From the Coast to the Coral Reef Crest: Management of Back Reef Systems

By D. Albrey Arrington and John Marr, NOAA’s Undersea Research Program Center for the Caribbean, the Caribbean Marine Research Center

Back reef habitats

While most people have some knowledge of coral reef ecosystems, many may not be aware of back reef systems (Figure 1). A back reef system is that part of the coral reef ecosystem that extends from the coast to the reef crest ¹. It consists of a mosaic of interconnected environments and associated animal and plant communities, including mangroves and seagrasses, which are of critical ecological value to a coral reef ecosystem.

Mangroves occur along shorelines and in tidal creeks or estuaries (Figure 2); and are critical components of the back reef system in that they provide complex habitat structure for numerous juvenile fish species. In fact, more than 75% of commercially caught fish in the Bahamas may inhabit mangroves at some point of their life ².

Seagrasses, such as turtle grass (Thallasia), are another highly valuable habitat that occur in the back reef system. Seagrasses form the base of the food web for species such as sea cows, sea turtles, fishes, and invertebrates. Similar to mangroves, seagrasses also provide a structurally complex refuge from predation for many juvenile fish species.

In addition to providing critical habitat, seagrasses and mangroves stabilize near shore sediments, help mitigate coastal erosion, and maintain water clarity. Due to the numerous roles back reefs play in coastal protection, tourism, and fisheries growth, back reef systems are of exceptional economic value. The U.S. Coral Reef Task Force (an interagency group established in 1998 by Presidential Executive Order 13089 to lead U.S. efforts to preserve and protect coral reef ecosystems) has identified the need to include assessment of back reef habitats in the restoration and management of coral reefs.

NURP Research

The Caribbean Marine Research Center (CMRC), NOAA's Undersea Research Program (NURP) Center for the Caribbean, has been at the forefront of research pertaining to the restoration and management of back reef systems. Using its field station at Lee Stocking Island in the Bahamas, CMRC has supported research projects that increase the scientific understanding of back reef systems and their value to coral ecosystems (Figure 3), including:

• Designing and assessing marine protected reserves. The Exuma Cays Land and Sea Park in the Bahamas (Figure 4) serves as a focal point for studies on the importance of marine protected areas (MPA) in long-term protection of coral ecosystems. The Exuma Cays Land and Sea Park is the oldest and largest MPA in the world to fully protect coral reefs by encompassing the terrestrial, back reef, and fore reef components of the coral reef ecosystem.
• Assessing the impact of hydrologic alterations. Coastal developers have in the past given little consideration to how back reef habitats may be impacted by changes in freshwater input and hydrologic connectivity (Figure 5). Research in the Bahamas has shown that roads built across estuaries without culverts to permit surface water flow often disrupt hydrological connectivity, which has been shown to fragment and seriously degrade the physical and biological state ³ of these estuaries.

  Back Reef Habitats in History The construction of Florida's Overseas Railway provides a striking example of the impact that hydrologic alterations can have on back reef habitats. In 1910, Henry Flager, a major developer of Florida's Atlantic Coast, extended his Florida East Coast Railway to Key West. This extension formed an overseas railway with an ambitious series of oversea trestle bridges. Some channels between neighboring islands were filled in with sediment to minimize the number of bridges that were to be constructed. The removal of open water channels resulted in a loss in water flow between islands and caused a negative impact on back reefs and their associated organisms. After almost a century, some of these channels will be re-opened as a result of efforts to restore the Everglades.

• Assessing habitat loss and degradation resulting from terrestrial inputs. Shallow nearshore habitats are critical components of back reef systems; and because of their proximity to land, they are also the first areas to be impacted by land-based pollution and coastal development. CMRC-supported research has verified that healthy back reef habitats are essential for the larval and juvenile stages of economically and ecologically important species such as grouper and lobster (Figure 6). These impacts can have a profound affect on back reef systems, including declines in fish stock populations and fish recruitment.

BackReefs I and II: Targeting Management Priorities

Though managers may be aware of the importance of back reef habitats to the health of corals at the reef crest, gaps in knowledge show that additional research is needed to define the management goals of back reef habitats.

CMRC has hosted two significant workshops, BackReef I and BackReef II, to define strategic research and management of back reef habitats. BackReef I was convened in December 2001 to discuss the state of science and management of back reef systems. A special issue of the Bulletin of Marine Science featured the research topics presented at BackReef I (Figure 7), including characterizing: the importance of back reef systems to fish and invertebrate populations (Figure 8); the landscape ecology of back reef systems; the influence of ecological processes on back reef communities; the examination of anthropogenic disturbances to back reef systems; and an evaluation of management strategies for back reef systems.

BackReef I resulted in the publication of a list of priority management goals for the effective protection and restoration of back reef systems. Goals identified were:

• Minimize disturbances over time.
• Ensure sustainable use of resources.
• Preserve ecological function of back reef systems.
• Restore back reef systems that are deemed restorable.

Following the success and momentum of BackReef I, CMRC hosted a second workshop in January 2005, BackReef II: the Importance of Back Reef Habitats to the Sustainability of Coral Reef Ecosystems. The purpose of the BackReef II workshop was to identify gaps in scientific knowledge to improve the management of back reef habitats. The research and monitoring priorities identified at the workshop were intended to complement ongoing research and monitoring efforts supported by the U.S. Coral Reef Task Force member agencies, including NOAA's Coral Reef Conservation Program and the Environmental Protection Agency's coral disease and biocriteria assessment program; and assist local, state, territorial, federal and international partners by providing resource managers with information to improve their management decisions. The forthcoming workshop report and a presentation at the Association of Marine Laboratories of the Caribbean's 32nd Annual Meeting are being designed to increase the proportion of the population that is acting as wise stewards of back reef systems and will be distributed to a wide variety of audiences including marine scientists, resource managers, policy makers, educators, and conservationists.

¹ Dahlgren, C. and J. Marr. 2004. Back reef systems: Important but overlooked components of tropical marine ecosystems. Bulletin of Marine Science 75: 145-152.

² Sullivan-Sealey, K., B. Brunnick, S. Harzen, C. Luton, V. Nero, and L. Flowers. 2002. An Ecoregional Plan for the Bahamian Archipelago. Taras Oceanographic Foundation, Jupiter, FL.

³ Layman, C. A., D. A. Arrington, R. B. Langerhans, and B. R. Silliman. 2004. Degree of fragmentation affects fish assemblage structure in Andros Island (Bahamas) estuaries. Caribbean Journal of Science 40: 232-244.