Habitat Destruction: Terrestrial Runoff

As we explored in our last post, coastal development is on the rise as the world’s population continues to increase along the coast lines. Coastal development is not only responsible for the direct removal and destruction of nearshore habitats like mangroves, it is also responsible for the increase in terrestrial runoff. Terrestrial runoff from agriculture and industry has been directly linked to reduced water quality, and the increase of sedimentation and pollutant levels (Knip, Heupel, & Simpfendorfer, 2010).

Terrestrial Runoff [Digital Image] Retrieved from http://coraloha.weebly.com/uploads/4/4/3/9/44394941/_6474801_orig.jpg

Terrestrial runoff poses a risk to aquatic environments by introducing excessive amounts of nutrient richness to an area. This increases the risk for algae blooms. These blooms can grow so large that they smother all other organisms in the region by reducing available oxygen levels. The result is an aquatic dead zone. This is called eutrophication (Knip, et al., 2010).

Algae Bloom
Algae Bloom (2014, January 23). Retrieved from https://www.flickr.com/photos/mapbox/12108111176


Sharks and rays are very sensitive to water quality conditions. Leopard sharks (Triakis semifasciata), for example, are a nearshore species which utilize estuaries along the coast of California to mate, gestate, and even pup their young. However, they have been documented vacating these areas during periods of anoxia, or depleted oxygen levels, caused by terrestrial runoff (Carlisle & Starr, 2009). In recent weeks, leopard sharks have been found stranding themselves along the southern Californian coast. The cause of these strandings is still under investigation by scientists, though it has been suggested that rainwater runoff and pollution may be to blame.  

Flannery, A. [Amanda Flannery]. (2017, April 23). Leopard Sharks Wash Ashore in O.B. After Storm, March 2, 2017 CW6 News Team . Retrieved April 23, 2017, from https://www.youtube.com/watch?v=WJ8c9fyfRjg

Runoff has been documented to cause other health problems in elasmobranchs as well. A family of pesticides that was used extensively from the 1940’s through the 1960’s for agriculture and mosquito control called organochlorines, which contains chlorinated hydrocarbons, have been linked to causing infertility in bonnethead sharks (Sphyma tiburo) (Delaware Health and Social Services, 2010; Gelsleichter et al., 2005).

Juvenile Bonnethead Shark
Thekohser (Photographer) (2008, August 15). Juvenile Bonnethead Shark [Digital Image] Retrieved from https://upload.wikimedia.org/wikipedia/commons/2/28/Juvenile_Bonnethead_shark.JPG

You can make a difference for marine ecosystems by calling your Congress man or woman and tell them that you care about the quality of our waters! Sharks, rays, and other marine organisms cannot speak or be represented in Congress. They need your voice. Get involved and stand up for sharks.

In my next blog post, I will conclude examining how human coastal development is leading to habitat destruction and loss for sharks and rays by looking at coral communities and reef sharks.

The new Ocean For Sharks Shop is open! There’s handmade ocean inspired plush animals, canvas paintings, and of course my children’s book, Winifred the Wondrous Whale Shark, available in print and PDF. Be sure to stop by. Remember proceeds benefit shark research and conservation with a donation to Project AWARE!

As always, I look welcome comments and feedback! Thanks for following and liking!


Featured Image Source

Post Rain Pic [Digital Image] (2015). Retrieved from https://sandiego.surfrider.org/wp-content/uploads/2015/05/TRV-Post-Rain-Pic.jpg

Literature Cited

Carlisle, & Starr. (2009). Habitat use, residency, and seasonal distribution of female leopard sharks Triakis semifasciata in Elkhorn Slough, California. Marine Ecology Progress Series, 380, 213–228.

Delaware Health and Social Services. (2010). Organochlorine pesticides: What are organochlorine pesticides? Retrieved March 23, 2017, from http://dhss.delaware.gov/dhss/dph/files/organochlorpestfaq.pdf

Gelsleichter, J., Manire, C. A., Szabo, N. J., Cortés, E., Carlson, J., & Lombardi-Carlson, L. (2005). Organochlorine concentrations in bonnethead sharks (Sphyrna tiburo) from four Florida estuaries. Archives of Environmental Contamination and Toxicology, 48(4), 474–483.

Knip, D. M., Heupel, M. R., & Simpfendorfer, C. A. (2010). Sharks in nearshore environments: models, importance, and consequences. Marine Ecology Progress Series, 402, 1–11.

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