ac¬cording to the increase of area of hard substrata. This area of shore became the place of ac¬tive amateur fishing of gobies (Zaitsev, Yatsenko 1983).General ecological effect in connection with the AR building from the improvement of water quality was evaluated for 568,300 rubles (~ 56,800 US dollars), or more than 10 rubles on 1 м2 of AR (Lapchinskaya et al., 1987).
At the same time an AR of a sprawling type was built in the Odessa Bay. It was made up of granite rubble covered with lattice concrete sections and submerged to 1.5 – 2 m depth from the surface breakwater. In contrast to an ordinary breakwater submerged to a depth of 0.5 m, it had a larger specific surface. Comparative studies of the seaweed on the reef and breakwater have shown that in spite of low diversity, algae of the AR had greater functional activity. This is evident in the high water transparency and increase in phosphorus compounds near the reef due to the mussel fouling activity. Intense development of algae led to decline in nitrogen con¬centration of nitrates, which in turn illustrates the anti-eutrophicating effect of ARs.
Seasonal changes in glycogen content in two groups of mussels (2-3, 3-4 cm) in the Odessa Bay fouling show that it is higher in the areas with intense water exchange 2.88 and 3.80% wet weight correspondingly. Similarly, the biomass of mussels was higher than in bot¬tom settlements. A direct correlation (r =0.82) has been noted between glycogen content in mussels and temperature (Lisovskaya et al., 2002)
In 1983 an experimental “Reef” construction for growing mussels was installed at Bolshoy Fontan Cape at an 11 m depth. It was made up of 9 six-meter metallic tubes of 20 cm diameter vertically attached to a 2 x 2 m concrete frame (Vityuk et al., 1987). By 1990 up to 20 reefs were installed in Odessa Gulf. Special studies performed showed high bioameliorative qualities of “Reef” fouling, which helped to reduce the general number of heterotrophic bacteria in the water leaching them by 44% (Govorin et al., 1994).
In 1985 installation for hydrobiological treatment of oil polluted water for the Sheskharis oil base in Novorossiysk was set up and this will be discussed later. In 1987-1989 Anapa Munici¬pal Council ordered to install ARs of rubble type of large size limestone at a depth of 3-12 m in the Anapa Bay (Black Sea coast of Russian Federation). Three- year studies from an underwater apparatus showed intense development of fouling on the reef and lack of bacterial films near it showing almost complete utilization of organic matter transformed by ARs.
|Fig. 5.1. Reef made of car tires constructed at Cape Severniy, Odessa Gulf (Ukraine)|
Fig. 5.2. Car tires reef installed in Obitochniy Bay, Sea of Azov (Ukraine), 1984-1987.
|Fig. 5.3. Concrete stabilopods used for protecting the coastal zones of the sea against wave action, ports
of Varna (Bulgaria), Constanta and Mamaia resort (Romania), 1980-1982
In Turkey AR project for the Black Sea was started in 2000. Aims of the project were to prevent illegal trawling, to enhance small-scale fishery and to provide attachment substrate for mussels. AR consisted of 1000 hollow cubic units with the size 1.5 x 1.5 x 1.5 m each (deployment depth 25-30 m) in western part of the Black Sea coast of Turkey, Zonguldak city (Fig. 5.4). Realization of the project is not finished yet because of financial problems. If not taking into consideration the exploitation of a “star” type construction for cultivating mussels (Konsulov, 1980) and the tetrapods, the first ARs of a special designation were installed in November 1999 in Varna Bay for protection of benthic biocoenoses from siltation due to illegal trawling of sea snail, Rapana. These reefs were 45 truncated concrete pyramids each of 300-700 kg weight (Fig. 5.5) which were sited 4 miles from the shore on an area of 0.65 km2 .
In the Black Sea Environmental Program (GEF, UN), the building of ARs is considered to be a necessary measure for increasing mussel and benthic algae populations (including use of mariculture methods) for increasing water transparency, saturation with oxygen, binding of biogenic substances by the hydrobionts biomass (Black Sea transboundary 1997). Beside ARs are regarded as a real means of restoring the population of 20 goby species – endemic Black Sea species, half of which have commercial significance.
Summarizing the achievements of ARs in the Black Sea and the Sea of Azov it can be noted that ARs are effective in ecological amelioration of coastal waters, increasing production and biomass in the aquatic ecosystem and increasing self-purifying intensity. ARs allow management of distribution and behavior of hydrobionts. The use of ARs as an effective tool for management of aquatic ecosystems has received special attention. It has been observed that cultivated mussels have higher values of biochemical composition, especially those cultivated at upper levels of mussel culture structures or collectors than those growing wild.
As biologically positive structures, ARs affect not only the narrow coastal strip along the beaches. Animal larvae and plant spores developing on reefs are dispersed by currents at large distances inhabiting other parts of the seabed and restoring benthic communities after mortalities caused by hypoxia. ARs are not only a means of increasing the biological productivity of the shelf, but also serve as a means of hydrobiological amelioration.
After a slight lag tied with economic difficulties in former FSU countries, work on AR development has been reviewed. Since 1994 in Ukraine a project for theoretical substantiation of ARs of the National Agency of Marine Investigations and Technology on elaboration of profitable technology for optimization of the quality of sea coastal waters in highly trophic and urbanized areas of the Ukrainian Black Sea coast has been implemented (Alexandrov, 1998). Main results on elaborating the theoretical bases of hydrobiological amelioration using artificial hard substrates were received on financial support of the project.
Starting from 2007 there were new levels of activities in preparation of artificial reefs. Constructions of “reefballs” type are used practically for a long time, for example by USA and serve as basic. Nowadays 10 – 20 pilot installations of “reefballs” have been set in Ukraine, in the coastal zone of Yalta and Odessa (Fig. 5.6) AR by the project “ATLANT-M” (www.reef.atlant-m.ua) has been installed in October 2007 in the Koktebel Bay (Ukraine) at the depth of 9 m. General weight of the reef -111, height – 90 cm, bottom square – about 20 m2 (Fig. 5.7).
Unfortunately total area of the Black Sea with artificial reefs is too small – about 1 km2: Bulgaria – 650000 m2, Ukraine – 256155 m2, Romania – 155000 m2, Russian Federation -200 m2, Turkey-10 m2.
|Fig. 5.4 Artificial reefs at the coast of Turkey (Zonguldak, 1999) for protecting from illegal trawling trade||Fig. 5.5 Artificial reefs at the coast of Bulgaria for protecting from illegal trawling trade of Rapana (Varna Bay,1999)|
|Fig. 5.6 Artificial reefs “Reefball” at the coast of Odessa ( beach “Arcadia”, 2011)||Fig. 5.7 Artificial reef “ATLANT-M” in Koktebel Bay (2007)|
|Fig. 5.8 The hydrobiological purification system mounted on the pier piles in the Sevastopol Bay 15 years ago (2008)|