| Abstract | Dolaskom u nova staništa, invazivne strane vrste mogu negativno utjecati na stabilnost ekosustava. Jedna od 100 najinvazivnijih vrsta na Sredozemlju je plavi rak (Callinectes sapidus Rathbun, 1896) koji je detektiran i u slanoj močvari ornitološkog rezervata Palud – Palù na zapadnoj obali Istre. Kako bi se na tom području utvrdile njegove biološko - ekološke značajke, analizirane su jedinke plavih rakova prikupljene vršama i ručno od svibnja do listopada 2022. godine. Nakon određivanja spola i vaganja, jedinkama su uzete morfometrijske mjere; širina glavopršnjaka (CL) za izračun indeksa kondicije (FI %) te je analiziran sadržaj želudca. Izvagani su hepatopankreas i gonade kako bi se izračunali hepatosomatski (HSI %) i gonadosomatski indeks (GSI %) tijekom sezona. U populaciji plavih rakova u rezervat Palud – Palù od sveukupno 79 sakupljenih jedinki prevladavali su mužjaci (82 %). Najveće vrijednosti FI % zabilježene su kod mužjaka ljeti u kolovozu (9,14), a u ženki u rujnu (7,64) s trendom pozitivnog rasta. HSI % najveću srednja vrijednost oba spola pokazala je u rujnu (3,44). Kod mužjaka najveću vrijednost je imala u srpnju (2,96), a kod ženki u rujnu (6,59). Srednja vrijednost GSI % za oba spola je bila najveća u svibnju (1,61), odnosno u vrijeme mrijesta. U mužjaka najveću vrijednost imala je u svibnju (1,64), dok su u ženki visoke vrijednosti GSI % bile u svibnju (1,03) te kolovozu (2,54). Od 79 analiziranih rakova, tek 12 jedinki (15 %) imalo je prazan želudac, dok ih je šest (8 %) imalo popunjenost želudca od 75 %, a 10 jedinki popunjenost od 50 %. Jedna jedinka (1 %) imala je u potpunosti pun želudac, međutim najviše jedinki (27) imalo je popunjenost želudca od 25 %. Općenito su u prehrani plavog raka u ornitološkom rezervatu Palud – Palù prema vrijednostima F % dominirali mekušci (37,22 %), slijede ribe sa 11,7 %, dok su rakovi, kukci te morske cvjetnice imali jednake vrijednosti F % (3,19 %). U želudcu nije bilo moguće identificirati 10,64 % sadržaja, dok F % detritusa iznosi 6,38 %. Ovi preliminarni podaci o biološko-ekološkim značajkama plavog raka ukazuju da je vrsta na području ornitološkog rezervata Palud – Palù uspostavila populaciju koja može negativno utjecati na autohtonu faunu ptica, u vidu smanjenja njima raspoloživih energetskih resursa kao i na cijeli ekosustav rezervata, Stoga je potrebno redovito provoditi monitoring i razmotriti odgovarajuće mjere u cilju smanjenja njegova prodora u rezervat i/ili uklanjanje iz tog biološki vrijednog staništa. |
| Abstract (english) | Upon arriving in new habitats, invasive alien species can negatively impact ecosystem stability. One of the 100 most invasive species in the Mediterranean is the blue crab (Callinectes sapidus Rathbun, 1896), which has been detected in the saline marsh of the Palud-Palù ornithological reserve on the western coast of Istria. To determine its biological and ecological characteristics in this area, individuals of blue crabs were collected from May to October 2022. After sex determination and weighing, morphometric measurements were taken, including the width of the carapace (CL) to calculate the condition index (FI %), and stomach contents were analyzed. Hepatopancreas and gonads were weighed to calculate hepatosomatic (HSI %) and gonadosomatic indices (GSI %) during the season. In the blue crab population at the Palud-Palù reserve, out of a total of 79 collected individuals, males were predominant (82 %). The highest FI % values were recorded in males in August (9,14) and in females in September (7,64), showing a positive growth trend. The highest HSI % mean value for both sexes was observed in September (3,44). Among males, the highest value was in July (2,96), while among females, it was in September (6,59). The mean GSI % value for both sexes was highest in May (1,61), during the spawning season. In males, the highest value was in May (1,64), while in females, high GSI % values were observed in May (1,03) and August (2,54). Out of the 79 analyzed crabs, only 12 individuals (15 %) had empty stomachs, while six (8 %) had stomach fillings of 75 %, and 10 had stomach fillings of 50 %. One individual (1 %) had a completely full stomach, but the majority of individuals (27) had stomach fillings of 25 %. In the diet of the blue crab in the Palud-Palù ornithological reserve, mollusks dominated (37,22 %), followed by fish at 11,7 %, while crabs, insects, and seagrass had equal F % values (3,19 %). It was not possible to identify the content of 10,64 % of the stomach contents, while the detritus F % was 6,38 %. These preliminary data on the biological and ecological characteristics of the blue crab indicate that the species has established a population within the ornithological reserve Palud - Palù, which can have a negative impact on the native bird fauna by reducing their available energy resources, as well as on the entire ecosystem of the reserve. Therefore, it is necessary to regularly conduct monitoring and consider appropriate measures to reduce its intrusion into the reserve and/or its removal from this biologically valuable habitat. |
