Aim Invasive species are of increasing global concern. Nevertheless, the mechanisms driving further distribution after the initial establishment of non‐native species remain largely unresolved, especially in marine systems. Ocean currents can be a major driver governing range occupancy, but this has not been accounted for in most invasion ecology studies so far. We investigate how well initial establishment areas are interconnected to later occupancy regions to test for the potential role of ocean currents driving secondary spread dynamics in order to infer invasion corridors and the source–sink dynamics of a non‐native holoplanktonic biological probe species on a continental scale. Location Western Eurasia. Time period 1980s–2016. Major taxa studied ‘Comb jelly’ Mnemiopsis leidyi. Methods Based on 12,400 geo‐referenced occurrence data, we reconstruct the invasion history of M. leidyi in western Eurasia. We model ocean currents and calculate their stability to match the temporal and spatial spread dynamics with large‐scale connectivity patterns via ocean currents. Additionally, genetic markers are used to test the predicted connectivity between subpopulations. Results Ocean currents can explain secondary spread dynamics, matching observed range expansions and the timing of first occurrence of our holoplanktonic non‐native biological probe species, leading to invasion corridors in western Eurasia. In northern Europe, regional extinctions after cold winters were followed by rapid recolonizations at a speed of up to 2,000 km per season. Source areas hosting year‐round populations in highly interconnected regions can re‐seed genotypes over large distances after local extinctions. Main conclusions Although the release of ballast water from container ships may contribute to the dispersal of non‐native species, our results highlight the importance of ocean currents driving secondary spread dynamics. Highly interconnected areas hosting invasive species are crucial for secondary spread dynamics on a continental scale. Invasion risk assessments should consider large‐scale connectivity patterns and the potential source regions of non‐native marine species.

In this study, size compositions of Aurelia aurita (Linnaeus, 1758), Pleurobrachia pileus (O. F. Müller, 1776) and Mnemiopsis leidyi A. Agassiz, 1865 were presented seasonally between March 2015 and February 2016 at the Sinop Peninsula of Black Sea. Sampling was carried out monthly at the 6 stations by plankton net (50 cm diameter mouth opening, 500 µm mesh size for horizontal tows, 210 µm mesh size for vertical tows). Small sized individuals of A. aurita, M. leidyi and P. pileus were found dominant in summer. Bigger size individuals were observed for A. aurita in spring, M. leidyi in winter, and P. pileus in autumn. A. aurita ˂4 cm was determined as 57%, M. leidyi ˂2 cm was 58% and P. pileus ˂ 0.6 was determined as 67%. Maximum and minimum lengths were measured 28 cm and 0.5 cm for A. aurita, 2 cm and 0.2 cm for P. pileus, 9 cm and 0.2 cm for M. leidyi, respectively. The size distribution of A. aurita, M. leidyi and P. pileus showed significantly different (ANOVA, p˂0.05) between seasons.

ÖZBu çalışmada Karadeniz'de avlanan mezgit (Merlangius merlangus euxinus) balığının aylık olarak boy-ağırlık ilişkisi ve boy kompozisyonu belirlenmiştir. Araştırma verileri Kasım 2012-Ekim 2013 tarihleri arasında Sinop ve Samsun bölgelerinde avcılık yapan ticari balıkçı gemilerinden (dip trolü ve uzatma ağı) elde edilmiştir. Örneklenen mezgit balıklarının total boy ve ağırlık ölçümleri kaydedilmiş ayrıca balıklarda cinsiyet tespiti yapılmıştır. Araştırma süresince tüm veriler genel, dişi, erkek ve belirsiz olmak üzere değerlendirilmiştir. Türün genel, dişi, erkek, belirsiz olarak ortalama total boyu 13.25 ±0.04 cm, 13.72 ±0.05 cm, 13.01 ±0.04 cm, 10.78 ±0.12 cm ve genel boy-ağırlık ilişkisi W=0.0068L3.0202 (n=2173; R=0.987) şek-linde hesaplanmıştır. Mezgit balığının boy kompozisyonu ve boy-ağırlık ilişkisinin aylık olarak farklılık gösterdiği (p<0.05), "b" değerinin aylara göre <3 yada >3 şeklinde değiştiği tespit edilmiştir. Türün genel olarak izometrik bir büyümeye sahip olduğu, Aralık 2012, Ocak, Şubat, Ağustos ve Eylül 2013 aylarında pozitif allometrik büyüme, diğer aylarda ise negatif allometrik büyüme gösterdiği saptanmıştır. Balıklarda boy-ağırlık ilişkisi çalışmalarının belirli bir veya birkaç dönem dikkate alınarak yapılması "b" değeri üzerinde yanıltıcı olabilmektedir. Balığın yaşamı boyunca birçok iç ve dış faktörler (beslenme, üreme, büyüme, tür içi ve dışı rekabet, yaşam sahası, mevsim, sıcaklık, tuzluluk ve kirlilik gibi) nedeniyle etkilenebileceğin-den populasyon dinamiği çalışmalarında daha geniş ölçekli ve detaylı veri alımına dikkat edilmelidir.Anahtar Kelimeler: Mezgit (Merlangius merlangus euxinus), Boy-ağırlık ilişkisi, Boy kompozisyonu, Aylık izleme, Karadeniz ABSTRACT DETERMINATION OF MONTHLY LENGTH-WEIGHT RELATIONSHIPS AND LENGTH COMPOSITION OF WHITING (Merlangius merlangus euxinus) CAPTURED FROM THE BLACK SEA COASTS (SİNOP-SAMSUN)Monthly length-weight relationship and length composition of whiting (Merlangius merlangus euxinus) were determined from the Black Sea coasts in the study. Study data were obtained between November 2012 and October 2013 from commercial fishing vessels (demersal trawl and gillnets) in the Samsun and Sinop regions. Total length and weight of sampled whiting were measurement and also determined gender of fishes. Mean length for general, female, male, unsexed and general lengthweight relationship of whiting were calculated 13.25 ±0.04 cm, 13.72 ±0.05 cm, 13.01 ±0.04 cm, 10.78 ±0.12 cm and W=0.0068L 3.0202 (n=2173; R=0.987) respectively. It was determined that length composition and length-weight relationship of whiting monthly differed. Values of "b" for the months were found to change as <3 or >3. Whiting has as generally isometric growth but positive allometric growth showed for December 2012, January, February, August and September 2013 and negative allometric growth showed for other months were established. It may be inaccurate on the value of "b" that the studies of length-weight relationship in fishes is done considering specific or several periods. Because of...

Some population parameters of gelatinous macrozooplankton species, Mnemiopsis leidyi, were studied in the present study carried out from January 2008 to December 2008 along the coasts of Sinop in the Black Sea. A total of 980 M. leidyi specimens were measured and weighed. The estimated average length and weight of the species were 3.2±0.060 cm and 7.3±0.250 g, respectively. The observed maximum and minimum lengths were 10.8 cm and 0.2 cm. The maximum and minimum weights measured were 63 g and 0.1 g. The length-weight relationship equation for M. leidyi was determined to be W = 0.7905L1.6406.