Why are leafy sea dragons important

Broad, flat appendages resembling seaweed branch from the plates surrounding the body Groves Amidst these appendages on the sides of the body are several sharp spines that aid in defense against predators Dragon Search The frond-like appendages and thin body vary on adults from green to yellow-brown to light brown; some have thin white lines radiating from the eye and extending over the body Dragon Search ; Wheeler Color variation occurs and depends on age, location, diet, and environmental stressors Dragon Search Unlike most fish species, in P.

The female develops between and eggs. Concurrently, the male forms many capillaries on the tail, which then proceeds to swell, wrinkle, and form about eggcups Dragon Search The eggs are then transferred from the female onto the male's tail and fertilized, although little is known exactly how this occurs successfully Groves Four weeks is the average incubation period, and hatching occurs over several days to maximize survival rates Dragon Search ; Zahl For the first few days, a yolk sac provides nutrients.

Soon after birth, the newborns are able to swim and hunt successfully. Between one and two years, the fish reaches maturity and can live for seven years in captivity Groves ; Dragon Search Much of the reproduction, such as yearly breeding frequency, is yet unknown Groves Those predators not fooled by its blending capabilities are often surprised by its bony exterior and long, sharp spines Zahl The species tends to swim alone or in pairs Groves Mimicking surrounding vegetation, P.

Leafy seadragons are very poor swimmers and rely on their camouflage to avoid predation. They are relatively large compared to their closely related species and reach lengths of up to one foot 30 cm long. Leafy seadragons eat small, plankton crustaceans but are small enough themselves and have sufficient vision to see and attack individual prey unlike large filter feeders.

Their heads are relatively large compared to their very small mouths, so they are able to concentrate enough pressure at their mouths to easily suck in their prey. Like in seahorses and pipefishes, male leafy seadragons care for the fertilized eggs. They do not have a specialized pouch like male seahorses but instead carry the eggs under the tail.

There, they remain exposed to the elements but safe, and the male provides them with necessary levels of oxygen through a specialized, nearby organ. Newly hatched leafy seadragons receive no further parental care. Slow-swimming and with fragile bodies, seadragons depend on camouflage to hide them from predators. Their leafy appendages, ability to change color to match their seaweed and seagrass habitats, and ability to sway like plants in the water current help protect them from predators.

These fish are in trouble because of habitat destruction due to human development, pollution, excessive fertilizer runoff, and fishing practices where they may be trapped as bycatch or poached. Additionally, their populations may be threatened by rough seas and limited food supply.

To help conserve syngnathid populations in their natural environment, construction and development in coastal areas should be limited; fisheries should be well regulated, especially in shallow water habitats where seadragons live; and pollutants should be prevented from entering the ocean through run-off.

Preserving and protecting the ecosystems that are home to the beautiful and intriguing syngnathid family of marine animals will improve their populations. Because they are inhabitants of temperate waters, seadragons may be impacted by an increase of water temperature as a result of global climate change.

By using our website, you agree to our cookie policy. Research Fieldwork. Plan Your Visit. Membership Home. Events Home. Full List Calendar View Upcoming. Virtual Live Streaming Online Academy. Exhibits Home. Learn Home.

Give Home. MtDNA diversity was measured as the number of variable sites S and haplotypes k , and haplotype diversity h in Arlequin. We investigated potential past demographic changes within the 2 main clusters, South Australia and Western Australia.

Bottleneck v. Three mutational models infinite allele, stepwise mutation, 2-phase under default conditions were considered. For the mtDNA, mismatch distributions were compared against the expectation under a model of demographic expansion using the sum of squared deviations SSD and raggedness r as calculated in Arlequin bootstrap replicates.

Small and nonsignificant SSD and r indicate a good fit of the data to an expansion Harpending In accordance with the Journal of Heredity data archiving policy Baker , we have deposited the primary data underlying these analyses as follows:. Sampling locations, microsatellite genotypes, mitochondrial DNA sequences: Dryad Both microsatellite genotypes and mtDNA haplotypes of P. One cluster spanned localities within the borders of South Australia, the other comprised the Western Australian localities Figure 2b.

This structure was reflected also in the mtDNA haplotype network, where South Australian samples comprised a set of related haplotypes that were separated by at least 2 substitutions from the haplotypes of Western Australian individuals Figure 2c. The divergence between the 2 clusters explained a large proportion of the genetic variation present in the data sets, namely F -statistics are based on microsatellite allele frequencies sat and on haplotypic mitochondrial data mt.

In the western cluster, an individual from Bremer Bay and a Western Australian sample of unknown locality had Differentiation between pairs of sample sets was generally similar regardless of the statistic used, but their magnitudes differed Figure 3a , b. Heatmaps of pairwise differentiation among sample sets of leafy seadragons Phycodurus eques. Darker colors indicate stronger differentiation. In South Australia, several sample sets showed considerable genetic differences from others in the region.

Divergence between sample sets accounted for However, this correlation appeared to be mainly driven by the genetic differentiation between the South Australian and Western Australian main clusters, which are also geographically far apart.

The 7 polymorphic microsatellite loci showed up to 9 alleles, but 3 loci had only 2 alleles mean 3. Nineteen haplotypes were observed among the 56 individuals sequenced based on the bp of concatenated ND4 and control regions sequences Figure 2c.

The mtDNA mismatch distribution of the South Australian samples fit well to a model of population expansion as shown by small and nonsignificant values for SSD and r , while values were larger in Western Australia Table 4. In Western Australia, the indices were consistently larger and did not deviate from the expectation of no growth Table 4. Neutrality statistics for groups of leafy seadragons Phycodurus eques based on mtDNA.

Negative and significant values for D and F S , and small and significant values for R 2 , as well as small and nonsignificant values for SSD and r are indicative of a demographic expansion. Our study provides insight into the molecular genetic variation and population structure of P. The leafy seadragon has clear geographic structure, with the most prominent separation between South Australia and Western Australia, and shallower structuring in South Australia.

Genetic diversity was low overall, but was particularly depressed in Western Australia. South Australian samples showed signatures of previous growth, which may have been caused by the increased availability of habitat in the area due to the flooding of large embayments after the last glacial maximum. Leafy seadragons occur in 2 major partitions, one in the western part of the range, here represented by individuals from Albany and Bremer Bay in Western Australia WA , the other located in the bays and gulfs of South Australia SA.

Western Australian and South Australian groups were reported also in Larson et al. A few records of leafy seadragons indicate that they occur in at least parts of the Bight Baker , but without genetic samples it will remain unclear if populations are sustained continuously across the entire extent, or if a phylogeographic break separates the 2 groups.

In any case, the subdivision into the geographical units was probably rather recent and low levels of gene flow could exist, given that some samples from South Australia showed low levels of genetic ancestry with respect to Western Australia, and vice versa Figure 2b. The apparent admixture could also be due to the small number of loci used here. The mitochondrial haplotypes are clearly split into 2 clusters over the Great Australian Bight but their divergence is relatively shallow.

Only 2 substitutions 0. This degree of mtDNA differentiation across the Great Australian Bight is comparable other syngnathids across similar geographic scales e. A notable exception is the closely related common seadragon P. At the finer geographical scale, substructure existed as significant allele frequency differences between most of the South Australian bays Figure 3a. The absence of an isolation-by-distance signal within South Australia was therefore somewhat unexpected but may be due to the limited number of sites available for analysis.

Despite the mostly high and significant differentiation, Structure did not pick up additional groups in South Australia.

Again, this may point to the low power of the genetic markers employed here and should be revisited with high-resolution markers. Our sampling in the western part of the range was not sufficient to comment on putative substructuring within the Western Australian cluster, but given the overall patterns, it appears likely that further sampling in Western Australia could reveal additional distinct populations.

The South Australian cluster showed some signal for past demographic growth, while the Western Australian group appeared demographically stable. In southwestern WA, the continental shelf is relatively narrow Conolly and Von Der Borch , which could have ensured a stable range size despite changing sea levels.

When the gulfs were dry, seadragons must have existed outside of the bays. Each flooding event would have quickly opened large areas of new habitat.

Founding colonizations may have resulted in a genetic bottleneck with subsequent growth consistent with the genetic signal detected here. The 3 haplotypes that are shared between embayments may have been ancestral haplotypes that spread from a common source into the bays. After recolonization, these common haplotypes could have given rise to several low-frequency haplotypes, each restricted to a single bay Figure 2c.

A similar impact from glacial cycles has been proposed for southeast Asian seahorses, where flooding of the Sunda Shelf reconnected populations that were previously isolated Lourie et al. The scenario for the leafy seadragon is similar but here the colonization after flooding has resulted in differentiation of populations at the local scale. Both mitochondrial and nuclear DNA revealed moderate to low levels of genetic diversity in leafy seadragons.

Microsatellite variation of P. With the small sample sizes in Western Australia, statements have to be made cautiously. This low diversity was likely not due to the genotyping of closely related individuals since there were at least 3 mtDNA lineages Figure 2c and mitochondrial diversity indexes were moderately high Table 3. A more general statement about genetic diversity in Western Australia is not possible with our data, as we only had 2 other individuals from Albany.

Additional sampling of leafy seadragons in Western Australia is needed to investigate if the low genetic diversity is a general phenomenon in the area.

Comparison of genetic diversity of Syngnathidae from studies using microsatellites. Samples are ordered by increasing expected heterozygosity H e. On the basis of the genetic data currently available, leafy seadragons have at least 2 major genetic clusters within their geographic range. Western Australian individuals were genetically distinct from those in South Australia and are likely demographically independent. Until the distribution of these 2 clusters in the Great Australian Bight is established, the range of the clusters correspond to the political boundaries of these Australian states.

This should facilitate potential conservation actions at the state level, but concerted activity may be necessary to ascertain long-term connectivity over the Great Australian Bight through protection of their habitat. Additional conservation units may be present within the states, as indicated by relatively high differentiation between and within several bays in South Australia, but this should be substantiated with additional data before conservation recommendations can be made.

Genetic diversity in leafy seadragons is low and priority should be given to maintaining the standing diversity. The particularly low estimates of diversity in Bremer Bay are concerning and further research is needed to establish the full scope of the issue.

In South Australia, much of the available genetic diversity was found in Spencer Gulf. Populations of both leafy and common seadragons in Spencer Gulf may require monitoring because of seagrass decline Kirkman and the catch of seadragons through trawl fishing Knight and Vainickis This implies that seadragons either avoid trawled areas, or are fished out locally in trawled areas. Maintaining the high genetic diversity in Spencer Gulf should therefore be a specific target for conservation.

Given their unique appearance, leafy seadragons appear to have evolved in close association with their macroalgal and seagrass habitats Figure 1. Hence, the most persistent threat to leafy seadragon populations may be the degradation of their habitat, which has already been documented within their range Edyvane ; Connell et al. Among the most important findings here is the high differentiation of leafy seadragons at some of the neighboring localities.

This differentiation could further increase through fragmentation. Fragmented populations may lose genetic diversity faster, which can limit their ability to respond to environmental challenges Reed and Frankham Genetic diversity was already found to be lower in leafy seadragons than in other syngnathids.

The monitoring of leafy seadragon populations may be timely and management actions may focus on maintaining and encouraging gene flow between the populations through the protection of seagrass and kelp habitat. Leafy seadragons are also caught for the aquarium trade Martin-Smith and Vincent ; Martin-Smith and Vincent and as incidental by-catch during fishing operations Currie et al.

Although the numbers caught are low, continued regulation and monitoring of these catches will be necessary. We thank two anonymous reviewers and the associate editor for insightful comments that greatly improved the manuscript. We thank Catherine Ramsey and Shawn Larson Seattle Aquarium for supplying tissue samples and information on their origin. Forthcoming Mol Ecol Resour. Google Scholar.