Tidal variation in fish assemblages and trophic structures in tropical Indo-Pacific seagrass beds

Abstract

Background: Tidal cycle is an important factor which regularly changes coastal fish assemblages in shallow waters. However, the variations in fish assemblage and trophic structure across tidal cycles in tropical seagrass beds are rarely discussed. We used underwater visual censuses to quantify fish abundance and diversity from the shallow intertidal to the subtidal zone during both flood and ebb tides in seagrass beds surrounding the Dongsha Island, South China Sea. We also recorded fish feeding habits by analyzing stomach contents.

Ontogenetic Habitat Usage of Juvenile Carnivorous Fish Among Seagrass-Coral Mosaic Habitats

“…The shallow northern waters (depth: 1-3 m) of Dongsha Island are often calm and clear and covered with high seagrass coverage (covering approximately 80-90% of the study area). Previous studies [30,31] showed a high abundance of reef fish, seagrass, and coral in the northern waters of Dongsha. Seagrass species in the canopies are mainly mixtures of Thalassia hemprichii, Cymodocea rotundata and Cymodocea serrulata.…”

“…In total, eight surveys were conducted bimonthly only during the warm season (from April to October) in 2010 and 2011 to avoid intense northeastern monsoons during the cool season and coincide with the main recruitment season for reef fishes at Dongsha Island [30]. The surveys were conducted using six 20 × 2 m replicated transects that had been placed at one of six haphazardly chosen locations in each of the four habitat types (Figure 1c).…”

“…All transects were carefully placed and at least 10 min were allowed to pass between establishment of transects and the commencement of underwater visual census (UVC) survey (conducted on SCUBA) to limit disturbance to the fish. All four habitat types were surveyed during flood tides between 9 am and 4 pm to avoid confounding effects resulting from tidal and diel fauna movement [30]. In total, we collected 24 datasets (4 habitat types, each with 6 replicate transects) at each of the eight survey times, leading to a total of 192 data points used in the analyses described below.…”

“…obsoletus, Let. harak (Lethrinidae) and Lutjanus fulviflamma (Lutjanidae) are all dominant carnivorous fish species around Dongsha Island [30], and they all clearly show ontogenetic habitat shifts from seagrass beds to coral reefs in their early life history stages [12,19,22]. We defined three body length categories to study ontogenetic habitat usage pattern according to our own and other previous studies [12,14,19]: (1) small (TL < 5 cm, newly recruited fish that feed mostly on small crustaceans), (2) medium (TL = 5-15 cm, juvenile stage, diets shift to large invertebrates, as mentioned below), and (3) large (TL > 15 cm, sub-adult to adult stage; [14,34]).…”

Threats to Seagrass Ecology and Indicators of the Importance of Seagrass Ecological Services in the Coastal Waters of East Lombok, Indonesia

“…In this case, the group of fish is the most dominant carnivores on seagrass beds in the study areas. Similarly, the group of fish carnivores contributed about 70% of the total fish abundance in seagrass beds at Donghsa Island's (Lee et al, 2014), but there was differences, the group of fish carnivores (20%) and herbivores (20%) in the Formoso River estuaryPernambuco, Brazil (Pereira et al, 2010). Besides that, (Appendix 6) showed that seagrass provides a diversity of fish food on seagrass in the study area.…”