11th ICRS Abstract book - Nova Southeastern University

20-1
The Comparative Demographic Of Two Scleractinian Corals On A Shallow
Caribbean Reef
Peter EDMUNDS* 1
1 California State University, Northridge, Northridge, CA
Oral Mini-Symposium 20: Modeling Concepts and Processes on Coral Reefs
In light of the consequences of anthropogenic disturbances for coral reefs, considerable
effort has been expended to understand the mechanisms by which such phenomena result
in coral death, and how affected populations change over time. There has been less
attention however, to the question of which corals might endure the adverse conditions,
and to what extent might their populations increase in size? This study focused on two
Caribbean corals that have survived better than most on shallow reefs (1 showing that the populations were growing independent of the input
from recruitment. Over the next 25 years, population projections suggest that both
species will increase in abundance, regardless of the effects of catastrophic disturbances
or periodic recruitment failure. Both P. astreoides and D. strigosa appear to have
characteristics favoring high adult survival and successful fission under contemporary
environmental conditions, both of which contribute to population growth in an era when
most corals are declining in abundance.
20-2
Simulating the Growth and Spread of Key Macroalgae in Florida Reefs
Aletta YÑIGUEZ* 1 , John MCMANUS 2
1 National Center for Coral Reef Research (NCORE)/ Marine Biology & Fisheries (MBF),
RSMAS, University of Miami, Muntinlupa City, Philippines, 2 National Center for Coral
Reef Research (NCORE)/ Marine Biology & Fisheries (MBF), RSMAS, University of
Miami, Key Biscayne, FL
The growth patterns of macroalgae can provide important information regarding the
environments in which they live, and insights into changes that may occur when those
environments shift. To decipher these patterns and their attendant mechanisms and
influencing factors, a spatially-explicit model was developed. Using the threedimensional
agent-based model SPREAD (SPatially-explicit REef Algae Dynamics),
which incorporates key morphogenetic characteristics of clonality and morphological
plasticity, the influences of light, temperature, nutrients and disturbance on how the
dominant macroalgae in the Florida Reef Tract grow and occupy space were investigated.
At the individual level, SPREAD yielded several morphological types for Halimeda tuna,
Halimeda opuntia, and Dictyota sp. under a large range of light, temperature, nutrient and
disturbance levels. These morphological types approximated those measured for
individuals in two inshore patch reefs and two offshore spur and groove reefs, and were
formed in conditions similar to the environmental (light, nutrient and disturbance)
conditions in the field sites. At the macroalgal population level, increasing disturbance in
SPREAD such that the fragment pool was increased, but not enough so that fragments
could not survive, led to the highest potential for space capture. Enabling fragmentation
also allowed for comparable abundances in the three species between the model and the
actual study sites, and, for Halimeda spp., captured the observed disparity in abundances
between the sites. The variation in growth and disturbance conditions, as well as each
species’ capacity for success with fragmentation, seemed to play a strong role in the
distinct differences in macroalgal abundances between inshore patch and offshore reef
study sites. These mosaics of scenario-running and empirical studies have enabled us to
tease out potential mechanisms and factors responsible for the growth patterns observed
in reality at different levels.
20-3
Recovery Dynamics Of diadema Antillarum And The Potential For Active Rebuilding
Measures
Alice ROGERS* 1 , Kai LORENZEN 1
1 Biology, Imperial College London, London, United Kingdom
In recent decades, Caribbean coral reefs have suffered a shift in community structure from a
healthy coral-dominated state to a less resilient and less productive macroalgae-dominated state.
This shift is believed to be related in part to the functional extinction of the previously dominant
grazer of macroalgae, the sea urchin Diadema antillarum following a mass mortality event in
1983.
Diadema antillarum has failed to recover to pre-mortality densities in many locations. In light
of recent studies suggesting that large scale recovery of Diadema antillarum could reverse
community change and improve the health of Caribbean coral reefs, interest has arisen around
the potential for active rebuilding measures such as hatchery enhancement to aid and increase
population recovery.
We developed a size- and spatially structured, combined population dynamics and grazing
impact model for D. antillarum. The model accounts for compensatory density-dependence in
recruitment and individual growth, and depensatory density effects mediated by fertilization
success, the possible refuge function of adults for juveniles, and ‘cultivation’ of settlement
habitat by grazing. Results show that the population can exist in two distinct states, i.e. a lowabundance
equilibrium associated with high macroalgal cover, and a high-abundance
equilibrium associated with low macroalgal cover.
In order to ‘kick start’ recovery and switch from the low to the high abundance state the
population needs to overcome multiple depensatory processes. This may require both, prior
reduction in algal cover by other herbivores or human intervention, and a high recruitment event
based on dispersal from recovered populations or the stocking of hatchery-reared D. antillarum.
Hatchery releases could contribute effectively to recovery, but this would require stocking
densities that are high relative to the natural population and may result in substantial ecological
and genetic interactions with the natural population.
20-4
Spatial Dynamics Of Herbivory And Coral Growth: Implications For Reef Conservation
And Recovery
Dylan MCNAMARA 1 , Stuart SANDIN* 2
1 Duke University, Atlantic Beach, NC, 2 Scripps Institution of Oceanography, La Jolla, CA
Competition for space is a critical dynamic affecting patterns and rates of growth of sedentary
organisms both on land and in the sea. Understanding the aggregate impact of spatial dynamics
on competitive hierarchies along shared margins is important for gaining insight into large-scale
systematic shifts, such as catastrophic phase shifts within coral reefs. Predictive insights are
fundamental for both understanding conditions leading to coral loss and, perhaps more
importantly, for designing strategies for restoring coral populations.
To explore this question, we have constructed a cellular automata model for coral reefs to
mimic the dominant dynamics of coral reefs. State transitions are governed by probabilitydriven
rules based on dynamics of growth, death, succession and recruitment. Explicit spatial
dynamics are depicted both through size-dependent patterns of growth in corals and
autocorrelated patterns of foraging for some herbivores. These assumptions are based on two
main field observations: (i) small corals are more susceptible to overgrowth by macroalgae than
larger colonies, and (ii) patterns of herbivory are distinct between fishes and urchins, especially
in reference to the level of spatial autocorrelation of foraging. We find that algal dominated
reefs are particularly stable because coral recruitment is severely reduced in the presence of
macroalgae. Although clonal growth allows adult corals to increase in size even in the presence
of high macroalgal cover, only in the presence of significant herbivory is coral recruitment
facilitated. Additionally, because urchins open larger contiguous sections of benthos from algal
coverage than do fishes, coral recruitment will be particularly facilitated in the presence of
herbivorous urchins. The wide-spread mortality of both fast-growing corals (e.g., acroporids)
and herbivorous urchins in the Caribbean, the dynamic attractor of macroalgal domination is
particularly stable. These model predictions mimic closely a growing number of empirical
observations from across the Caribbean.
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