Figure 1. An aerial photograph of southern Andros in the Bahamas
illustrates the spatial mosaic of the interconnected environments
that make up the back reef system. Photo credit: D. A. Arrington,
Figure 2. Mangroves are a critical component of most tropical
and subtropical back reef systems. Andros, Bahamas. Photo
Credit: D. A. Arrington, CMRC.
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
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
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
Figure 3. Divers quantify quality of
a back reef system at Lee Stocking Island. Photo Credit: J.
Figure 4. The Exuma Cays Land and Sea
Park established in 1959 is the world's first land and sea
park. Photo credit: The Nature Conservancy.
Figure 5. A small tidal creek on Andros
in the Bahamas, functions as a critical nursery habitat for
many reef-associated fish species. Fragmentation of the landscape
can have unexpected impacts on offshore coral reefs. Photo
Credit: D. A. Arrington, CMRC.
Figure 6. Nassau grouper (Epinephelus
striatus), an endangered species, lives in the back reef
habitat. © C. Dahlgren, CMRC.
- 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
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.
Figure 7. Topics discussed at the BackReef
I workshop were published in a special issue of the Bulletin
of Marine Science in September 2004. (larger
Figure 8. Back reef systems, including
turfs of macroalgae function as critical nursery habitat for
many reef-associated fish species. Photo credit. D. A. Arrington,
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,
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.