[填空题]
In recent years, climate chbd4s*n f 5*xo1i htu-sange has causzma8,fze:p 9uyq2kt* ed serious threats to the survival of coral reefs. Th9etzu*paq2 8,ymk f :ze surface waters of the oceans have been monitored for both temperature and salinity values over time. As global mean surface temperatures rose, sea surface salinity patterns have also intensified, with saline areas experiencing increases in salinity and fresher areas experiencing decreases in salinity.
The following table shows the changes in Sea Surface Temperature (SST), Surface Air Temperature (SAT) and Sea Surface Salinity (SSS) from the 1870s to the 1950s and from the 1950s to the present.
1.1.State the period of time when sea surface temperature and salinity changes were the greatest.
The graph shows the Sea Surface Salinity (SSS) changes as compared to Sea Surface Temperature (SST) changes. The wavy line shows the changes in SST, and the dotted line shows the changes in SSS. The average temperatures and sea surface salinity values were set to zero in the period 1950 to 1959.The period from to
1.2.Describe the trends seen in the graph for changes in SST and SSS over the time period shown.
The changes in temperatures and salinity caused by climate change have been shown to affect the growth and survival of corals in ocean waters. There have been attempts to grow corals in aquaculture to help understand the threats to corals.
Researchers carried out studies to look at the effects of temperature and salinity on the coral Goniopora columna. Results obtained from these studies might be used to grow and maintain corals on farms.
The corals were reared in seawater and kept in different beakers, in which the temperatures and salinity were varied. At the end of 8 weeks, the specific growth rate (SGR%) was calculated as shown in the equation below. The graph below shows the effect of varying temperature and salinity on the SGR (%).
2.1.State the most suitable temperature for the growth of G.columna.
The most suitable temperature for growth is $^{circ}C$.
2.2.State the most suitable salinity value for the growth of G. columna.
The most suitable salinity for growth is psu.
After the experiment, the researchers used a dissecting microscope to examine the tissue residues in the coral skeletons. If no coral tissue was found, the G. columna was assumed to be dead. The survival rate of the coral was calculated using the following formula:
3.1.State the range of salinity that G.columna can survive.
The range of salinity that G. columna can survive is to psu
3.2.Deduce the conditions of temperature and salinity that showed a 100% survival rate.
Temperature and salinity changes can increase reactive oxygen in corals, leading to oxidative damage to the coral–zooxanthellae algae symbiotic system. Zooxanthellae algae are expelled during stress caused by climate change which leads to the bleaching of the corals which has been widely observed.
4.Suggest a possible benefit to corals of having photosynthetic symbiotic algae.1
Researchers carried out further experiments to check if adding nutrients to corals being grown in a recirculating filtered seawater system fish tank could counter the effects of bleaching.
Nutrients were added at varying salinity levels between 25 and 40 psu at temperatures of 20, 25 and 30°C for an appropriate period of time. The feed diet contained a mixture of intact and hydrolyzed marine and terrestrial ingredients.
Growth was monitored by measuring the increase in the number of polyps per week for eight weeks. The average increase in polyp number is shown for group Y, which was fed, and group N, which was not fed.
5.1.Calculate the percent increase in growth when nutrients were added to group Y as compared to group N, at 25 °C and 30 psu.
Percentage increase in growth %
5.2.Comment on the effect of adding nutrients on polyp number at different values of temperature and salinity.
When a coral egg is fertilised by a sperm cell, an embryo is eventually produced which develops into a coral larva called a planula. The planulae float in the ocean for days before dropping to the floor to settle. The planulae prefer to settle on hard coralline algae. Larval settlement is a period in early coral development when they disperse and eventually settle on a substrate.
The researchers studied the developmental phase of coral growth in Briareum violacea species to see if feeding nutrients could encourage larval settlement. After spawning, coral eggs were put into glass tanks and allowed to develop. The ‘larval settlement’ was checked by counting the larvae that were attached to the aquarium tank walls.
The graph below shows the results obtained. Both salinity levels and temperatures have been varied throughout the experiment. Group Y refers to the corals with added nutrients in a recirculating filtered seawater system, and N refers to the corals with no added nutrients.
6.Analyse the effects of adding nutrients on larval settlement and the trend seen with the varying temperatures.
7.Suggest, based on all the data presented, how this research can be used for the growth and maintenance of corals.
