Opportunistic Feeding Research Articles

Opportunistic consumption of coral spawn by the ruby brittle star (Ophioderma rubicundum).

Many reef invertebrates reproduce through simultaneous broadcast spawning, with an apparent advantage of overwhelming potential predators and maximizing propagule survival. Although reef fish have been observed to consume coral gamete bundles during spawning events, there are few records of such predation by benthic invertebrates. Here, we document several instances of the ruby brittle star, Ophioderma rubicundum, capturing and consuming egg-sperm bundles of the mountainous star coral, Orbicella faveolata, and the symmetrical brain coral, Pseudodiploria strigosa, during spawning events in the Cayman Islands in 2012 and the Florida Keys in 2022. These observations are widely separated in space and time (>600 km, 10 years), suggesting that this behavior may be prevalent on western Atlantic reefs. Since O. rubicundum spawns on the same or subsequent nights as these coral species, we hypothesize that this opportunistic feeding behavior takes advantage of lipid-rich coral gamete bundles to recover energy reserves expended by the brittle star during gametogenesis. The consumption of coral gametes by adult brittle stars suggests an underexplored trophic link between reef invertebrates and also provides evidence that ophiuroid-coral symbioses may oscillate between commensalism and parasitism depending on the ontogeny and reproductive status of both animals. Our observations provide insights into the nuanced, dynamic associations between coral reef invertebrates and may have implications for coral reproductive success and resilience.

A review of caracal and jungle cat diets across their geographical ranges during 1842-2021.

Co-occurring carnivore species that are phylogenetically related or of similar size, morphology, and ecological needs often reduce competition by partitioning shared resources through temporal, spatial, and dietary niche segregation via behavioral adaptations. Caracals (Caracal caracal) and jungle cats (Felis chaus) co-occur in portions of their geographical ranges and are expected to display resource segregation in these ranges. We compiled scat, stomach content, and prey remains found data from published and unpublished sources to summarize information on the diets of caracals and jungle cats across their geographical ranges during 1842-2021. We obtained 63 sources from 26 countries in Europe, Asia, and Africa, in which caracal diet included 151 species while jungle cat diet included 61 species. We found that caracals and jungle cats did not exhibit dietary niche partitioning and had greater dietary similarities in areas of range overlap. We also found that caracals consumed more diverse prey species including prey with greater average body mass compared to jungle cats. Our results suggest that greater prey diversity in areas of range overlap, caracal predation on wide range of prey, and opportunistic feeding behavior that facilitates consumption of more diverse prey species compared to jungle cats, may facilitate co-occurrence between these two felid species.

Ecomorphological variation of the penguin wing.

Penguins (Aves, Sphenisciformes) are pursuit divers that feed mainly on krill, fish, and squid. Although they are opportunistic feeders, some species are more generalists than others and many show dietary preferences towardkrill and other crustaceans or fish and squid. Their diving depth seems to follow a body size pattern and relates to the type of item that they prey on. Penguins dive with their wing; hence their wing musculature is responsible for the animal maneuverability and strength while diving. In the present study, ecological traits such as diving depths and prey composition are used to explore if morphology relates to foraging habits. A geometric morphometric approach is used to quantitatively address these morphological differences in the wing apparatus of all extant penguins and a fossil species taking into consideration allometric and phylogenetic factors. Results show that morphological differences among penguins with different diets are significant and strong; groups are well separated with the greatest differences found between piscivorous and crustacivorous penguins. Dive depth has a moderate covariation with morphology and a strong correspondence with wing area. Last, Madrynornis mirandus, an exceptionally well-preserved fossil from the Miocene of Patagonia, is found to be close to the piscivorous and generalist piscivorous species. It is proposed that swimming styles correlate with specific traits of the anatomy of wing and pectoral girdle skeleton and muscles.

Host associations of biting midges (Diptera: Ceratopogonidae: Culicoides) at deer farms in Florida, USA.

Documenting the host use of vector species is important for understanding the transmission dynamics of vector-borne pathogens. Biting midges (Diptera: Ceratopogonidae: Culicoides) are vectors of epizootic hemorrhagic disease virus (EHDV) and bluetongue virus (BTV) worldwide. However, relative to mosquitoes and many other vector groups, host associations of this group are poorly documented. In this study, we used PCR-based bloodmeal analysis to determine species-level host associations of 3,603 blood-engorged specimens belonging to 18 Culicoides species at 8 deer farms in Florida, USA. We used a binomial mixed model with a Bayesian framework to compare the effect of host composition on the feeding patterns of Culicoides spp. and employed the Morisita-Horn Index to investigate the similarity of host use between farms for Culicoides stellifer and Culicoides insignis. Results show that the estimated probability of Culicoides spp. feeding upon white-tailed deer depends on the availability of cattle or exotic game and demonstrates differences in host-feeding selection among species. Culicoides insignis had high host similarity across farms suggesting that its host-use patterns are somewhat conserved. Culicoides stellifer had lower host similarity across farms suggesting that it is a more opportunistic feeder. White-tailed deer are fed upon by many Culicoides species on deer farms in Florida, and while most Culicoides species feed on white-tailed deer, the ratio of white-tailed deer bloodmeals to other bloodmeals is likely influenced by host availability. Culicoides spp. taking a majority of their bloodmeals from farmed white-tailed deer should be assessed for their vector competence for EHDV and BTV.

Ontogenetic social behavior and seasonal abundance of the subtropical krill Nyctiphanes simplex in northwestern Mexican waters

Abstract Nyctiphanes simplex (Euphausiidae) is the key prey for numerous pelagic predators because it is the most abundant of the 12 krill species present in the Gulf of California, forming dense and complex ontogenetic social interactions throughout its life cycle. We describe the diverse social behaviors of N. simplex and estimate its seasonal abundance in the Gulf of California accounting on average 74% of the krill assemblage. N. simplex exhibited complex and dynamic social repertoires of intraspecific behavioral interactions as early as Calyptopis 1 to adult phase, showing all possible ranges of social behavior known for pelagic invertebrates (aggregations, swarms, schools, shoals). We conclude that N. simplex displays different degrees of social behavior that concentrate abundance throughout their life cycle in epibenthic, pelagic and near surface habitats being highly adaptive behavior for feeding and reproduction. However, social interactions also pose a negative effect, facilitating parasite and disease transmission among conspecifics and facilitate predation for diverse visual predators adapted to find and prey on N. simplex aggregations and swarms. We report the most complete integrated evidence of social behavior and dataset of abundance data of any krill species in tropical and subtropical regions that have remained overlooked using traditional zooplankton net sampling methods.

Diet of a threatened rattlesnake (eastern massasauga) revealed by DNA metabarcoding.

Characterizing the diet of imperiled species using minimally invasive methods is crucial to understanding their ecology and conservation requirements. Here, we apply a DNA metabarcoding approach to study the diet of the eastern massasauga rattlesnake (Sistrurus catenatus), a Federally Threatened snake found throughout the Great Lakes region. Eighty-three fecal samples collected across 10 different massasauga populations located in Michigan, USA, were sequenced, with 70 samples containing prey DNA. We used universal metazoan primers and developed a host-specific oligonucleotide blocker to characterize their diet. We identified at least 12 different prey species, with eastern massasaugas exhibiting opportunistic feeding and a strong preference towards small mammals. Meadow voles (Microtus pennsylvanicus) were the most common prey item (70% of diet) followed by the northern short-tailed shrew (Blarina brevicauda) and masked shrew (Sorex cinereus; 15.7% of diet each), along with occasional bird and snake prey. Adult individuals exhibited a more generalized diet, consuming a larger number of prey taxa on average. Younger snakes consumed a smaller variety of prey items and tended to consume smaller-sized mammals such as masked shrews (Sorex cinereus) and northern short-tailed shrews (Blarina brevicauda). We conclude that small mammals are a crucial part of eastern massasauga rattlesnake diet and recommend this be taken into consideration when conservation strategies are developed. The methods developed in this study can be applied to other reptile species, providing an accurate, minimally invasive, and thorough diet assessment for at-risk reptile species.

Diet and Plastic Ingestion in the Blackmouth Catshark Galeus melastomus, Rafinesque 1810, in Italian Waters.

Galeus melastomus is the most common Pentanchidae in the Mediterranean Sea. A scavenger and opportunistic feeder, and despite the wide distribution, little is known about its feeding habits in Italian waters. The main purpose of this study was to investigate the diet of the blackmouth catshark by analysing the stomach contents. The specimens analysed were obtained from five populations of the Tyrrhenian and of the Ionian Seas, collected from a depth between 40 and 700 m. A total of 259 stomachs were analysed. The stomach contents were grouped into macro-categories and identified to the lowest taxonomic level possible. Crustaceans such as Parapenaeus longirostris, the Cephalopods Heteroteuthis dispar and Onychoteuthis banksii, and Osteichthyes, mostly Myctophidae, were identified. Plastic debris was also found among the stomach contents and classified according to its colour and shape. Osteichthyes represent the most abundant item (44%), above all the Myctophidae family, except for the catshark population from Tuscany, in which the most frequent species were Cephalopods, such as Abralia veranyi and Heteroteuthis dispar. Differences in the plastic debris contents were also observed between the Tuscany population and other populations. These could be explained as a probable consequence of the different depths at which the blackmouth catshark populations were sampled.

Zooplankton community succession and trophic links during a mesocosm experiment in the coastal upwelling off Callao Bay (Peru)

Abstract. The Humboldt Current Upwelling System (HCS) is the most productive eastern boundary upwelling system (EBUS) in terms of fishery yield on the planet. EBUSs are considered hotspots of climate change with predicted expansion of mesopelagic oxygen minimum zones (OMZs) and related changes in the frequency and intensity of upwelling of nutrient-rich, low-oxygen deep water. To increase our mechanistic understanding of how upwelling impacts plankton communities and trophic links, we investigated mesozooplankton community succession and gut fluorescence, fatty acid and elemental compositions (C, N, O, P), and stable isotope (δ13C, δ15N) ratios of dominant mesozooplankton and microzooplankton representatives in a mesocosm setup off Callao (Peru) after simulated upwelling with OMZ water from two different locations and different N:P signatures (moderate and extreme treatments). An oxycline between 5 and 15 m with hypoxic conditions (<50 µmol L−1) below ∼10 m persisted in the mesocosms throughout the experiment. No treatment effects were determined for the measured parameters, but differences in nutrient concentrations established through OMZ water additions were only minor. Copepods and polychaete larvae dominated in terms of abundance and biomass. Development and reproduction of the dominant copepod genera Paracalanus sp., Hemicyclops sp., Acartia sp., and Oncaea sp. were hindered as evident from accumulation of adult copepodids but largely missing nauplii. Failed hatching of nauplii in the hypoxic bottom layer of the mesocosms and poor nutritional condition of copepods suggested from very low gut fluorescence and fatty acid compositions most likely explain the retarded copepod development. Correlation analysis revealed no particular trophic relations between dominant copepods and phytoplankton groups. Possibly, particulate organic matter with a relatively high C:N ratio was a major diet of copepods. C:N ratios of copepods and polychaetes ranged 4.8–5.8 and 4.2–4.3, respectively. δ15N was comparatively high (∼13 ‰–17 ‰), potentially because the injected OMZ source water was enriched in δ15N as a result of anoxic conditions. Elemental ratios of dinoflagellates deviated strongly from the Redfield ratio. We conclude that opportunistic feeding of copepods may have played an important role in the pelagic food web. Overall, projected changes in the frequency and intensity of upwelling hypoxic waters may make a huge difference for copepod reproduction and may be further enhanced by varying N:P ratios of upwelled OMZ water masses.

Feeding Behavior of Finishing Pigs under Diurnal Cyclic Heat Stress

The impact of cyclic heat stress (CHS) and turning the lights on and off on pig feeding behavior (FB) was investigated. The FB of 90 gilts was recorded in real-time under two ambient temperatures (AT): thermoneutrality (TN, 22 °C) or CHS (22/35 °C). The day was divided into four periods: PI (06-08 h); PII (08-18 h); PIII (18-20 h); and PIV (20-06 h). Automatic and Intelligent Precision Feeders recorded each feed event for each pig. An estimated meal criterion (49 min) was used to calculate the FB variables. Feed behavior in both ATs followed a circadian pattern. The CHS reduced the feed intake by 6.9%. The pigs prioritized feed intake during the coolest hours of the day; however, nocturnal cooling did not allow the pigs to compensate for the reduced meal size due to CHS. The highest meal size and most of the meals were observed during the lighting-on period. The pigs reduced their interval between meals during PII and PIII. The lighting program increased the meal size when the lights were switched on and reduced the meal size when the lights were switched off. Thus, the dynamics of the FB were largely influenced by AT, whereas the meal size was affected by the lighting program.

Year-round use of anthropogenic food sources in human modified landscapes by adult and young Kelp Gulls

Predictable anthropogenic food subsidies attract species with generalist and opportunistic feeding habits, often resulting in conflicts with human populations. We assessed the spatio-temporal distribution and abundance of Kelp Gulls (Larus dominicanus) during the annual cycle at anthropogenic food sources located along 70 km of urban and agricultural-livestock landscapes in the lower Chubut River valley, Argentina. We quantified the seasonal abundance of adult and young Kelp Gulls through monthly counts from July 2021 to June 2022 at six identified anthropogenic food sources, complemented with strip transect sampling along cultivated land and cattle grazing areas. In addition, we analysed the differential use of waste types by adult and young Kelp Gulls at a mixed livestock waste dump where different food remains (cattle remains, poultry remains and urban waste) are disposed in independent pits. The total number of Kelp Gulls counted each month along the river valley was variable, with a mean number of 2585 ± 822.7 individuals (range = 276 in December and 8958 in June). The highest gull abundance was recorded at a pig farm (mean = 1784.5 ± 640.1 individuals). The transect survey showed a relatively low use by gulls of the cultivated land and cattle grazing areas, with a mean of 29.7 ± 11.2 individuals recorded per survey (range = 0–96). Kelp Gull abundance patterns recorded in the river valley throughout the annual cycle evidenced a contrasting seasonal use of anthropogenic food sources between the breeding and non-breeding seasons, being clearly less abundant during the former, when gulls move to their main breeding grounds and adjacent marine habitats in coastal Chubut. At the mixed livestock waste dump, Kelp Gull numbers varied among the three waste patches, with higher numbers and a significantly higher proportion of adults at the cattle remains pit. This study shows the high trophic plasticity of Kelp Gulls and their use of alternative foraging habitats. Further monitoring and evaluations of the use by Kelp Gulls of predictable anthropogenic food sources along the Chubut River valley, particularly those related to the growing livestock production, are needed to support management decisions.

Chironomus calligraphus Goeldi, 1905 (Diptera: Chironomidae) Larvae: Feeding Habits, Growth, and Maturation.

Chironomus calligraphus Goeldi, 1905 has a flexible life cycle with several generations per year, which can be modified by the quality and type of food. To categorize the functional feeding group of the species, food preference was evaluated in larval instars III and IV, through laboratory experiments and gut content analysis. To evaluate the influence of the type of food on the duration of the life cycle growth and maturation, experiments were carried out. Instar III preferred conditioned leaves and animal food, while instar IV preferred algae and fine particulate organic matter. Gut contents of instar IV collected from streams showed increased consumption of fine particulate organic matter than other items. All these observations allowed us to assign the species to the gatherer collector group. The duration of the life cycle varied between the different types of foods, being the conditioned leaves, animal food, and algae the items that caused a greater growth in the larvae and a faster passage to the pupal instar. Our results suggest that the opportunistic feeding behavior of C. calligraphus allows it to use several different foods, but the quality of the foods influences the length of the life cycle and this contributes to its plasticity.

Opportunistic vs selective feeding strategies of zooplankton under changing environmental conditions.

The plankton community consists of diverse interacting species. The estimation of species interactions in nature is challenging. There is limited knowledge on how plankton interactions are influenced by environmental conditions because of limited understanding of zooplankton feeding strategies and factors affecting trophic interactions. In this study, we used DNA-metabarcoding to investigate trophic interactions in mesozooplankton predators and the influence of prey availability on their feeding behavior. We found that mesozooplankton feeding strategies vary within species across an environmental gradient. Some species, such as Temora longicornis consistently used a selective strategy, while diets of Centropages hamatus and Acartia spp. varied between stations, showing a trophic plasticity with the prey community. We found a dominance of Synechococcales reads in Temora's gut content and a high prey diversity for the cladoceran Evadne nordmanni. Our study shows the wide range of prey species that supports mesozooplankton community and helps to understand the spatial and temporal complexity of plankton species interactions and discriminate the selectivity ability of four zooplankton key species. Due to the central role of plankton in marine waters, a better comprehension of the spatiotemporal variability in species interactions helps to estimate fluxes to benthic and pelagic predators.

Establishing Critical Leaf Nutrient Concentrations and Identification of Yield Limiting Nutrients for Precise Nutrient Prescriptions of Oil Palm (Elaeis guineensis Jacq) Plantations

African oil palm (Elaeis guineensis Jacq.) is a bulk feeder of nutrients. In this study, we aimed at devising strategies for efficient nutrient management in the oil palm plantations of the Krishna River basin located in Andhra Pradesh, India by assessing soil fertility status, establishing optimal leaf nutrient concentrations and identifying yield restrictive nutrients. In total, 67 oil palm plantations were surveyed from this area in 2020, soil samples were collected and analysed for different soil properties, including pH, EC, SOC, available P, K, S, exchangeable Ca and Mg, and hot water-soluble boron (HWB) in surface (from 0–20 cm depth), subsurface (from 20–40 cm depth) and deep (from 40–60 cm depth) soil layers. As per DRIS (Diagnosis and Recommendation Integrated System) indices estimated in this study, the order of requirement of nutrients is Nitrogen (N) > B > K > P > Mg for this area. Optimum leaf nutrient concentrations ranged between 2.07–4.29%, 0.13–0.27%, 0.52–0.94%, 0.44–0.76% and 44.97–102.70 mg/kg for N, P, K, Mg and B, respectively. In surveyed plantations, about 15, 6, 16, 9 and 12 percent of leaf samples had less than optimum concentration of N, P, K, Mg and B respectively. Nitrogen and Boron are the major yield limiting factors in this region. Leaf nutrient concentrations need to be maintained at the optimum ranges as estimated above for higher productivity in the Krishna basin area.

Dietary Preferences of Loggerhead Sea Turtles (Caretta caretta) in Two Mediterranean Feeding Grounds: Does Prey Selection Change with Habitat Use throughout Their Life Cycle?

According to their life stage, the loggerhead sea turtle (Caretta caretta) is found in a wide range of habitats, from neritic to more oceanic areas. Their feeding habits are expected to change as they develop, along with habitat use. Juvenile sea turtles are hypothesized to feed on pelagic species in oceanic areas, shifting to more benthic prey during the subadult and adult stages. We analyzed the gastrointestinal content from 150 loggerhead sea turtles stranded and/or bycaught along the Adriatic coast of the Abruzzo and Molise regions (n = 89) and the Tyrrhenian coast of the Lazio and Campania regions (n = 61) from 2018 to 2021. Food items were identified to the lowest taxonomic level, and the frequency of occurrence was calculated for each taxon and most recurrent species to assess changes in prey selection during the development. The marine litter was categorized, and the frequency of occurrence was calculated for the ingestion of litter. The most recurrent taxonomic prey group recorded in the Adriatic sample was Arthropoda (94%), followed by Mollusca (63%) and Chordata (34%). In the Tyrrhenian sample, loggerhead sea turtles fed mostly on Mollusca (84%), Arthropoda (38%), and Chordata (26%). Surprisingly, the Adriatic-Tyrrhenian sample groups showed similar feeding behavior between juveniles, subadults, and adults. A similar correlation has been observed concerning the ingestion of litter. Moreover, this study confirms the opportunistic feeding behavior of loggerhead sea turtles and their high adaptability.

Patterns of Aedes aegypti abundance, survival, human-blood feeding and relationship with dengue risk, Kenya

Dengue virus (DENV) transmission risk is influenced by the bionomic traits of the key vector, Aedes aegypti. We investigated patterns of abundance, survival, and human blood-feeding of Ae. aegypti populations in two environments in Kenya: peri-urban Rabai (coastal Region, dengue-endemic) and rural Kerio Valley (Rift Valley Region, no reported dengue outbreak). In both environments, Ae. aegypti survival (estimated by parity), was inversely correlated with vector abundance, and this was influenced by weather conditions, notably temperature and relative humidity. In Rabai, Ae. aegypti mostly fed on humans (human blood index=51%), a pattern that corroborates with dengue cases in the coastal region. Aedes aegypti additionally, exhibited opportunistic feeding (livestock, rodents, reptiles, birds), suggesting the risk of human exposure to zoonotic pathogens via spillover transmission events aided by the vector. Abundance and human blood-feeding rates were consistently lower in Kerio Valley likely related to the degree of urbanization. Remarkably, the periods of high human feeding in Rabai coincided with high vector survival rates, a trend that could potentially drive intense DENV transmission at certain times of the year. We found a genetic influence of Ae. aegypti on the degree of anthropophagy but this could be influenced by potential seasonal shifts in human feeding. The findings of this study have implications both for DENV transmission risk and vector control strategies, but also in modeling which should integrate vector bionomic factors beyond vector abundance.

Food habits of the Red Fox Vulpes vulpes (Mammalia: Carnivora: Canidae) in Dachigam National Park of the Kashmir Himalaya, India

Food habits of the Red Fox Vulpes vulpes were studied in Dachigam National Park of the Kashmir Himalaya from December 2017 to November 2018 by scat analysis. A total of 246 scats were collected across seasons from different habitat types of the park. The diet of the Red Fox was characterized by a wider prey spectrum with small rodents, plants, and Himalayan Grey Langur Semnopithecus ajax as the major food items. The dietary behaviour showed slight seasonal variation with more invertebrates and plant material (fruits, berries, & grasses) during spring and summer. The food niche of the canid was wider in the warm season than in the cold season. Diet analysis revealed substantial use of anthropogenic food sources (human refuse and livestock carrion) by the Red Fox. The frequency of occurrence of human refuse and livestock carrion in the scats of the canid species varied seasonally. The results show that the Red Fox is an opportunistic feeder, and capable of adapting to a variety of dietary items.

Head anatomy of a lantern shark wet-collection specimen (Chondrichthyes: Etmopteridae).

In this study, we apply a two-step (untreated and soft tissue stained) diffusible iodine-based contrast-enhanced micro-computed tomography array to a wet-collection Lantern Shark specimen of Etmopterus lucifer. The focus of our scanning approach is the head anatomy. The unstained CT data allow the imaging of mineralized (skeletal) tissue, while results for soft tissue were achieved after staining for 120 h in a 1% ethanolic iodine solution. Three-dimensional visualization after the segmentation of hard as well as soft tissue reveals new details of tissue organization and allows us to draw conclusions on the significance of organs in their function. Outstanding are the ampullae of Lorenzini for electroreception, which appear as the dominant sense along with the olfactory system. Corresponding brain areas of these sensory organs are significantly enlarged as well and likely reflect adaptations to the lantern sharks' deep-sea habitat. While electroreception supports the capture of living prey, the enlarged olfactory system can guide the scavenging of these opportunistic feeders. Compared to other approaches based on the manual dissection of similar species, CT scanning is superior in some but not all aspects. For example, fenestrae of the cranial nerves within the chondrocranium cannot be identified reflecting the limitations of the method, however, CT scanning is less invasive, and the staining is mostly reversible and can be rinsed out.

Pliocene Pre-GABI herbivorous mammals from Espinar, Peruvian Andean Plateau

ABSTRACT Pliocene South American mammals prior to the Great American Biotic Interchange comprise the evolutionary pinnacle of a long-lasting process of continental isolation, in which large-scale orogeny and climate change were instrumental. These processes resulted in unique assemblages of extinct groups with peculiar anatomies. However, interpretation of the functional roles that these organisms would have played in the ecosystem is challenging because well-preserved fossils of this time interval in South America are scarce. Here, we describe a new Early Pliocene assemblage of native herbivorous megamammals documented by skeletons in anatomical connection from the Peruvian Andean plateau (city of Yauri in Espinar, Cusco Department). Fossil-bearing deposits pertain to Member C of the El Descanso Formation dated at 4.75 ± 0.5 Ma, when the plateau attained near-modern elevations and a Puna-type plant ecosystem. The mammal assemblage is dominated by xenarthrans, including three ground sloths (cf. Megatheriops rectidens, Simomylodon uccasamamensis, and Proscelidodon sp.) and Andinoglyptodon mollohuancai gen. et sp. nov., the first Pliocene glyptodontine known by a well-preserved cranium and dermal armor. Notoungulates are represented by the toxodontid Posnanskytherium viscachanense. Both selective and bulk feeders are identified, suggesting the existence of diverse plant resources in the Pliocene Puna ecosystem. These native mammals constituted the typical Pliocene herbivorous guild of the central Andean plateau and provide an opportunity to investigate the structure of mammalian communities just before the arrival of Holarctic immigrants.

In situ microplastic ingestion by neritic zooplankton of the central Mexican Pacific

Microplastics (MPs) are present across the global ocean and can be encountered by many species, including zooplankton. Although they fall within the size range of zooplankton prey, there are few studies on MPs ingestion carried out in situ. In this study, we analyzed MPs ingestion during two seasons (rainy and dry) of organisms from 5 taxonomic groups of zooplankton from two bays of the Mexican central Pacific: Manzanillo and Navidad. In total, 2643 individuals were analyzed, and of those 23 individuals contained MPs. The ingestion rate by taxonomic group was 1 MP/36 copepods (0.02), 1 MP/30 decapods–mysis (0.03), 1 MP/29 decapods–megalopa (0.03), and 1 MP/200 fish larvae (0.005). No plastics were found in chaetognaths, amphipods, or decapods–zoea. The average length of the ingested particles was 468.1 ± 113.8 μm, with a minimum of 15.6 and a maximum of 647.6 μm. All MPs >300 μm were fibers, with diameters <50 μm. Fragments were the most abundant MPs (54.2%), followed by fibers (34.2%) and spheres (11.4%). Statistical analyses showed no significant differences (p > 0.05) between the bays or seasons. Using RAMAN spectroscopy, it was possible to identify 6 different types of polymers, with poly (ethylene:propylene) being the most abundant (42.8%). This polymer is commonly used to manufacture plastic bags, ropes and fishing nets. The results confirm that certain zooplankton groups are consuming MPs and suggest that omnivorous species are more likely to ingest MPs, possibly due to their capacity for foraging flexibility and opportunistic feeding strategies. However, the ingestion of MPs cannot be attributed to a single factor; it is necessary to consider variables such as the sampling area, feeding strategy, size, and seasonality to understand the dynamics of MPs ingestion by zooplankton groups.

Trophic ecology of crustacean endoparasites Petrarca and Baccalaureus (Ascothoracida, Thecostraca) in scleractinian and zoantharian corals

Coral reefs house a great variety of symbiotic associations, including parasitic ones. One of the crucial issues in host-symbiont interactions is the mode of parasite feeding. Most of the parasitism in scleractinian and zoantharian corals is endosymbiotic (endoparasitic). Their trophic interactions are difficult to identify since they only occur in intact associations. Petrarca and Baccaulareus are endosymbiotic crustaceans. In scleractinian corals, Petrarca forms galls in the coral skeleton. Baccaulareus lives inside zoantharians’ gastric cavities. δ13C and δ15N stable isotope analysis (SIA) of Petrarca and its host (holobiont tissue) Turbinaria revealed similar isotopic signatures of the parasite and host (δ13C, -11.77 to -12.69‰; δ15N, 3.66 to 5.52‰), indicating that Petrarca feeds on its host coral. Petrarca has developed mandibles with a row of sharp and dense teeth to cut coral (holobiont) tissue, while maxillules with compound teeth and massive maxillae are involved in further chewing the food. SIA of Baccaulaureus and its host (holobiont) Palythoa revealed that the parasite and its host differ by &gt;12‰ in δ13C, indicating that Baccalaureus does not feed on its host. The analyzed specimens of Baccalaureus revealed 2 groups with different δ15N values; these specimens may obtain food from different trophic levels. The mouth parts of Baccalaureus have reduced mandibles and maxillules with weak armament. Baccalaureus seems to be an opportunist feeder that steals food directly from the host gastric cavity, resulting in significant variations in δ13C and δ15N values.