http://sanctuaries.noaa.gov

Coral Reef Fish & Marine Zones 

Coral Reef Fish are Vital to Healthy Coral Reef 

Coral reef fish have tremendous economic and ecological value in the Florida Keys. They 

are vital for sustaining a healthy coral reef ecosystem--the foundation of the ocean-based 

economy of the Florida Keys. Species like grouper and snapper are prized by recreational 

anglers and support an important commercial fishery, while colorful parrotfish and 

angelfish benefit tourism by entertaining divers and snorkelers. Herbivorous fish keep 

seaweeds from overgrowing corals and carnivorous fish keep populations of smaller fish 

and invertebrates in balance. Healthy populations of diverse reef fish help sustain the 

productive coral reef so important to the Keys ecology and economy. 

Marine Zones Protect Coral Reef Fish Habitat

Designated by Congress in 1990, Florida Keys National Marine Sanctuary manages nearly 

2900 square nautical miles of Florida Keys waters, balancing conservation of sanctuary 

resources with sustainable human uses. One management tool at the sanctuary’s disposal 

is marine zones — areas set aside for specific uses ranging from wildlife protection to recreational activities like scuba diving. In 

1997, several different types of marine zones, each with a different primary objective, were established in the sanctuary. Sanctuary 

Preservation Areas (SPAs) and Ecological Reserves were created to protect critical habitat and have restrictions on fishing and other 

consumptive activities. These highly protected zones* provided an opportunity for scientists to study the effects of zone protection 

on reef fish.

Scientists Study Long-Term Effects of Marine Zones on Reef Fish 

The Florida Keys sanctuary’s management plan (1996, 2007) outlines a strategy for scientifically monitoring the long-term effects 

of marine zones on sanctuary marine life and habitats. Several scientific studies have investigated coral reef fish populations and 

marine zones, focusing primarily on the SPAs and the two much larger ecological reserves.

Scientists from NOAA Fisheries, the University of Miami and the state of Florida collaborated on a 10-year study that began in 1997 

to document the effects of zone protection on reef fish, including both target (fished) species as well as non-target species. To collect 

data for this study, researchers recorded reef fish size, abundance 

and diversity over the course of thousands of dives in and around 

the SPAs and the Western Sambo Ecological Reserve. They used 

observations from similar dives conducted before the marine zones 

were established as a baseline for comparison.

Density of Reef Fish Increases in Protected Zones

Using the data collected, scientists calculated population density — 

the number of fish in a given area — for each reef fish species. Since 

the SPAs and the Western Sambo reserve were implemented, the 

overall average density of several species in these protected zones 

has increased significantly over the pre-zone baselines. Density 

increases were seen for yellowtail snapper, gray snapper, mutton 

snapper, black grouper, red grouper, graysby and hogfish. Essentially, 

there were significantly more of these fish in 2007 than prior to zone 

establishment 10 years earlier. 

Florida Keys National Marine Sanctuary

http://floridakeys.noaa.gov/

Scientists conducted a visual census at 327 sites in 2007.

Figure: NOAA Fisheries

Hogfish prefer low relief reef habitats.

Photo: William F. Precht, FKNMS
To learn more about these and other accomplishments, 

visit sanctuaries.noaa.gov

Hurricanes May Have Redistributed Fish

For most years of the study, densities of fished 

species were also significantly higher in the protected 

areas in comparison to fished areas, although some 

declines were observed following severe storms. 

Storms may have physically disturbed reef fish, 

causing the redistribution of individual fish. Yellowtail 

snapper followed a pattern typical of most target fish 

in the study. Densities inside protected zones were 

significantly higher during the first several years, then 

declined following hurricanes in 2004 and 2005 

before increasing again in 2007 (see graph on right). 

For comparison purposes, two non-target species — 

stoplight and striped parrotfish — were tracked as part 

of this study. As might be expected for species that are 

not fished, densities remained relatively stable in both 

the highly protected zones and the fished reference 

sites (see graph on right). 

Density Increases Seen in Fished Areas 

Significant density increases were also seen in five 

target species (gray snapper, mutton snapper, black 

grouper, red grouper and hogfish) found in fished 

zones. The magnitude of these increases at the fished 

sites was much smaller, however, when compared 

with the increases seen in the protected zones. 

A number of factors could have contributed to the 

upward trends seen in fished areas. More restrictive 

fishing measures became effective for several 

target species. Hogfish, for example, came under 

a larger minimum size limit in 1994. In 2001, the 

Tortugas Ecological Reserve, which protects the 

spawning grounds of reef fish and pink shrimp, was 

implemented. Years of good recruitment of young 

fish into the protected zone could also help boost fish 

densities. 

Protected Areas See Increases in Spawning Stock

From the data, scientists calculated the abundance of reproductive adults, or “spawning stock,” for six target species. Increases in 

spawning stocks may have positive benefits on fish populations. Significant increases in spawning stocks were observed for yellowtail 

snapper, black grouper and mutton snapper when compared with their pre-zone baselines. Spawning-sized gray snapper and red 

grouper were also more abundant inside the zones, but densities were not significantly different. Spawning stock increases were 

not observed for hogfish, a fish that typically shows a low preference for the high-relief reef formations that were most prevalent. 

Research Shows Marine Zones Contribute to Healthy Reef Fish Populations

This long-term study shows that SPAs and the Western Sambo Ecological Reserve have had positive effects on populations of 

target reef fish species by increasing the size and densities of snappers and groupers. The abundance of reproductive adults 

in protected zones has also increased in some instances. Reef fish populations seemed to respond relatively quickly to zone 

protection in many cases. The benefits of larger protected areas, especially those with diverse habitats and spawning grounds, may 

not become fully apparent for years because protected fish may live for decades. In the future, scientists will likely revisit these 

studies to gain further insights into the long-term benefits of zone protection. For more information, visit http://floridakeys.noaa.

gov/research_monitoring to read the sanctuary’s zone monitoring report.

* Also called No-take Marine Reserves (NTMRs)

Principle Investigator: Dr. James A. Bohnsack, NOAA Southeast Fisheries Center

Written by: Nancy Diersing, Florida Keys National Marine Sanctuary

Published: January 2011

Observed changes in fish density (number/sample) inside (red) and outside (black) 

Sanctuary Protected Areas for target yellowtail snapper (top) and non-target striped 

parrotfish (bottom). Vertical bars show 95% confidence intervals. The four year 

combined baseline data (1994-1997), collected before reserve protection in 1997, are 

summarized at the left for sites that eventually were closed to fishing or that continued 

to be fished. Figure: NOAA Fisheries