11th ICRS Abstract book - Nova Southeastern University

10-41
Substrate Effects On Reef Fish Distribution
Karen NEELY* 1
1 Ecology, Duke University, Beaufort, NC
Oral Mini-Symposium 10: Ecological Processes on Today's Reef Ecosystems
Western Atlantic coral reefs host up to 750 species of fish. It has been hypothesized that
substrate characteristics control the abundance and distribution of these fish, but this has
traditionally been examined at a community level. I conducted a correlational study in
Curacao, Netherlands Antilles, that addressed fish abundances at the level of species and
age class. I also experimentally tested habitat preferences in two ways. Choice
experiments on adults of common species determined the influence of live coral and
rugosity in an isolated environment, while habitat preferences of adults and juveniles in a
multi-species environment were tested using in situ artificial reefs that differed in live
coral cover. As a whole, these studies showed rugosity to greatly affect total abundance
and diversity, while live coral cover had a slight effect on these community parameters.
However, this small effect of live coral masks large differences at the species and age
class level. For coral cover and other measures of substrate, both positive and negative
selections were seen among species, but these preferences did not follow a readily
identifiable taxonomic or niche classification. Algae-feeding species within the genus
Stegastes, for example, showed both positive and negative preferences for live coral.
Ontogenetic changes in habitat preferences were also documented. These results suggest
that changes in live coral cover on a reef would affect fish communities in ways not
observable using the standard community measures of fish distribution.
10-42
Competitive Displacement Vs. Habitat Structure: The Selection Agents That Shape
Microhabitat Recognition Of A Damselfish Over Time
Mati HALPERIN* 1 , Yehuda BENAYAHU 1
1 Department of Zoology, The George S. Wise Faculty of Life Sciences, Tel Aviv
University, Tel Aviv, Israel
The three-spot dascyllus, Dascyllus trimaculatus Rüppell, has generally been described
as recruiting to sea-anemones. However, in a preliminary survey in Eilat, northern Red
Sea, we recorded D. trimaculatus individuals mainly in branching coral colonies.
Intrigued by the lack of D. trimaculatus juveniles in their typical microhabitat, we studied
the fish abundance and distribution there through a survey of types of microhabitat and
their structural features, in addition to a fish census, aimed at developing and
experimentally testing a hypothesis regarding microhabitat preferences. We addressed the
question of whether the distribution of D. trimaculatus is regulated by the presence of
competitor fish species through mechanisms of displacement, or whether it is
microhabitat-dependent, taking into account specific microhabitat recognition by
damselfish at their various life stages. A distinct pattern of distribution of corals and
damselfish was revealed, in which the marine lab site constituted the major habitat for D.
marginatus while the jetty site hosted D. trimaculatus. We also found that it is the
abundance of Pocillopora coral microhabitats that determines the population distribution
of D. trimaculatus in Eilat. Consequently, it is suggested that the abundance and
distribution of both Dascyllus species may follow the general pattern of the competition
model, emphasizing their apparent need for specific microhabitats. In addition to the
competitive displacement, which excludes D. trimaculatus individuals from their
congeners’ microhabitat (i.e. Stylophora colonies), and determines the population
distribution at the microhabitat level, we also suggest that the specific recognition of a
microhabitat by juvenile D. trimaculatus may play a major role in determining the
distribution of its population at the macrohabitat level. The demographics of Dascyllus
fish in Eilat may reflect a unique situation in which the selection forces of microhabitat
recognition by D. trimaculatus have undergone alteration over time.
10-43
Fish Grazers As Gatekeepers Of The Species Composition Of Coral Reefs
Paul YOSHIOKA* 1
1 Marine Sciences, University of Puerto Rico, Mayaguez, Lajas, Puerto Rico
In this report I propose that intermediate-sized (about 15 cm long) fish mesograzers play a
critical role in determining the species composition of sessile coral reef communities. Fish
mesograzers include parrotfishes (Scaridae), wrasses (Labridae) and surgeonfish (Acanthuridae)
that feed on small prey. I describe these fish as gatekeepers in the sense that they control the
entry of small (newly recruited) prey individuals into coral reefs. In contrast, keystone grazers
control the ‘post entry’ abundances of larger sized prey. The gatekeeper scenario is based on
several well-recognized features of coral reef ecology: (1) Fish grazing has major impacts on
overall abundances of benthic organisms; (2) Artificial substrates in tropical open coast habitats
are often colonized by fouling communities characterized by species such as the octocoral
Carijoa (Telesto) riisei, the sponge Tedania ignis, the tunicate Ascidea nigra and the anemone
Aiptasia tagetes; and (3) Many prey species in coral reefs enjoy a refuge in size from grazers
due to structural/chemical defenses. Differences between keystone and gatekeeper effects
probably arise from features (2) and (3) because many fouling (and typical coral reef) species
are vulnerable to gatekeepers when small and inconspicuous, but enjoy a refuge in size from
keystone species when large. Due to these size-specific effects, assemblages of prey species
controlled by gatekeepers and keystone predators will differ to some degree. Escape from
gatekeeper grazing will also have indirect effects on community structure because of
interactions (e.g., competition) among prey populations. From a more general perspective, both
the gatekeeper and keystone concepts emphasize species-specific effects on prey populations.
In addition, the gatekeeper scenario posits that the size of prey individuals also plays a key role
in the ecological structure of coral reef communities.
10-44
Coral Morphology Modulates The Benefits Of Resident Fishes To Coral Growth?
Andrew BROOKS* 1 , Sally HOLBROOK 2 , Russell SCHMITT 2 , Hannah STEWART 3
1 Marine Science Instititute, University of California, Santa Barbara, Santa Barbara, CA,
2 Department of Ecology, Evolution and Marine Biology, University of California, Santa
Barbara, Santa Barbara, CA, 3 Friday Harbor Labs, University of Washington, Friday Harbor,
WA
Hermatypic corals are functional mixotrophs that rely on water flow for the delivery of
dissolved nutrients and prey. As the external morphology of individual colonies affects the rate
of water flow through the colony, coral morphology may exert a strong influence on the flux of
materials within the interior spaces of the colony itself. We explored the relationships between
local water flow, abundance of resident fishes, external coral morphology and coral growth
rates for a common species of branching coral, Pocillopora eydouxi, in lagoons of Moorea,
French Polynesia. Colonies of P. eydouxi provide structural habitat and refuge space for a
variety of reef fishes. In turn, these fishes may augment nutrient supply to their host coral while
sheltering through the natural excretion of ammonia. To measure coral growth rates, we
outplanted small coral nubbins into colonies of P. eydouxi. Mesh cages were used to exclude
resident fishes from half of these colonies. Flow rates within host corals were measured using
fluorescent dye and external morphology was quantified using digital photographs. Our
experiments revealed that colonies of P. eydouxi containing resident fishes grew substantially
faster than neighbors that did not. Coral growth rates were significantly correlated with within
colony concentrations of ammonia. Our estimates of water flow within coral colonies indicated
that this flow varied considerably among experimental colonies experiencing the same general
flow regime, suggesting that coral morphology may modulate the effects of resident fishes on
coral growth rates by influencing the overall flux of nutrients within a coral colony.
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