Food preferences of juvenile corallivorous crown-of-thorns (Acanthaster planci) sea stars

Population outbreaks of adult Acanthaster planci cause significant reductions in coral cover and reduce the resilience of coral reefs, but little is known about the behaviour and food preference of juvenile A. planci. In 2014, food preferences and feeding rates of recently settled (<1 year) juvenile A. planci were tested and determined at the National Sea Simulator facilities of the Australian Institute of Marine Science. Juveniles were offered eight species of coral (Acropora formosa, A. millepora, A. tenuis, Pavona cactus, Echinopora lamellosa, Pocillopora damicornis, Stylophora pistillata and Porites lutea), known to be either consumed or avoided by adult sea stars, in a multiple-choice and a no-choice experiment. In the multiple-choice experiment, a preference for A. tenuis was detected, while S. pistillata, E. lamellosa and P. lutea were avoided. The no-choice experiment showed that the avoidance of these species was not influenced by the presence of other coral species, the exception being E. lamellosa, which was only consumed when no other choice was offered. Interestingly, all juveniles consuming E. lamellosa died post-predation. The study suggests that as A. planci matures it feeds on a wider range of species, even those which would have been lethal to them if consumed as a juvenile.

Discerning the timing and cause of historical mortality events in modern Porites from the Great Barrier Reef

The life history strategies of massive Porites corals make them a valuable resource not only as key providers of reef structure, but also as recorders of past environmental change. Yet recent documented evidence of an unprecedented increase in the frequency of mortality in Porites warrants investigation into the history of mortality and associated drivers. To achieve this, both an accurate chronology and an understanding of the life history strategies of Porites are necessary. Sixty-two individual Uranium–Thorium (U–Th) dates from 50 dead massive Porites colonies from the central inshore region of the Great Barrier Reef (GBR) revealed the timing of mortality to have occurred predominantly over two main periods from 1989.2 ± 4.1 to 2001.4 ± 4.1, and from 2006.4 ± 1.8 to 2008.4 ± 2.2 A.D., with a small number of colonies dating earlier. Overall, the peak ages of mortality are significantly correlated with maximum sea-surface temperature anomalies. Despite potential sampling bias, the frequency of mortality increased dramatically post-1980. These observations are similar to the results reported for the Southern South China Sea. High resolution measurements of Sr/Ca and Mg/Ca obtained from a well preserved sample that died in 1994.6 ± 2.3 revealed that the time of death occurred at the peak of sea surface temperatures (SST) during the austral summer. In contrast, Sr/Ca and Mg/Ca analysis in two colonies dated to 2006.9 ± 3.0 and 2008.3 ± 2.0, suggest that both died after the austral winter. An increase in Sr/Ca ratios and the presence of low Mg-calcite cements (as determined by SEM and elemental ratio analysis) in one of the colonies was attributed to stressful conditions that may have persisted for some time prior to mortality. For both colonies, however, the timing of mortality coincides with the 4th and 6th largest flood events reported for the Burdekin River in the past 60 years, implying that factors associated with terrestrial runoff may have been responsible for mortality. Our results show that a combination of U–Th and elemental ratio geochemistry can potentially be used to precisely and accurately determine the timing and season of mortality in modern massive Porites corals. For reefs where long-term monitoring data are absent, the ability to reconstruct historical events in coral communities may prove useful to reef managers by providing some baseline knowledge on disturbance history and associated drivers.

Geochemistry-based coral palaeoclimate studies and the potential of ‘non-traditional’ (non-massive Porites) corals : recent developments and future progression

Understanding the natural variability of the Earth's climate system and accurately identifying potential anthropogenic influences requires long term, geographically distributed records of key climate indicators, such as temperature and precipitation that extend prior to the last 400. years of the Holocene. Reef corals provide an excellent source of high resolution climate records, and importantly represent the tropical marine environment where palaeoclimate data are urgently required. Recent decades have seen significant improvement in our understanding of coral biomineralisation, the associated uptake of geochemical proxies and methods of identifying and understanding the effects of both early and late, post depositional diagenetic alteration. These processes all have significant implications for interpreting geochemical proxies relevant to palaeoclimatic reconstructions. This paper reviews the current 'state of the art' in terms of coral based palaeoclimate reconstructions and highlights a key remaining problem. The majority of coral based palaeoclimate research has been derived from massive colonies of Porites. However, massive Porites are not globally abundant and may not provide material of a particular age of interest in those regions where they are present. Therefore, there is great potential for alternate coral genera to act as complimentary climate archives. While it remains critical to consider five key factors - vital effects, differential growth morphologies, geochemical heterogeneity in the skeletal ultrastructure, transfer equation selection and diagenetic screening of skeletal material - in order to allow the highest level of accuracy in coral palaeoclimate reconstructions, it is also important to develop alternate taxa for palaeoclimate studies in regions where Porites colonies are absent or rare. Currently as many as nine genera other than Porites have proven at least limited utility in palaeothermometry, most of which are found in the Atlantic/Caribbean region where massive Porites do not exist. Even branching taxa such as Acropora have significant potential to preserve environmental archives. Increasing this capability will greatly expand the number of potential geochemical archives available for longer term temporal records of palaeoclimate.

Steroidogenesis in the desensitized rat corpora-lutea

Earlier workers have observed that in the leydig cell desensitization brings results in addition to down regulation of receptors, in leisons in the steroidogenlc pathway. In the present study immature rats having heavily leutinized ovaries were given 50 iu hCG and the desenasitized CL removed 48h later were used. At that time no change in the 5 3MSD activity and CAMP binding activity(a measure of CAMP dependent protein kinase) was observed.Followlng desensitization however,l)a significent increase in phosphodiestrase activity,ii)a 50% reduction in total mitochondrial cholesterol level, iii)a significant reduction in its ability to utilize cholesterol or hydrolyse its ester and iv)a significant lowering(by 66%)in cholesterol side chain clean age activity(by measuring pregnanalone formed) was observed. Pregnanalone production was restored to normalcy if exogenous cholesterol was added to the mitohondrial preparation. The results suggest that luteal desensitization is due in addition to down regulation of LH receptors, to a marked reduction in available cholesterol pool in the mitochondrial compartment. The increase in phosphodiestrase activity, though probably a secondary effect,might effectively contribute to the overall reduction in the steroid out-put by increasing the catabolism of CAMP.(Aided by grants from ICMR,New Delhi and WHO, Geneva).