Due to the protein needs of the rapidly growing global population and fishing pressure on marine stocks, aquaculture is the main way to meet the growing demand for sustainable resource use and to provide healthy food in an environmentally friendly way (Anderson et al. 2017; FAO 2018; Boyd et al. 2020; Papa et al. 2021). In shellfish culture, live feed such as phytoplankton are only used for larval rearing in the hatchery; there is no need extra feed requirement for culture in the marine area. Because of this feature, shellfish aquaculture has a lower ecological impact on coastal ecosystems and is therefore considered highly sustainable and is referred to as a green industry (Shumway et al. 2012; Papa et al. 2021).
Bivalve culture has expanded considerably following the successful development of methods for collecting spat. The most common method is to supply species such as scallops and pearl oysters from the wild with polyethylene mesh and netlon bags (Yiğitkurt et al. 2020; Papa et al. 2021). Spat formation after metamorphosis is influenced by environmental factors, such as food availability, spawning density, water temperature, and light intensity (Lök & Acarli, 2006; Tsotsios et al. 2016). During metamorphosis, bivalve spat tend to attach to a suitable substrate (Southgate 2011), for which collectors can be used. Successful attachment depends on the depth, biological and chemical changes in the water, and the type of collector material (Acarli et al. 2011). Collecting spat is more economical than producing larvae in a hatchery. To sustain the production of bivalves, spat collection should continue annually or seasonally. The sustainability of this process depends on the survival of newly collected spat in growing systems (Burke et al. 2008; Yiğitkurt et al. 2017).
The aim of this study is to investigate the efficiency of collectors in terms of the amount of smooth scallop
This study was conducted on the Ozbek coast (38°20′19.95″N, 26°40'51.09″E) between September 2017 and August 2018 in Izmir Bay, Türkiye (Fig. 1).
The depth of the study area was approximately 6–7 m. The bottom in this area consists of sandy and partly stony sediment. This area has less fishing activity.
Temperature (°C) and salinity (PSU) were measured in situ using a mercury thermometer and a refractometer, respectively. Seawater samples were collected at two depths using a five-liter Niskin bottle. Thereafter, each liter of the seawater samples was filtered using 0.45-μm filters (Whatman GF/C). The chlorophyll-
The collector systems were positioned at the surface (1 m depth) and at the bottom (5 m depth) about 15 m away from the coast in August 2017. Samples were collected monthly from the systems between September 2017 and August 2018.
The collector systems were made from polyethylene mesh bags with PVC pipes. The height and width of the mesh bags were 50 and 20 cm (1 m2), respectively, with a mesh size of the polyethylene bag of 5 × 4 mm. A total of 72 collectors were placed in groups of three replicates in August 2017. The collector system was designed as a “surface collector” and “bottom collector” as shown in Figure 2. Each collector system consisted of eight mesh bags, four of which were placed at the surface and four at the bottom. Nine of these units were prepared and placed in the area and sampled for 12 months. The mesh bags were tied to PVC pipes with a plastic rope at 15-cm intervals. Two PVC pipes (diameter = 5 cm) were attached to the main rope at depths of 1 and 5 m, with the surface and bottom collectors on either side. A buoy (20 litres) at the top and an anchor (100 kg) at the bottom were used to keep each system stable in the water column. Six mesh bags were cut from each collector system (three surface and three bottom collectors) to be transferred to the laboratory for visual inspection at each sampling time.
In order to determine the newly attached spat and those growing on the collectors, the scallop spat were classified as <10 mm, 11–20 mm, or >20 mm according to their height. This was measured at the dorsal (hinge) and ventral edges using a Mitutoyo digital caliper (IP66). Other non-target species were counted to determine their ratio on the collector.
The Kolmogorov–Smirnov test was applied to test whether the distribution was normal. Pearson's correlation analysis was used to determine the relationship between spat attachment and environmental parameters (temperature, salinity, chlorophyll-
The water temperature at the surface was 28.4°C and 12.0°C in August and February, respectively (Fig. 3a). The bottom water temperature was highest in August (27.6°C) and lowest in January (11.3°C) (Fig. 3b). The highest salinity was recorded in August 2018 at the surface (37.5 PSU) and in June and the bottom (36.4 PSU) (Figs. 3a and 3b). While the highest value of chlorophyll-
The total number of smooth scallops detected on the all collectors throughout the study was 270.33 ± 43.54 spat m−2. Although the number of spat collected on the bottom collectors (145.66 ± 18.03 spat m−2) was higher than that of the surface collectors (Fig. 4), there was no statistically significant difference between the counts on the surface and bottom collectors (
The maximum counts of scallop spat on the surface and bottom collectors were 20 ± 3 and 44.66 ± 1.26 spat m−2, respectively. The best month for scallop spat on the bottom collectors was found to be April (Fig. 5).
The average height of the scallops on the surface collector was 4.5 mm in September and 18.47 ± 7.64 mm in August (Fig. 6a). The height of the scallops on the bottom collectors in the same months was 5.5 mm and 16.41 ± 6.71 mm, respectively (Fig. 6b). There was a statistically significant difference between the height growth of individuals in surface and bottom collectors (
During the study,
Height range of the smooth scallop on the surface collector P.S: (spat number ± SD)
Surface | n (spat m ± Sd) | Height Range (mm) | <10 mm (%) | 10–20 mm (%) | >20 mm (%) |
---|---|---|---|---|---|
Sep | 1.33±0.57 | 4.50 | 100 | 0 | 0 |
Oct | 15.00±2.00 | 6.32–18.73 | 46.66 | 53.33 | 0 |
Nov | 2.00±1.00 | 5.27–14.96 | 50.00 | 50.00 | 0 |
Dec | 18.66±1.52 | 4.00–13.40 | 84.21 | 15.78 | 0 |
Jan | 19.00±2.00 | 8.02–28.07 | 10.52 | 84.21 | 5.26 |
Feb | 12.00±2.00 | 7.40–23.40 | 16.66 | 66.66 | 16.66 |
Mar | 13.00±2.00 | 10.19–34.48 | 0 | 92.30 | 7.69 |
Apr | 2.66±2.08 | 19.50–20.50 | 0 | 50.00 | 50.00 |
May | 6.33±3.05 | 13.00–22.20 | 0 | 66.66 | 33.33 |
Jun | 4.00±2.00 | 17.00–22.20 | 0 | 50.00 | 50.00 |
Jul | 12.00±4.58 | 8.60–25.60 | 33.33 | 25.00 | 41.67 |
Aug | 20.00±3.00 | 8.50–28.90 | 30.00 | 20.00 | 50.00 |
P.S: (spat number ± SD)
Most of the scallops were collected on the bottom collector in April, including 82.22% of the scallops between 10 and 20 mm in height. No
Height range of the smooth scallop on the bottom collector
Bottom | n (spat m ± Sd) | Height Range (mm) | <10 mm (%) | 10 – 20 mm (%) | >20 mm (%) |
---|---|---|---|---|---|
Sep | 1.00 | 5.50 | 100 | 0 | 0 |
Oct | 6.00 ± 3.00 | 11.16 – 15.47 | 0 | 100 | 0 |
Nov | 9.00 ± 4.00 | 11.31 – 19.51 | 0 | 100 | 0 |
Dec | 3.00 | 6.60 – 15.40 | 66.66 | 33.33 | 0 |
Jan | 10.00 ± 1.00 | 12.43 – 28.56 | 0 | 80.00 | 20.00 |
Feb | 8.00 | 9.99 – 22.66 | 0 | 87.50 | 12.50 |
Mar | 19.00 ± 4.00 | 10.14 – 18.69 | 0 | 100 | 0 |
Apr | 44.66 ± 1.26 | 7.40 – 35.40 | 6.66 | 82.22 | 11.11 |
May | 5.00 ± 3.00 | 15.70 – 18.60 | 0 | 100 | 0 |
Jun | 14.33 ± 0.57 | 15.60 – 23.50 | 0 | 64.28 | 35.71 |
Jul | 12.33 ± 0.57 | 7.60 – 24.60 | 33.33 | 50 | 16.66 |
Aug | 13.33 ± 0.57 | 8.40 – 28.90 | 23.08 | 30.76 | 46.15 |
P.S: (spat number ± SD)
A total of 7770 non-target bivalves were collected during the study: 69.31% from the surface collector and 30.68% from the bottom collector. Economically valuable species such as
Shellfish spat of economic value on the surface collector
Sep | 11.00 ± 2.00 | 0 | 0 | 0 | 0 | 0 |
Oct | 291.00 ± 9.00 | 2.00 ± 1.00 | 48.00 ± 14.00 | 0 | 1.00 | 0 |
Nov | 189.00 ± 21.00 | 7.00 ± 2.00 | 3.00 ± 2.00 | 0 | 0 | 0 |
Dec | 160.00 ± 40.00 | 6.00 ± 5.00 | 11.00 ± 6.00 | 15.00 ± 10.00 | 1.33 ± 0.57 | 4.00 ± 2.00 |
Jan | 153.00 ± 2.00 | 9.00 ± 4.00 | 71.00 ± 30.00 | 1.33 ± 0.57 | 1.33 ± 0.57 | 1.00 |
Feb | 205.00 ± 10.00 | 23.00 ± 10.00 | 98.00 ± 30.00 | 4.00 ± 2.00 | 0 | 3.00 ± 2.00 |
Mar | 166.00 ± 20.00 | 32.33 ± 20.00 | 26.00 ± 3.00 | 0 | 1.33 ± 0.57 | 0 |
Apr | 112.00 ± 30.00 | 9.00 ± 8.00 | 1.33 ± 0.57 | 1.00 | 0 | 0 |
May | 220.00 ± 12.00 | 65.00 ± 4.00 | 14.33 ± 10.01 | 8.00 ± 4.00 | 1.33 ± 0.57 | 0 |
Jun | 180.00 ± 20.00 | 43.00 ± 30.04 | 5.00 ± 2.00 | 4.00 ± 3.00 | 1.00 | 0 |
Jul | 210.00 ± 4.00 | 35.33 ± 7.50 | 3.00 ± 2.00 | 2.00 ± 1.00 | 1.00 | 0 |
Aug | 250.00 ± 22.00 | 32.00 ± 6.00 | 2.00 ± 1.00 | 1.00 | 1.00 | 0 |
P.S: (spat number ± SD)
From the bottom collectors,
Shellfish spat of economic value on the bottom collector
Sep | 19.00 ± 4.00 | 0 | 0 | 0 | 0 | 0 |
Oct | 103.33 ± 22.54 | 2.00 ± 1.00 | 9.33 ± 3.51 | 0 | 0 | 0 |
Nov | 182.33 ± 16.25 | 19.00 ± 4.00 | 6.33 ± 2.51 | 1.00 | 0 | 0 |
Dec | 140.00 ± 20.00 | 3.00 ± 1.00 | 3.66 ± 2.08 | 21.66 ± 5.03 | 0 | 3.00 ± 2.00 |
Jan | 110.00 ± 5.00 | 39.00 ± 9.00 | 4.33 ± 2.30 | 0 | 0 | 1.00 |
Feb | 123.00 ± 10.00 | 16.66 ± 6.50 | 3.33 ± 1.52 | 0 | 0 | 0 |
Mar | 50.00 ± 12.00 | 10.66 ± 5.50 | 9.66 ± 6.02 | 0 | 1.00 | 0 |
Apr | 16.00 ± 10.00 | 11.33 ± 6.02 | 0 | 0 | 0 | 0 |
May | 24.00 ± 10.00 | 5.66 ± 2.08 | 0 | 0 | 2.00 ± 1.00 | 1.00 |
Jun | 49.00 ± 4.00 | 11.33 ± 5.50 | 0 | 0 | 0 | 2.00 ± 1.00 |
Jul | 110.00 ± 8.00 | 10.66 ± 6.02 | 0 | 0 | 0 | 1.00 |
Aug | 159.00 ± 20.00 | 9.33 ± 5.50 | 0 | 0 | 0 | 1.00 |
P.S: (spat number ± SD)
Undesirable species such as
Undesirable species on the surface collector
Ae | Ms | Li | Pl | Ph | Ml | Bs | Sc | |
---|---|---|---|---|---|---|---|---|
Sep | 13.00 ± 8.00 | 0 | 0 | 0 | 0 | 0 | 1.00 ± 0.00 | 0 |
Oct | 226.33 ± 100.59 | 1.00 ± 0.00 | 0 | 13.00 ± 4.00 | 2.33 ± 0.57 | 0 | 0 | 0 |
Nov | 313.33 ± 100.16 | 2.00 ± 1.00 | 0 | 7.00 ± 4.00 | 2.00 ± 1.00 | 0 | 0 | 0 |
Dec | 25.00 ± 3.00 | 1.00 ± 0.00 | 0 | 5.00 ± 4.00 | 7.00 ± 2.00 | 0 | 3.00 ± 2.00 | 0 |
Jan | 240.00 ± 25.00 | 4.00 ± 1.00 | 0 | 2.33 ± 0.57 | 1.33 ± 0.57 | 0 | 0 | 0 |
Feb | 457.00 ± 45.13 | 10.00 ± 2.00 | 0 | 2.00 ± 1.00 | 1.33 ± 0.57 | 0 | 0 | 0 |
Mar | 534.00 ± 50.02 | 1.33 ± 0.52 | 0 | 2.66 ± 0.57 | 0 | 0 | 0 | 0 |
Apr | 33.00 ± 10.00 | 0 | 2.00 ± 1.00 | 1.00 ± 0.00 | 2.33 ± 0.57 | 0 | 0 | 0 |
May | 270.00 ± 100.00 | 0 | 1.00 ± 0.00 | 5.33 ± 2.51 | 3.33 ± 0.57 | 0 | 0 | 0 |
Jun | 150.00 ± 25.00 | 0 | 1.00 ± 0.00 | 3.00 ± 2.00 | 3.33 ± 0.57 | 0 | 0 | 0 |
Jul | 89.00 ± 10.00 | 0 | 1.33 ± 0.57 | 4.00 ± 3.00 | 2.00 ± 1.00 | 0 | 0 | 0 |
Aug | 110.00 ± 15.00 | 0 | 1.00 ± 0.00 | 2.66 ± 0.57 | 2.00 ± 0.00 | 0 | 0 | 0 |
(BC – bottom collector, Ae –
The maximum number of
Undesirable species on the bottom collector
Ae | Ms | Li | Pl | Ph | Ml | Bs | Sc | |
---|---|---|---|---|---|---|---|---|
Sep | 6.33 ± 1.52 | 0 | 4.33 ± 1.52 | 0 | 0 | 0 | 0 | 0 |
Oct | 81.33 ± 16.92 | 0 | 14.33 ± 8.08 | 7.33 ± 2.51 | 4.66 ± 2.08 | 0 | 0 | 0 |
Nov | 276.66 ± 70.23 | 0 | 6.66 ± 2.08 | 2.00 ± 0.00 | 3.66 ± 2.08 | 0 | 0 | 0 |
Dec | 21.00 ± 7.54 | 0 | 0 | 3.00 ± 1.00 | 4.33 ± 1.52 | 1.00 ± 0.00 | 0 | 0 |
Jan | 253.33 ± 83.57 | 3.00 ± 2.00 | 5.66 ± 3.05 | 7.66 ± 2.08 | 1.00 ± 0.00 | 0 | 0 | 5.33 ± 3.51 |
Feb | 35.00 ± 8.54 | 3.00 ± 2.00 | 0 | 3.33 ± 0.57 | 0 | 0 | 0 | 4.33 ± 1.52 |
Mar | 187.33 ± 26.57 | 0 | 29.66 ± 7.63 | 1.00 ± 0.00 | 3.00 ± 1.00 | 0 | 0 | 0 |
Apr | 9.66 ± 3.05 | 0 | 7.33 ± 2.51 | 1.00 ± 0.00 | 3.00 ± 1.00 | 0 | 0 | 0 |
May | 0 | 0 | 11.33 ± 5.50 | 4.33 ± 2.51 | 4.66 ± 0.57 | 0 | 0 | 0 |
Jun | 0 | 0 | 16.00 ± 8.54 | 5.66 ± 2.08 | 7.00 ± 1.00 | 0 | 0 | 3.66 ± 1.15 |
Jul | 0 | 0 | 10.33 ± 8.08 | 6.00 ± 3.00 | 5.33 ± 1.52 | 0 | 0 | 1.33 ± 0.57 |
Aug | 0 | 0 | 6.33 ± 3.05 | 3.66 ± 1.15 | 4.33 ± 0.57 | 0 | 0 | 1.33 ± 0.57 |
(BC – bottom collector, Ae –
The collection of scallop spat has historically been the most common way of obtaining young scallops. It was greatly improved in the 1960s due to the success in collecting natural scallop spat (Kosaka, 2016). Spat collectors are set in areas of high scallop productivity where spat numbers are naturally high. Trial collectors are often laid at a variety of different sites to define the most appropriate areas. The high variability in the natural collection of scallops is a common feature of many pelagic bivalve species in the larval stage; therefore, detailed knowledge of settlement patterns and spat availability is needed to reduce costs and labor (Cry et al. 2007; Papa et al. 2021). The abundance of spat on collectors can be influenced by several factors: spawning season, time of collector deployment, suitability of the substrate, fouling and/or predation, food availability, and water conditions (Avendano et al. 2007; Acarli et al. 2011; Yiğitkurt et al. 2020; Yigitkurt 2021). After spawning, scallop larvae swim for 3–4 weeks until metamorphosis; it is very important to deploy the collectors two weeks before this period (to ensure that a microfilm layer forms on the collectors). Cry et al. (2007) reported that spat were obtained by placing artificial collectors four to six weeks after scallop spawning. Four weeks after the collectors were set out in August, 1 spat m−2 of
The spawning peak can be estimated from the recruitment of newly settled scallops by submerging artificial collectors throughout the settlement period (Cyr et al. 2007), because it takes approximately three to four weeks from veliger larvae to spat settlement. Therefore, reproduction time also may be guessed from the duration of spat attachment. The reproductive cycle may differ according to geographical region or water temperatures. For example, in the northwestern Adriatic Sea, there are two spawning peaks in July and September (Marceta et al. 2016) and spat can be collected in shallow water (2–20 m deep) in spring and summer (Tsotsios et al. 2016). In this study, the number of newly attached scallop spat settled on the collectors also allowed the reproductive period, population density, and reproduction ability of the scallops to be predicted. While the total number of spat may increase with the condition of spat attached in previous months, all individuals less than 10 mm in height in the month of sampling represent newly settled spat. Considering the months when individuals under 10 mm in height are concentrated, breeding peaks can be determined in November/December and July/August.
Prato et al. (2016) reported that the water temperatures of the study area where they collected scallop spat in Taranto varied between 12°C and 27°C and the salinity was 37–38 PSU throughout the year. Yiğitkurt et al. (2017) reported that bivalve spat were detected from collectors placed off Karantina Island, where the water temperature was between 12.5°C and 27°C and the salinity was 36.21 ± 0.15 PSU throughout the year. In this study, the water temperature varied between 12°C and 28.4°C at the surface and between 11.3°C and 27.6°C at the bottom. The average salinity was determined to be 36.30 ± 0.67 PSU at the surface and 35.8 ± 0.41 PSU at the bottom. Yigitkurt et al. (2020) reported that the most important environmental parameters triggering reproduction in bivalves are temperature and chlorophyll-
During the study,
Studies on the collection of
Location | Species | Temperature (°C) | Salinity (PSU) | Spat m−2 | Author(s) |
---|---|---|---|---|---|
Gulf of Taranto (The Mediterranean, Italy) | 12–27 | 37–38 | 181 | Prato et al. 2016 | |
Amvrakikos Gulf (Ionian Sea, Greece) | 18–29 | 22–32 | 31 | Tsotsios et al. 2016 | |
Izmir Bay (Karantina Island, Aegean Sea, Türkiye) | 12.5–27 | 36–36.5 | 160 | Yigitkurt et al. 2017 | |
Izmir Bay (Özbek Coast, The Aegean Sea, Türkiye) | 12–28.4 | 35.1–37.5 | 270 | This study | |
Izmir Bay (The Aegean Sea, Türkiye) | 12–28.4 | 35.1–37.5 | 145 (Bottom) | This study | |
Izmir Bay (The Aegean Sea, Türkiye) | 12–28.4 | 35.1–37.5 | 124 (Surface) | This study |
Fouling organisms were found on the surface and bottom collectors in varying numbers each month. In general, fouling organisms were more abundant on the surface collectors than the bottom collectors. In particular,
The observation of non-target species was expected on the surface and bottom collectors. Yigitkurt et al. (2017) reported that
As a result, it was determined in our study that scallop spat can be collected in surface and bottom waters and that the difference in depth was not statistically significant. However, there was a difference in depth in terms of newly attached spat on the collectors. Polyethylene collectors can be used in the region to collect many types of economically valuable bivalve spat. Moreover, many fouling organisms and predators were detected and recorded on the collectors. The collectors were not damaged for 12 months, and the scallops were able to grow inside the collectors. It is necessary to determine whether it is possible to create a spat stock for possible entrepreneurial activities thus there is not commercial enterprise for scallop farming in Türkiye. This study is the first in the region to collect scallop spat, so the results will guide further studies and entrepreneurial activities.