Vėjažuvės Belone belone (Linnaeus, 1761) nerštaviečių pasiskirstymas Lietuvos Baltijos jūros priekrantėje ir makrodumblių svarba ikrų išgyvenamumui
Gečaitė, Sandra |
Šio darbo tikslas buvo nustatyti vėjažuvės ikrų pasiskirstymo dėsningumus šiaurinėje Lietuvos Baltijos jūros priekrantės dalyje ir įvertinti makrodumblių svarbą ikrų išgyvenamumui. Darbo metu naudoti duomenys gauti iš Europos jūrų reikalų ir žuvininkystės fondo Mokslininkų ir žvejų bendradarbiavimo priemonės „Mokslininkų ir žvejų partnerystės“ projekto ,,Vėjažuvių populiacijos dinamika ir reprodukcijos ypatumai Lietuvos priekrantėje“ ir Klaipėdos universiteto Jūros tyrimų instituto mokslininkų pagalba atliktų tyrimų. Iš viso tiriamuoju laikotarpiu (2020 m., 2022–2024 m.) Lietuvos Baltijos jūros priekrantėje rastas 391 vėjažuvės ikras. Santykinis ikrų gausumas statistiškai reikšmingai yra didesnis ant raudondumblių grupės – Vertebrata fucoides, Ceramium spp., Furcellaria lumbricalis (1,82 vnt./g SB), negu žaliadumblių – Cladophora rupestris ir Cladophora glomerata (0,62 vnt./g SB). Įvertinus ikrų gausumą Lietuvos Baltijos jūros priekrantėje, nustatyta, kad vėjažuvės ikrų vidutiniškai yra aptinkama 19 vnt./m2 plote. Taikant geoinformacinių sistemų metodus nustatytos vėjažuvės potencialios nerštavietės Lietuvos Baltijos jūros priekrantėje, kurios yra išsidėsčiusios ties Šaipiais ir nuo Nemirsetos iki Palangos, iki 6 m gylyje, o jų bendras plotas yra 295 ha. Klaipėdos universiteto, Jūros tyrimų instituto Žuvininkystės ir akvakultūros laboratorijoje, atliktas vėjažuvės ikrų inkubacijos eksperimentas, palaikant natūralias vyraujančias aplinkos sąlygas (vandens temperatūra 18,9 °C ir druskingumas 6,9 psu) vizualiai pastebėta, kad praėjus 6 dienoms iš 10 ikrų išsirito 2 laisvai plaukiojančios lervos, kurių ikrai buvo prisitvirtinę ant žaliadumblio Cladophora rupestris, o ant raudondumblio Vertebrata fucoides lervų išsiritimas nebuvo užfiksuotas.
The garfish (Belone belone (Linnaeus, 1760)) is a marine species broadly distributed across the northeastern Atlantic Ocean, the North Sea, the Mediterranean Sea, and the Black Sea. During the spawning season, it also occurs in the coastal waters of the Baltic Sea (Veneranta and Urho, 2021). Over the past 35 years, climate change has led to an increase of 1,75 °C in the surface temperature of the Baltic Sea, which has not only triggered an earlier onset of garfish migration but has also contributed to the expansion of their reproductive range within this region (IPCC, 2013). In the coastal waters of Lithuania, B. belone typically spawns from May to June, when surface water temperatures reach approximately 15 °C. Observational data from the past decade suggest that garfish reproduction now occurs even in the northernmost parts of the Baltic Sea, including the Bothnian Bay and the Gulf of Finland. However, in these northern regions, reproductive success appears to be constrained by the low salinity levels characteristic of the area. Successful garfish spawning has been documented in the Wadden Sea, where reproductive conditions include a salinity of 31–34 psu and water temperatures ranging from 17,5 to 19,5 °C (Fonds et al., 1974). Eggs incubation experiments conducted by von Westernhagen (1974) determined the optimal temperature range for garfish embryonic development to be between 15–18 °C, with the most favorable salinity conditions ranging from 15 to 33 psu. Although embryonic development is still possible at salinities below 10 psu, however 5,6 psu represents a critical lower threshold (Fonds et al., 1974). The data used in this study were obtained from the European Maritime and Fisheries Fund (EMFF) under the Scientists and Fishermen Cooperation Measure, as part of the project “Population dynamics and reproductive characteristics of garfish (Belone belone) in the Lithuanian coastal zone”, and through research conducted with the support of scientists from the Marine Research Institute of Klaipėda University. Qualitative data were collected using benthic dredging with a double – sided rake equipped with barbed wire and quantitative samples were obtained through manual collection by divers, either by scraping macroalgae off the substrate by hand or by using a metal spatula within a 0.04 m² frame. The samples were analyzed using tactile examination methods: macroalgae were identified, and the number of eggs attached to them was counted. Subsequently, the macroalgae were dried at 60 °C for two days, after dry biomass was measured. The aim of this study was to determine the distribution of garfish (Belone belone) spawning grounds in the northern coastal waters of the Lithuanian Baltic Sea and to assess the significance of macroalgae for egg survival. During the study period (2020, 2022–2024), a total of 391 garfish eggs were found in the coastal waters of the Lithuanian Baltic Sea, of which 57 % were found on red macroalgae Vertebrata fucoides. The relative egg abundance on the dry macroalgal biomass is statistically significantly higher on red algae species, Furcellaria lumbricalis, Vertebrata fucoides and Ceramium spp. (1,82 pcs./g DB), compared to filamentous green algae species – Cladophora rupestris and Cladophora glomerata (0,62 pcs./g DB). The potential spawning grounds of garfish in the coastal waters of the Lithuanian Baltic Sea were identified by applying geographic information system (GIS) methods: spawning grounds are located near Šaipiai and extending from Nemirseta to Palanga, at depths of 2–6 meters, these areas cover a total of 295 hectares. Based on the egg abundance in the coastal waters of the Lithuanian Baltic Sea, it was determined that garfish eggs are found at a density of 19,2 eggs per m² in the spawning grounds. Also, an incubation experiment of garfish eggs was conducted at the Fisheries and Aquaculture Laboratory of the Marine Research Institute, Klaipėda University, on filamentous macroalgae under controlled environmental conditions (18,9 °C, 6,85 psu). Visual observations revealed that after 6 days incubation period, 2 free swimming larvae hatched from 10 eggs that were attached to the green algae C. rupestris, while no larval hatching was recorded from eggs attached to the red algae V. fucoides.