Not all species of elasmobranchs are coastal. Many species, like blacktip reef sharks (Carcharhinus melanopterus), inhabit offshore coral reefs.
Coral reefs are delicate habitats that require very specific conditions to flourish. Corals prefer temperatures before 23-25 °C, but can tolerate temperatures as low as 18° and as high as 30°. They also require low sedimentation and a salinity of 35, and do not have much room for fluctuation, which is why corals do not occur in river mouths. Corals also require a great deal of wave energy to create turbulent waters to add in cleaning, sedimentation removal, and growth enhancement (Gericke, & Stump, 2016). Because of these requirements, corals are found almost exclusively between the Tropic of Cancer, 23.4°N of the Equator, and the Tropic of Capricorn, 23.4°S of the Equator.
While coral reefs make up only 0.1% of the ocean floor, they have been estimated to support over 25% of life in the ocean (Riegl, Purkis, Al-Cibahy, Abdel-Moati, & Hoegh-Guldberg, 2011). But rising global temperatures have led to coral bleaching epidemics across many areas of the world, including the Great Barrier Reef (Eakin, et al., 2016). Bleaching occurs when corals become too stressed and expel a photosynthetic algae, called zooxanthellae which gives the corals their color (Eakin, et al., 2016; Riegl, et al., 2011). The corals have not died when they expel the zooxanthellae. They are able to survive for a time without the algae, however time is not on their side, and if left in this stressed state for too long, the corals will die (Eakin, et al., 2016).
Each year many marine species make migrations for a number of reasons: prey availability, seasonal temperature changes, breeding purposes, pupping grounds, and potentially for reasons we do not yet understand(Hammerschlag, Gallagher, & Lazarre, 2011; Papastamatiou, Friedlander, Caselle, & Lowe, 2010; S. G. Wilson, Polovina, Stewart, & Meekan, 2006; Steven G. Wilson, Taylor, & Pearce, 2001). Black tip reef sharks (Carcharhinus melanopterus) along Florida’s coast aggregate in the thousands and migrate along the coast every year (Papastamatiou, et al., 2010).
In order to make these journeys each year, reef sharks require a network of reef habitats to be available to them. As corals continue to become stressed due to climate change and die off, fewer networks are available for migratory reef species and they are forced to find new networks of reefs to make these journeys possible (Duncan & Holland, 2006; Wilson, et al., 2001). Even if new suitable coral habitats can be reached, for some species it may not be possible to establish a stable population in these new habitats due to competition or predation events (Duncan & Holland, 2006).
You can get involved in coral restoration projects by volunteering or donating to these causes.
- Coral Restoration Foundation is a nonprofit ocean conservation organization working to restore coral reefs, educating others on the importance of the oceans, and using science to further research and monitoring techniques. Coral Restoration Foundation is dedicated to creating offshore nurseries and restoration programs for threatened coral species. These programs have allowed Coral Restoration Foundation to take the lead in innovative nursery and restoration techniques that are implemented worldwide.
- Originally founded in 1994 to galvanize the dive community around conservation, CORAL has grown from a small, grassroots alliance into a world-renowned organization with a history of successfully working with local communities in coral reef regions around the world to protect their coral reefs. Coral believes that for conservation to be durable, their interventions must be aligned with the social, cultural, and economic needs of each community, and that local leaders must be empowered to lead the effort.
- The NOAA Coral Reef Conservation Program brings together expertise from across NOAA for a multidisciplinary approach to studying these complex ecosystems to inform more effective management. They work closely with NOAA scientists in the National Ocean Service, National Marine Fisheries Service, Office of Oceanic and Atmospheric Research, and National Environmental Satellite, Data and Information Service.
In my next installment of this blog series exploring anthropogenic influences of shark population decline, I will be moving away from habitat degradation and toward the effects of climate change on elasmobranchs.
As always I welcome and appreciate your comments and feedback! Thanks for reading.
Featured Image Source
Flannery, A. (Photographer). (2016, May 12). Porites astreoides and Porites porites [Digital Image].
Duncan, K. M., & Holland, K. N. (2006). Habitat use, growth rates and dispersal patterns of juvenile scalloped hammerhead sharks (Sphyrna lewini) in a nursery habitat. Marine Ecology Progress Series, 312, 211–221.
Eakin, C. M., Liu, G., Gomez, A. M., De La Cour, J. L., Heron, S. F., Skirving, W. J., … Strong, A. E. (2016). Global coral bleaching 2014-2017. Reef Encounter, 31(43), 20–25.
Gericke, R., & Stump, K.. (2016, April 16). Coral Reefs 1: History, Distribution, Morphology, Zonation. Lecture presented at Marine and Island Ecology in Shedd Aquarium, Chicago.
Hammerschlag, N., Gallagher, A. J., & Lazarre, D. M. (2011). A review of shark satellite tagging studies. Journal of Experimental Marine Biology and Ecology, 398(1–2), 1–8.
Papastamatiou, Y. P., Friedlander, A. M., Caselle, J. E., & Lowe, C. G. (2010). Long-term movement patterns and trophic ecology of blacktip reef sharks (Carcharhinus melanopterus) at Palmyra Atoll. Journal of Experimental Marine Biology and Ecology, 386(1–2), 94–102.
Riegl, B. M., Purkis, S. J., Al-Cibahy, A. S., Abdel-Moati, M. A., & Hoegh-Guldberg, O. (2011). Present limits to heat-adaptability in corals and population-level responses to climate extremes. PLoS ONE, 6(9), e24802.
Wilson, S. G., Polovina, J. J., Stewart, B. S., & Meekan, M. G. (2006). Movements of whale sharks (Rhincodon typus) tagged at Ningaloo Reef, Western Australia. Marine Biology, 148(5), 1157–1166.
Wilson, S. G., Taylor, J. G., & Pearce, A. F. (2001). The seasonal aggregation of whale sharks at Ningaloo Reef, Western Australia: Currents, migrations and the El Niño/ Southern Oscillation. Environmental Biology of Fishes, 61(1), 1–11.