11th ICRS Abstract book - Nova Southeastern University

12-14
Ocean Dynamics Drive Coral Reef Processes in The Andaman Sea
Claudio RICHTER* 1 , Mélanie BON 1 , Laura FILLINGER 1 , Carin JANTZEN 1 , Cornelia
RODER 1 , Gertraud SCHMIDT 1 , Niphon PHONGSUWAN 2 , Somkiat
KHOKIATTIWONG 2
1 Center for Tropical Marine Ecology, Bremen, Germany, 2 Phuket Marine Biological
Center, Phuket, Thailand
Coral reefs are rich benthic ecosystems thriving in nutrient-poor waters. A striking
feature of the Andaman Sea is the exposure of offshore reefs to large amplitude internal
waves. These solitary-like waves (or solitons) are generated by the ebb and flow of water
across the shallow ridges of the Andaman-Nicobar island arc and propagate along the
density discontinuity (pycnocline) between warm surface and colder deep waters
pycnocline with speeds of ~2 m s -1 and amplitudes of up to 80 m. Here, we show that the
dissipation of the solitons’ energy in shoaling water enhances pelagic-benthic coupling
along the continental margin, due to turbulent mixing near the sea bed, entrainment of
interstitial and subpycnocline nutrients, and formation of bores. These 'solibores' supply
nutrients and plankton to the benthos of the Similan Islands. Lowered temperature, pH
and light hamper, however, coral photosynthesis and calcification, and their resilience
against macroalgal competitors and grazers, resulting in low or negative reef growth. The
frequency and intensity of cold bores (with temperatures drops of up to 10°C within only
minutes) may on the other hand increase the corals’ resilience to thermal stress. The
findings have important repercussions on the Similan reefs which have been impacted by
earlier bleaching and recent Tsunami. Because solitons are ubiquitous in the Andaman
Sea and elsewhere, they may be an important yet so far overlooked mechanism
structuring benthic communities in tropical waters.
12-15
Opposing Effects Of Water Quality On Coral Bleaching Resistance And Recovery
David OBURA* 1 , Haji MACHANO 2 , January NDAGALA 3 , Monica ZAVAGLI 4
1 CORDIO East Africa, Mombasa, Kenya, 2 WWF Tanzania, Dar es Salaam, Tanzania,
3 Mafia Island Marine Park, Mafia Island, Tanzania, 4 Ramsar Secretariat, Gland,
Switzerland
The Mafia-Rufiji-Kilwa system of coral reefs and islands in central Tanzania is
influenced strongly by outflow from the Rufiji river, which forms the largest delta system
in Tanzania. Within this area, the impact of coral bleaching and mortality in 1998 varied
considerably among reefs, with estimated mortality of corals varying from 0 to 100%,
from surveys and observations conducted in the subsequent 9 years from 1999 to 2007. A
new assessment method that includes estimation of a broad scope of factors hypothesized
to influence coral resistance and tolerance to bleaching, and reef recovery following
mortality, was conducted in November-December 2007 on 15 reefs in the region,
sampling coral communities in 10-12 and 3-5 m depth zones. Quantitative and semiquantitative
data were collected on benthic cover, coral community structure, coral
population structure, coral condition, herbivorous fish community structure, and
indicators of physical site properties including connectivity, cooling and flushing,
shading and screening and acclimatization potential. The two major factors that affected
coral community structure related to a) initial resistance to bleaching - reefs with highest
indicators of mainland river influence showed the lowest evidence of mass mortality in
1998, with turbidity likely providing the greatest degree of protection from thermal
stress; and b) recovery following mortality - a combination of factors that included clear
water (least mainland influence), substrate robustness (maximize coral survival) and high
larval supply. These factors act in direct opposition to one another: turbid waters
maximized coral survival during thermal stress, but clear water maximizes coral
recruitment and survival under normal conditions. Thus current status of reefs is a result
of multiple interacting factors; these need to be considered in a holistic way in prioritysetting
for active management to minimize climate impacts to coral reefs.
Oral Mini-Symposium 12: Reef Resilience
12-16
Two-Years Monitoring Of Water Flow Effects On Photosynthesis And Growth Of The
Coral acropora Digitifera
Takashi NAKAMURA* 1,2 , Seitaro S. YAMAZAKI 1 , Yeong Shyan YUEN 1 , Hideo
YAMASAKI 1
1 Faculty of Science, University of the Ryukyus, Okinawa, Japan, 2 Amakusa Mar Biol Lab,
Kyushu University, Kumamoto, Japan
We conducted an outdoor aquarium experiment to clarify long-term influence of water flow on
corals. Water motion has significant impacts on the physiology of corals; limitation in watermotion
causes severe bleaching in the coral Acropora digitifera during a period with strong
light and high water temperature. Although there are numbers of investigations that report the
effects of water flow in short-term (hours to weeks) experiments, long-term effects especially
on the interaction with seasonal change in weather are not fully understood. In this study we
report effects of water flow on the coral A. digitifera in several water-flow conditions
(flow/wave/limited-flow) over two-year period in Okinawa, southern Japan. We monitored
algal photosynthesis in hospite of A. digitifera weekly with a Diving-PAM chlorophyll
fluorometer. Colony growth was measured monthly by the underwater buoyant weight method.
In subtropical southern Japan under the influence of monsoon climate, seasonal change in
weather had strong impacts on the photophysiology of A. digitifera. A. digitifera was evenly
stressed in spring as well as in summer. Notably, high photosynthetic efficiency was often
recorded just after the period of rainy season. Throughout the entire experimental period,
photosynthesis of A. digitifera in limited-flow condition showed lower activity level than that of
in flow conditions. Less colony growth with the disappearance of axial polyps was also
observed under limited-flow condition in contrasted with flow conditions. These adverse effects
of limited-flow could be diminished by the subsequent exposure to flow. The results confirm
that water-flow can keep photosynthesis as well as growth of A. digitifera in good conditions
throughout the years. We suggest that water-flow is an important factor that should be taken
into the consideration of coral reef conservation.
12-17
Wave Effects On Coral Reefs
Malcolm L. HERON 1 , William J. SKIRVING 2 , Scott F. HERON* 3
1 Marine Geophysical Laboratory, James Cook University, Townsville, Australia, 2 NOAA Coral
Reef Watch, Silver Spring, MD, 3 NOAA Coral Reef Watch, Siver Spring, MD
The work aims to evaluate the extent to which wave mixing mitigates the phenomenon of coral
bleaching on isolated reefs. The physical conditions which allow coral bleaching are high
insolation, low currents and low winds. Under these conditions a stable warm layer can form at
the surface of the ocean. In this work we argue that very low swell wave energy should be
added to the list, not because of linear waves passing through, but because of wave breaking at
the reef front. For most reefs which rise abruptly from a nearly flat seabed, linear wave theory
is sufficiently accurate for estimating the amplitude of a swell wave as it propagates from open
water to the encounter with the reef. At the reef front, the wave energy is redistributed into a
reflected component, localized turbulent mixing, and a forward bore across the reef top and
onto the reef flats beyond. Under almost all conditions the mixing at the reef front is sufficient
to destroy any tendency for a stable warm surface layer to form. Therefore, corals on the
exposed sides of a reef are less likely to suffer from bleaching during an event where the surface
temperature is elevated elsewhere in the vicinity; unless the full water column is warmed. The
bore water which overflows the reef front is well mixed and during a bleaching event carries the
cooler mixed water across the reef and onto the flats nearby. The main outcome from this work
is that we predict that corals on the exposed sides of a reef and those on the adjacent reef top
will be protected from bleaching under any but the most severe thermal stress. Further work
should discover whether these corals can act as brood stock for subsequent reef recovery.
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