Miquel Planas
Michele Gristina
Jorge Palma
Geng Qin
Emily Rose
Olivia Roth
Peter R. Teske- 1Department of Marine Ecology and Resources, Instituto de Investigaciones Marinas-Spanish National Research Council (IIM-CSIC), Vigo, Spain
- 2Institute of Anthropic Impacts and Sustainability in Marine Environment (IAS), National Research Council of Italy, Palermo, Italy
- 3Centre of Marine Sciences (CCMAR), Centro de Ciências do Mar, Universidade do Algarve, Faro, Portugal
- 4Chinese Academy of Sciences (CAS) Key Laboratory of Tropical Marine Bio-Resources and Ecology, South China Sea Institute of Oceanology, Chinese Academy of Sciences (CAS), Guangzhou, China
- 5Department of Biology, Valdosta State University, Valdosta, GA, United States
- 6Marine Evolutionary Biology, Zoological Institute, Kiel University, Kiel, Germany
- 7Centre for Ecological Genomics and Wildlife Conservation, Department of Zoology, University of Johannesburg, Auckland Park, South Africa
Editorial on the Research Topic
Syngnathid fishes: biology, ecology, physiology, conservation and innovative rearing techniques
Syngnathids (a bony fish family that includes seahorses, pipefishes and seadragons) have unique morphological and biological traits that include fused jaws, an exoskeleton and male parental care (Ahnesjö and Craig, 2011). They are mostly found in shallow coastal areas, and their unconventional life history renders them particularly vulnerable to population depletion (Foster and Vincent, 2004). Although some species have been listed as Vulnerable, Endangered, and even Critically Endangered by the IUCN Red List of Threatened Species, many are classified as Data Deficient (DD) due to insufficient information (IUCN, 2020; Pollom et al., 2021). Therefore, further research is needed to understand their distribution, population trends and main threats. A significant portion of the research on syngnathids is relatively recent (Cohen et al., 2017; Segaran et al., 2023). This Research Topic provides 12 original research and review contributions that provide an overview of current trends in research related to the biology, physiology, ecology and conservation of syngnathids.
We have gained considerable insights into syngnathid evolutionary innovation, particularly concerning the evolution of male pregnancy (Lin et al., 2016; Roth et al., 2020). The review by Parker et al. sheds light on the unique modification of the syngnathid immune system and its associations with physiology and reproduction, and highlights future research objectives.
Climate change forces species to extend their physiological tolerance limits, or undergo range shifts. Efforts to minimize future biodiversity losses should consider: (1) species’ distributions correlated with environmental conditions (Mascaró et al., 2016; Hernández-Urcera et al., 2021; Pierri et al., 2022; Borges et al., 2023), (2) adaptive mechanisms responding to environmental changes (Aurélio et al., 2013; Faleiro et al., 2015; Qin et al., 2018; Carneiro et al., 2021; Carneiro et al., 2022; Gomes et al., 2023), and (3) prediction and modeling of future environmental scenarios for species distribution.
Most syngnathids inhabit variable environments and face anthropogenic threats, resulting in habitat loss and population declines. Of particular concern is the use of dried syngnathids in Traditional Chinese Medicine (TCM) (Vincent et al., 2011). Seahorses, in particular, are believed to be nutritionally beneficial for humans, and Cabral et al. focused on the nutritional value of cultured Hippocampus hippocampus. The relative fatty acid composition was similar to that of other seahorse species valued in TCM, with males exhibiting a more suitable profile for human consumption.
Information on stressors is required for estimating future distributional shifts under a global warming scenario. Current knowledge on threats is limited (McCauley et al., 2015), but attempts have been made to estimate its cumulative human impacts. High-accuracy models predicted that 5 of 17 DD seahorses are threatened, and indicated that bycatch and pollution are the best predictors of threat category (Zhang and Vincent, 2019). Silveira et al. evaluated bycatch captures of H. patagonicus in trawling fisheries in Brazil, and reported annual incidental captures exceeding 2 million seahorses (6 individuals/day/vessel). Conservation management at a fine scale should consider local ecological knowledge and social perceptions of human communities that depend on wild syngnathid resources, especially for data-poor species. Fontelles Ternes et al. investigated the perception of seahorse-watching operators regarding abundance, local threats, and conservation insights in Brazilian mangrove ecosystems. All survey participants considered seahorses to be threatened (55% highlighted declines in abundance) and proposed environmental surveillance, zoning and education as the main conservation actions to limit the further decline of seahorse populations.
Shallow coastal areas, such as estuaries and lagoons, receive chemicals that influence the reproduction of aquatic animals. Long-term exposure to low levels of endocrine-disrupting chemicals can cause population collapse. When studying the brood pouch transcriptome in male Syngnathus scovelli during synthetic estrogen exposure, Rose et al. (2023) observed female-specific ornamentation, and identified candidate brood pouch genes as future biomarkers. Changes in iridescence, an important sexual signal in several pipefish species (Rosenqvist and Berglund, 2011), may disrupt sexual selection (Sárria et al., 2011). With an algorithm, Tosto et al. aimed to detect geographical variation in female ornamentation of S. scovelli, indicating that external factors such as chemicals could affect the strength of sexually selected iridescence signals.
The effects of global warming were experimentally investigated in adult H. guttulatus by Costa et al. In agreement with previous findings in juveniles (Planas et al., 2012), no increased growth gain was identified under extreme temperature increases (24°C), despite higher activity and food consumption. Although thermal stress at extreme temperatures could not be confirmed, Del Vecchio et al. (2022) reported that prolonged exposure of H. erectus to even sublethal temperatures resulted in the accumulation of injurious effects, resulting in cell death. Furthermore, Aurélio et al. (2013) reported great resilience to heat stress in adult H. guttulatus. However, early life history stages displayed greater thermal sensitivity with potential cascading consequences for their growth and survival. Faleiro et al. (2015) suggested that future ocean changes might further threaten seahorse conservation as a consequence of the combined effects of warming and acidification. Monteiro et al. identified areas of environmental suitability for European syngnathids over the next century. Particularly dramatic changes are predicted within semi-enclosed seas (e.g., the Baltic, Mediterranean and Black Sea), resulting in the northward range expansions.
The distribution of syngnathids is linked to vegetation cover, which determines feeding ecology (Moreau and Vincent, 2004; Teske et al., 2007; Borges et al., 2023). The interaction and competition between sympatric species might select for behavioral changes, as shown experimentally for European seahorses by Spatafora et al. (2023). The authors concluded that an increased density of the seahorse H. guttulatus resulting from greater habitat availability affected the behavior of H. hippocampus, reducing its activity, and modifying the distributions of both species. Most syngnathids feed on small prey, mainly crustaceans, but show local trophic adaptations, depending on both prey availability and snout characteristics (Manning et al., 2019). Although gut content analysis is useful for assessing dietary regimes, the analysis of stable isotopes provides potentially more precise information on the contribution of food sources to the diet (Peterson and Fry, 1987). However, Planas reported variability of estimates in the reconstruction of the dietary regime in S. acus, depending on the time lag between the sampling of both potential dietary resources and target fishes. Tamara et al. elucidated the diet of H. guttulatus using a non-invasive DNA metabarcoding technique, improving our understanding of habitat-specific prey selection. Diet composition differed between habitats, as did trophic flexibility, which may be essential for the resilience of this species. Due to some limitations of metabarcoding compared to metagenomics because not all prey species may be detectable using the former, Serite et al. compared both techniques to assess the diversity of prey items in two estuarine pipefishes, S. watermeyeri and S. temminckii. In addition to determining that dietary competition is limited because each pipefish has a preferred type of prey, their findings suggest that metagenomics may, in some cases, outperform metabarcoding.
Syngnathids face a range of challenges and threats. This Research Topic of research and review articles provides valuable insights, and highlights key areas for future research. Although interesting advances have been made in the knowledge of syngnathids’ biology and ecology, much research is still needed to safeguard these fascinating creatures. Advancing our knowledge of syngnathids requires generating data by means of a multidisciplinary approach encompassing several key areas of research that should be prioritized in the future: population assessment, distribution, habitat use and niche partitioning, bycatch mitigation, molecular research (particularly genomics), species interactions, habitat protection and restoration, climate change impact and resilience, aquaculture and husbandry, conservation and community engagement, and legal protection. Further advances on these topics are fundamental prerequisites for formulating effective and rational conservation strategies for the family Syngnathidae.
Author contributions
MP: Writing – original draft, Writing – review & editing. MG: Writing – review & editing. JP: Writing – review & editing. GQ: Writing – review & editing. ER: Writing – review & editing. OR: Writing – review & editing. PT: Writing – review & editing.
Funding
The author(s) declare that no financial support was received for the research, authorship, and/or publication of this article.
Acknowledgments
The authors would like to extend their heartfelt thanks to all syngnathids used in the studies of this Research Topic.
Conflict of interest
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
The author(s) declared that they were an editorial board member of Frontiers, at the time of submission. This had no impact on the peer review process and the final decision
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Keywords: syngnathids, biology, ecology, physiology, seahorse, pipefish
Citation: Planas M, Gristina M, Palma J, Qin G, Rose E, Roth O and Teske PR (2023) Editorial: Syngnathid fishes: biology, ecology, physiology, conservation and innovative rearing techniques. Front. Mar. Sci. 10:1309683. doi: 10.3389/fmars.2023.1309683
Received: 08 October 2023; Accepted: 31 October 2023;
Published: 09 November 2023.
Edited and Reviewed by:
Rui Rosa, University of Lisbon, PortugalCopyright © 2023 Planas, Gristina, Palma, Qin, Rose, Roth and Teske. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
*Correspondence: Miquel Planas, mplanas@iim.csic.es