ORIGINAL ARTICLE Bulletin of the Maritime Institute in Gdańsk

Distribution and abundance of larvae of elegans () in the southern Rozmieszczenie i liczebność larw (Decapoda) w południowym Bałtyku

Diana Dziaduch Maritime Institute in Gdańsk, Department of Aquatic Ecology, Gdańsk, Poland

Article history: Received: 29.04.2016 Accepted: 23.08.2016 Published: 07.09.2016

Abstract: The assessment of the appearance of non-indigenous residing in benthic habitats are primarily based on know- ledge obtained from their adult stage. However, most of benthic organisms have a planktonic larval stage during their early developmental phase and such a trait is believed to be behind their efficient large-scale spread. The prawn Palaemon elegans invaded into the western part of the Baltic Sea in the 1990s and by 2011 the species had colonized almost the whole sea. Currently, P. elegans has become the most common prawn species inhabiting coastal and open sea areas. The aim of this preliminary survey is to examine spatial distribution, abundance and dispersal ability of the larvae of P. elegans. Ma- terial for the studies was collected from the open waters of the southern Baltic Sea (the Gdańsk and Bornholm Basins and the Słupsk Furrow) in summers 2007 and 2008. Larvae (zoeal stages) and also postlarval stages of P. elegans were common in the whole study area and their densities were highest in the Bornholm Basin. Their maximum abundance reached up to 500 ind. · 1000 m-3 in August 2007. In the Słupsk Furrow and the Gdańsk Basin these prawns were found in much lower numbers (about 10 ind. · 1000 m-3). The current study indicates that the dispersal of the larvae of P. elegans with the water currents is one plausible mechanism of the large scale spread of this invasive species to the south-eastern coast of the Baltic Sea as well as, the study confirmed, that the new prawn has high reproductive potential.

Keywords: larvae, Palaemon elegans, Baltic Sea, distribution, abundance

Streszczenie: Kolonizowanie siedlisk bentosowych przez gatunki obce stwierdza się przede wszystkim po obecności ich form doro- słych. Większość organizmów bentosowych posiada w swoim cyklu życiowym postać larwalną i to na tym etapie roz- woju następuje efektywne i rozległe rozprzestrzenianie się gatunków obcych. Krewetka Palaemon elegans pojawiła się w zachodniej części Bałtyku w latach 90. XX wieku i do 2011 r. skolonizowała prawie całe morze. Obecnie, P. elegans jest najbardziej powszechnym gatunkiem krewetki zasiedlającym przybrzeżne i otwarte wody Bałtyku. Niniejsze badania wstępne mają na celu przedstawienie rozkładu przestrzennego, liczebności oraz możliwości rozprzestrzeniania się larw P. elegans. Materiał do badań zebrano z wód otwartych południowego Bałtyku (Basen Bornholmski, Rynna Słupska i Basen Gdański) latem 2007 i 2008 r. Larwy (stadia zoea) oraz postlarwy P. elegans były powszechne w całym rejonie badań, jednak najliczniej występowały w Basenie Bornholmskim. Ich maksymalna liczebność wyniosła 500 osob. · 1000 m-3 w sierpniu 2007 r. Krewetki te odnotowano również w Rynnie Słupskiej i Basenie Gdańskim, jednak w dużo niższej liczbie, około 10 osob. · 1000 m-3. Niniejsza praca potwierdziła, że rozprzestrzenianie się larw P. elegans na wielką skalę wraz z prądami morskimi ku południowo-wschodnim wybrzeżom Bałtyku oraz wysoki potencjał rozrodczy krewetki jest jednym ze sposobów kolonizacji Bałtyku przez ten inwazyjny gatunek.

Słowa kluczowe: larwy, Palaemon elegans, Morze Bałtyckie, rozmieszczenie, liczebność 148

BMI, 2016; 31(1): 148-152 DOI: 10.5604/12307424.1216581 www.bullmaritimeinstitute.com ORIGINAL ARTICLE Bulletin of the Maritime Institute in Gdańsk

INTRODUCTION of meroplankton structure such as the distribution and abun- dance of larvae of Decapod in the open waters of the Most Decapoda crustaceans pass through a complex life history Baltic Sea is scarce so far. comprising a benthic (juvenile-adult) and a planktonic (larval) phase. Late stage larvae settle into shallow habitats, where adult The aim of this preliminary survey is to examine the spatial dis- prawns are an important component of coastal ecosystems. The tribution and dispersal ability of larvae of P. elegans in open wa- stock-recruitment of these crustaceans depends on the variability ters of the southern Baltic Sea. of the environmental condition affecting early life history stages.

The Baltic Sea ecosystem has been especially dynamic over recent MATERIALS AND METHODS decades. The prawn Palaemon elegans is native to the Atlantic coast of Europe and the North and Mediterranean Seas (Campbell 1994). Material for the studies was collected during cruises of the Until recently, it inhabited only the western and southern part of research vessel “Baltica” in the open waters of the southern the Baltic Sea (Köhn and Gosselck 1989, Janas et al. 2004, Grabows- Baltic Sea (the Gdańsk and Bornholm Basins and the Słupsk ki et al. 2005, Grabowski 2006, Janas and Mańkucka 2010) and very Furrow) in August 2007 (50 stations) and August 2008 (46 sta- recently the species rapidly colonized the eastern part of the Baltic tions). Samples were taken during oblique hauls of a Bongo Sea (Kotta and Kuprijanov 2012, Katajisto et al. 2013). Until now, net (500 µm and 333 µm mesh size). Sampling was indepen- P. elegans has become the most common prawn species inhabiting dent of time and daylight. The volume of filtered water was the coastal area and open waters of the Baltic Sea. measured with a flowmeter attached to the mouth of the gear. The temperature, salinity and oxygen concentration On the basis of genetic analyses and morphology, Reuschel et were recorded at each stations by CTD sonde. al. (2010) suggested that the species did not extend its natural range from the North Sea, but its colonization in the Baltic Sea is In the laboratory, the larvae of Decapoda crustaceans were most likely due to human-induced introduction from the Black or counted in the whole sample and identified to species level Mediterranean seas. The phenomenon of biological invasions in and developmental stage in accordance with the key of Fin- coastal waters is widely recognized globally including the Baltic cham (1977, 1979, 1985). The number of organisms in 1000 m3 Sea (Ojaveer and Kotta 2015). [ind. · 1000 m-3] was calculated based on the volume of filtered water during each haul. Currently, the studies of P. elegans in the southern Baltic Sea, in terms of its colonization and distribution, primarily concern the The catch efficiency of the Bongo 333 µm net, based on the length shallow water of benthic habitats and adult organisms. The data structure of the analysed palaemonid prawns, is expected to be

149 Fig 1. Spatial distribution and abundance of larvae of P. elegans [ind. · 1000 m-3] caught by the Bongo 333 µm net in the southern Baltic Sea in August 2007 in relation to seawater temperature in the surface layer.

BMI, 2016; 31(1): 148-152 DOI: 10.5604/12307424.1216581 www.bullmaritimeinstitute.com ORIGINAL ARTICLE Bulletin of the Maritime Institute in Gdańsk

Fig 2. Spatial distribution and abundance of larvae of P. elegans [ind. · 1000 m-3] caught by the Bongo 333 µm net in the southern Baltic Sea in August 2008 in relation to seawater temperature in the surface layer.

higher than the Bongo 500 µm net. Therefore, results from the Gdańsk Basin these pelagic crustaceans were found at lower den- Bongo 333 µm net was used for presentation of the distribution sities up to 10 ind. · 1000 m-3 (Fig. 1.). and abundance of the larvae of P. elegans in the study area. In August 2008, the larvae of P. elegans were less numerous in comparison to August 2007. Larvae of P. elegans dominated in RESULTS the Bornholm Basin with the highest number of 100 ind. · 1000 m-3 in the northern part of this basin, but at many sampling sta- In the Gdańsk Basin, surface water temperature reached maxi- tions in the central part of the Bornholm Basin as well as in the mally 19°C in August 2007 and 18°C in August 2008. In the Słupsk Słupsk Furrow abundance of larvae reached only 10 ind. · 1000 Furrow in August 2007 and 2008 water temperature in the surface m-3. In the Gdańsk Basin pelagic forms of P. elegans appeared layer was the same - 17°C. In the Bornholm Basin in August 2007, only sporadically at shallower stations, also in density up to surface water temperature ranged between 17°C (northern part 10 ind. · 1000 m-3 (Fig. 2.). of the basin; 16°C at one station) and 18°C (southern part of the basin), but in August 2008 temperature was there lower by one degree - 16°C in the northern part of the basin (and 14°C at two sta- DISCUSSION tions) and 17°C in the southern part of the basin (Fig. 1., Fig. 2.). Until recently the spatial range of P. elegans in the Baltic Sea Among larvae of Decapoda, two species of Palaemon were iden- was limited only to the identification of the adults. These in- tified: P. elegans and , but in this biological dividuals usually inhabit littoral zone or sublittoral. However, material the larvae of P. adspersus were very rare (only 10 indi- the larvae of the palaemonid prawns appear in open waters viduals). Also the larvae of Crangon crangon occurred in high den- of the seas (Bascinar et al. 2002). Similarly, in this study the sity during the study period. First of all, larvae (zoeal stages) and author observed the larvae of P. elegans in the whole southern also postlarval stages of P. elegans were common in the whole Baltic Sea study area. study area. The invasive P. elegans has quickly spread all over the Baltic Sea In August 2007 the larvae of P. elegans had highest densities in the and the native P. adspersus was displaced by P. elegans, which is Bornholm Basin. Their maximum abundance ranged from 101 to now the most abundant prawn in the Baltic Sea (Grabowski et 500 ind. · 1000 m-3, but at many stations in the northern and cen- al. 2005, Katajisto et al. 2013). This study also confirmed the 150 tral part of the Bornholm Basin abundance of larvae was between dominance of P. elegans larvae over other prawns in open wa- 11 and 100 ind. · 1000 m-3. Besides, in the Słupsk Furrow and the ters of the southern Baltic Sea.

BMI, 2016; 31(1): 148-152 DOI: 10.5604/12307424.1216581 www.bullmaritimeinstitute.com ORIGINAL ARTICLE Bulletin of the Maritime Institute in Gdańsk

The reproduction period of P. elegans occurs in the southern Baltic ics (Krauss and Brügge 1991, Lehmann and Hinrichsen 2000) and Sea mainly during summer seasons when environmental factors high participation of western winds, especially from the NW di- such as temperature, light cycle and food condition are the most rection (Dailidiene and Davuliene 2008), so mainly the direction favorable during the year (Guerao and Ribera 1995). The appear- of this stream runs from the Bornholm Basin through the Słupsk ance of larvae of P. elegans lasts from May to August in the Atlan- Furrow to the Gdańsk Basin and later to the east (Jankowski and tic (Fahy et al. 1998, Łapińska and Szaniawska 2005) as well as in Staśkiewicz 1994, Lehmann and Hinrichsen 2002). Dispersal of the Black Sea (Bilgin et al. 2008). During the life cycle of prawns, larvae of P. elegans with the water currents may be probably one their planktonic stages in the form of zoea and postlarvae are way of the colonization of south-eastern coast of the Baltic Sea in well adapted to swimming by bearing several pairs of functional the eastern direction that was confirmed by the occurrence of P. el- biramous thoracic legs (Knowlton and Vargo 2004). Larvae avoid egans in July 2011 in the Gulf of Finland, the Gulf of Riga, the West contact with predators living in the water column by aggregation Estonian Archipelago Sea and the Baltic Proper, that is three years and shoaling preferences beneath the water surface layer (Vino- after the present study (Kotta and Kuprijanov 2012, Katajisto et al. gradov 1970, Fincham and Figureas 1986). Megalopal forms of 2013), but it can be also the result of human introduction to new Decapoda before the transformation may be passively transport- harbors and the neighborhood. ed with the currents above the thermocline to the coastal zone (Levinton 2001). The Słupsk Furrow is a deep corridor and water from the North Sea is flowing through it in the direction of the Gdańsk and Got- During the whole study period, larvae of P. elegans were recorded land Deep. The rate of this flow is the highest in comparison with at surface water temperatures ranging from 14 to 20°C. The prawn other regions of the Baltic Sea (Drzycimski 2000, Lehmann and had highest densities in the Bornholm Basin in 2007 (17-18°C), Hinrichsen 2000, Herman and Jankowski 2001). Hence, it can be when temperature of the water in the surface layer was about 1°C assumed that the low frequency of occurrence of larvae of P. e l - higher than in the same time in 2008. Figureas (1987) stated that egans in the Słupsk Furrow is associated primarily with the strong the highest abundance of larvae of palaemonid prawns occur in dynamics of currents compared to neighboring basins (Lehmann August based on in situ study. In laboratory conditions, eggs in- and Hinrichsen 2000, 2002) and their transport in lower abun- cubation of P. elegans is possible at a temperature of at least 17°C dance eastward and northward, where low salinity did not pre- (Al-Khafaji et al. 2016). vent reproduction of P. elegans (Janas and Mańkucka 2010).

While larval survival and development could be influenced by A second hypothesis would be that larvae have limited time be- environmental conditions such as temperature and salinity (Kelly fore their metamorphoses into a first juvenile, therefore it is im- et al. 2012), dispersal ability of larvae depending on the hydrody- possible that they could reach these basins of the southern Baltic namic characteristic in the marine area, i.e. direction and velocity Sea. In this case, it is not excluded that larvae of P. elegans which of currents or derive from anthropogenic vectors from which ship were recorded in the open water of the Gdańsk Basin constituted ballast water discharges is the most popular introduction vectors broods of P. elegans population inhabiting the Gulf of Gdańsk. (Galil 2009). In like manner, Torres et al. (2012) presented several hypotheses Based on results of this study it is probable that larvae of P. elegans for explaining the presence of larvae of Palaemon macrodactylus in have been appearing in open waters of the southern Baltic Sea, the area of the Balearic Islands and exporting the larval stages to especially in the region already colonized by the species, which offshore marine areas, taking into account larval transport by cur- in 2008 was mainly the south-western part of the Baltic Sea (Dol- rents from the nearest known settled adult population. men et al. 2004, Grabowski et al. 2005, Grabowski 2006) and then were transported from the Bornholm Basin in accordance with Nevertheless, the present study of the distribution of larvae in the the circulation of surface water through the Słupsk Furrow to open waters in the light of recent ranges (Kotta and Kuprijanov Gdańsk Basin. 2012, Katajisto et al. 2013) and the good reproductive strategy of P. elegans (Janas and Mańkucka 2010) confirmed that a new species In the Baltic Sea, the direction of the water flows in the surface lay- of Decapoda in the southern Baltic Sea rapidly achieved reproduc- er depends on surface circulation resulting from Ekman dynam- tive success.

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Scientific Disciplines: Life sciences section

DOI: 10.5604/12307424.1216581

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Cite this article as: Dziaduch D.: Distribution and abundance of larvae of Palaemon elegans (Decapoda) in the southern Baltic Sea: BMI, 2016; 31(1): 148-152

Copyright: © 2016 Maritime Institute in Gdańsk. Published by Index Copernicus Sp. z o.o. All rights reserved.

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Corresponding author: Diana Dziaduch; Maritime Institute in Gdańsk, Department of Aquatic Ecology; Abrahama 1; 80-307 Gdańsk; Poland; phone: +48 58 552 00 93 or e-mail: [email protected]

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BMI, 2016; 31(1): 148-152 DOI: 10.5604/12307424.1216581 www.bullmaritimeinstitute.com