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Biomedical subjects

Helen T Yap

Publications and source records attributed to Helen T Yap.

6 recordsLinked to original sources
PubMed2006

Effects of multiple perturbations on the survivorship of fragments of three coral species.

Fist-sized fragments of Porites cylindrica, Porites rus and Pavona frondifera were deployed in single-species (P. cylindrica) and mixed-species (all three) plots in a shallow reef area in the northwestern Philippines. After 6 months, the corals in half of the plots were broken into smaller pieces to simulate an episodic physical disturbance. The survival of all corals was monitored from March 2000 to July 2001 during which the corals experienced 2 typhoons and episodes of algal overgrowth. For both intact and broken treatments, there was significantly higher survival in the mixed-species plots than in the single-species treatments. Fragment mortality varied between disturbances of varying frequencies and magnitudes, namely: one-time fragmentation stress, seasonal overgrowth by cyanobacteria and macroalgae, short-term (1 day) and long-term (more than 1 week) burial. The mixed-species assemblages had higher fragment survivorship than the monospecific assemblages during small-scale perturbations (e.g., algal overgrowth), but not in the face of subsequent, larger scale disturbances. This study emphasizes that coral responses to disturbance are both species- and context-specific.

Animals↗
PubMed2005

Survivorship of coral juveniles in a fish farm environment.

Intensive fish farming is an emerging coastal activity that can potentially enhance sedimentation and promote eutrophication in fringing coral reefs. Here, we investigate the effect of fish farm effluent on the juvenile survivorship of the reef-building coral Seriatopora caliendrum. One-month old juvenile corals (on terracotta tiles) were deployed in fish farm and reference (reef) sites in Bolinao, the Philippines at a depth of 2m. After forty days, no survivor was recovered in the fish farm, while survivorship was low (11%) in the reference site, with the survivors' growth rate at 3.3polypsmo(-1) or 1.3mm(2)mo(-1). The fish farm deployed tiles were covered with muddy sediment and were colonized by barnacles, whereas those in the reference site were overgrown by a short stand of filamentous macroalgae. Environmental monitoring revealed higher nutrient levels (ammonia and phosphate), sedimentation rate, and organic matter flux, as well as diminished water transparency and dissolved oxygen levels in the fish farm compared to the reference site. Hence, intensive fish farming offers a suite of physical, chemical and biological modifications of the coastal marine environment which have a detrimental effect on the survivorship of coral juveniles.

Analysis of Variance↗
PubMed2004

Differential survival of coral transplants on various substrates under elevated water temperatures.

Closely related scleractinian coral species that exhibited similar survival patterns under relatively normal field conditions responded very differently to the occurrence of an environmental disturbance. The two species studied were Porites cylindrica and Porites rus which occur in the same reef zones in shallow reef flats. Transplants of both species were evenly distributed and attached to three different types of substrate: live coral colonies of P. cylindrica, dead coral colonies (also of P. cylindrica), and epoxy coated metal grids that were raised above the sandy substrate. With the onset of above-normal water temperatures due to the El Niño episode of 1998, P. cylindrica transplants immediately showed signs of bleaching stress and tissue necrosis, followed by algal overgrowth and mortality soon afterwards. In contrast, transplants of P. rus bleached more slowly and suffered less mortality, with a few actually showing signs of recovery at the end of the experimental period which covered a total of 14 weeks. These differences in responses could be attributed to properties of the symbiotic zooxanthellae, of the host coral tissue itself, or both. Over-all, survival was good on the metal grids (average of 35%), and on the live coral (average of 22%). It was poor on the dead coral (average of 6%). The metal grids as well as live coral tissue apparently provided a favorable substrate for the attached coral fragments, even for those of a different species. Under the conditions of this particular study, attachment of live coral fragments on already dead colonies for the purpose of increasing live coral cover on the reef did not yield favorable results. This is an area that requires further investigation.

Animals↗
PubMed2003

Comparison of coral growth and survival under enclosed, semi-natural conditions and in the field.

Two closely related scleractinian coral species, Porites cylindrica and Porites rus, were transplanted to two different locations: the natural environment on the reef flat, and culture tanks on land. The use of tanks enabled the regulation of certain environmental factors, and, hence, the evaluation of specific responses of the corals to these factors. For both species, growth and survival were much better in the field than in the land-based tanks most probably due to unrestricted water circulation. Since the two species were subjected to identical experimental treatments, it was possible to distinguish inherent differences between them in terms of responses to external variables. Porites cylindrica was more susceptible than P. rus to predation by corallivores. Predators, as well as grazers, occurred in significant numbers in the field, but not in the land-based tanks. Porites rus, on the other hand, succumbed more readily to overgrowth by macroalgae which thrived in the culture tanks presumably because of significantly higher nutrient levels and the conspicuous absence of grazers. These results have broader ecological implications because of accelerated environmental changes taking place in present-day reefs due to human impact. Major examples are eutrophication and alterations in water circulation which frequently result in sub-optimal conditions for coral survival and growth.

Animals↗