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- Creator:
- Bramanti, Lorenzo, Lenz, Elizabeth Ann, Lasker, Howard R., and Edmunds, Peter J.
- Description:
- The decline in abundance of scleractinian corals over the past three decades in the Caribbean has raised the possibility that other important benthic taxa, such as octocorals, are also changing in abundance. We used photoquadrats taken over 20 yr from reefs (7-9 m depth) at six sites on the south coast of St. John, US Virgin Islands, to test the hypothesis that octocorals have changed in abundance since 1992. Octocorals were counted in 0.25 m2 photoquadrats at 2- to 3-yr intervals and identified to genus or family. Overall, there was variation over time in population density of octocorals (pooled among taxa, and also separately for Antillogorgia spp., Gorgonia spp., and plexaurids) at each site, and densities remained unchanged or increased over 20 yr; where increases in density occurred, the effects were accentuated after 2002. The local-scale analysis was expanded to the Caribbean (including the Florida Keys) by compiling data for octocoral densities from 31 studies for reefs at ?25 m depth between 1968 and 2013. At this scale, analyses were limited by the paucity of historical data, and despite a weak trend of higher octocoral densities in recent decades, statistically, there was no change in octocoral abundance over time. Together with data from the whole Caribbean, the present analysis suggests that octocorals have not experienced a decadal-scale decline in population density, which has occurred for many scleractinian corals.
- Resource Type:
- Article
- Identifier:
- 0722-4028
- Campus Tesim:
- Northridge
- Creator:
- Lenz, Elizabeth Ann
- Description:
- Tropical reef structure and topographical complexity is a product of coral morphology, which greatly enhances biodiversity, ecological function, and ecosystem services. However, reef-building corals have declined in cover by 50-80% in response to the accumulated effects of natural and anthropogenic disturbances over the last 3 to 4 decades. This thesis is comprised of two different studies that address potential changes in shallow reef communities and benthic structure in response to natural and anthropogenic disturbances. The first objective was to examine changes in Caribbean benthic communities as scleractinians have declined and the second objective was to determine differential responses of contrasting morphotypes of corals to acidified conditions in Moorea, French Polynesia. In Chapter 2, I assessed the abundance of arborescent gorgonians (AGs) at local and regional scales to test the hypothesis that AGs have increased in abundance on Caribbean reefs over multiple decades. In St. John, mean abundance of AGs increased 42% from 1992-2012, with each of the dominant genera (Gorgonia, Antillogorgia, and pooled genera: Sea Rods) increasing 11-221% over the same period. Regionally, the compiled data show that AGs have increased in abundance, with mean densities rising from 7.0 to 15.1 colonies m-2 over the last 45 years. This study highlights the apparent success and importance of AGs on contemporary Caribbean reefs, where scleractinian percent cover has remained at ~10%. In Chapter 3, I evaluated the calcification rates of branches and plates of Porites rus in response to ocean acidification (OA) (~800 µatm and 1000 µatm PCO2) with temperature, light and water flow. Skeletal morphology of reef-building hermatypic corals is influenced by abiotic factors, but calcification of coral skeleton is expected to decline as ocean acidification (OA) increases. Theory predicts that hermatypic corals with contrasting morphologies will differ in calcification rates due to differences in: 1) light absorption by Symbiodinium spp. for photosynthesis to enhance coral calcification, and 2) differential mass transfer characteristics (e.g., modulating the flux of dissolved inorganic carbon and hydrogen), which may mitigate the negative effects on calcification in high PCO2. In the second study, I determined that branches and plates were both tolerant of elevated temperature and PCO2. However, branches had higher variability in calcification rates than plates in response to light, and flow. Together these results of this research demonstrate two successful taxa (gorgonians and a weedy scleractinian) in tropical reef communities that have relatively high tolerances against natural and anthropogenic disturbances. Although, gorgonians and P. rus may be alternatives to formerly dominant, slow growing, and diverse communities of hermatypic corals, the functional roles and the ecosystem services they provide will likely differ.
- Resource Type:
- Thesis
- Campus Tesim:
- Northridge
- Department:
- Biology
- Creator:
- Edmunds, Peter J. and Lenz, Elizabeth Ann
- Description:
- This study tested the hypothesis that intraspecific morphological plasticity within a scleractinian coral elicits differential responses to elevated PCO2 and temperature. In Mo'orea, French Polynesia, two short-term laboratory experiments (21 and 14 days) were conducted to test the effects of PCO2 (400 vs. 700 μatm), and PCO2 (400 vs 1000 μatm) combined with temperature (27.0 vs. 29.8 °C), on branches and plates of Porites rus. Experiments employed two irradiances (~ 1000 vs 200 μmol photons m− 2 s− 1), which characterized the microenvironments on the shallow fringing reefs where branching and plating morphologies are common, respectively. Calcification of both morphologies was insensitive to PCO2, as well as the combined effects of elevated PCO2 and temperature. Mean calcification rates were faster in high light than in low light for both morphologies, and biomass was greater in plates than branches in all treatments. Together, our results suggest P. rus is robust to increased PCO2 and high temperature within the constraints of the treatments applied. Morphological plasticity in this species does not mediate physiological resistance to low pH and high temperature.
- Resource Type:
- Article
- Identifier:
- 0022-0981
- Campus Tesim:
- Northridge