Katherine Lam

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.

First report of the European flat oyster Ostrea edulis, identified genetically, from Oyster Harbour, Albany, south-western Western Australia

Ostrea angasi is the only large native ostreine species in southern Australian waters (i.e. New South Wales, Victoria, Tasmania, South Australia and Western Australia (WA)). It has also been recorded as a fossil from Late Pliocene calcarenites of the Roe Plain along the south-eastern coast of WA. Wild populations were harvested for food before and after European settlement. A sample of flat oysters from Oyster Harbour, Albany, WA, was typed for 16S and cytochrome oxidase 1 (CO1) mitochondrial (mt) DNA markers previously shown to be diagnostic for species of Ostreidae. Ostrea edulis was identified in the sample at an approximate 30% occurrence with O. angasi. Interspecific partial 16S and CO1 mtDNA sequence divergences, estimated using Kimuras two-parameter model, were 0.83% and 1.45%, respectively. The occurrence of O. edulis among native O. angasi populations has not hitherto been suspected and, thus, there has not been a legitimate morphological separation of the two. These results emphasise the value of molecular markers in: (1) discriminating morphologically plastic and closely related species; and, thus (2) the monitoring of species introduced into morphologically similar stocks. We caution against such introductions because of the possibility of the importation of oyster diseases (e.g. bonamiasis) and of this and other adverse impacts upon native species.

A Novel Actuator for Underwater Robots

Pneumatic muscles have been used for a number of years as actuators in robotic systems, usually for those that mimic human actions. They are most commonly used in systems designed to aid physically handicapped people. This feasibility study reports mechanical testing and modeling results for the Shadowtrade artificial muscle pneumatic actuator working in both air and underwater. The static and dynamic tension-contraction measurements were recorded through both the force and contraction relationship test and the dynamic response and time relationship test. A model of the properties of the muscle working in water was derived from the measurements of the tests that can be considered for its feasibility for use in undersea robotics.

Exploration for novel uses of air muscles as hydraulic muscles for underwater actuator

Since a dextrous robotic arm has been designed for use on land and in space, further development could be its use underwater for performing delicate tasks, just like a human hand, for operations such as picking up small or irregular size objects. Hitherto there has been no report on studies on modelling and control of rubber artificial muscles in hydraulic mode. The feasibility of developing these actuators using water as the articulating medium for underwater robots was therefore investigated by studying the properties of the hydraulic rubber muscle actuator. The rubber muscles used in the present tests were developed by the Shadowtrade Robot Co. Ltd. for installing in dextrous robotic arms. The objectives of this study were, thus, first, to define the kinematics of the hydraulic muscle. A test set up was designed to obtained contraction, force and response time values based on reference of a model defined for the rubber muscle when used in air. Second, to compare the performance of the rubber muscle in air and underwater using the test set up and thus third, to obtain a modelling of the hydraulic rubber muscle which was derived from that of the air rubber muscle.

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.

Physiological Adaptations of Fishes to Tropical Intertidal Environments

Publisher Summary This chapter presents physiological adaptations of fishes to tropical intertidal environments. The chapter focuses on the tropical intertidal zone and describes the habitat types, the nature of environmental changes that fishes are likely to experience therein, and the major groups of resident fish. The intertidal zone is a unique environment between the land and the sea. It is characterized by changes in physical and chemical factors brought about by the day/night and tidal cycles. Mangroves, water-filled burrows on mudflats, tidepools on rocky shores, shallow seagrass beds and coral reef lagoons are typical habitats for intertidal fishes. Physical factors in the intertidal environment, such as temperature, salinity, pH, oxygen and carbon dioxide content of the water change according to day/night, the tidal cycle, and climatic change. Fishes that have evolved in this extreme habitat have special physiological, behavioral, and morphological adaptations to it. The intertidal zone is occupied by fishes with differing degrees of affinity to the habitat. Intertidal fish populations demonstrate a considerable degree of convergent evolution in searches to improve their fitness to the intertidal environment. The intertidal zone is also the place where fish, with considerable phenotypic plasticity, have evolved and spread to more stable environments such as sub‐tidal marine and freshwater systems.

Real-time monitoring of fish activity on an inshore coral reef

This paper describes an underwater camera and instrumentation system for monitoring fish species activity on an inshore coral reef in a Marine Park in Hong Kong. The system consists of a high-resolution pan, tilt and zoom camera with associated instrumentation package for measuring the local environment, including dissolved oxygen, temperature, pressure, salinity and ambient light conditions. It is connected to the shore base station via a fibre-optic cable with power conductors. The system is designed to be used for long periods of time, continuously. The first period chosen was for 100 days during the coral spawning season from June to August 2004. The system has also been used regularly for 2-3 weeks at a time to monitor changes in fish behaviour in different climatic conditions. Results from the initial experiment show that fish species activity is generally markedly different from that recorded by human divers. There is also some correlation between species, time of day, and climatic and environmental conditions - correlations that have not been reported before. The paper will give details of the results of the observations, as well as technical details of the system. It will also refer to an associated project using an ROV for transect measurements on the reef, data from which has a bearing on the subject of the paper.

An underwater camera for security and recreational use

The objective of this project was to design an underwater camera and instrumentation system that could be used to detect and follow moving objects, and be able to be deployed at a depth of up to 100 m for an extended period of time. This was achieved by using a pan, tilt and zoom high resolution camera connected to a base station via a powered fibre optic cable. The camera was successfully deployed for 100 days continuously, recording video on to a DVD recorder in real time.

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.

An Underwater Camera and Instrumentation System for Monitoring the Undersea Environment

It is impossible to use human divers carrying underwater cameras, with limited battery and recording capacity, to monitor marine life and coral behaviour, and to record for 24 hours a day over three months. As a result, the use of an instrumentation platform, remotely controlling a deployed underwater camera systems and sensors, is an alternative approach that can provide long-time monitoring and image recording.