Jorge Palma

Poleward range‐shifts occur as climate warming alters the distribution of species. This is likely also true for the recent observations of the short‐snouted seahorse ( Hippocampus hippocampus ) and long‐snouted seahorse ( Hippocampus guttulatus ) in Scandinavia. These charismatic and iconic fishes are of high conservation concern, yet understudied throughout most of their ranges. Both species are small and cryptic, which makes their true distributions challenging to estimate using traditional surveys and novel methods such as multispecies metabarcoding assays. Here, we present the development of two species‐specific environmental DNA assays to evaluate the real‐time presence of these seahorses. Two assays: Hiphip and Hipgut were designed for digital PCR in silico and were then validated in vitro for their specificity against other species and sensitivity to low concentrations of target DNA. Following this, the assays were tested in situ using field samples in which the species were detected. First in positive controls from Ria Formosa Natural Park in Portugal or San Sebastian in Spain. Finally, the assays also detected both species at a Swedish site where a seahorse was observed on a live camera. These two assays represent novel tools to be applied to monitoring and conservation of these two charismatic yet cryptic species.

This study evaluated the effects of copepod use and copepod conditioning strategies on the growth and survival of long-snouted seahorse (Hippocampus guttulatus) juveniles from 1 to 60 days post-parturition (DPP). Four dietary treatments were tested: Artemia enriched for 24 h with Isochrysis galbana (control), daily collected copepods, copepods unfed for 48 h, and copepods enriched for 24 h with I. galbana. Juveniles fed copepod-based diets exhibited significantly higher growth and survival (p < 0.05) than those fed enriched Artemia. Mean standard length increased from 1.3 ± 0.1 cm at release to 5.9 ± 0.2, 7.5 ± 1.4, 7.1 ± 1.2, and 7.3 ± 1.1 cm at 60 DPP for the enriched Artemia, daily collected copepods, unfed copepods, and enriched copepods treatments, respectively. Wet weight increased from 0.002 ± 0.001 g to 0.44 ± 0.07, 0.81 ± 0.40, 0.68 ± 0.30, and 0.76 ± 0.40 g, while final survival reached 20%, 60%, 33.3%, and 56%, respectively. Compared with enriched Artemia, copepod-based diets markedly enhanced juvenile performance, supporting faster growth and promoting favorable behavioral traits that contributed to improved survival. These results demonstrate that copepods constitute a superior live feed for early juvenile H. guttulatus; however, copepod conditioning strategies directly influence their nutritional quality and, consequently, seahorse growth and survival. The use of copepods throughout the first 60 DPP is therefore not only feasible but strongly recommended for optimizing juvenile H. guttulatus rearing performance.

This study investigated the effects of copepods and copepod conditioning strategies on the growth and survivorship of long-snouted seahorse (Hippocampus guttulatus) juveniles from 1 to 60 days post-parturition (DPP). Four dietary treatments were tested: 24h Isochrysis galbana enriched Artemia (control), freshly collected copepods, 48h unfed copepods, and 24h I. galbana enriched copepods. Juveniles fed any copepod-based diet exhibited significantly higher growth (P < 0.05) and survival than those fed enriched Artemia. Mean standard length increased from 1.3 ± 0.1 cm at release to 5.9 ± 0.2, 7.5 ± 1.4, 7.1 ± 1.2, and 7.3 ± 1.1 cm at 60 DPP for the respective treatments. Wet weight rose from 0.002 ± 1 g to 0.44 ± 0.07, 0.81 ± 0.4, 0.68 ± 0.3, and 0.76 ± 0.4 mg, while final survival reached 20%, 60%, 33.3%, and 56%, respectively. Compared with Artemia, copepods markedly enhanced juvenile performance, supporting faster growth and promoting beneficial behavioral traits which contributed to improved survival. These results demonstrate that copepods as a superior live feed for early juvenile H. guttulatus, but copepod conditioning strategies directly influence their nutritional quality and, consequently, seahorse growth and survivorship. The use of copepods for the first 60 DPP is therefore not only feasible but strongly recommended.

This experiment aimed to determine the temperature limits beyond which seahorse growth and reproduction become suboptimal due to climate change. Four temperatures (16, 20, 24, and 28 °C) were tested to evaluate their effect on juvenile (1–56 days post-parturition (DPP)) and adult (one year old) long-snout seahorses, Hippocampus guttulatus. Additionally, the reproductive performance of adults was observed. Another experiment measured oxygen consumption (MO₂) in the same age groups and temperatures. Adults showed significantly higher growth rates at 20 and 24 °C compared to 16 and 28 °C. Adult mortality rates were 0%, 0%, 6.2%, and 62.5% at the respective temperatures. Juvenile growth performance was higher at 20 °C and 24 °C but significantly lower at 16 °C and null at 28 °C, with survival rates of 8%, 62%, 10%, and 0%, respectively. Oxygen consumption increased with temperature, ranging from 106.3 ± 3.1 to 203.3 ± 3.1 μmol O₂/g BW/h at 16 °C, and from 127.6 ± 3.5 to 273.3 ± 3.1 μmol O₂/g BW/h at 28 °C for adults and 1 DPP juveniles, respectively. The study highlights that juvenile and adult H. guttulatus have narrow thermal boundaries, beyond which reproduction, growth, and survival are seriously affected. Under climate change, the species appears unable to cope, potentially leading to their rapid disappearance.

Seahorses (Hippocampus spp.; Family Syngnathidae) are mainly targeted by Traditional Chinese Medicine, curio and ornamental trade, as dried or live specimens. Traceability tools may help fill the gaps on supply chains, securing information on geographic origin and identification of traded specimens. Fin-clipping, a non-lethal and well-established method in seahorse research, offers a potential approach to trace the geographic origin and certify the aquaculture of these flagship species. As such, this study aimed to investigate the existence of differences in isotopic profiles of four seahorse species cultured at research centers located in southern Portugal and northern Spain, as well as between cultured Hippocampus guttulatus sourced from two research centers, and between wild and cultured specimens of this species. This research also evaluated the potential of combining isotopic and elemental fingerprints for seahorse species discrimination, through inductively continuous-flow isotope ratio mass spectrometry (IR-MS) and plasma mass spectrometry (ICP-MS). Species cultured at the same research centers exhibited similar stable isotope composition (δ¹³C and δ¹⁵N), except in the case of temperate H. guttulatus from northern Spain, which differed significantly from tropical species H. kuda and H. reidi. These differences could be due to phylogenetic dissimilarities and differences in seawater temperature. The δ¹⁵N composition allowed to discriminate between cultured H. guttulatus from the two research centers and between cultured and wild specimens. While dorsal fin isotopes alone did not prove to be a reliable tool for the discrimination of different cultured species, combining them with elemental profiles from seahorses’ whole-body allowed to successfully discriminate between H. kuda and H. reidi. This preliminary research demonstrates the potential of stable isotope and elemental analyses for tracing seahorses’ geographic origin and species identification. However, further research should be performed to validate these findings for wild specimens, particularly those from illegal, unreported and unregulated (IUU) fisheries and trade.