A multidisciplinary approach to identify priority areas for the monitoring of a vulnerable family of fishes in Spanish Marine National Parks

Abstract

Background: Syngnathid fishes (Actinopterygii, Syngnathidae) are flagship species strongly associated with seaweed and seagrass habitats. Seahorses and pipefishes are highly vulnerable to anthropogenic and environmental disturbances, but most species are currently Data Deficient according to the IUCN (2019), requiring more biological and ecological research. This study provides the first insights into syngnathid populations in the two marine Spanish National Parks (PNIA-Atlantic- and PNAC-Mediterranean). Fishes were collected periodically, marked, morphologically identified, analysed for size, weight, sex and sexual maturity, and sampled for stable isotope and genetic identification. Due the scarcity of previous information, habitat characteristics were also assessed in PNIA.

Results: Syngnathid diversity and abundance were low, with two species identified in PNIA (Hippocampus guttulatus and Syngnathus acus) and four in PNAC (S. abaster, S. acus, S. typhle and Nerophis maculatus). Syngnathids from both National Parks (NP) differed isotopically, with much lower δ¹⁵N in PNAC than in PNIA. The dominant species were S. abaster in PNAC and S. acus in PNIA. Syngnathids preferred less exposed sites in macroalgal assemblages in PNIA and Cymodocea meadows in PNAC. The occurrence of very large specimens, the absence of small-medium sizes and the isotopic comparison with a nearby population suggest that the population of Syngnathus acus (the dominant syngnathid in PNIA) mainly comprised breeders that migrate seasonally. Mitochondrial cytochrome b sequence variants were detected for H. guttulatus, S. acus, and S. abaster, and a novel 16S rDNA haplotype was obtained in N. maculatus. Our data suggest the presence of a cryptic divergent mitochondrial lineage of Syngnathus abaster species in PNAC.

Conclusions: This is the first multidisciplinary approach to the study of syngnathids in Spanish marine NPs. Habitat preferences and population characteristics in both NPs differed. Further studies are needed to assess the occurrence of a species complex for S. abaster, discarding potential misidentifications of genus Syngnathus in PNAC, and evaluate migratory events in PNIA. We propose several preferential sites in both NPs for future monitoring of syngnathid populations and some recommendations for their conservation.

Keywords: Conservation; Genetic identification; Habitat; National park; Stable isotopes; Syngnathids.

Fig. 1

PNIA—Principal coordinates ordination of samples for Transect x Season pairwise combinations in seaweed assemblages on spring (green) and summer (grey). Overlay vectors are species whose cover has a Spearman correlation > 0.65 with any axis

Fig. 2

PNIA—Maxent habitat suitability map for syngnathids (pooled specimens of S. acus and H. guttulatus) in Cíes Archipelago. Environmental suitability is depicted using a color gradient from blue (low environmental suitability) to red (high suitability). The bottom panel shows the results of the jackknife test of variable importance training data

Fig. 3

NJ tree (p-distance) for the Syngnathus genus. “SA” and “SAb” show S. acus and S. abaster haplotypes, respectively. Numbers on branches indicate the bootstrap value for their confidence (1000 replicates). GenBank reference sequences for S. abaster (AF356060_S23; JX228141_SCA1), S. typhle (AF356042_S4; AF356059_S22; JX228148_KLU1), S. acus (AF356040), S. rostellatus (AF356041_S3), S. taenionatus (AF356061_S24; JX228146_VEN89) and S. exilis (JF273424_S64) are also included. Following Mwale et al. [58], S. exilis was used as outgroup

Fig. 4

Scatter plot of stable isotopes-length relationships in Syngnathus acus captured in spring and summer 2016 in Cíes Archipelago (PNIA). Data for Arcade Cove pipefish (M. Planas, unpublished observations) and for S. abaster from PNAC (December 2016) are provided for comparative purposes. Arcade Cove specimens were collected on spring and summer 2016

Fig. 5

Schematic representation of the relationships between isotopic values (δ¹³C and δ¹⁵N and Syngnathus acus from Cíes Archipelago (present study) and Arcade Cove (M. Planas, unpublished observations). Samples collected in spring and summer 2016. Similarity groups (polygons) from hierarchical clustering (Ward's method) are shown

Fig. 6

PNIA—Study area and transects (red lines; TR1 to TR10) surveyed for syngnathids in Cíes Archipelago (Galicia, NW Iberian Peninsula). Transects TR2-TR5 included rocky outcrops and sandy substrates, but resolution in the map at the presented scale do not show the rocky outcrops. We acknowledge the information provided by OAPN on GIS layers

Fig. 7

PNAC—Study area and surveyed sites for syngnathids in Cabrera Archipelago (Balearic Islands, West Mediterranean). Upper: Presences and absences of syngnathids. Below: Capture sites in Cabrera Island. We acknowledge the information provided by OAPN on GIS layers