<<  <  >  >>

 

E  C O S Y S T E M FU N C T I O N I  N D I C AT O R S

HERBIVORY

Conservation Objective

Maintain or restore herbivory levels in the MAR to rates high enough to prevent algal overgrowth. The

overall aim is to have higher populations of herbivores.

Threats

Although most fishing effort generally targets carnivorous fishes, herbivorous fishes are also taken on

an opportunistic basis and can account for a large percentage of the total catch. Any decrease in their

abundance can have significant effects on reef condition. Human activities that degrade water quality

and increase nutrification can create environments more favorable for algae than corals, thus requiring

even more herbivores to control algal populations. Green turtles in the MAR are at risk due to long-term

harvesting of eggs and adults, plus habitat degradation and loss.

Management Actions

· Reduce fishing of herbivores, especially large-bodied parrotfishes, through species protection

or gear restrictions.

· Determine the feasibility and effectiveness of restoring Diadema populations at high-priority

sites.

· Assess the effectiveness of marine reserves and herbivore restoration programs in increasing

herbivorous fish and Diadema populations.

· Reduce activities that introduce nutrients into the marine environment.

· Promote regional monitoring of sea turtles, and promote coordinated management strategies

to reduce human impacts on turtles. Such strategies would include reduction of destructive

development practices on nesting beaches, elimination of illegal take and trade, increased

enforcement of existing regulations, and restoration of nesting and foraging habitats.

Herbivory (the consumption of plant material) is

composition. Their presence in moderate abundances

probably the single most important factor influencing

tends to be associated with low levels of large algae,

interspecific  interactions  on  Caribbean  reefs.

relatively sparse algal turfs and high levels of coralline

Corals and fleshy macroalgae are locked in a fierce

algae -- conditions that foster coral recruitment and

competition for precious reef space, and the presence

higher live coral cover. A 1983 die-off of long-spined

or absence of herbivores to eat the macroalgae can tip

sea urchins throughout the Caribbean coincided with

the scales one way or the other. Reduced herbivory

a dramatic and rapid increase in macroalgal cover on

rates can rapidly result in a significant shift from a

many reefs.

(calcifying) coral-dominated community to a (non-

Grazers like parrotfishes and surgeonfishes are

calcifying) macroalgae-dominated community.

especially effective herbivores because they occur in

Sea urchins and fishes are the two most important

large numbers. However, their feeding can also result

groups of reef herbivores. They control the abundance

in incidental coral loss, as they scrape and chew at

and species composition of both corals and algae

the reef surface.

-- particularly the larger macroalgae that are in direct

Other key species include megaherbivores, such as

competition for space with corals. Thus, a decline in

green sea turtles and manatees, which were once

sea urchins or herbivorous fishes can result in a rapid

responsible for significant grazing on seagrass beds.

increase in macroalgae.

Now, however, their numbers are low, and their

The long-spined sea urchin (Diadema spp.) is perhaps

herbivorous influence has dramatically declined,

the most significant herbivore on Caribbean reefs,

leaving many seagrass meadows looking like

in terms of influence on coral reef structure and

overgrown fields.

70