1 Introduction

Scyphomedusae, commonly known as true jellyfish, constitute a phylogenetically ancient lineage of pelagic cnidarians characterized by impressive bell diameter, vibrant coloration, and extensive tentacles. These jellyfish belong to the Phylum Cnidaria and Class Scyphozoa. They have a complex life cycle, involving alternating sexual and asexual phases, beginning as a polyp and developing into a medusa (the adult jellyfish form). The medusa stage is the most familiar phase, often seen pulsating through the water column [1]. Their conspicuous morphological features contribute to their prominence within the gelatinous zooplankton community. Beyond their visual distinctiveness, Scyphomedusae demonstrably influence marine ecosystem dynamics by promoting primary productivity and supporting diverse ecological functions. However, despite their recognized ecological and socioeconomic significance, jellyfish, including lesser-known taxa like Drymonema (Drymonematidae: Semaeostomeae), remain relatively understudied species of marine ecosystems, highlighting a substantial gap in understanding their ecological roles and impacts. This deficiency primarily arises from inherent challenges in developing effective detection and sampling methodologies, particularly for cryptic or less abundant species such as the Drymonema [2].

Exemplifying these challenges, Drymonema dalmatinum Haeckel, 1880, also known as Dalmatian mane jellyfish or stinging cauliflower, remains understudied compared to other Scyphomedusae species [3]. Widely considered as one of the largest cnidarian in the Mediterranean Sea, D. dalmatinum has an established presence within the region. Documented occurrences also exist in the Adriatic Sea [4], the Sea of Marmara [5], and the northern Alboran Sea [6]. However, owing to its rarity, sightings of D. dalmatinum in the eastern Mediterranean Sea are relatively scarce. Previous records of the species in the region include a specimen documented in the Gulf of İzmir, Türkiye, in 1887 [7], and another in the same area in 2003 [8]. Additionally, there have been reports of the species presence in the Sporades Islands, Greece, in 2015 and 2021, though these observations have not been formally confirmed or validated.

Here we report the first documented record of the Dalmatian mane jellyfish, D. dalmatinum [9], in Greek waters, adding to the limited records from the eastern Mediterranean Sea.

2 Materials and methods

Data were obtained during a routine SCUBA-based underwater biodiversity survey conducted in the Greek Aegean Sea from March to late August between 2012 and 2017. These surveys involved close-up observations and detailed documentation of encountered marine biota at depths ranging from the surface to a maximum of 20 m. Standard SCUBA equipment was employed along with a Canon PowerShot G15 high-resolution underwater camera housed in a protective casing, to capture high-quality images of observed species. Additionally, water temperature at the survey site was measured using a calibrated digital thermometer. Detailed field notes were kept, recording the date, time, specific location, depth, and water temperature to support the identification and analysis of the species encountered during the survey.

3 Results and discussion

On May 31, 2015, at 14:00 h local time, during a routine underwater biodiversity survey approximately 8 km offshore Porto Rafti, East Attica, Greece, a significant jellyfish encounter was documented (Fig. 1). The encounter transpired at 37°51′38.4"N, 24°03′00.6"E, at a depth of approximately 8 m. The water temperature at the time of the observation was 17.7 °C.

Fig. 1
figure 1

The locality of the observed Drymonema dalmatinum in the Greek waters

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The observed jellyfish was identified as D. dalmatinum based on a comparison of its morphological characteristics with established descriptions in relevant scientific literature [4, 6, 8, 13]. These characteristics comprised a translucent, milkish-white shield-shaped and flatly rounded umbrella with a thicker central part measuring approximately 24 cm in diameter, numerous tentacles longer than the bell diameter, varying in length and thickness and not grouped in distinct clusters, and intricately folded veil-like oral arms nearly matching the bell diameter in length (Fig. 2). Although the observed diameter falls short of the maximum reported size for D. dalmatinum (up to 75 cm), the presence of all these distinctive morphological features strongly supports our identification. It is important to note that the observed jellyfish could be a juvenile, which might account for its smaller size compared to fully mature individuals.

Fig. 2
figure 2

Drymonema dalmatinum observed in the Greek waters. Multiple views (a–e) highlight key morphological features (Image credit: Christos Kotselis)

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This single observation of D. dalmatinum in the Greek Aegean Sea underscores its relatively sparse occurrences in the eastern Mediterranean region. Alterations to oceanographic conditions, such as shifts in temperature regimes and current patterns, driven by anthropogenic climate change, could render the Aegean Sea a more hospitable environment for D. dalmatinum establishment [10, 11].

However, the documented record of D. dalmatinum in the Greek Aegean Sea while noteworthy, it does not indicate a range expansion or recent arrival. Due to the species' cryptic nature and the challenges associated with its detection, it is plausible that D. dalmatinum has been present in the region longer than previously detected. The species' intermittent appearances in the Aegean Sea may be attributed to its bentho-pelagic life cycle, which includes a benthic polyp stage [12]. Such a life cycle can result in prolonged absences followed by sudden reappearances, influenced by factors like temperature and food availability, which play a crucial role in jellyfish population dynamics.

The presence of D. dalmatinum in the Aegean Sea, whether consistent or sporadic, raises important considerations. As a predator of moon jellyfish, (Aurelia aurita, Linnaeus, 1758), D. dalmatinum may introduce novel trophic interactions and potentially alter existing ecosystem dynamics [13, 14]. To better understand these dynamics, particularly the predator–prey interactions between D. dalmatinum and A. aurita populations, long-term monitoring is essential. Such efforts will facilitate the development of effective management strategies to address potential impacts on marine ecosystems and human activities. These programs should incorporate citizen science initiatives to enhance data collection and provide comprehensive insights into the species' distribution and behavior. Additionally, addressing contributing factors such as climate change, eutrophication, and oceanographic conditions is crucial for developing sustainable and adaptive management approaches [11].