Swimming nets have positive effects on populations of the endangered White's seahorse Hippocampus whitei

Abstract

Habitat degradation and destruction arising from rapidly increasing urbanization represents one of the most significant threats to biodiversity. Human populations are continuing to increase around coastal regions, and as marine habitats are displaced by artificial structures it is important to understand how marine species may be impacted by these changes in habitat availability. The endangered seahorse Hippocampus whitei has been observed inhabiting protective swimming nets in Sydney Harbour, Sydney, Australia, even in the presence of natural habitats. This study tested whether the presence of a swimming net results in increased seahorse numbers at sites around Sydney Harbour, or whether seahorses are attracted away from natural habitats. Density surveys and mark–recapture population estimates were done at sites with pre‐existing swimming nets and compared to control sites where only natural habitat was present. A manipulative experiment was conducted in which panels of swimming net material were installed at two sites in Sydney Harbour, with comparisons to control sites over a period of 14 months (April 2018 to June 2019) to test whether the installation of swimming nets would affect seahorses on surrounding natural habitat or increase site abundance. The pre‐existing and installed swimming nets were found to support greater densities of H. whitei as well as some increases in site‐scale abundance, with no effects on seahorse density on natural habitats. It is likely that increased seahorse production is occurring on the nets, with no evidence that seahorses are being attracted away from natural habitat; however, effects may vary across survey occasions and sites. Furthermore, swimming nets may serve as a useful replacement habitat in locations where natural habitat has become sparse or absent.

Diversity of Seahorse Species (Hippocampus spp.) in the International Aquarium Trade

“…A broad habitat spectrum, as seen in H. reidi [120][121][122], probably enhances a species' suitability as an aquarium pet. As seahorses are poor swimmers, the availability of a holdfast is an important habitat factor [123,124], which may explain why some species have no problem in using artificial substrates to cling on [125][126][127][128][129][130][131][132]. Large seahorse species that are commonly fished, such as H. reidi (Figure 3b), are overall less specific in their habitat requirements but share several traits with small congenerics, such as the use of camouflage and an immobile body posture while using the tail as holdfast [29,108] (Figure 3b), but some species are able to change coloration as part of their courtship behavior [109,110] or need for camouflage [103].…”

“…A broad habitat spectrum, as seen in H. reidi [120][121][122], probably enhances a species' suitability as an aquarium pet. As seahorses are poor swimmers, the availability of a holdfast is an important habitat factor [123,124], which may explain why some species have no problem in using artificial substrates to cling on [125][126][127][128][129][130][131][132].…”

Assessing the Effectiveness of Conservation Stocking for the Endangered White’s Seahorse Hippocampus whitei

“…Whilst habitats have declined across its range, H. whitei has shown an ability to adapt by utilising artificial habitats such as protective swimming nets (Hellyer et al, 2011;Simpson et al, 2021a;Simpson et al, 2021b) and purposefully designed artificial habitats known as seahorse hotels (Simpson et al, 2020). It was recently shown that adult H. whitei select artificial habitats over natural habitats (Simpson et al, 2019), similar to that of the only other Endangered seahorse species, Hippocampus capensis in South Africa (Claassens et al, 2018).…”

Implications of holdfast availability and patchiness on juvenile seahorse (Hippocampus reidi) condition and welfare: Simulations in captivity

“…Caulerpa prolifera ) are rarely used (Olivotto et al., 2008), likely due to difficulties in their long‐term maintenance. While inter‐specific differences may exist regarding holdfast preferences and seahorse size, only a few studies have focussed on this topic in the wild or in rearing facilities (Claassens et al., 2018; Correia et al., 2013, 2015; Faleiro et al., 2008; Simpson et al., 2019, 2020a, b). Understanding seahorse preferences will help to improve seahorse fitness at high stocking densities and to increase fish production by providing better conditions for growth.…”