Overfishing: Corals of the Caribbean under threat from Sponges

Fish populations living in coral reefs are substantially overfished in many areas across the world. The depletion of highly sensitive coral reefs is especially prevalent in Caribbean waters, where warming due to climate change, ocean acidification, storms, diseases and of course overfishing are all interacting to cause decline in biodiversity. It has even be stated that an incredibly alarming 80% of Caribbean coral reefs have disappeared over the last 50 years (Catlin Seaview Survey 2013).

Overfishing of slow-growing fish from the upper levels of the food web has been found to have large impacts on the species in the levels below. If these fish are overfished, there will be less herbivorous action on the algae in the ocean surface. This means that algae are able to thrive, especially the 'macroalgae' (macro meaning large). This has a detrimental smothering affect on our precious coral species. This has been deemed by some as causing a 'slippery slope to slime'. As corals are smothered by algae, coral reefs are degraded and we are left with a very anaesthetically pleasing underground slimy swamp of algae. 

Corals also have another detrimental competitor; sponges. We are all aware of what sponges are. Those frequently sold 'natural sponges' you can buy to help scrub yourself clean are in fact dried out organisms from the ocean. Sponges have recently been linked to further decline in corals in the Caribbean. They steal habitat space from the corals and frequently produce deadly toxins to directly kill the coral. An example of this in the Caribbean waters is the brain coral being continuously smothered by lavender branching sponges (see below).

Brain coral being smothered by competitive lavender branching sponge (Image source: http://cdn.phys.org/newman/gfx/news/hires/2015/2-endangeredco.jpg)
In less fished areas, these sponges are controlled by the upper level fish species, for instance, angelfish and parrotfish. This means that corals are less at risk from this vicious sponge competitors. This has led to researchers to say that if we want to save our beautiful Caribbean coral species, we must focus on maintaining sustainable populations of the angelfish and parrotfish that eat the sponges.

Bicolour Parrotfish found in the Caribbean waters (Image source: http://upload.wikimedia.org/wikipedia/commons/d/dd/Bicolor_parrotfish.JPG)

Queen Angelfish found in the Caribbean waters (Image source: http://www.ramblincameras.com/carsrd33.jpg)

The decline in corals has be noticed more in recent years and the World Conservation Union has included 10 species of coral on its Red List of Threatened Species. Even though is it incredibly difficult to try to eradicate all of the problems associated with coral reef declines; including diseases and coral bleaching caused by warming oceans, it is a great start to focus on limiting the impact of overfishing on corals. Hopefully this will help to further guide fishery management strategies in the future and reduce the stress on our beautiful tropical coral reefs.