Habitat degradation

Seahorses live in seagrasses, mangroves, corals, macroalgae, estuaries and more.

This wide array of seahorse habitats – all concentrated in coastal and inshore areas – is vitally important for marine life and people alike but also hugely threatened.

About 40% of the world’s population lives within 100 km of the coast and 66% of the world’s largest cities are on the coast.1 Such intense human presence translates into great human impacts on the coastal seas. The dominant problems are habitat damage and destruction. However, evidence is mounting that eutrophication and chemical pollutants are also problematic for seahorses. Moreover, the effects of climate change are felt most intensely in shallow and inshore waters, as sea levels and sea surface temperatures both rise.

Estuaries and other transitional waters are experiencing enormous pressures, often because of coastal development and land-based run off and discharges.

Estuaries are home to some of the most threatened seahorse species, particularly Hippocampus capensis in South Africa – where it is only found in three small lagoons with limited suitable habitat – and Hippocampus whitei in eastern Australia. For these species, it is habitat loss rather than fishing that poses the greatest threats. Eutrophication (excessive nutrients) poses a major challenge in the South African lagoons while occasional freshwater flooding also kills seahorses. In Australia, habitats are again heavily impacted by coastal development, pollution, and sedimentation.

Seagrasses are among the most important habitats for seahorses – and vital for humans and other marine life, including 1000 fish species2 – yet are subject to enormous damage and destruction. Expansive meadows of seagrasses – the only flowering plant in the ocean – are being reduced at a rate of 110 km2 per year.3

Pressures on these shallow water habitats include sea filling (also erroneously called land reclamation), dredging, smothering, coastal development, pollution, eutrophication from industrial and agricultural run-off, aquaculture development, boat damage, thermal stress… and destructive fishing.

Bottom trawlers scour the ocean floor repeatedly, laying waste to seagrasses in trails that can be seen from space. In so doing, they contribute to releasing carbon that would otherwise be sequestered by the expanses of seagrass globally.

Mangroves are homes to many tropical species of seahorses, which live among their inundated roots. These fabulous trees are found at the edge of the land, where it meets the ocean, and are subject to pressures from both land and sea. Such shoreline forests provide nursery habitats for juvenile fishes, as well as birds, crustaceans, shellfish, reptiles and mammals. Yet they are frequently cut down for domestic use and are also cleared to make way for shrimp farming and other aquaculture.

Recently, mangroves have been removed at a rate of 1-2% per year,4 with huge ecological and economic costs. For example, studies show that removing one ha of mangroves results in the loss of 480 kg/year of fish and shrimp in tropical areas.5 In addition to cutting and clearing, climate change – e.g. sea level rise and altered rainfalls – is placing great pressure on mangroves.

Corals – the homes for many seahorse species – are a subject of huge global concern, because of direct and indirect damage and because of the effects of climate change.

Although coral reefs only constitute 0.1% of ocean waters, they host 8,0006 species of fish and healthy reefs can provide US$130,000 to $1.2 million7 of economic benefits per ha each year; one estimate puts the total worth of coral reefs at $375 billion annually.8

Humans remove corals from the ocean, break corals and release sediment to smother the corals. In addition, there is huge concern about how climate change is damaging corals: higher sea surface temperatures are leading to bleaching of corals (when the symbiotic algae leave) and increasingly acid waters are affecting coral skeletons. Globally, warm water corals have declined 50% in the past 30-50 years.9

Macroalgae (seaweeds) dominate about 25 % of the world’s coastlines and need much more conservation attention.10,11 These highly productive ecosystems provide shelter and nursery grounds for many seahorse species.

The three biggest threats to these amazing organisms are direct damage (e.g. coastal construction), pollution and introduction of exotic (alien) species, which causes community shifts. That said, climate change is leading to range retractions of kelp as waters warm, and thus creating shifts toward the poles.12

People use seaweeds for food, feed, and fertilisers while seahorses use them as safe spaces with wonderful holdfasts. Available long-term data sets suggest that 61% of macroalgae communities are in decline and only 5% are increasing.13,14

  1. United Nations 2017. The Ocean Conference. Factsheet: People and Oceans
  2. Cullen-Unsworth, L.C., Jones, B.L., Lilley, R. and R.K.F. Unsworth. 2018. Secret gardens under the sea: What are seagrass meadows and why are they important. Frontiers for Young Minds 6(2)
  3. Waycott, M., Duarte, C.M., Carruthers, T.J.B., Orth, R.J., Dennison, W.C., Olyarnik, S., Calladine, A., Fourqurean, J.W., Heck Jr., K.L., Hughes, A.R., Kendrick, G.A. Kenworthy, W.J., Short, F.T. and S.L. Williams. 2009. Accelerating loss of seagrasses across the globe threatens coastal ecosystems. PNAS 106(30): 12377-12381
  4. Carugati, L., Gatto, B., Rastelli, E., Martire, M.L., Coral, C., Greco, S. and R. Danovaro. 2018. Impact of mangrove forests degradation on biodiversity and ecosystem functioning. Scientific Reports 8:13298
  5. Anwar C, Gunawan H. 2006. Peranan ekologis dan sosial ekonomis hutan mangrove dalam mendukung pembangunan wilayah pesisir. Proceedings of Exposure Research Results. p 23-34. As cited in: Eddy, S. Ridho, M.R., Iskandar, I. and A. Mulyana. 2016. Community-based mangrove forests conservation for sustainable fisheries. Journal of Tropical Silviculture 7(3)
  6. Lieske, E. and R. Myers, R. 2001. Coral Reef Fishes: Indo-Pacific and Caribbean. Harper Collins Publishers, Milan, 400 pp
  7. Moberg, F. and C. Folke. 1999. Ecological goods and services of coral reef ecosystems. Ecological Economics 29(2) 215-233
  8. Hoegh-Guldberg, O., Poloczanska, E.S., Skirving, W. and S. Dove. 2017. Coral reef ecosystems under climate change and ocean acidification. Frontiers in Marine Science 4(158)1-20. 29
  9. Hughes 1994; Gardner et al. 2003; Bruno and Selig 2007; De’ath et al. 2012
  10. Steneck, R. S., and C.R. Johnson. 2013. Kelp forests: dynamic patterns, processes and feedbacks. in Marine Community Ecology, eds M. Bertness, B. Silliman, and J. Stachowitz (Sunderland, MA: Sinaur Associates Inc., 315–336.
  11. Wernberg, T., Krumhansl, K., Filbee-Dexter, K., and M.F. Pedersen 2019. Status and trends for the world’s kelp forests. In: World Seas: an Environmental Evaluation, ed C. Shepherd (Amsterdam: Elsevier), 57–78
  12. Khan, A.H., Levac, E., Van Guelphen, L., Pohle, G. and G.L. Chmura. 2018. The effect of global climate change on the future distribution of economically important macroalgae (seaweeds) in the northwest Atlantic. Facets 3(1) and references therein
  13. Krumhansl, K. A. and R.E. Scheibling 2012. Production and fate of kelp detritus. Mar. Ecol. Prog. Ser. 467: 281–302
  14. Wernberg, T., Smale, D. A. and M.S.  Thomsen. 2012. A decade of climate change experiments on marine organisms: procedures, patterns and problems.Glob. Chang. Biol. 18, 1491–1498