Feeding behavior of the longsnout seahorse Hippocampus reidi Ginsburg, 1933

Impacts of acute hypoxia on the short-snouted seahorse metabolism and behaviour

Seahorses are one of the most unique and enigmatic animals, recognized as flagship species for several conservation issues. Unfortunately, seahorses' populations have been declining and their unique lifestyle may constrain the ability of these animals to evolve in the future climate scenarios. They inhabit shallow coastal waters that display daily or seasonal environmental fluctuations. Yet, few studies have scrutinized the impacts of climate changes on these iconic species. Within this context, the objective of this work was to test the effects of an extreme hypoxia exposure (~27 % dissolved oxygen for approximately 7 h) on the metabolism, behaviour and food intake of the temperate seahorse Hippocampus hippocampus. Regarding metabolism, hypoxia exposure led to a significant reduction in metabolic rates and an increase in ventilation rates. Seahorses showed signs of movement lethargy under oxygen depletion. The results show that a small but extreme exposure to hypoxia is tolerable by seahorses despite inducing metabolic and behavioural changes, that may jeopardize the future development and survival of these iconic organisms.

Feeding Strategy of the Wild Korean Seahorse (Hippocampus haema)

The feeding and spawning grounds for seahorses have been lost due to nationwide coastal developments in South Korea. However, little information on the feeding ecology of the Korean seahorse (Hippocampus haema) is currently available. The main objective in this study was to understand the feeding strategy of H. haema on the basis of DNA analysis of the contents of the guts. This is the first study on the feeding ecology of H. haema. Crustaceans were found to be major prey for H. haema in this study. Among the 12 identified species, arthropods were predominantly observed as potential prey of H. haema in this study. The Caprella sp. Was detected in all summer specimens followed by the Ianiropsis sp., whereas isopods were dominant, and amphipods accounted for a small proportion in winter specimens. According to the results in this study, there appears to be a seasonal shift in the major prey of H. haema. Moreover, a potential change in the habitats for adults was further discussed. Since this is a pilot study, further studies should be conducted for a better understanding of the feeding ecology of H. haema.

The adaptive value of camouflage and colour change in a polymorphic prawn

Camouflage has been a textbook example of natural selection and adaptation since the time of the earliest evolutionists. However, aside from correlational evidence and studies using artificial dummy prey, experiments directly showing that better camouflaged prey to predator vision are at reduced risk of attack are lacking. Here, we show that the level of camouflage achieved through colour adjustments towards the appearance of seaweed habitats is adaptive in reducing predation pressure in the prawn Hippolyte obliquimanus. Digital image analysis and visual modelling of a fish predator (seahorse) predicted that brown prawns would be imperfectly concealed against both brown and red seaweed respectively, whereas pink prawns should be well camouflaged only in red weed. Predation trials with captive seahorses (Hippocampus reidi), coupled with high-speed video analyses, closely matched model predictions: predation rates were similar for brown prawns between seaweed types, but pink individuals were attacked significantly less on red than brown weed. Our work provides some of the clearest direct evidence to date that colour polymorphism and colour change provides a clear adaptive advantage for camouflage, and also highlights how this can be asymmetric across morphs and habitats (i.e. dependent on the specific background-morph combination).

Seahorses in focus: local ecological knowledge of seahorse-watching operators in a tropical estuary

BACKGROUND

Seahorses are endangered teleost fishes under increasing human pressures worldwide. In Brazil, marine conservationists and policy-makers are thus often skeptical about the viability of sustainable human-seahorse interactions. This study focuses on local ecological knowledge on seahorses and the implications of their non-lethal touristic use by a coastal community in northeastern Brazil. Community-based seahorse-watching activities have been carried out in Maracaípe village since 1999, but remained uninvestigated until the present study. Our goal is to provide ethnoecological understanding on this non-extractive use to support seahorse conservation and management.

METHODS

We interviewed 32 informants through semi-structured questionnaires to assess their socioeconomic profile, their knowledge on seahorse natural history traits, human uses, threats and abundance trends.

RESULTS

Seahorse-watching has high socioeconomic relevance, being the primary income source for all respondents. Interviewees elicited a body of knowledge on seahorse biology largely consistent with up-to-date research literature. Most informants (65.5 %) perceived no change in seahorse abundance. Their empirical knowledge often surpassed scientific reports, i.e. through remarks on trophic ecology; reproductive aspects, such as, behavior and breeding season; spatial and temporal distribution, suggesting seahorse migration related to environmental parameters.

CONCLUSIONS

Seahorse-watching operators were aware of seahorse biological and ecological aspects. Despite the gaps remaining on biological data about certain seahorse traits, the respondents provided reliable information on all questions, adding ethnoecological remarks not yet assessed by conventional scientific surveys. We provide novel ethnobiological insight on non-extractive modes of human-seahorse interaction, eliciting environmental policies to integrate seahorse conservation with local ecological knowledge and innovative ideas for seahorse sustainable use. Our study resonates with calls for more active engagement with communities and their local ecologies if marine conservation and development are to be reconciled.

Advances in tagging syngnathids, with the effects of dummy tags on behaviour of Hippocampus guttulatus

Artificial marking and tagging techniques have been used to study movement, population dynamics, behaviour, ecology, survival and growth of at least 25 syngnathid species. External necklace-style tags and injection of visible implant elastomer have been the most used techniques, uniquely identifying hundreds of individual syngnathids to study population dynamics, mortality, behaviour, ecology and growth in at least 13 and 12 species, respectively. Only two studies, both on larger syngnathid species, have tested the use of internal or electronic tags. This new case study reveals that dummy tags, weighing up to 6% of individual body mass, have minimal effect on normal ex situ behaviour of the long-snouted seahorse Hippocampus guttulatus, a smaller syngnathid. In paired aquarium trials, tags did not affect movement, holdfast use or general behavioural state, and only had a short-term effect (1 day) on vertical orientation. Tagged H. guttulatus gained more mass during the 5 day trials, a result which warrants further exploration but indicates that tags did not reduce feeding. This study shows promise for using electronic tagging to study H. guttulatus and similarly sized syngnathids in the wild.

Isolation and experimental infection with Vibrio alginolyticus in the sea horse, Hippocampus reidi Ginsburg, 1933 (Osteichthyes: Syngnathidae) in Brazil

The aim of this study was to evaluate the pathogenicity of Vibrio alginolyticus isolated from an outbreak of sea horse Hippocampus reidi reared in the State of Santa Catarina, Brazil, by experimental infection. Sea horses with necrosis on the mouth epithelium were collected from aquaria at the Aquaculture Department, UFSC and the bacterium isolated from the mouth, liver, heart and blood in tiosulphate citrate bilesalt sucrose agar broth. The strains were identified by API 20E kit with 99.1% probability as Vibrio alginolyticus. Twelve adult sea horses (9.63 ± 2.42 g and 15.12 ± 0.87 cm) were distributed in six aquaria of 10 L capacity with aerated sea water. Fish from three aquaria were submitted to an immersion bath in a solution containing 1.0 × 10(7) CFU of V. alginolyticus/mL for 15 minutes. Fish from the other three aquaria received the same procedure without bacteria. Twenty four hours after this challenge, 100% mortality was observed in the animals infected with V. alginolyticus. No mortality was observed in non-infected fish. Hyperplasia, displacement and fusion of secondary lamellae of the gills; leukocyte infiltration and necrotic foci in the kidney; hyperplasia, sinusoidal deformation and necrotic foci in the liver were observed in histopathological analysis. The V. alginolyticus isolated in this study was pathogenic to H. reidi and constitutes an important sanitary problem to its culture.

Novel sex-related characteristics of the longsnout seahorse Hippocampus reidi Ginsburg, 1933

This paper presents novel sex-related characteristics in Hippocampus reidi, expressed as a prominent and pigmented keel (males only), and by a row of dorsolateral spots mostly (97.4%) found in males. While the keel was found even in the smallest males sampled, the dorsolateral spots appear to be associated with body size. Ex situ observations revealed that during courtship males highlighted both characters by turning pale their background body colour. Understanding such colour and behavioural patterns is relevant to increase our knowledge about sexual selection in a morphologically and biologically unique group of fishes.

Assessing diet composition of seahorses in the wild using a non destructive method: Hippocampus reidi (Teleostei: Syngnathidae) as a study-case

This paper presents the results of the first analysis of the natural diet of Hippocampus reidi, one of the most sought after seahorse species in the international aquarium trade. Its main goals were to investigate food items and prey categories consumed by the species, and to discuss feeding strategy and inter and intra-individual components of niche breadth. Data were gathered from October 2005 to September 2006 at the Mamanguape estuary, State of Paraíba, NE Brazil. Food items from seahorses anaesthetized with clove oil were obtained by using a modified version of the flushing method, and were counted and identified to the lowest possible taxonomic level. Specimens were marked and had their height, sex, life and reproductive stage recorded, and then returned to the same place where they were found for the further assessment of anaesthetization/gut flushing on seahorses. Food items were analyzed using frequency of occurrence, relative abundance, index of preponderance and prey-specific abundance using the points method. The graphic method of Amundsen et al. (1996) was used to interpret the feeding strategy and contribution to niche breadth. Nematodes and crustaceans were the most important items found, the latter item usually being the most commonly found in the gut contents of syngnathids. No significant differences in diet composition were found between reproductive stages, however, a higher proportion of large items were consumed by the larger seahorses. The feeding strategy and niche breadth analysis suggests that H. reidi has a generalist feeding strategy, with high variation between phenotypes. Our results suggest that the anaesthetization-flushing technique has the potential to be a useful tool in seahorse research.

Population characteristics, space use and habitat associations of the seahorse Hippocampus reidi (Teleostei: Syngnathidae)

This paper provides a case study of a threatened seahorse species, Hippocampus reidi, highlighting the importance of using ecological information to assist conservation and management initiatives. Underwater visual sighting data (50 x 2m transect) gathered along the NE, SE and S portions of the Brazilian coast revealed an unequal distribution across localities, perhaps related to harvesting pressure, and a mean density of 0.026 ind.m-2. Our findings suggest some restricted spatial use by H. reidi, which was consistent with its estimated home range, and with re-sighting of specimens. Reproduction was recorded year-round, however productive peaks may exist. Components of habitat structure mostly used as anchoring points were mangrove plants, macroalgae, cnidarians, seagrass, sponges, and bryozoans. Conservation recommendations include: further characterization and mapping of habitats; assessment of availability and condition of microhabitats in selected areas, and studies on dispersal routes during initial life stages.