Paul Hodgson

Severe bioerosion caused by an outbreak of corallivorous Drupella and Diadema at Hoi Ha Wan Marine Park, Hong Kong

In November 2006 at Coral Beach, Hoi Ha Wan Marine Park, Hong Kong, approximately 300 colonies of Platygyra acuta and Platygyra carnosus within an area of 700 m were found to be severely bioeroded at their base. In many cases this had resulted in a ‘‘mushroom’’ shape (Fig. 1a), with some corals breaking away from their bases. This unusual bioerosion was caused by the muricid gastropod Drupella rugosa (Fig. 1b) and the long-spined urchin Diadema setosum (Fig. 1c), the abundance of which had increased since April 2006. Morton et al. (2002) reported that D. rugosa fed mainly on the tissue of the coenosarc. In the present case, it appears that the initial grazing of the upper layers of coral tissue was caused by D. rugosa followed by bierosion of the coral skeleton by D. setosum. Minute pieces of coral skeleton were found in the gut of D. setosum collected from the area. The cause of the outbreak of these predators is unknown. It has been suggested that the natural predators of both the sea urchin and gastropods such as the large predatory fishes and crabs, have decreased due to overfishing. Another possible reason may be a change in physical factors such as water temperature and salinity. The Agriculture, Fisheries and Conservation Department of the Hong Kong S.A.R. Government has re-established the broken coral colonies using underwater cement and removed ~20,000 each of Drupella rugosa and Diadema setosum from the area. The affected area has also been closed to human activities for 1 year from May 2007, hopefully to assist recovery of the coral communities.

Impact of hypoxia on the structure and function of benthic epifauna in Tolo Harbour, Hong Kong.

In Tolo Harbour, Hong Kong, where hypoxia occurs periodically, a large amount of benthic epifauna was found to be absent in the summer but become abundant again in the winter. This observation may indicate that some species are sensitive in detecting low dissolved oxygen (DO) levels and are able to escape from the harbour to more oxygenated, open waters when conditions deteriorate and return when DO levels are improved. Analysis of biological traits of these animals showed that 58% of the categories showed significant differences between the community structure in summer and winter. The significant biological traits of the few species, which remained in the harbour under the summers hypoxic conditions suggested adaptation rather than opportunism to the low DO levels. Our data also showed that trawling can increase DO at the bottom and may benefit the less sensitive species that remained in the habitat during the summer.

Application of a real-time underwater surveillance camera in monitoring of fish assemblages on a shallow coral communities in a marine park

An underwater surveillance camera has been designed for monitoring fish species activity on an inshore coral reef in a Marine Park in Hong Kong. The system consisted of a high-resolution camera. It was connected to the shore base station via a fibre-optic cable with power conductors. The camera could record video on a DVD recorder with hard disk in real time. The system was designed to be used for long periods of time up to three months continuously without maintainence. It was used to monitor changes in coral fish abundance with respect to time of day and among months. The present results thus showed two major behavioural patterns of coral fish in Hoi Ha Wan. The first is the diurnal activities as most fish species are active during the daylight rather than at night. Both mean number of species and fish density showed an increase in daylight and a decrease at night. The second was the seasonal migratory pattern. A seasonal variation of fish abundance on a subtropical reef was recorded with water temperature changes from 29degC in summer to 17degC in winter. Mean maximum number of species during daylight in warmer months was ~10-12 while that in colder months decreased to 2-3.

Terramechanics based traction control of underwater wheeled robot

The Bekker Theory of Locomotion has long been the leading applied theory when it comes to calculating and predicting soil-tyre interaction for terrestrial wheeled and tracked vehicles. Whilst the theory is applicable for terrestrial systems, there is no evidence to suggest it also applies under water. Furthermore, the complications of measuring the required soil parameters in marine substratum makes it difficult to apply. This paper explores the slip-based approach to the Bekker theorem and suggests an experiment designed to validate this theorem for underwater applications.

A low-cost, three-dimensional and real-time marine environment monitoring system, Databuoy with connection to the internet

The monitoring of environmental parameters of Hong Kong waters has usually been achieved by accumulating collected data from single point sources just below the sea surface, once or twice a month by the Hong Kong Environmental Protection Department. There has also been some experimentation involving data loggers placed on the seabed. However all of the above data collecting methods produce only historical datasets months or even years before such data is processed and made available. For a timely response to changing environmental conditions, it will be important that the data is received and processed in real-time if there is going to be a quick remedial action to changes. City University has developed a low-cost system, Databuoy, for collecting basic marine environmental parameters. This system is equipped with up to 10 sensor packs suspended in different depths in the water column under a floating buoy. Each sensor pack measures a physical parameter such as temperature, salinity or light intensity. All sensors, under each buoy, are connected to a single multiplexer that is in turn connected to a PC via a simple MODEM connection. The DataBuoy I system consisted of a single buoy with a string of sensors underneath it. The more advanced configuration, DataBuoy II, connect several nearby DataBuoys together for a 3-D representation of the measured parameters to be constructed from the data. The system has four basic components, that is, the supporting structure, the sensor packs and two levels of signal multiplexing and transmission units. Connection to the internet and other systems are then possible via this connection. The application for this type of system extends beyond the collection of field data. Real time water parameters exceeding warnings, data processing involving the rate of change of parameters and the control of marine area polluting equipment or discharges via closed loop feedback connections are all possible.

Establishment of a three dimensional, real-time marine environment monitoring system, DataBuoy™ I, in the Hoi Ha Wan Marine Park, Hong Kong, with connection to the internet

DataBuoyTM I, a three dimensional, real-time marine environment monitoring system with connection to the internet, has been developed by the Department of Electronic Engineering, City University of Hong Kong (CityU). This equipment can multiplex up to five sensors placed at different depths in the water column for monitoring of temperature, salinity and light intensity. It was installed on a site in the Hoi Ha Wan Marine Park between June and July 2006. Data collected was transferred to the CityU Marine Laboratory at the Hoi Ha Wan Marine Life Centre. Preliminary results showed that Hoi Ha Wan has had a wide salinity variation (9 ppt to 33 ppt) among sites and within two days. During that data collecting period, the water temperature recorded at 30 cm from sea surface reached a maximum of 33.5degC, while that at 7 m deep was 25.5degC. The DataBuoyTM, therefore, could detect the hypoxia in shallow water caused by low salinity at the water surface whereas the deeper sensors could detect the thermocline associated with the hypoxia in deeper water, if any. Future work involves the setting up of a DataBuoyTM II network to monitor three areas in Hoi Ha Wan. The data could be collected every few seconds and consolidated in a computer server located in the CityU Marine Laboratory. It would be formatted for display at the Marine Life Centre for visitors " information on a mimic panel and on the CityUs WWW site. This would allow world wide access to the information, making it available on line to the Government Authority, schools and the general public for information and research purposes.

A systematic analysis of blast fishing in South-East Asia and possible solutions

Destructive fishing is a significant area of focus for fisheries management. It is at odds with a sustainable fisheries management policy. Key examples of destructive fishing include blast fishing, cyanide fishing, illegal netting, and bottom trawling. It is characterized by indiscriminate killing, stunning, and/or waste of marine life. These methods are attractive to fishermen due to the high initial value of catches, however, the value of catch rapidly depletes as the habitat and surrounding eco-system is damaged or destroyed. For many South-East Asian (SEA) countries the loss of fisheries resource has been a sensitive topic that has been largely ignored. The traditional paradigm towards combating this problem has been to only consider the use of marine-based enforcement strategies. However, even under optimum conditions, current marine based enforcement strategies are ineffective, ineffiecient, and wasteful; failing to distrupt the majority of blast fishermen. This paper considers three major aspects of blast fishing; the problem, the strategies used to eradicate it, and the motivations of the fishers. This study utilizes a database of over 850,000 blast records collected by detectors in Hong Kong, Malaysia, and Phillipines since 2006. Analysis shows three different groups of blast fishermen as well as an increase in the size of explosive charges over time, the latter compensateing for the reduction in fish stocks. Futhurmore interviews with blast fishermen reaafirm the different groups. Potential solutions based on providing fishermen and their family with alternative livelihoods, education, and associated actions are suggested. Progress of any eradication method implemented can be monitored through the continued collection of bacground blast data from areas. The results can also regularly indicate the effectiveness of the efforts made to stop blast fishing.

A checklist of fish species identified from Conic Island Cave, Hong Kong

The Swire Institute of Marine Science, The University of Hong Kong, Cape d’Aguilar, Hong Kong; Hoi Ha Wan Marine Science and Engineering Laboratory, City University of Hong Kong, Kowloon Tong, Hong Kong; Agriculture, Fisheries and Conservation Department, Cheung Sha Wan Government Offices, Kowloon, Hong Kong; Department of Zoology, The Natural History Museum, London, UK; Oceanway Corporation Limited, Sai Kung, Hong Kong

Ahermatypic corals (Scleractinia: Dendrophylliidae, Oculinidae and Rhizangiidae) recorded from submarine caves in Hong Kong

Sixteen species of ahermatypic scleractinian corals have been collected from two submarine caves in Hong Kong. These are Ballanophyllia eguchii, B. ponderosa, Dendrophyllia arbuscula, D. ehrenbergiana, D. coccinea, D. compressa, D. gracilis, Turbastrea coccinea, T. faulkneri, T. diaphana, T. sibogae, T. turbinata, Cyathellia axillaris, Culicia japonica, C. rubeola and Oulangia stokesiana. Eleven of the species are new records for Hong Kong. This study has thus obtained the most diverse collection of ahermatypic corals from Hong Kong hitherto. None of the corals is a cave endemic, however, all being widely distributed in the Indo‐West Pacific. Nevertheless, such cave habitats may be locally important for ahermatypic corals and it is recommended that they be designated as Sites of Special Scientific Interest and possibly receive wider protection under the Marine Parks Ordinance (1995).

Development of a multi-drive submersible platform for deep seabed research

This paper describes the early development of autonomous vehicle for undersea exploration at depths of as much 1000 m. It is to combine several methods of propulsion, including wheels and legs.