I. J. Hodgkiss

Are changes in N:P ratios in coastal waters the key to increased red tide blooms?

There is mounting evidence of a global increase in nutrient levels of coastal waters through riverine and sewage inputs, and in both the numbers and frequency(as well as the species composition) of red tides. However, it is still not possible to conclude the extent to which the increase in red tides in coastal waters can be attributed to the increase in nutrient levels, since so many other factors are involved.Undoubtedly, a relationship exists between red tides and the N and P load of coastal waters, and many nutrient enrichment experiments have shown that marine phytoplankton blooms are often nutrient limited. What is now becoming clear, however, is that although in classical Liebigian terms minimum amounts can be limiting, nutrient ratios (such as N:P and Si:P) are far more important regulators.This paper reviews evidence collected by the authors from Tolo Harbour, Hong Kong together with data collected in Japanese and North European coastal waters by various authors, which indicates that both long term and relatively short term changes in the N:P ratio are accompanied by increased blooms of non-siliceous phytoplankton groups and, furthermore,that the growth of most red tide causative organisms in Hong Kong coastal water is optimized at a low N:P(atomic) ratio of between 6 and 15.

Some observations on harmful algal bloom (HAB) events along the coast of Guangdong, southern China in 1998

The year 1998 was an unusual year for Guangdong Province and Hong Kong, both in southern China, as the frequency and intensity of harmful algal blooms (HAB) were much higher than usual. This paper describes the causative organisms found associated with these blooms and speculates on the possible causes of these blooms, including the effects of increased temperature, reduced salinity, eutrophication and meteorological and oceanographic events on the initiation and spread of these blooms.

The effects of nutrients and their ratios on phytoplankton abundance in Junk Bay, Hong Kong

Eutrophication has been considered to be undoubtedly one of the key factors stimulating phytoplankton growth, since it involves the enrichment of a water mass with both inorganic and organic nutrients supporting plant growth. Nutrient enrichment as a result of anthropogenic activity occurs in estuaries and coastal waters as well as in lakes and freshwater impoundments, and blooms of phytoplankton are one of the effects of such an accelerated process of nutrient enrichment. This paper presents the results of a two-year survey of the nutrients and phytoplankton at 3 stations in Junk Bay, Hong Kong, carried out from 1997 to 1998. The relationships between nitrogen, phosphorus, and their ratio, with phytoplankton abundance have been studied. The results show that the highest nitrogen concentration was in Station 2 which is close to a sewage input, whereas the highest phosphorus concentration was in Station 1 which is close to a landfill area. The mean N:P ratios at the three stations were between 8 and 14. The diatoms were the dominant group during most of the year but it seems that diatoms were more sensitive than dinoflagellates and other algal groups to the increase in nutrients.

Observations on vertical distribution of fungi associated with standing senescent Acanthus ilicifolius stems at Mai Po Mangrove, Hong Kong

The present study was carried out to investigate the higher fungi colonizing the herbaceous mangrove associate Acanthus ilicifolius. This paper reports part of an investigation to determine if there is vertical distribution of fungi on the standing plant.

Occurrence of fungi on submerged pine and teak blocks in Hong Kong coastal waters

An investigation of the lignicolous marine fungi in Hong Kong coastal waters was carried out for 18 months in order to determine successional patterns of fungal occurrence. Submerged blocks of pine (Pinus massoniana Lambert) and teak (Tectona grandis Linnaeus) were used as baits and were scraped at intervals to remove surface fouling organisms. Occurrence of fungi is described in terms of the composition of the fungal flora and the number of fungal colonies developed on the test blocks before and after incubation. The scraped teak and pine blocks supported slightly different fungal floras, and the selective effect of these substrates on fungal colonization is discussed.

Factors affecting the distribution of lignicolous marine fungi in Hong Kong

An investigation into the effect of environmental factors on the general distribution and occurrence of lignicolous marine fungi using submerged blocks of pine (Pinus massoniana Lamb.) and teak (Tectona grandis L.) was carried out for 18 months in the coastal waters of Hong Kong. Five test sites, with environmental conditions varying from estuarine to oceanic, and from polluted to non-polluted, were selected. During each collection, salinity, temperature, pH, dissolved oxygen, biochemical oxygen demand, nitrate-nitrogen, inorganic phosphate-phosphorus and light transmission were measured. A total of 51 species of fungi were recorded among which only 28 were either obligate or facultative marine forms. Neither the general distribution pattern nor the distribution of the more frequent fungi could be solely accounted for by differences in salinity at the test sites and it is suggested that other ecological factors such as heavy sediments in the waters, low pH, and the presence of an abundant source of inocula may be important.

Seasonal patterns of primary colonization by lignicolous marine fungi in Hong Kong

During a 14-month investigation of the seasonal pattern of primary colonization by lignicolous marine fungi in the coastal waters of Hong Kong, a pine block (Pinus massoniana Lamb.) was submerged each month at each of the five stations and recovered in the following month. Thirty-eight species of fungi were isolated, three of which were not identified. In this first recorded attempt to describe fungal colonization on submerged blocks quantitatively, five species (Periconia prolifica, Cirrenalia macrocephala, Ceriosporopsis halima, Trichocladium achrasporum and Halosphaeria quadricornuta) were the most frequent and most abundant fungi on the monthly blocks. Statistical analyses of seasonal abundance of these fungi are presented and their occurrence in relation to varying temperature and salinity throughout the year, including the Phoma pattern, are discussed.

Effects of surface fouling organisms on the occurrence of fungi on submerged pine blocks in Hong Kong coastal waters

During an investigation into the distribution of lignicolous marine fungi in Hong Kong coastal waters, pine blocks (Pinus massoniana Lambert) were used as one of the baiting substrates. The results from unscraped and scraped pine blocks showed that, in general, the presence of surface fouling organisms did not affect the pattern of occurrence of fungi either quantitatively or qualitatively. Apart from the presence of a few fungal species on the calcareous substrates provided by barnacles and shipworms, no other associations between fungi and fouling organisms were detected.

Ecological studies of phytoplankton in Tai Tam Bay, Hong Kong

Of the 141 phytoplankton species found during the sampling period, the Bacillariophyceae was the most important group and included 70% of the total number of species; the Dinophyceae comprised a smaller percentage (28%) of the taxa; and only 3 chrysophyte species occurred throughout the study period. In terms of numbers of individuals, the Bacillariophyceae remained as the dominant group and contained 97% of the total numbers whereas the Dinophyceae represented only 3% of the total phytoplankton population.The most dominant diatom species was Thalassiosira allenii Takano which constituted 35% of the Bacillariophyceae group whereas the most abundant dinoflagellate was Prorocentrum gracile Schutt which represented 40% of the total Dinophyceae numbers.Chlorophyll a levels varied from 0.40 to 32.31 mg m−3 at the surface and from 0.33 to 33.91 mg m−3 at the bottom.Seasonal trends of phytoplankton abundance and chlorophyll a concentration were observed in the survey area with generally high peaks in summer and low values during winter months. Such variations can be attributed to the interactions between, and changes of, various environmental parameters, such as temperature, salinity and nutrient availability (particularly silicate).