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

Abstract

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.Este artigo apresenta os resultados do primeiro estudo sobre a alimentação natural de Hippocampus reidi, uma das espécies de cavalos-marinhos mais intensamente comercializadas pelo mercado aquarista. Seus principais objetivos foram descrever os itens alimentares e categorias de presas consumidos pela espécie e fornecer informações acerca da estratégia alimentar e dos componentes inter e intra-individuais para a largura de nicho. As amostragens foram realizadas mensalmente por meio de busca intensiva, entre outubro de 2005 e setembro de 2006, no estuário do rio Mamanguape, Paraíba, onde os cavalos marinhos foram marcados, anestesiados com óleo de cravo e submetidos à técnica da lavagem estomacal. Para cada cavalo-marinho registrouse a altura, sexo, estágio de vida e estado reprodutivo. Após a coleta de dados, todos os cavalos-marinhos foram devolvidos ao mesmo local onde haviam sido encontrados e o material obtido através da lavagem foi identificado, em laboratório, até o menor nível taxonômico possível, com o auxílio de especialistas. Os itens alimentares foram descritos através de freqüência de ocorrência, abundância relativa, índice de preponderância e abundância específica; já a estratégia alimentar e contribuição para a largura de nicho foram descritos através do método de Amundsen. Os pri...

Trophic relationships among fish assemblages in a mudflat within Brazilian marine protected area

“…There is a well-preserved mangrove in the area, composed of Avicennia germinans, Avicennia schaweriana, Conocarpus erectus, Laguncularia racemosa and Rhizophora mangle, which grows around the primary channel and tidal creek and extends to 600 ha, in addition to Atlantic Forest remnants (ROCHA et al 2008). Endangered species, such as the seahorse, Hippocampus reidi, and the West Indian manatee, Trichechus manatus, are also found in this estuary NORDI, 2003, CASTRO et al, 2008.…”

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

“…(daily intense tidal depth variations in the estuary)2681Yes [2] Occurrence determinant1Determined by the presence of mangrove roots as anchoring points and shelter32100Yes [30] Exposition to water currents2Preferentially inhabit backwater areas protected from strong currents3197Yes [3, 30] Salinity1In the mangrove, are abundant in sites with high salinity levels32100Yes [3, 35] Water transparency1Abundant in high transparency level conditions32100No data Seasonal abundance2Abundant in summer (dry season), scarce in winter (wet season).3197Yes [3] Migration period2Rainy season, in winter (May to September)32100Yes [3] Reason for migration2To avoid low salinity levels caused by the rainy season’s freshwater input. Also are removed out of the mangrove to the sea by floods and currents32100Yes [3] Anchoring points6Mangrove roots32100Yes [30, 33, 44]Trophic ecology Diet7Shrimp larvae32100Yes [3, 37, 38]Fish larvae2578 Feeding behavior4Sucks the prey3197Yes [2, 36] Predators10Crabs and fishes32100Yes [3, 40, 44] Is camouflage related to color shift?2Yes. Is capable of changing its own color3094Yes [24]Reproduction Sexual dimorphism1Brooding pou...…”

“…Seahorses are indeed generalists and voracious ambush predators, feeding on live moving preys [2, 36], from zooplankton to small fishes, especially microcrustaceans [37, 38]. The “mud worms” quoted by jangadeiros are possibly nematodes, polychaetes and oligochaetes.…”

Trophic relationships among fish assemblages on a mudflat within a Brazilian Marine protected area

“…There is a well-preserved mangrove swamp in the area, composed of Avicennia germinans, Avicennia schaweriana, Conocarpus erectus, Laguncularia racemosa and Rhizophora mangle, which extends for 600 ha around the primary channel and tidal creek, in addition to Atlantic Forest remnants (ROCHA et al, 2008). Endangered species, such as the seahorse, Hippocampus reidi, and the West Indian manatee, Trichechus manatus, are also found in this estuary NORDI, 2003;CASTRO et al, 2008).…”