'%Healthy Reefs for Healthy People - A Guide to Indicators of Reef Health and Social Well-being in the Mesoamerican Reef Region%'%by Melanie McField and Patricia Kramer%

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Lisa Carnes

Thetermcommunitystructurereferstotheorganization

and increases in macroalgae (to 57%) by 200015.

of a biological community -- in this case, a coral reef

Herbivorous and carnivorous fishes are the other key

-- in terms of what organisms live there and in what

players in influencing a reef's community structure.

quantities or proportions. Many complex factors,

If herbivorous fishes crop down fleshy macroalgae,

physical and biological, control a reef's community

then coral larvae have a better chance of settling and

composition.

surviving on the reef.

Fierce competition for limited "prime real estate" --

Rugosity -- a measure of the physical complexity of

especially between macroalgae and corals -- is one

the reef surface -- is also important. The physical

of the most important determinants of benthic (sea

"roughness" of the reef strongly influences -- and is

bottom) community structure on a reef. An established,

influenced by -- the reef's community composition.

dense cover of macroalgae, sponges or turf algal/

Reefs with higher topographic complexity, for example

sediment mats greatly reduces the availability of the

provide diverse habitat for fish and other reef biota,

clean, hard substrate needed for coral recruitment

and they generally support communities of higher

and recovery. This substrate (space) limitation can

biodiversity.

have lasting effects on community structure and

function, and can even threaten the very existence of

Indicators selected to track community structure

reef frameworks.

include:

Several case studies have documented an overall shift

Coral Cover

from coral to algal domination on many Caribbean

reefs in the last few decades, including some in the

Coral:Algae Ratio

Mesoamerican region. The patch reefs of Glover's

Reef Atoll (Belize), for example, had approximately

Fish Abundance

80% coral and 20% macroalgae in 1971 but had

Rugosity

shifted to about 20% coral and 80% macroalgae by

1996, followed by further declines in coral (to 13%)