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Terrestrial-based nutrient pollution has emerged as one of the most detrimental factors to coral health in many reef habitats. Recent studies have shown that excessive dissolved inorganic nutrients can reduce coral thermal tolerance thresholds and even exacerbate bleaching during thermal stress, yet the effects of minor nutrient enrichment under heat stress have not been extensively studied. In this study, Lobactis scutaria, Montipora capitata, and Pocillopora acuta colonies under heated conditions (~30.5 °C) were exposed to low and balanced nitrogen and phosphorous concentrations over a 31-day heating period. Coral colonies were collected from Kāne'ohe Bay, O'ahu, which has a unique history of nutrient pollution, and held in mesocosms that allowed for environmental manipulation yet are also influenced by local field conditions. Principal findings included delays in the bleaching of nutrient-enriched heated colonies as compared to heated-only colonies, in addition to relatively greater calcification rates and lower proportions of early-stage paling. Species-specific outcomes were prevalent, with L. scutaria demonstrating no difference in calcification with enrichment under heat stress. By the end of the heating stage, however, many heated colonies were at least partially impacted by bleaching or mortality. Despite this, our findings suggest that low levels of balanced nutrient enrichment may serve as a mitigative force during thermal events. Further field-based studies will be required to assess these results in different reef habitats. [ABSTRACT FROM AUTHOR]

Successful reproduction and survival are crucial to the continuation and resilience of corals globally. As reef waters warm due to climate change, episodic largescale tropical storms are becoming more frequent, drastically altering the near shore water quality for short periods of time. Therefore, it is critical that we understand the effects warming waters, fresh water input, and run-off have on sexual reproduction of coral. To better understand the effects of these near shore stressors on Hawaiian coral, laboratory experiments were conducted at the Institute of Marine Biology to determine the independent effects of suspended sediment concentrations (100mgl-1 and 200mgl-1), lowered salinity (28h), and elevated temperature (31 °C) on the successful fertilization, larval survival, and settlement of the scleractinian coral Montipora capitata. In the present study, early developmental stages of coral were exposed to one of three near shore stressors for a period of 24 h and the immediate (fertilization) and latent effects (larval survival and settlement) were observed and measured. Fertilization success and settlement were not affected by any of the treatments; however, larval survival was negatively affected by all of the treatments by 50% or greater (p>0.05). These data show that early life stages of M. capitata may be impacted by near shore stressors associated with warming and more frequent storm events. [ABSTRACT FROM AUTHOR]

Ocean temperatures have been accelerating at an alarming rate mainly due to anthro-pogenic fossil fuel emissions. This has led to an increase in the severity and duration of coral bleaching events. Predicted projections for the state of reefs do not take into account the rates of adaptation or acclimatization of corals as these have not as yet been fully documented. To determine any possible changes in thermal tolerances, manipulative experiments were conducted to precisely replicate the initial, pivotal research defining threshold temperatures of corals nearly five decades ago. Statistically higher calcification rates, survivorship, and lower mortality were observed in Montipora capitata, Pocillopora damicornis, and Lobactis scutaria in the present study at 31 °C compared to the original 1970 findings. First whole colony mortality was also observed to occur sooner in 1970 than in 2017 in M. capitata (3 d vs. 15 d respectively), L. scutaria (3 d vs. 17 d), and in P. damicornis (3 d vs. 13 d). Additionally, bleaching occurred sooner in 1970 compared to the 2017 experiment across species. Irradiance was an important factor during the recovery period for mortality but did not significantly alter calcification. Mortality was decreased by 17% with a 50% reduction in irradiance during the recovery period. These findings provide the first evidence of coral acclimatization or adaptation to increasing ocean temperatures for corals collected from the same location and using close replication of the experiment conducted nearly 50 years earlier. An important factor in this increased resistance to elevated temperature may be related to removal of the discharge of treated sewage into Kane'ohe Bay and resulting decrease in nitrification and eutrophication. However, this level of increased temperature tolerance may not be occurring rapidly enough to escape the projected increased intensity of bleaching events, as evidenced by the recent 2014 and 2015 high coral mortality in Hawai'i (34%) and in the tropics worldwide. [ABSTRACT FROM AUTHOR]