Trinchesiidae (F. Nordsieck, 1972)

Broms, Fredrik, 2024, Diversity of nudibranchs in shallow water habitats in the region of Tromsø, northern Norway, Fauna norvegica 43, pp. 84-109 : 103-104

Family Trinchesiidae (F. Nordsieck, 1972)

Catriona aurantia (Alder and Hancock, 1843) Figure 6C

Material examined: One specimen, 18 October 2020, HIL, FB, photographic record ( Figure 6C ) ; Two specimens, HIL, 27 November 2021, 24, 16 mm, FB, NTNU-VM-84458/NUIT-1074, NTNU-VM-85717/NUIT-1075 ; One specimen, HIL, 26 May 2022, 8 mm, FB, NTNU-VM-85687/NUIT-1167 ; One specimen, HIL, 15 October 2022, 22 mm, FB, NUIT-1231 .

Localities: HIL, SFJ

Distribution and remarks: Catriona aurantia has been reported to have a wide but scattered distribution in Norway ( Evertsen &

Bakken 2005; Moen & Svensen 2020; Lundin et al. 2020). Very few Zelentia pustulata (Alder & Hancock, 1854) records exist from northern Norway. A single specimen was collected Figure 6F from Dalne-Zelenetskaya Inlet, Russia in 2006 ( Martynov et al. 2006). The present study found the species all year round. Animals were Material examined: One specimen, TPR, 30 December 2020, always found in close association with the hydroid Ectopleura larynx . FB, photographic record; One specimen, TPO, 16 February 2022, 13 Spawning was observed continuously over the year and egg masses mm, FB, NUIT-1133 ( Figure 6F ). were found close to the basal stolons of the Ectopleura colonies. The Localities: TPO, TPR present records are the first records from the Tromsø region. Distribution and remarks: Zelentia pustulata is a rare species in

Norway with only a few scattered observations ( Evertsen & Bakken

2005; Artskart 2024). The species has also been registered around Jan Trinchesia foliata (Forbes & Goodsir, 1839) Mayen and Svalbard in the Arctic. The records by the present study Figure 6D were made during winter at fouling community localities and are the first records of the species from the Tromsø region. Material examined: One specimen, HIL, 29 July 2020, FB, photographic record; One specimen, KVA, 23 October 2021, 4 mm, FB, NUIT-1055; Two specimens, KVA, 25 December 2021, 5, 2 DISCUSSION mm, FB, NTNU-VM-84538/NUIT-1098, NTNU-VM-85725/NUIT-1099; One specimen, HIL, 09 January 2022, 2.8 mm, FB, NTNU- This study presents an annotated and illustrated inventory of the VM-85705/NUIT-1116; One specimen, KVA, 30 January 2022, 3.5 marine nudibranch fauna in shallow water habitats of the Tromsø mm, FB, NUIT-1118; One specimen, HIL, 03 December 2022, 5 mm, region. Data were collected during field surveys from land between FB; NUIT-1254; One specimen, HIL, 14 November 2023, 6 mm, FB; May 2020 and December 2023. In total, 49 species or taxa, belonging NUIT-1335 ( Figure 6D ). to 19 different families were recorded during the study period. This Localities: ESU, HIL, KVA, SFJ, TVK corresponds to more than double the number of species previously Distribution and remarks: Trinchesia foliata has previously reported from northern Norway. New northerly distribution records been recorded north to Helgeland ( Evertsen & Bakken 2005) and are presented for approximately a quarter of the Norwegian nudibranch Lofoten ( Lundin et al. 2020) in Norway. Only very few and scattered fauna. In the most recent review of nudibranch distribution and records exist. In the Tromsø region, T. foliata was found to occur all diversity along the Norwegian coast, 18 different species have year round at fouling community localities. The present records are previously been recorded from the Tromsø region (Evertsen & Bakken the first from the Tromsø region and significantly extends the known 2005). Thirteen of these 18 species were observed also by the present range in distribution for the species northwards to 69 degrees N. study, whereas six of the species were not found ( Table 2). These all include deep-water species. Online records from the Tromsø region

( Artskart 2024) have recorded three further species or taxa not Zelentia ninel ( Korshunova, Martynov & Picton, 2017) recorded by the present study: Atalodoris pusilla Alder & Hancock , Figure 6E 1845, Okenia nodosa Montagu, 1808 and Rostanga sp. Bergh, 1879.

When comparing the findings of this study with the latest available Material examined: One specimen, TPR, 19 December 2021, checklists from neighboring areas to the north ( Svalbard, Palerud et 7.0 mm, FB, NUIT-1097; Two specimens, THA, 16 March 2022, al. 2004) and north-east ( Russia, Martynov et al. 2006), almost all 4, 6 mm, FB, NTNU-VM-85727/NUIT-1148, NUIT-1149 (Figure species reported from these areas were also found in Tromsø. By such 6E); One specimen, TTE, 02 April 2022, 4.9 mm, FB, NTNU- direct comparisons as above, the species richness recorded by this VM-85644/NUIT-1153; One specimen, THA, 10 November 2022, 6 study, is considerably higher than what has previously been reported mm, FB, NUIT-1243; Three specimens, THA, 29 December 2022, from the Tromsø region. In fact, the number of recorded species 1.9, 7.1, 3.8 mm, FB, NTNU-VM-85653/NUIT-1264, NUIT-1265, compare more favorably with areas such as the Maldivian Archipelago NTNU-VM-85665/NUIT-1266; Two specimens, THA, 14 January in the Indian Ocean, where 52 different species of nudibranchs were 2023, 5.0, 6.5 mm, FB, NTNU-VM-85675/NUIT-1269, NUIT-1270; collected ( Cunha et al. 2023). Similarly, from the Gujarat coast in One specimen, TPO, 03 March 2023, 2.9 mm, FB, NUIT-1271; India, 65 different nudibranch species were presented in a recent One specimen, TPO, 16 March 2023, 5.1 mm, FB, NUIT-1273; One checklist based on sampling from the area between 2014-2019 (Vadher specimen, EKJ, 29 July 2023, 5.9 mm, FB, NUIT-1302; One specimen, et al. 2020). While such comparisons make little or no sense, the TPO, 09 August 2023, 5.0 mm, FB, NUIT-1313. reason for the high species richness found in the shallow waters Localities: EKJ, HMY, KVA, THA, TPO, TPR, TTE investigated in the Tromsø region needs to be addressed. Several Distribution and remarks: Zelentia ninel was described as a reasons may explain the high species richness. First of all, rapid new species in 2017 and was then only known from the Barents Sea advances in DNA-based taxonomy and phylogeny over the past coast of northern Russia ( Korshunova et al. 2017d). The first records decades, has dramatically increased the knowledge on species from Norway, where Z. ninel was reported to occur in Troms and diversity. Consequently, several new nudibranch taxa have recently Finnmark, were recently published ( Broms et al. 2023). In Tromsø, been uncovered in northern and Arctic regions (e.g. Ekimova et al. the species was observed both at fouling community localities and in 2015, 2019, 2022; Shipman & Gosliner 2015; Kienberger et al. 2016; the stony intertidal. Animals were mainly encountered during winter Korshunova et al. 2016, 2017a, 2017b, 2017c, 2017d, 2018, 2020a, but were also occasionally found during summer. Adult animals with 2020b, 2020c, 2021, 2023a, 2023b; Lundin et al. 2017; Martynov & eggs inside their bodies were observed at all seasons. Together with Korshunova 2017; Sørensen et al. 2020; Descôteaux et al. 2021; recently published records from the Tromsø region these records Martinsson et al. 2021; Neuhaus et al. 2021; Korshunova & Martynov constitute a new southernmost distribution record and a considerable 2022). While it is beyond the scope of this study to compile or update range extension for the species. checklists outside of the study area, the true diversity in the larger geographic region of the high north is unquestionably far higher than what is reflected by regional checklists. The fact that most regional checklists are outdated in nomenclature and composition gives rise to several concerns that must be kept in mind when comparing older taxonomic inventories with more recent ones. When a species is split into several new species, old records should ideally be re-examined to avoid spurious occurrence data, but are typically left with the name they were recorded under. For example, many of the “old” records in Table 2 are records of species which has later undergone splitting, so that it is impossible to reliably compare records without re-examination. In this study, the nature of such records has, to the best of my knowledge, been addressed. It is, however, important to acknowledge that updated information of the fauna in a region is a necessary prerequisite, before it is possible to make direct comparisons or attribute new distributional data as shifts in geographical ranges (Nakhaev 2016). Indeed, many recent studies have ascribed previously low sampling effort as one of the chief factors, explaining observations of higher recorded diversity in an area compared with previous knowledge ( Bouchet et al. 2002; Evertsen & Bakken 2013; Cunha et al. 2023). Other influencing factors include sampling methodology, as well as spatial and temporal variations in populations (e.g. Nybakken 1978; Evertsen & Bakken 2002; Domenech et al. 2002; Betti et al. 2017; Cyrne et al. 2018; Lombardo & Marletta 2021). As for methodology, all sampling in the present study was conducted from land in very shallow waters, with most observations being made at depths no greater than 0.5 meters. Surveys were also to a large degree conducted at fouling community localities. Such localities are difficult to compare with natural habitats, as they may be affected by anthropogenic activities which can increase connectivity between distant localities ( Bishop et al. 2017). Of the few studies that have investigated nudibranch diversity in shallow waters, Clarke (1975) found that the maximum occurrence of most species occurred in a zone extending from the low subtidal to a depth of about 3 m below mean low water. Whereas highest diversity was found in this shallow belt, most species did not utilize the actual intertidal zone despite the presence of food items there ( Clarke 1975). The low diversity of intertidal species was instead explained by the high thermal sensitivity of nudibranchs, and the wide temperature range of the intertidal. Other studies have reported high diversity in the intertidal ( Morley & Hayward 2015). Some nudibranchs have even been found to tolerate emersion above water during low tides ( Cyrne et al. 2018). This phenomenon was frequently observed also in the present study. Even in wintertime in Tromsø, when ice formed rapidly between tides, several species ( Acanthodoris pilosa , Cuthonella concinna , Dendronotus frondosus and Palio dubia ) were found to tolerate emersion between tides (F. Broms, personal observation). Previous studies from northern Norway have emphasized SCUBA-diving as a crucial methodology for documentation of this otherwise difficult to sample species group ( Evertsen & Bakken, 2002). The area investigated by the present study, have next to no overlap with previous sampling conducted by SCUBA divers, or traditional sampling techniques from research vessels. The diversity recorded here is, therefore, likely to only represent a fraction of the true diversity of the region. Yet, while SCUBA diving probably remains the most versatile sampling method for nudibranchs, it may, nonetheless, under-sample shallow habitats. While sampling in shallow waters miss out on deeper living species, the accessibility of the habitat makes it possible to carry out more exhaustive surveys. The risk of overlooking small species is also reduced compared with SCUBA diving. Of even higher importance is probably spatial and temporal variations in populations. If we want to understand species richness in an area, long-term observations of populations are crucial, but such data is very scarce in the literature. Most nudibranch species are short-lived, and sudden and dramatic changes in nudibranch populations have been widely reported by many authors ( Nybakken 1978; Todd 1981; Claverie & Kamenos 2008). Peaks in occurrence are therefore easily missed, unless long-term monitoring of populations are conducted ( Larkin et al. 2017). In addition, annual and interannual variation in water temperature may have profound effects on dispersal, settling and survival of larvae and thus diversity ( Clarke 1975). The present study is by no means a complete inventory of the nudibranch fauna of the Tromsø region. Long term survey efforts of assemblages are needed to study whether newly recorded occurrences reflect actual range expansions, or only temporary appearances due to favorable environmental conditions. Whereas it is beyond the scope of the present study to investigate seasonal occurrence in the area, locality surveys were nevertheless performed at all seasons of the year, during both night and day during a total study period spanning 44 months. It is therefore likely that this study was able to document most of the species occurring in shallow water habitats in the region. While all the above-mentioned factors may influence the diversity recorded in regional inventories, the high diversity recorded in the Tromsø region is, nonetheless, striking. While no comparative measurements of diversity were performed, species richness was found to be high both at fouling community localities and in the intertidal. Maximum number of recorded species during a single locality survey was 24 species. The fact that a higher number of species was recorded on a single locality visit, than the number of species previously recorded historically from the two northernmost counties in Norway pooled together, is noticeable. Such species richness compares, or even exceeds, that recorded at the biodiversity hot spot “Scoglio del Corallo” in the Tyrrhenian Sea, Italy. There, 23 different species of nudibranchs were found using SCUBA-diving during a project period spanning between 2013 – 2015 ( Furfaro & Mariottini 2016). Other recent studies reporting high diversity, include a survey from the coastal western Mediterranean where 16 nudibranch species were recorded throughout a year ( Salvador et al. 2022). A survey across the Indonesian coral reef ecosystem recorded 18 nudibranch species from 16 localities ( Dharmawan et al. 2021). While many new records presented by the present study are, likely, a result of increased sampling effort, there is also strong reason to believe that several species have expanded their distribution northwards in recent years. Many of the species found in Tromsø for the first time were fairly large and conspicuous and were found in easily accessible habitats. Such factors, together with the fact that many of the records were made of spawning populations over several consecutive years, indicate possible real shifts in distribution patterns. Several of the species that were found to be commonly occurring in Tromsø, while never previously recorded from the region, include species that have recently been found for the first time in Arctic Russia. Such species, where poleward range extensions have been attributed to climate warming ( Martynov et al. 2006; Ekimova et al. 2019; Korshunova et al. 2021), include Catriona aurantia , Carronella sp. , Doris pseudoargus , Doto fragilis , Eubranchus scintillans , Polycera quadrilineata and Tergipes tergipes . These species do, in all probability, have a wide distribution along all the coast from Tromsø to the Russian border. Several other species are likely to belong to the same category, e.g.: Aeolidia filomenae , Amphorina andra , Candiella plebeia , Coryphella browni , Coryphella chriskaugei , Coryphella gracilis , Coryphella lineata , Dendronotus europaeus , Dendronotus lacteus , Dendronotus robustus , Facelina auriculata , Favorinus branchialis and Polycera norvegica . None of these species have previously been recorded in the Tromsø region, yet they were found to be commonly occurring during this study. These species are therefore anticipated to have a wider distribution along the Norwegian coast than currently known. However, as pointed out in the Results, re-examination of old records is needed to establish if these species have already been recorded in northern Norway, but under other names.Yet other, more inconspicuous species, such as Cuthonella concinna , Doto cf. maculata , Eubranchus rupium , Trinchesia foliata and Zelentia ninel probably also have well established populations in northern Norway. Because of their tiny size and low sampling effort in shallow waters, they may simply have been overlooked previously. Most of these species have also been recorded from Russian waters, and the present findings from Tromsø do not imply any recent change in distribution. Species only rarely encountered in this study such as Aegires punctilucens , Aeolidiella glauca , Coryphella cf. monicae , Coryphella cf. orjani , Doto cf. millbayana , Edmundsella pedata , Eubranchus exiguus , Facelina bostoniensis , Hero formosa , Limacia clavigera , Palio nothus and Zelentia pustulata probably reflect true rarity, spatio-temporal rarity, or species that are only infrequently encountered in such shallow waters as those investigated by the present study. In conclusion, this study reports on a high species richness from a region which is positioned in a biogeographic transition area from boreal to Arctic waters ( Spalding et al. 2007; Jirkov 2013). While several studies have found recent shifts in nudibranch distribution ranges to be explained by climate change, or other changes in environmental factors ( Schultz et al. 2011; Nimbs & Smith 2018; Goddard et al. 2018), range shifts have also been explained by the lack of pre-existing baseline data or improvement of previous knowledge due to increased search effort and differences in sampling methodology ( Bertsch 2014; Nekhaev 2016; Chow et al. 2022; Salvador et al. 2022; Cunha et al. 2023). In light of this, the results from this study highlights the importance of an updated understanding of the distribution of marine species for effective monitoring of marine systems. As such knowledge requires reliable identifications, this study underscores the indispensability of adding molecular methods, such as DNA barcoding, to delimit species in future studies. Furthermore, the need for long term monitoring of spatial and temporal variability in nudibranch occurrences, is crucial in order to understand the persistence of species in their new ranges and determine whether the observed occurrences are persistent or temporary. Long term monitoring in relation to life history traits and environmental factors should be investigated across a wider biogeographical region in the sub-Arctic and Arctic sectors of the Northeast Atlantic. By presenting baseline biodiversity data of nudibranchs from the Tromsø region for the first time, this study hopes to serve as a baseline for more detailed studies focused on monitoring biodiversity in the Arctic region in the future.

Figures

Figure 6. A. Eubranchus scintillans, NTNU VM-85695/NUIT-1183, B. Tergipes tergipes, NTNU VM-84516/NUIT-1068, C. Catriona aurantia, photo record, 18 October 2020, D. Trinchesia foliata, NUIT-1335, E. Zelentia ninel, NUIT-1149, F. Zelentia pustulata, NUIT-1133. Scale bar: 10 mm. All photos: Fredrik Broms.