جستجوی مقالات مرتبط با کلیدواژه « مرجان » در نشریات گروه « زیست شناسی »

 Coral reefs are one of the world's most attractive ecosystems. They have been covering large parts of the world in the tropic areas. Coral reefs in the Iranian waters of the Persian Gulf are largely limited to the Islands. Many factors, including natural and anthropogenic activities cause stress to the reef communities affecting reef development. Coral bleaching events due to raised temperatures are increasing in both frequency and magnitude worldwide. Coral bleaching is considered a major threat to coral reefs worldwide, especially because large-scale bleaching events have been linked to global warming. The most intense global coral bleaching events reported have occurred worldwide in the last three decades. The Persian Gulf is considered the warmest coral sea in the world. Temperature conditions associated with coral bleaching in the Persian Gulf are higher than in any other area in the world. Therefore, the coral reefs in the Persian Gulf are also at assailable to temperature anomalies and their long-term effects. Sea surface temperature is one of the most important physical factors that affects the life of coral reef communities. Coral bleaching occurs in the Persian Gulf in the recent years due to the global warming and increased sea surface temperature (SST) resulting in high mortality in the coral. Thus, in this research the effects of coral bleaching and its threats in Kish Island have studied. The study area includes coral reefs in the around Kish Island in the Persian Gulf and the effects of stresses.

In this research, sea surface temperature (SST) daily values from 1985 to 2017 (in 1°×1° spatial resolution) prepared by the National Oceanic and Atmospheric Administration (NOAA). The degree heating week index (DHW) was examined to check the cumulative effect of heat stress, which indicate the severity of the whitening threshold based on a long-term period for each site. For trend analysis of sea surface temperature (SST) changes in studying regional, the Mann-Kendall non-parametric test has been used.

The results indicated that the maximum of sea surface temperature is 35.17 ˚C (August, 11th, 2017). Analysis of sea surface temperature trend indicates that SST has increased trend. The DHW threshold for the study region is 5.3 which is warning for whitening of coral communities on Kish Island. The results illustrate the ability of the DHW index to predict bleaching events in the coral reef communities of Kish Island, and can be an effective tool in managing this ecosystem.

The thermal analysis showed that there is an overlap between the recorded bleaching events in different years and the years of the El Niño occurrence. Therefore, these results help in years when there are no reports of bleaching or the data isn’t recorded properly, using overlap, the reconstructed this lack of information.

Since the Persian Gulf is a semi-closed water ecosystem, climate change has more severe impacts on organisms, especially on non-motile ones. The harmful effects on organisms can be studied at all biological levels of morphology, anatomy, physiology, to cellular and molecular levels. The collapse of the symbiotic relationship between coral and its symbiont algae can result in bleaching and it is the first effect of changing favorable conditions on hard coral. The cells produce Heat Shock Proteins (hereinafter referred to as HSP) in response to heat stress. The rate and way of HSP production in corals depend on the expression of the genes encoding these proteins. In this study, we investigated the expression of heat shock gene HSP70 in response to elevated temperature in Acropora downingi (Wallace, 1999) coral reef. After sampling hard corals in March 2018 and adapting them to laboratory conditions, their ambient water temperature increased to 9 °C (from 25 °C to 34 °C). The samples were adapted to laboratory conditions for 2 weeks after being transferred to the laboratory. The water temperature was 25 °C under control conditions, which was increased to 34 °C to create thermal stress. The expression of the gene Hsp70 was evaluated at control time and also 24 h and 48 h after temperature rise. The study showed that gene expression was significantly increased 24 h after stress and it decreased at 48. However, the corals were bleached, which could be due to the deterioration and reduced resistance to heat shock.

This study was conducted to identify and study the communities structure of adhesive organisms or the fouling of 13 years old artificial reefs on the coast of Bahrakan along the west of the Persian Gulf. fouling sample was collected seasonally from spring 2016 to winter 2016 from 4 sampling sites using quadrates 25 × 25 cm by diving operation. Based on the biomass (wet weight), Anthozoa corals with 88% of the total biomass, contain the most adhesive mass, followed by sponges (10%) and hydrozoa corals and Arthropod with 1% of the total biomass. The spring season showed the highest average rate, which was due to the biomass of the Antozoa group with 89% in this season. Based on the cluster test, the two winter and autumn seasons have a similar percentage of 80% and the summer and spring seasons show a similar percentage of 50%. Also, based on cluster analysis of two structures A, D, the similarity level of 45% and B, C indicate the similarity level of 80%

The effects of using the biorock method on the growth and survival of coral (Pocillopora damicornis( in the Chabahar Bay were evaluated. Coral pieces were placed on steel structures under a 6V electric field in the biorock process. The coral growth, growth performance and survival rates of corals during the twenty-eight weeks were studied. The mean coral growth in the biorock structure was 10.66 ± 0.3cm and the mean coral growth was 5.27 ± 0.2 cm in the non biorock structure. The results show a significant difference between coral growth in the biorock with non biorock structures (p <0.05). The results of this survey on the growth rate of Coral (P.damicornis( in the biorock structure compared to the control structures showed a two-fold increase in growth and a higher survival rate. The results of this study indicated that stimulation of coral growth by biorock method as well as the rapid responses of this species to the electrical field during the biorock process which could be used to stimulate coral growth survival for the protection and rehabitation program.