Endoparasites of the Imperial Cormorant (Leucocarbo atriceps) in the Falkland Islands: investigation of secondary hosts and detection methods
Hannah Métaireau, Carlos Hermosilla, Petra Quillfeldt
TL;DR
This study investigates parasites in Imperial Cormorants in the Falkland Islands, linking diet and parasite presence to understand their ecology and health impacts.
Contribution
The first report of a fish-borne trematode in free-ranging Imperial Cormorants and evidence of ray-thinned fish as paratenic hosts for anisakid nematodes.
Findings
Ray-thinned fish (Patagonotothen spp.) likely act as paratenic hosts for Contracaecum (Anisakidae) in Imperial Cormorants.
A fish-borne trematode (Heterophyidae) was detected for the first time in free-ranging Imperial Cormorants.
No direct relationship was found between the trematode and specific prey items.
Abstract
Seabirds are important apex predators and valuable sentinels of marine ecosystem health. Because they integrate signals from multiple trophic levels, their diet provides important insights into marine food-web dynamics, gastrointestinal parasite fauna, and the impacts of human activities. Changes in diet composition can affect seabird reproductive success, health status and parasite load. Many protozoan and helminth parasites depend on predator-prey interactions to complete their life cycles, making dietary analysis a useful tool for understanding parasite transmission and ecology. Here, 82 pellets were collected from an Imperial Cormorant (Leucocarbo atriceps) colony in the Falkland Islands/Malvinas Islands (51°43’S, 61°19’W) in 2020 and 2022. Preys were identified using hard remains and metazoan endoparasites using morphological and genetic identification. Parasitological analysis of…
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Figure 4- —Justus-Liebig-Universität Gießen (3114)
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Taxonomy
TopicsParasite Biology and Host Interactions · Bird parasitology and diseases · Turtle Biology and Conservation
Introduction
Knowledge of helminth associations with their hosts is crucial in understanding their complex life cycles, particularly in the marine ecosystem. However, detecting endoparasites in each host and their role during their life cycle is challenging (Garbin et al. 2019a). Several studies have been conducted to establish the life cycle of Contracaecum species experimentally (Huizinga 1966; Semenova 1979; Køie and Fagerholm 1995). Nevertheless, studying the life cycle in situ is particularly difficult due to its complexity, involving paratenic and intermediate hosts and the significant morphological similarity between the larval stages of the different species. Methods such as cadaver examination or pellet analysis are valuable for addressing such questions, as they enable the detection of adults, larval stages and/or prey items (Garbin et al. 2008, 2019a, b). Endoparasites, including protozoan and metazoan parasites, have also been detected as cysts and eggs using the standard sodium-acetate-formaldehyde (SAF) technique (Kleinertz et al. 2014). This method is commonly employed for scat sample analysis. In this study, we aimed to apply the SAF method to the remains of the pellets to determine whether this type of sample was compatible with this method for detecting endoparasites. Furthermore, we sought to investigate whether this approach could enhance the detection results of the conventional use of pellets for identifying larvae and eggs.
The Imperial Cormorant or Imperial Shag (Leucocarbo atriceps), known locally as the King Shag (order Pelecaniformes, family Phalacrocoracidae) is endemically distributed in South America, from central Chile and Argentina to their coasts and the Falklands Islands (Johnsgard 1993). Imperial Cormorants consume various marine prey, primarily feeding from the benthic zone. However, it has been shown that while females forage in coastal waters, males move into pelagic waters to feed on larger prey (Quillfeldt et al. 2011). Three groups can be identified as the primary food sources: fish, crustaceans, and cephalopods, with fish being the most important prey (Thompson 1989; Punta et al. 1993, 2003; Malacalza et al. 1994; Gosztonyi and Kuba 1998; Ferrari et al. 2004; Bulgarella et al. 2008; Michalik et al. 2010; Yorio et al. 2010; Ibarra et al. 2018; Morgenthaler et al. 2022). They are prone to endoparasites as their diet is mainly composed of fish. The Natural History Museum Host-Parasite database (Gibson et al. 2022) records helminths found parasitising Imperial Cormorants, and various studies have documented other helminths in different regions of South America (Gutiérrez 1943; Torres et al. 1990; Malacalza et al. 1998; Garbin et al. 2008, 2013, 2019a; Garbin 2009; Diaz et al. 2009; Oyarzún-Ruiz and Muñoz-Alvarado 2015). However, to our knowledge, no study has specifically investigated the parasites of the Imperial Cormorant in the Falkland Islands.
Our work aimed to assess the diet and associated endoparasites of the Imperial Cormorant colony on New Island in the Falkland Islands. This assessment was conducted by analysing pellets [regurgitated casts, primarily composed of hard food items (Michalik et al. 2010)]. Specifically, we aimed to characterise the prey and endoparasites of the Imperial Cormorant, assess whether the SAF technique can be applied to pellet remains and determine parasite-prey associations.
Materials and methods
Study area
The study was conducted at New Island, Falkland/Malvinas Islands (51°43’S, 61°19’W) in the South Atlantic, east of southern Argentina (Fig. 1). The Falkland Islands comprise 778 islands and islets, with two major islands, West and East Falkland, covering 12,200 km^2^ (Woods 2001). New Island is located in the southwest of the Falkland Islands and has been managed by Falklands Conservation since 2020. The island hosts 39 breeding bird species, accounting for 65% of the total breeding species in the Falkland Islands, and most are seabirds. Several endangered species breed on New Island, such as the Magallanic Penguin (Spheniscus magellanicus), Gentoo (Pygoscelis papua) and Rockhopper Penguins (Eudyptes chrysocome) and Black-browed Albatross (Thalassarche melanophris), which all share their rookeries with the Imperial Cormorant (Falklands Conservation 2023). The Falkland Island ecosystem is highly productive due to nutrient upwelling from the Falkland Current and the Antarctic Circumpolar Current (Agnew 2002; Van Der Grient et al. 2023), making this area attractive to many species, including seabirds. On New Island, approximately 3,000 breeding pairs of Imperial Cormorants are present in the colony. They arrive at the colony in early October for courtship and nest-building (Michalik et al. 2010). They lay eggs between early November and late December, and nestlings are present from December to March (Quillfeldt et al. 2011).
Fig. 1. Map of the Falkland Islands. The study colony is shown by a red cross
Pellet sampling
Samples were collected during the austral summer (January-February) of two breeding seasons, 2020 and 2022. The collection involved slowly walking around the colony and searching for intact pellets without major disturbance of seabirds. When a pellet was found, a protective board was used to collect pellets close to the birds, preventing bites safely. The pellets were placed in labelled tubes and stored at −20 °C until examination. A total of 82 pellets were collected, with 42 from 2020 to 40 from 2022.
Diet analysis
Once in the laboratory, the pellets were removed from the freezer and left to thaw for dissection. Each pellet was placed in a Petri dish and dissected under a binocular magnifying glass. Hard remnants, such as otoliths, squid beaks, fish bones, and polychaete jaws were removed, sorted, and placed inside tubes. The remaining material from the pellets was returned to the containers with ethanol (70%) for preservation and further analysis. The identification of the hard prey remnants was carried out under the stereomicroscope with reference guides. Otoliths were sorted by size and shape and then paired when possible. For pellets containing only fish bones, they accounted for the presence of fish. For the identification of the otoliths, the Otoliths Reference Collection available on the Global Biodiversity Information Facility (gbif.org) was used as well as some identification books (Hecht 1987; Reid 1996; Volpedo and Echeverría 2000) and help from experts (cf. Acknowledgments). Cephalopod beaks were identified using a reference guide (Xavier and Cherel 2021) and the help of experts (cf. Acknowledgments). Crustaceans were identified using an identification guide (Xavier et al. 2020). Other prey items (e.g. polychaete jaws, gastropods, and bivalves) found were identified with the help of experts (cf. Acknowledgments).
Parasite analysis
Morphological methods
Parasite larvae found inside the pellets, during the dissection, were put inside a labelled tube with ethanol (70%) to preserve them for identification. Pictures of the larvae, the anterior part, and the tail were taken, and the length of all individuals was measured using the stereomicroscope (Leica MZ 7.5). Photos were taken using an Olympus SC30 camera and the software cellSens Dimension, and can be found in the Supplementary file. Identification of the larvae was done using identification guides and articles (Anderson 2000; Garbin 2009; Garbin et al. 2013, 2019b, 2023; González-Acuña et al. 2020). Because identification based on morphology cannot provide precise information at the species level (Bhadury et al. 2006), we decided to use DNA barcoding for final species identification.
DNA amplification and sequencing
Larvae preserved in 70% ethanol were first dried to remove residual ethanol prior to DNA extraction. When multiple small larvae were recovered from a single pellet, they were pooled for a single extraction to obtain sufficient DNA for sequencing. All other samples contained a single larva, resulting in a total of 46 extraction samples. Molecular analyses were restricted to nematodes, and no protozoan-specific PCR assays were performed.
DNA extraction from the larvae was then performed using the QIAwave DNA Blood and Tissue Kit according to the manufacturer’s instructions. The extracted DNA was stored at −18 °C, and Nanodrop measurements (NanoDrop 2000, Thermo Scientific) were used to determine DNA concentration (optimal DNA concentration: 20ng/µl). A negative control was used in all PCR tests.
The mitochondrial cytochrome c oxidase subunit I (COI) region was amplified using the primer pair JB3/JB4.5 (Bowles et al. 1992). The ITS1 and ITS2 regions were amplified using the primer pairs SS1/NC13R and SS2/NC2, respectively (Shamsi et al. 2008). These primers are widely used for molecular identification of anisakid/ascaridoid nematodes. For the JB3/JB4.5 primers, PCR was performed in 25 µl containing 12.5 µl of Dream Taq Buffer (DreamTaq DNA Polymerase (ThermoScientific), 5.5 µl of water, 2.5 µl of each primer and 2 µl of DNA. The PCR conditions for the JB3/JB4.5 primer pair were as follows: initial denaturation (94 °C for 3 min), 40 cycles at 94 °C for 45 s (denaturation), 53 °C for 45 s (annealing), and 72 °C for 45 s (extension), and 72 °C for 10 min (final extension). For the SS1/NC13R and SS2/NC2 primers, the PCR mixture of 25 µl contained 12.5 µl of Dream Taq Buffer (DreamTaq DNA Polymerase (ThermoScientific), 9 µl of water, 1.25 µl of each primer and 2 µl of DNA. The PCR conditions were as follows: initial denaturation (94 °C for 5 min), 30 cycles at 94 °C for 30 s (denaturation), 55 °C for 30 s (annealing), and 72 °C for 30 s (extension), and 72 °C for 5 min (final extension). A QIAxcel Advanced (Qiagen, Switzerland) high-resolution capillary gel electrophoresis was used to visualize band heights. The PCR amplicons of positive samples were sent to Seqlab (Göttingen, Germany) for bi-directional Sanger sequencing after being purified. The results were read and assembled with CLC Main Workbench 7.6.4 (CLC Bio, Aarhus, Denmark). The resulting consensus sequences were checked, and any conflicting bases were assigned manually as far as possible. Using the NCBI Blast (GenBank), every sequence was checked for its closest match to determine the parasite genus.
SAF method
The remains of the pellets were then taken to the Institute of Parasitology of the Justus Liebig University for examination of intestinal parasites. The SAF technique was used to detect parasitic stages of helminths. Under a fume hood, a small quantity of the sample was taken (bean size) and placed in a tube containing 10 ml of the SAF solution [sodium acetate: 15 g, glacial acetic acid: 20 ml, formaldehyde (37%): 40 ml, water: 925 ml]. The sample was mixed with the liquid to make it homogeneous and then filtered over a funnel containing double-layer gauze. The tubes were centrifuged at 2000 rpm for 3 min at room temperature (RT). The supernatant was then drained. A sodium chloride solution (7 ml) was added, and the deposit was mixed using a Pasteurizer pipette. Acid ethyl ester (2.5–3 ml) was added, and the tube was shaken using a stopper. The tubes were centrifuged again at 2000 rpm for 3 min at RT, and the supernatant was drained. To identify the intestinal parasites, 2–3 drops of the sample were allocated on top of a microscope slide and examined under an Olympus BX43 light microscope (x20 – x40 magnification). Pictures were taken using an Olympus SC30 digital camera and the software cellSens Dimension, and can be found in the Supplementary file. The eggs were identified using images from (Pennycott 2016a, b).
Data analysis
The frequency of occurrence was calculated, expressed as a percentage, for the prey items and can be defined as the proportion of pellets containing a certain prey type per pellet. Prevalence expressed as percentage (i.e. the number of hosts infected with 1 or more individuals of a particular parasite species divided by the number of hosts examined for that parasite species) and mean intensity (i.e. the total number of parasites of a particular species found in a sample divided by the number of hosts infected with that parasite) were calculated for the parasites (Bush et al. 1997). Only larvae were taken into account for the mean intensity. Confidence intervals were calculated using the binom package (Dorai-Raj 2022).
To test if the detection of parasites was similar between the larvae found in pellets and the SAF, Cohen’s kappa was calculated (Cohen 1960) with the DescTools package (Signorell 2024). The results were interpreted as follows: no agreement for values ≤ 0, none to slight for values between 0.01 and 0.20, fair for values between 0.21 and 0.40, moderate for values between 0.41 and 0.60, substantial for values between 0.61 and 0.80, and almost perfect agreement for values between 0.81 and 1.00. The Cohen’s kappa is reported, along with its 95% CI. Chi-squared tests were used to compare the prevalence of parasites, and Kruskal-Wallis tests were performed to compare the intensities of the different parasites, followed by a Pairwise Wilcoxon Rank Sum Test. A correspondence analysis was performed for prey with an occurrence above 5% to visualise parasite-prey association. Chi-squared tests were performed using observed frequencies of prey and parasites to investigate associations. The level of significance was set at α = 0.05 throughout this study.
Results
Analyses of Imperial Cormorant pellets revealed 14 prey items belonging to 6 different taxa: fish, cephalopod, crustacea, gastropod, bivalve, and polychaete (Table 1).
Table 1. Frequency of occurrence (FO%) of prey items found inside the pellets (n = 82) of the Imperial Cormorant Leucocarbo atriceps from the Falkland IslandsFO (%)Fish95.1Nototheniidae Patagonotothen sp 57.3 Eleginops maclovinus 1.2Moridae Salilota australis 2.4Unidentified^a^67.1 Cephalopoda
12.2 Gonatidae Gonatus antarticus 1.2Loligonidae Doryteuthis gahi 4.9Octopodidae Enteroctopus megalocyathus 4.9Sepiolidae1.2 Crustacea
59.8 Galatheidae Munida sp 59.8Talitridae1.2 Gastropoda
7.3 Buccinidae Pareuthria atrata 3.7 Pareuthria fuscata 2.4Unidentified3.7 Bivalvia
2.4 Veneridae Ameghinomya antiqua 2.4Unidentified1.2 Polychaeta
14.6 Nereididae11.0Polynoidae6.1Unidentified2.4^a^Based on otoliths and fish bones
Based on the morphological analyses, isolated larvae corresponded to L3 according to Anderson et al. (1974). Pellet dissection detected larval stages, whereas the SAF method detected parasite eggs. Only Contracaecum spp. were detected with both methods, whereas the other parasites were detected only as larvae and trematode eggs (Heterophyidae) were detected only with SAF (Fig. 2). Considering all parasites, agreement between the two methods was considered fair with a k value of 0.31 (0.09–0.53). For Contracaecum, the agreement was moderate, with a k value of 0.45 (0.23–0.67).
Fig. 2. Prevalence of the different parasites inside pellets depending on the detection method. The bars correspond to the 95% Confidence Intervals. Numbers correspond to the prevalence for each parasite depending on the detection method
PCR amplification was successful for 43 out of 46 parasite larvae samples. The JB3/JB4.5 primers yielded a success rate of 82.6%, followed by SS2/NC2 (76.1%) and SS1/NC13R (71.4%). For three samples, only one sequence was obtained using the SS1/NC13R primers. The three samples that failed to amplify were identified as Anisakidae based on morphological examination, while all other samples were identified using genetic analyses. Sequence quality was sufficient for reliable taxonomic assignment in 45 out of 46 samples, with sequence similarity values above 90%, and one sample showing 89.8% similarity. No protozoan was detected using the SAF method, and only helminth larvae were genetically identified. Among the identified larvae, two nematode families were detected: Anisakidae and Raphidascarididae. For Anisakidae, species composition within each genus (based on successfully sequenced larvae) was as follows: Contracaecum (C. chubutensis and C. osculatum; 77.8% and 3.7%, respectively), Anisakis (A. simplex and A. pegreffii; 50% and 25%, respectively), and Pseudoterranova (P. decipiens and P. cattani; 81.8% and 18.2%, respectively). The Raphidascarididae were represented by Hysterothylacium aduncum (100%), with nine larvae detected in a single sample. In addition, eggs belonging to the trematode family Heterophyidae were detected using the SAF method, but no genetic analyses were performed on these eggs.
Anisakidae and Raphidascarididae were more prevalent than Heterophyidae (X^2^= 21.8, df = 1, p < 0.001). The genus Contracaecum had the highest prevalence, followed by Anisakis, Pseudoterranova and Hysterothylacium (Fig. 2). The difference in prevalence between the Anisakidae and Raphidascarididae parasites was significantly different (X^2^= 57.6, df = 3, p < 0.001).
In terms of mean intensities, Hysterothylacium had the highest mean intensity, although a large range was attributed to only two samples with different intensities (Fig. 3). The range of intensities for Pseudoterranova was lower, with an average of 3 larvae per pellet for this parasite genus. Contracaecum and Anisakis intensities were the lowest, with most pellets containing only 1 larva of these parasites (Fig. 3). The difference in intensities was significant (Kruskal-Wallis - X^2^ = 9.9, df = 3, p = 0.019). However, the only significant difference was between Contracaecum and Pseudoterranova (Pairwise Wilcoxon Rank Sum Test – p = 0.041).
Fig. 3. Mean intensities of parasites found as larvae inside pellets. Each dot represents the number of parasite larvae found in one pellet
The Correspondence Analysis (CA) showed an association between three anisakid parasites (i.e. Contracaecum, Anisakis and Pseudoterranova), the trematode (Heterophyidae) and ray-thinned fish (Patagonotothen sp.; Fig. 4). Hysterothylacium was not associated with any prey. Only the association between Contracaecum and Patagonotothen sp. was significant (X^2^ = 5.9, df = 1, p = 0.015).
Fig. 4. Results of the correspondence analysis showing the parasite-prey associations. Anisk: Anisakis sp; Contr: Contracaecum sp; Heter: Heterophyidae; Hyst: Hysterothylacium sp; Pseudo: Pseudoterranova sp; Dor: Doryteuthis gahi; Enter: Enteroctopus megalocyathus; Mun: Munida sp; Nerei: Nereididae sp; Patag: Patagonotothen sp; Poly: Polynoidae sp
Discussion
The Imperial Cormorant diet in the Falkland Islands consisted mostly of fish, followed by crustaceans, polychaetes, and cephalopods. This finding is consistent with other studies in this location and colonies along the Argentinian coast (Casaux et al. 1997; Punta et al. 2003; Bulgarella et al. 2008; Michalik et al. 2010; Yorio et al. 2010, 2017; Quillfeldt et al. 2011; Quintana et al. 2011; Harris et al. 2016; Ibarra et al. 2018; Morgenthaler et al. 2022). Among the fish prey, Patagonotothen sp. was found to be the most common, with some biases due to the exclusive use of otoliths for fish identification (Jobling and Breiby 1986; Johnstone et al. 1990).
Endoparasites found in the Imperial Cormorant population on the Falkland Islands were primarily nematodes from the Anisakidae family. Previous research also documented anisakid nematodes in Imperial Cormorants at various locations (Gutiérrez 1943; Torres et al. 1990; Malacalza et al. 1998; Garbin et al. 2008, 2013, 2019a; Diaz et al. 2009; Oyarzún-Ruiz and Muñoz-Alvarado 2015), many of which belong to the genus Contracaecum. The three genera of Anisakidae found in our study (Contracaecum, Anisakis, Pseudoterranova) were also found in Imperial Cormorant at the Chubut province, and Hysterothylacium was found in Red-legged cormorant (Poikilocarbo gaimardi) in the Santa Cruz province (Garbin et al. 2019a).
This study found lower mean intensity compared to others. The mean intensity of infection by Contracaecum sp. was 7.1 and 6.6 in Punta Leon for the years 1991/1992 and 1992/1993, respectively (Malacalza et al. 1998). A more recent study at the same location found similar mean intensities for three Anisakidae genera, except for Pseudoterranova, which had the highest intensity (Garbin et al. 2019a). The differences in prevalence and intensity of parasites in our study compared to others may be attributed to disparities in location. In fact, Fonteneau and Cook (2013) reported different prevalences and intensities of Contracaecum rudolphii in Kerguelen Shags (Phalacrocorax verrucosus) breeding at two colonies 25 km apart. Our findings suggest that the diet of Imperial Cormorants at our location may be less diverse than in other locations, which may be associated with lower parasite diversity.
The SAF method has enabled us to detect fish-borne trematode eggs of the Heterophyidae family. This is the first record of this intestinal fluke family parasitising the Imperial Cormorant. However, the prevalence of this endoparasite is lower than for Anisakidae. This family is frequently found in fish-eating birds (Sepulveda et al. 1994, 1996, 1999). Santos and Borges (2020) review records of Heterophyidae in South America. In Argentina, records of this family showed a predominance of the genus Ascocotyle, followed by Cryptocotyle and Pygidiopsis. However, no cormorant in Argentina was found to be infected by Heterophyidae; such infections were observed only in Brazil, Ecuador, Venezuela, and Chile (González-Acuña et al. 2020; Santos and Borges 2020). A more precise identification was impossible because Heterophyidae were only found as eggs. Other methods could be useful to gain better insight into the trematode parasites, such as nested PCR used by Hermosilla et al. (2018).
The two methods employed to evaluate the prevalence of parasites in the Imperial Cormorant produced divergent results in detecting the presence of endoparasites. Anisakids were the most prevalent parasites found with both methods. However, only larvae or eggs were found for some pellets, resulting in a lower agreement between the methods. Only Contracaecum from the Anisakidae family was found as larvae inside pellets and as eggs with the SAF technique. The other Anisakidae genera were not found by using the SAF method. This may reflect differences in host suitability among parasite genera. Heterophyid eggs were detected solely through the SAF method, with neither juvenile nor adult trematodes found in pellets. This result is surprising because we would have expected to find adult stages in the pellet when eggs are found.
Pellets are a non-invasive method that are simple to collect and have already been used in previous studies on parasites of the Imperial Cormorant (Malacalza et al. 1998; Garbin et al. 2019a). Moreover, dead Imperial Cormorants have also been examined (Garbin et al. 2008). The SAF method was applied for the first time, to our knowledge, with remnants of dissected pellets, which has been used for faecal samples originating from marine mammals and seabirds (Kleinertz et al. 2014; Ebmer et al. 2020; Fusaro et al. 2024). However, our results indicate that this method can also be used with pellets. Fusaro et al. (2024) compared three sampling techniques (eviscerated hosts, faecal samples, and regurgitates) to study endoparasites in the Southern Giant Petrel (Macronectes giganteus) in Antarctica. Viscera and faecal matter yielded superior results compared to regurgitates, but they are a valuable addition as it is challenging to access recently deceased specimens. Non-invasive techniques in parasitology have gained popularity in recent years (Hermosilla et al. 2018; Ebmer et al. 2020) compared to invasive methods like endoscopy, which necessitates a comprehensive evaluation of ethical considerations (Burthe et al. 2013). The absence of parasitic protozoa in the remaining pellets after SAF treatment may be due to the pellet material, which may not preserve protozoan cysts effectively. The SAF method could be used with scat samples from the Imperial Cormorant to confirm this hypothesis, or protozoan-specific PCR assays could be performed.
Among the parasites, the results showed a visual association between Rock cods and three parasite genera (Contracaecum, Anisakis, Pseudoterranova) and one family (Heterophyidae), but this association was significant only for Contracaecum. The lack of association between Hysterothylacium and other species is probably due to its low prevalence, which reduces the likelihood of association. In fact, studies carried out around the Falkland Islands on Rock cods have shown a wide diversity of parasites, including the nematodes found here (González et al. 2007; Brickle et al. 2021).
Among the Anisakidae, the genus Contracaecum is the only one maturing into adults in birds (Garbin et al. 2019a). In the case of this genus, several studies on its life cycle showed that copepods are the main intermediate host of Contracaecum sp., with euphausiids and amphipods playing a lesser role (Huizinga 1966; Bartlett 1996; Anderson 2000; Moravec 2009). These prey items were found in the diet of rock cods (Laptikhovsky 2004) and rock cods (Patagonotothen ramsayi) from around the Falkland Islands were found to have a high parasite diversity (González et al. 2007; Brickle et al. 2021). Together with our association results, this is consistent with rock cod likely acting as paratenic hosts for parasites infecting Imperial Cormorants. Studies on intermediate hosts around the Falkland Islands should be carried out to gain a better understanding of the life cycle of these parasites.
Even if the occurrence of fish-borne trematode (Heterophyidae) was visually associated with rock cods, it was not significant. Surveys have been conducted in the past around the Falkland Islands to assess parasites of several fish and squid species (MacKenzie and Longshaw 1995; Brickle et al. 2001, 2006; Brickle and MacKenzie 2007; González et al. 2007; Brown et al. 2013; MacKenzie et al. 2013). Further surveys are needed to better characterise trematode diversity in seabirds from this region. Although parasites belonging to the Trematoda class were found inside them, none of the species belonged so far to the Heterophyidae family. In the case of Heterophyidae, the trematode parasite is acquired through the consumption of infected fish where the metacercariae encyst in the organs (Yamaguti 1971, 1975). It is by eating a mollusc (gastropod) that the fish becomes infected. Species from this family were found as adults in seals and in penguins from San Matias Gulf, Argentina. Heterophyid trematodes were also found in Cormorant species such as the Neotropic Cormorant (Phalacrocorax brasilianus) in coastal lagoons of Mexico (Violante-González et al. 2011), the Flightless Cormorant (Phalacrocorax harrisi) in the Galapagos Islands (Carrera-Játiva et al. 2014), and the Double-Crested Cormorant (Phalacrocorax auritus) in the Mississippi Delta region (O’Hear et al. 2014). This represents the first record of this heterophyid trematode in the Imperial Cormorant. However, the identity of the intermediate hosts involved in its transmission in the Falkland Islands remains unresolved.
In addition to morphological identification, the molecular analyses performed in this study provided an important complementary line of evidence for species identification. It enabled the detection and taxonomic discrimination of anisakid taxa (Contracaecum, Anisakis, and Pseudoterranova) and the species Hysterothylacium aduncum (Raphidascarididae) from degraded pellet material, where morphological identification alone was insufficient. This taxonomic resolution allowed evaluation of parasite-prey associations, since accurate identification is necessary to link parasites with specific prey sources. The integration of molecular and morphological approaches, therefore, increases confidence in these associations and provides a more robust framework for reconstructing trophic and transmission pathways. However, the use of pellets may have biased estimates of both prey and parasite diversity towards taxa that are more resistant to digestion. Although molecular analyses improved taxonomic resolution, PCR amplification was unsuccessful for some samples, and trematode eggs were not genetically characterised, limiting species-level identification.
Supplementary Information
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The reference list from the paper itself. Each links out to its DOI / PubMed record.
- 1Falklands Conservation (2023) New Island Wildlife. https://www.newislandtrust.com/wildlife/. Accessed 14 March 2024