Weakening macroalgal feedbacks through shading on degraded coral reefs

1. Extensive and dense macroalgal fields can compromise the ecosystem function of habitat mosaics on reefs owing to their limiting effect on patch connectivity. Macroalgae can maintain and increase their dominance with effective self-reinforcing feedback mechanisms. For example, macroalgae can form dense beds, supressing coral settlement and grazing by herbivores. This compromised ecosystem function can lead to major socioeconomic and ecological changes.
2. Dense macroalgal beds were shaded with submerged shade sails of two sizes and changes to the underlying benthos and feeding rates of herbivorous fishes were recorded. The shade sails reduced the algae's ability to photosynthesize by 29%. After 6 weeks, macroalgal cover was reduced by 24% under small sails and by 51% under large sails. Small shade sails reduced turf algal growth by 23%, while large sails reduced growth by 82%.
3. Three months after removal of the shade sails, algal beds had almost completely regrown. During this regrowth period, herbivore bites taken from the experiment's substrates were recorded, with grazing impact reducing significantly with time.
4. This study is the first to achieve macroalgal reduction via the alteration of the light regime. While macroalgae regrew in this relatively short-term experiment, shading may be a viable reef management approach that aims to maximize habitat mosaics on coral reefs, particularly if used in combination with other intervention methods.

     

Impact of ozonation on water quality in marine recirculation systems

Ozone (O₃) is a powerful oxidant and is becoming popular in various aquaculture systems for disinfection and improving water quality by oxidation of inorganic and/or organic compounds. However, the use of ozone in marine-based aquaculture systems has been limited because of the potential to form bromate, which is formed during the oxidation of naturally occurring bromide by ozone. Because bromate is a human carcinogen, there are concerns with its chronic impact on fish health. In addition, the use of O₃ is hindered by lack of quantitative as well as qualitative design and performance information on O₃ for recirculating systems. This study investigated the application of ozonation to control pathogens and enhance the process water quality in a recirculating aquaculture system while minimizing bromate formation. A field scale monitoring program was conducted on process water quality from Atlantic halibut (Hippoglossus hippoglossus) recirculating systems. Ozonated modules showed reduction of 15% total organic carbon (TOC) and less than 25 μg/l bromate concentration was formed. In addition, ozonated modules showed reduction in nitrate, color and suspended solids, as compared to those that did not use ozone. The results of this study elucidates the formation of bromate in marine water recirculation systems.     

Myxomatosis – A reply

Madam:— In the September issue (N.Z. vet. J. (1985) 33:154), D. and A.K. Dodd, and Messrs Jackson, Mulvaney, Bishop and Jopp write in support of the introduction of myxomatosis into New Zealand, seeing it “as the only means of protecting the fragile environment of the South Island High Country from complete destruction by the rabbit.”     

Retinal Disease in the N.Z. Working Dog

Sir, — It may be of interest to some rural practitioners, having an upsurge in requests for opthalmoscopic examinations of working dogs, to know that at present this practice is engaged in examinations at the National dog trials. Retinal disease is an increasing problem in both Huntaways and Heading dogs in this country. This is probably a result of the extensive use of selected strains and the tendency for the breeds to become more uniform with farmers keeping fewer better-bred dogs. Work on this complex condition is however in its infancy, and a great deal is yet to be resolved. At this stage histological sectioning suggests an inflammatory component, but computer pedigree analysis suggests a heretibility of 0.33 — 0.40. In the main the condition is not analogous to central P.R.A. present in the British Border Collie, despite its ancestral contribution particularly to the Heading dog.     

Disseminated mycobacteriosis in a cat (abstract)

A 12-year-old, FIV-positive domestic cat from rural Northland presented with diffuse and slowly progressive swellings of the vulva, tail base, head, and distal limbs. Fine needle aspirate biopsy of the subcutis revealed large numbers of pleomorphic acid fast bacteria. At necropsy, the dermis and subcutis in the affected areas were expanded by a pale yellow opaque infiltrate. Large ulcerated cutaneous swellings were present in the left maxillary area and bilaterally at the point of the jaw corresponding to the submandibular lymph nodes. Cutaneous nodules were present in the pre-auricular area. The skin of the carpi and tarsi was thickened and there was extensive hair loss, also evident over the tail base. The internal organs were normal in appearance. Histopathologically, the cutaneous swellings consisted of sheets of large foamy macrophages, macrophages, containing yellow/brown pigment and large numbers of acid-fast bacilli, that extended from the superficial dermis to the subcutis and fascia. Infiltrates of acid fast-laden macrophages were present in the liver, lung, spleen, and lymph nodes. Infection by a novel saprophytic Mycobacterium spp was considered most likely.     

Multicentric leiomyosarcoma in a young male horse

A 2-year-old male Thoroughbred was evaluated for multiple firm, raised nodules of the maxilla and mandible that had been present since 6 months of age. The horse was evaluated as a yearling with a final histologic diagnosis of fibrosarcoma. As a 2-year-old, the colt made a loud upper airway sound and was agitated after strenuous exercise. Results of upper airway endoscopy indicated severe narrowing of the nasal passages and pharynx with normal resting function. Radiography revealed multiple circular bony lesions in the mandible, maxilla, multiple long bones, and cervical vertebrae. Biopsy specimens of the left mandible and right facial bone were obtained. A diagnosis of leiomyosarcoma with extensive metastatic bone formation was made on the basis of histologic features and the immunohistochemical staining properties of the biopsy specimens. Because of the diffuse distribution of the lesions, prognosis was guarded; 4 years after diagnosis, the horse had not pursued an athletic career.