11th ICRS Abstract book - Nova Southeastern University

Oral Mini-Symposium 10: Ecological Processes on Today's Reef Ecosystems
10-13
Species Specific Habitat Selectivity Of Acropora Larvae In Subtropical Reefs
Go SUZUKI* 1,2 , Takeshi HAYASHIBARA 3 , Yoshihisa SHIRAYAMA 2 , Hironobu
FUKAMI 2
1 Division of Applied Biosciences, Graduate School of Agriculture, Kyoto University,
Wakayama, Japan, 2 Seto Marine Biological Laboratory, Field Science Education and
Research Center, Kyoto University, Wakayama, Japan, 3 Ishigaki Tropical Station, Seikai
National Fisheries Research Institute, Ishigaki, Japan
Acropora is one of the most abundant and diverse genera of scleractinian corals in the
Indo-Pacific reefs. Distribution of Acropora corals often showed a specific pattern of
zonation particularly on reef slopes, with corymbose and table colony shapes dominating
shallow waters (less than 5 m depth), and branch shaped colonies dominating deeper
waters. Environmental factors such as wave action and light intensity have been shown to
impact post-settlement survival of Acropora corals and play a role in the creation of this
pattern. To date the role of larval settlement in establishing Acropora zonation has been
rarely assessed because of the difficulty in species identification of new recruits. Here, to
test the hypothesis that larvae settle selectively on species specific suitable habitat, we
identified recruits with two-step molecular sorting process using mitochondrial and
nuclear markers to successfully distinguish the seven most dominant species in the study
area (Okinawa, Japan). The distribution of the larval settlement of the three dominant
species A. digitifera, A. hyacinthus and A. tenuis was significantly related to distribution
shown by adult colonies, suggesting that Acropora larvae selectively settle on suitable
habitats. This is the first in situ evidence showing selective settlement of coral larvae.
Although yet undocumented, pre-settlement behavior such as species specific swimming
abilities may play a role in determining the pattern of reef corals.
10-14
Influence Of Benthic Communities On The Settlement And Post-Settlement
Survival Of Two Reef Corals in The Florida Keys
Maggy NUGUES* 1,2 , Alina SZMANT 3
1 Dept. of Marine Ecology and Evolution, Royal Netherlands Institute for Sea Research,
Den Burg, Netherlands, 2 Center for Marine Science, University of North Carolina
Wilmington, Wilmington, 3 Center for Marine Science, University of North Carolina
Wilmington, Wilmington, NC
Coral reef recovery depends on the ability of reef corals to recruit successfully to
replenish depleted populations. Given the structural and ecological importance of reefbuilding
corals, it is important to understand the factors that determine their ability to
achieve successful sexual recruitment. To investigate the role of benthic communities on
coral recruitment, we experimentally settled larvae of Montastraea cavernosa and M.
annularis onto settlement plates pre-conditioned at three sites in the Florida Keys. The
coral spat were mapped and the composition of the encrusting community characterized
on each plate. The plates were then returned to their initial position in the field and
retrieved at different time intervals for further monitoring of coral spat and community
structure. Results showed that the side of the plates had a much larger effect than location
on coral settlement. Although the plates were placed vertically during experimental
settlement, the undersides had approximately 1 order of magnitude higher numbers of
settlers. 87% of the spat settled directly on microfilm (single cell algae) and only 9%
settled on crustose coralline algae, a well known cue for coral settlement. Post-settlement
survivorship was 2% after 9 months, with 71% of the spat dying the first 30 days.
Survivorship was not associated with the benthic community present on the plates during
the first month. However, there was a negative association between survivorship and the
cover of overgrowing invertebrates during the second and third months. Thus, biological
interactions appear as major factors influencing coral settlement and post-settlement, but
other factors must be sought to explain the high mortality of coral spat during the first
month of settlement.
10-15
Do Coralline Algae Influence Coral Recruitment On A Reef?
Nichole PRICE* 1
1 University of California, Santa Barbara, Santa Barbara, CA
Settlement preferences of sessile invertebrates may be adaptations to local community
interactions, particularly if selection of appropriate microhabitat influences early postsettlement
survivorship. Laboratory studies indicate that many reef-building corals can be
induced to settle by chemical cues in the cell walls of crustose coralline algae (CCA).
However, it is unclear if the availability and location of cue-containing CCA on the reef can
influence local recruitment patterns of scleractinian corals. This study examines biotic factors
influencing the abundance and distribution of CCA and subsequent consequences for coral
recruits using the settlement cue. Results of a field coral recruitment experiment indicated that
Pocilloporid and Acroporid corals exhibit a hierarchical selection for substrate among five
common CCA species. Electivity indices calculated for corals settling to coralline algae species
with thin crusts (eg., Titanoderma prototypum) were significantly greater than for species with
thicker thalli (eg., Porolithon onkodes and Lithophyllum insipidum). Pair-wise field
competition experiments revealed that thick-crusted coralline species were superior space
competitors when exposed to transient herbivores, but competitive dominance switched
otherwise. CCA producing thin thalli were most susceptible to grazing and were scarred more
deeply when exposed to herbivores. Therefore, Pocilliporid corals select to settle upon CCA
species exhibiting particular morphological characteristics that may influence the survival and
growth of settlers. Coral settlers may even be facilitated by T. prototypum as recruits found on
this CCA were less likely to be overgrown by other CCA or macroalgae and survivorship was
enhanced at least two-fold. T. prototypum can also influence coral recruitment indirectly by
indicating microhabitat that is protected from incidental mortality by large herbivores. Thus,
CCA that cannot withstand biotic disturbances and are competitive dominants in crevices may
indicate or even provide spatial refuges that are most suitable for recruitment of reef-building
corals.
10-16
Fishing-Induced Changes in Fish And Sea Urchin Abundance Cause Reductions in
Crustose Coralline Algae Cover And The Availability Of Coral Settlement Substrate
Jennifer O'LEARY* 1 , Tim MCCLANAHAN 2
1 Ecology and Evolutionary Biology, University of California, Santa Cruz, Santa Cruz, CA,
2 Wildlife Conservation Society, Mombasa, Kenya
Fishing can have cascading effects on trophic structure that influence ecosystem processes such
as primary production, calcification and reef stability. Crustose coralline algae (CCA) are a
calcifying component of reef ecosystems that comprise the primary settlement substrate for
corals. Using a 20-year dataset from coastal Kenya we demonstrate that a fishing-induced
change in the dominant grazers can dramatically impact CCA cover. CCA is highest in longterm
protected areas (reaching a percent cover similar to that of corals), intermediate in shortterm
protected areas, and lowest in fished areas. CCA cover is strongly positively correlated
with fish biomass and negatively correlated with sea urchin biomass. We use a short-term
experiment to investigate the direct impacts of fish and sea urchin grazing on CCA growth
rates. While both fish and sea urchins affect CCA growth, the effects are in opposite directions:
fish increase CCA cover, but sea urchins reduce CCA growth rates almost to zero. We
conclude that on the Kenyan coast, fish have a strong indirect positive effect on CCA (through
sea urchin predation) leading to high cover in marine protected areas, while sea urchins have a
strong direct negative impact on CCA, greatly reducing CCA cover in fished areas. Fishing can
thus lower the amount of settlement substrate available to corals, reducing the ability of reef
systems to recover from disturbance. Our results are in contrast with those of previous studies
on CCA from temperate systems that show a direct positive association between sea urchin
grazing and CCA, and with studies in the Caribbean that show a direct positive association
between fish grazing and CCA. Our study demonstrates an ecosystem effect of fishing on an
understudied but ecologically critical reef component (CCA), while challenging existing
paradigms regarding the relationship between grazers and CCA.
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