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Nature in Singapore, 14, 1-4

Rapid development has fragmented Singapore’s coastal habitats and converted them into artificial shorelines, with implications for the ecosystem services they provide. This study investigated the impact of urban development on two ecosystem services related to fisheries (direct provisioning and indirect nursery functions) by comparing adjacent mangrove and artificial rocky shore sites at two locations. In terms of fisheries provisioning ecosystem services, fish video data indicated that fish assemblage structure was significantly different between the two habitat types, with Ellochelon vaigiensis, Ambassis kopsii, Ambassis interrupta, and Zenarchopterus buffonis contributing most significantly. Trap data indicated that there were significantly more fish on the artificial rocky shore than mangrove at one of our locations in Pasir Ris. There were also significant differences in the size distribution of fish between habitat types at both locations, with high proportions of smaller fish in the mangroves. Even with higher juvenile presence, the role of urban mangroves in providing nursery ecosystem services is less clear, since we cannot determine whether this habitat type is essential for any individual fish species. This study indicates that mangroves provide a level of fisheries ecosystem services as part of a heavily developed and fragmented landscape in conjunction with other substrate types.

SummarySeveral animals are renowned for their cognitive skills, such as tool use, metacognition or social learning. However, it remains puzzling why some species excel whereas others — sometimes even closely related ones — do not [1,2]. Archerfish show a remarkable assembly of skills in the context of their unique hunting behavior in which they down aerial prey with shots of water [3,4]. Hoping to find ecological factors behind these skills, we have over the past years regularly traveled to archerfish mangrove habitats in Thailand (Figure 1A). One of our most consistent findings was the presence of other surface-feeding fish, particularly the similar-sized halfbeak Zenarchopterus buffonis, wherever we spotted groups of archerfish (Figure 1A; Supplemental movie S1). We describe here that Zenarchopterus is superbly equipped with water-wave detectors, rapidly detects the impact of prey even in the dark, is active at all times, is usually more numerous than archerfish and supplements its capabilities with visual skills. Without sophisticated additions to their hunting technique archerfish would thus lose most of their downed prey to halfbeaks. We suggest that the evolution of several skills of archerfish may have thus been influenced not only by intraspecific competition [5] but also by competition with other surface-feeding fish species.

Summary Length-weight relationships were determined for four fish species [Acentrogobius viridipunctatus (Valenciennes, 1837); Acentrogobius caninus (Valenciennes, 1837); Glossogobius olivaceus (Temminck & Schlegel, 1845); and Lutjanus ophuysenii (Bleeker, 1860)] belonging to two families. Samples were collected from 2002 to 2010 by cage net (50 × 15 × 15 cm, mesh size 0.5 cm) from Zhanjiang mangrove in China (20°36′N; 110°54′E). The total length ranged is between 2.3 and 18.1 cm and weighted between 0.3 and 90.2 g. The allometric coefficient (b) of length-weight relationship varied from 2.72 for Zenarchopterus buffonis to 3.48 for Acentrogobius viridipunctatus. Length-weight relationships for these four fish species were determined for the first time.

Information on the feeding mechanism and diet of halfbeak fish species in harsh estuarine environment ecosystem is still lacking. The present study investigates the fine structure of pharyngeal jaw apparatus and diets of halfbeak fish Zenarchopterus buffonis. A total of 84 halfbeak fish samples have been collected from the coastal water of Peninsular Malaysia using fishing rod. Scanning electron microscopy was used to examine the micrographs of fine microstructure of the pharyngeal teeth. The fundamental anatomy of pharyngeal jaw apparatus displayed that the upper pharyngeal jaw (third pharyngobranchials) displays larger size of hook-like or tricuspid teeth which was analogous to tricuspid morphology. The lower pharyngeal jaw (fifth ceratobranchial) bears mainly conical teeth and appears triangular shape with two, short projections. The estimated TROPH values (1 − 3.2±0.55) denoted that halfbeak fish were omnivores in nature. The findings of this study was found to be useful as a baseline information for a better representation of the trophic flows associated with large medium and small surface water fishes.

Anecdotal field observations are reported for the first time for the genus Zenatr chopterus. In Z. buffonis, a species with only slightly modified male dorsal and anal fin rays, male and female swim in parallel, the male flicking the posterior body part against the female. In Z. gilli, a species with highly modified male dorsal and anal fin rays, the male swims alongside the female, folding the dorsal and anal fins in her direction, to cling to her. The function of the modified fins of male Zenarchopterus had not yet been explained, and we hypothesize that in some species with dramatic modifications, the dorsal and anal fin function as a clasping mechanism.