Patrick C. Cabaitan

Multi-species spawning of corals in north-western Philippines

The Philippines has more than 30,000 km of reef area and hosts some of the world’s most diverse and endangered coral communities, however there is little information on patterns of coral reproduction (Bermas et al. 1992) and to date there are no published accounts of direct spawning observations. Sampling to determine the reproductive state of Acropora species and in situ observations of coral spawning was conducted in 2006 and 2007 at sites close to the Bolinao Marine Laboratory (BML) in northwestern Luzon, (16 22¢N 119 54¢E). Prior to the full moon in March 2006, 22 sampled Acropora species (67% of colonies, n = 208) contained white or pigmented oocytes large enough to be visible in branches that were fractured artificially underwater (for methods see Baird et al. 2002) suggesting a seasonal peak in reproduction from March to May. Night dives were carried out during the week following the full moons of 15 March and 14 April 2006; and 2 April, 2 May and 1 June 2007. Multi-species coral spawning was observed during all of the months of observation except in April 2007. Across all months of observation, a total of at least 36 scleractinian species belonging to 14 genera and 7 families (Acroporidae, Mussidae, Agariciidae, Faviidae, Oculinidae, Merulinidae and Poritidae) broadcast spawned (Fig. 1), with a maximum of 13 species observed on the fifth night after full moon in May 2007. Further studies are required to establish the extent of spawning at other times of the year and the reproductive patterns of corals elsewhere in the Philippines.

Successful Transplantation of a Fragmenting Coral, Montipora digitata, for Reef Rehabilitation

The scleractinian coral Montipora digitata (Acroporidae) is a common reef flat species that thrives under high levels of light and water turbulence, and propagates successfully by natural fragmentation. It was used for transplantation experiments in an attempt to restore a degraded lagoon environment in the northwestern Philippines. Branches about 5 cm high from a natural population in the lagoon were transplanted to dead coral outcrops or knolls in two locations (Binlab and Malilnep-Ac) with different environmental characteristics. Growth and survival were significantly better at Malilnep Ac, which resembled the natural habitat of the species more closely. Environmental conditions at this site also favored the establishment of a greater diversity of species around the coral transplants. There was no difference in performance between transplants on vertical and horizontal surfaces, and the transplants showed limited differences due to density within the experimental range. Significant survival of detached, transplanted colonies or fragments thereof around the bases of the experimental bommies at the more successful site was an additional positive outcome. Water motion showed significant effects on survival and growth, possibly enhancing the suitability of the more successful site for transplantation. These results demonstrate the potential of coral transplantation to initiate the establishment of natural communities in degraded reef areas, a concern for coastal managers in developing countries.

Differential Response of Coral Assemblages to Thermal Stress Underscores the Complexity in Predicting Bleaching Susceptibility

Coral bleaching events have been predicted to occur more frequently in the coming decades with global warming. The susceptibility of corals to bleaching during thermal stress episodes is dependent on many factors and an understanding of these underlying drivers is crucial for conservation management. In 2013, a mild bleaching episode ensued in response to elevated sea temperature on the sediment-burdened reefs in Singapore. Surveys of seven sites highlighted variable bleaching susceptibility among coral genera–Pachyseris and Podabacia were the most impacted (31% of colonies of both genera bleached). The most susceptible genera such as Acropora and Pocillopora, which were expected to bleach, did not. Susceptibility varied between less than 6% and more than 11% of the corals bleached, at four and three sites respectively. Analysis of four of the most bleached genera revealed that a statistical model that included a combination of the factors (genus, colony size and site) provided a better explanation of the observed bleaching patterns than any single factor alone. This underscored the complexity in predicting the coral susceptibility to future thermal stress events and the importance of monitoring coral bleaching episodes to facilitate more effective management of coral reefs under climate change.

The spaghetti sponge Callyspongia samarensis (Wilson, 1925) provides temporary habitat for reef fish recruits

The lagoon areas in the Bolinao reef complex (northwestern Luzon, the Philippines) used to harbor numerous live coral outcrops. However, coral cover here, as well as in nearby reef zones, has diminished since the 1998 bleaching event (Arceo et al. 2001), and the degradation is exacerbated during decades of blast fishing. Coral recruitment and reef recovery have been very slow recently and continue to be hampered by the apparent lack of larvae and suitable habitats for them to settle, particularly for corals and juvenile fish. Live coral cover has been reduced to about 1 % inside the lagoon, where dead corals prevail (48 %) and sponges are common (24 %). The latter are dominated by the spaghetti sponge Callyspongia samarensis (Wilson, 1925) , whose loose ly ar ranged branches may successfully compete for space with corals by means of overshadowing (Fig. 1a). More importantly, it might also potentially hinder the settlement and survival of coral recruits as some sponges have been observed to be aggressive towards adult corals (Chadwick and Morrow 2011). Recent field observations, however, have suggested that C. samarensis can serve as habitat and nursery site for some reef fishes (Fig. 1b). It appears to be a weedy species that can occur after disturbance events (Wulff 2012), and by doing so, it provides a three-dimensional structure that is otherwise lacking, retaining some ecological functions of the original environment (compare Schonberg et al. 2015). The tangles of the spaghetti sponge may provide shelter that was previously offered by branching corals, constituting protection for small fish. It is assumed that juvenile fish residing in the sponge thickets have the opportunity to grow in size until they are ready to colonize other reef habitats. Since the sponge is ephemeral, with abundances fluctuating seasonally, this protection is not permanent. Thus, the sponges, though putative space competitors for hard corals, offer an important benefit to the reef fish community. The present report demonstrates that the Communicated by B. W. Hoeksema

In situ nurseries enhance coral transplant growth in sedimented waters

ABSTRACT In situ nurseries have been a crucial part of coral reef restoration initiatives for the past two decades. However, the advantages over direct transplantation in sedimented waters has yet to be examined. In the present study, we showed that Pachyseris speciosa and Pocillopora damicornis fragments reared in in situ nurseries (NR) in Singapore’s sedimented waters grew significantly faster (by three to five times) than those which were directly transplanted (DT) onto the substrates. The increased growth rate during the nursery phase augmented the size of NR transplants, and had a flow-on effect on their performance during the post-transplantation phase. Overall, the maximum diameter of the NR transplants was 1.8–2.7 times larger than DT transplants after 11 months. The growth enhancement of the nursery-reared transplants improved the cost-effectiveness of our restoration effort: the estimated cost per centimetre growth of NR transplants was one-fifth of the DT corals despite the additional costs incurred to construct the nurseries. These results highlight that coral nurseries are beneficial to reef restoration in chronically sedimented waters.

Bringing back the giants: juvenile Tridacna gigas from natural spawning of restocked giant clams

Coral reef ecosystems are in rapid decline stemming from the effects of local human activities exacerbated by climate change. This has resulted in declining populations of many species, including the true giant clam, Tridacna gigas (MingoaLicuanan and Gomez 2002). Giant clams are especially vulnerable to extirpation because of their economic potential (Neo et al. 2015). Of all the tridacnine species, T. gigas is the most critically endangered and is locally extinct in many parts of its natural range. Since 1985, the BolinaoMarineLaboratory of theUniversity of the Philippines has been culturing giant clams to replenish locally extinct populations in the Philippines. More than 20,000 T. gigas and 50,000 individuals of other tridacnine species have been restocked at more than 40 sites around the country (Gomez and Mingoa-Licuanan 2006). Giant clams restocked more than 10 yr ago have potentially reached reproductive maturity. Here we report the first recorded sighting of juvenile T. gigas at Caniogan, Anda, a few hundreds of meters from the closest restocking site and 10–20 km from the Silaqui Island ocean nursery (Fig. 1a) and the Hundred Islands National Park, two sites with the largest restocked populations of tridacnines in northwestern Philippines. The juveniles are about 29 cm in shell length and are estimated to be around 2 yr old (Fig. 1b, c). These juveniles likely resulted from natural spawning of restocked individuals, and their distance from restocking sites signifies the dispersal potential of spawned larvae. The discovery of juvenile T. gigas indicates that restocked individuals can potentially replenish local populations. This marks an achievement for the Philippine giant clam conservation effort. However, it should be emphasized that continued success of the program requires a strong commitment from local communities to protect restocking sites. Further observation of recruits is needed to determine the full impact of the giant clam conservation program in the Philippines.

Gametogenesis and reproductive pattern of the reef-building coral Acropora millepora in northwestern Philippines

ABSTRACT Coral populations continue to decline in many regions because of natural and anthropogenic disturbances; and the persistence of coral populations mainly relies on natural recruitment through coral reproduction. However, studies on the reproduction of many important reef-building coral species in one of the most biodiverse region, the Coral Triangle, are very limited. Here, we investigated the reproductive biology of the coral Acropora millepora in Bolinao-Anda Reef Complex, northwestern Philippines from February 2014 to March 2015, through in situ assessment of gamete maturity, histological examination of gamete development and ex situ spawning observations. Results showed that A. millepora exhibited an annual gametogenic cycle. Formation of oocytes took place within 8 months, whereas spermatocytes developed in 3 months before the gamete release. Abundance and size of eggs in A. millepora were greatest during the months nearest to the spawning period, which coincides with the rapid increase in sea surface temperature. Ex situ broadcast spawning occurred around the months of February–March, which suggests an extended spawning pattern. Results provide additional information on coral reproduction in the region and reveal the potential of A. millepora in providing coral propagules for the replenishment and recovery of degraded coral populations.

Versatile habitat conditioning by damselfish cultivating turf algae on giant clams

Territorial farmer damselfishes are facilitators that selectively farm turf algae in degraded reef patches. The effect of damselfish on algae and corals has been widely studied but the ability of the damselfish to establish farms on other substrates is less understood. In the giant clam ocean nursery in Bolinao, northwestern Philippines, farmer damselfishes, particularly Stegastes nigricans, Dischistodus prosopotaenia, and D. chrysopoecilus, make use of giant clam shells as substrate for turf algae farms. To facilitate growth of the algal crop, damselfishes reduce shading and create more space for cultivation by trimming the overhanging mantles of Tridacna gigas within their colonies. This form of habitat modification occurs within weeks, with affected clams exhibiting mantle lesions and turf algae growth on their shells. These observations suggest that damselfishes can potentially extend their farmed turf algae patches in a manner that, although not typical of natural reef conditions, may be facilitated by the availability of giant clam shells as substrate. The versatility of damselfishes in establishing turf algae farms on a different substrate and their ability to condition the habitat through active modification of other reef biota emphasize the potential of the farmer damselfish to significantly influence reef community structure and biodiversity.

Relocating bleached Platygyra sinensis facilitates recovery from thermal stress during a minor bleaching event

Abstract The recovery of bleached corals is crucial in ensuring the persistence of the coral reef ecosystem function. This study investigated whether relocating bleached Platygyra sinensis colonies was a viable measure to accelerate their recovery. During a mild bleaching event in 2014, eight bleached colonies of P. sinensis were relocated from an affected reef at Sultan Shoal, Singapore, to a reef at Kusu that was less impacted. Another eight colonies at Sultan Shoal were tagged as controls. After five months, 88% of relocated bleached colonies at Kusu showed full recovery whereas only 25% of the control bleached colonies at Sultan Shoal had recovered. The differential coral recovery among the two sites was most likely due to lower seawater temperatures and faster water flow at Kusu, which helped to mitigate the effects of thermal stress on the bleached corals. This relocation study demonstrated that relocating bleached P. sinensis to sites with more favourable environmental conditions is a viable approach to reduce bleaching impacts for this species.