Spatial Patterns of Parrotfish Corallivory in the Caribbean: The Importance of Coral Taxa, Density and Size

The past few decades have seen an increase in the frequency and intensity of disturbance on coral reefs, resulting in shifts in size and composition of coral populations. These changes have lead to a renewed focus on processes that influence demographic rates in corals, such as corallivory. While previous research indicates selective corallivory among coral taxa, the importance of coral size and the density of coral colonies in influencing corallivory are unknown. We surveyed the size, taxonomy and number of bites by parrotfish per colony of corals and the abundance of three main corallivorous parrotfish (Sparisoma viride, Sparisoma aurofrenatum, Scarus vetula) at multiple spatial scales (reefs within islands: 1–100 km, and between islands: >100 km) within the Bahamas Archipelago. We used a linear mixed model to determine the influence of coral taxa, colony size, colony density, and parrotfish abundance on the intensity of corallivory (bites per m2 of coral tissue). While the effect of colony density was significant in determining the intensity of corallivory, we found no significant influence of colony size or parrotfish abundance (density, biomass or community structure). Parrotfish bites were most frequently observed on the dominant species of reef building corals (Montastraea annularis, Montastraea faveolata and Porites astreoides), yet our results indicate that when the confounding effects of colony density and size were removed, selective corallivory existed only for the less dominant Porites porites. As changes in disturbance regimes result in the decline of dominant frame-work building corals such as Montastraea spp., the projected success of P. porites on Caribbean reefs through high reproductive output, resistance to disease and rapid growth rates may be attenuated through selective corallivory by parrotfish

PERMANOVA results for colony-based E_i (Ivlev's electivity index).

<p>(d.f. = degrees of freedom, SS = sum of squares (type I), MS = mean sum of squares, ECV = percent estimated components of variation).</p

PERMANOVA results for area-based E_i (Ivlev's electivity index).

<p>(d.f. = degrees of freedom, SS = sum of squares (type I), MS = mean sum of squares, ECV = percent estimated components of variation).</p

Pairwise results from PERMANOVA for area-based E_i (Ivlev's electivity index).

<p>(x = not consistent between islands, ns = not significant, * = p<0.05, ** = p<0.01, *** = p<0.001). Taxa marked with ⁰ were present across all sites but not bitten by parrotfish.</p

Percent cover of coral taxa.

<p>(AGAR = <i>Agaricia</i> spp., MFAV = <i>Montastraea faveolata</i>, MANN = <i>Montastraea annularis</i>, MCAV = <i>Montastraea cavernosa</i>, PPOR = <i>Porites porites</i>, PAST = <i>Porites astreoides</i>, SSID = <i>Siderastrea siderea</i>, EUSM = <i>Eusmilia fastigiata</i>, FFAV = <i>Favia fragum</i>, MDEC <i>Madracis decactis</i>, STEP = <i>Stephanocoenia</i> spp., DIPL = <i>Diploastrea labyrinthica</i>, DICH = <i>Dichocoenia</i> spp., MANI = <i>Manicina</i> spp., MYCE = <i>Mycetophyllia</i> spp.).</p

PERMANOVA results for intensity of corallivory (bites per dm²).

<p>(d.f. = degrees of freedom, SS = sum of squares (type I), MS = mean sum of squares, ECV = percent estimated components of variation).</p

Parrotfish dynamics.

<p>Parrotfish density (a) and biomass (b) between islands and reefs (±SE), and Principle Components ordination (PCO) if parrotfish biomass community structure (c). SVI = <i>Sparisoma viride</i>, SVE = <i>Scarus vetula</i>, SA = <i>Sparisoma aurofrenatum</i>, TP = terminal phase, IP = initial phase). Error bars represent ± SE.</p

Map of study locations.

<p>Caribbean region (a), Bahamas (b) and inset (c) of study islands (i. Andros Island, ii. Exuma Cays, iii. San Salvador, iv. Turks & Caicos).</p

Coral community structure and corallivory.

<p>a) Coral cover, b) colony area, and c) colony density across islands and reefs (c). Error bars represent ± SE.</p