Effects of wave-driven water flow on the fast-start escape response of juvenile coral reef damselfishes

Fish often evade predators with a fast-start escape response. Studies typically examine this behaviour in still water despite water motion being an inherent feature of aquatic ecosystems. In shallow habitats, waves create complex flows that likely influence escape performance, particularly in small fishes with low absolute swimming speeds relative to environmental flows. I examined how wave-driven water flow affects the behaviour and kinematics of escape responses in juveniles of three coral reef damselfishes (Pomacentridae) with different body morphologies. Tropical damselfishes have similar fin and body shapes during early development with the exception of body depth, a trait deemed important for postural control and stability. Wave-driven flow increased response latency in two of the three species tested: fish with a fusiform body responded 2.4 times slower in wave-driven flow than in still water, whereas this difference was less pronounced in fish with an intermediate body depth (1.9 times slower response), and absent in fish with a laterally compressed body. The effect of wave-driven flow on swimming performance (cumulative escape distance and turning rate) was variable and depended on the timing and trajectory of escape responses in relation to the wave phase. Given intense predation pressure on juvenile coral reef fishes during settlement, interspecific differences in how wave-driven flow affects their ability to escape predators could influence the distribution and abundance of species across spatial and temporal scales.

Anguilliform Locomotion across a Natural Range of Swimming Speeds

Eel-like fish can exhibit efficient swimming with comparatively low metabolic cost by utilizing sub-ambient pressure areas in the trough of body waves to generate thrust, effectively pulling themselves through the surrounding water. While this is understood at the fish’s preferred swimming speed, little is known about the mechanism over a full range of natural swimming speeds. We compared the swimming kinematics, hydrodynamics, and metabolic activity of juvenile coral catfish (Plotosus lineatus) across relative swimming speeds spanning two orders of magnitude from 0.2 to 2.0 body lengths (BL) per second. We used experimentally derived velocity fields to compute pressure fields and components of thrust along the body. At low speeds, thrust was primarily generated through positive pressure pushing forces. In contrast, increasing swimming speeds caused a shift in the recruitment of push and pull propulsive forces whereby sub-ambient pressure gradients contributed up to 87% of the total thrust produced during one tail-beat cycle past 0.5 BL s−1. This shift in thrust production corresponded to a sharp decline in the overall cost of transport and suggests that pull-dominated thrust in anguilliform swimmers is subject to a minimum threshold below which drag-based mechanisms are less effective.

Phosphate bound to calcareous sediments hampers skeletal development of juvenile coral

To test the hypothesis that terrestrial runoff affects the functions of calcareous sediments in coral reefs and hampers the development of corals, we analysed calcareous sediments with different levels of bound phosphate, collected from reef areas of Okinawajima, Japan. We confirmed that phosphate bound to calcareous sediments was readily released into ambient seawater, resulting in much higher concentrations of phosphorous in seawater from heavily polluted areas (4.3–19.0 µM as compared with less than 0.096 µM in natural ambient seawater). Additionally, we examined the effect of phosphate released from calcareous sediments on the development of Acropora digitifera coral juveniles. We found that high phosphate concentrations in seawater clearly inhibit the skeletal formation of coral juveniles. Our results demonstrate that calcareous sediments in reef areas play a crucial role in mediating the impact of terrestrial runoff on corals by storing and releasing phosphate in seawater.

Effects of wave-driven water flow on the fast-start escape response of juvenile coral reef damselfishes

ABSTRACTFish often evade predators with a fast-start escape response. Studies typically examine this behaviour in still water despite water motion being an inherent feature of aquatic ecosystems. In shallow habitats, waves create complex flows that likely influence escape performance, particularly in small fishes with low absolute swimming speeds relative to environmental flows. I examined how wave-driven water flow affects the behaviour and kinematics of escape responses in juveniles of three coral reef damselfishes (Pomacentridae) with different body morphologies. Tropical damselfishes have similar fin and body shapes during early development, with the exception of body depth, a trait deemed important for postural control and stability. Wave-driven flow increased response latency in two of the three species tested: fish with a fusiform body responded 2.9 times slower in wave-driven flow than in still water, whereas this difference was less pronounced in fish with an intermediate body depth (1.9 times slower response) and absent in fish with a laterally compressed body. The effect of wave-driven flow on swimming performance (cumulative escape distance and turning rate) was variable and depended on the timing and trajectory of escape responses in relation to the wave phase. Given intense predation pressure on juvenile coral reef fishes during settlement, interspecific differences in how wave-driven flow affects their ability to escape predators could influence the distribution and abundance of species across spatial and temporal scales.

Sea Urchins Play an Increasingly Important Role for Coral Resilience Across Reefs in Taiwan

Herbivores are an important functional group that control algae, create new space, and promote recruitment for coral recovery. However, on many coral reefs, overfishing has greatly decreased the density of herbivores, especially fishes and gastropods, impairing coral resilience. On such overfished reefs, remnant herbivores that are not target species of local fisheries, e.g., sea urchins, are expected to play an increasingly important role, yet few studies, except for those in the Caribbean and Kenya have examined non-fish herbivores in relation to coral resilience. Here, we conducted field surveys at 30 sites along three coral reefs in Taiwan between 2016 and 2017, to examine the relative importance of six key factors for coral resilience: herbivore abundance (fishes, gastropods, sea urchins), coral cover, macroalgal cover, habitat complexity, water depth, and wave exposure. The density of juvenile coral was used as a proxy of coral resilience. Diadematid sea urchins (Echinothrix spp. and Diadema spp.) dominated most sites (19 of 30 sites) and multivariable regression models showed sea urchin density as the best positive predictor of coral juvenile density. The results elucidated the increasing role diadematid sea urchins play as remnant herbivores on overfished coral reefs in Taiwan. Given that overfishing is a widespread issue, this phenomenon may be occurring globally. More studies are needed to examine the role of remnant, but often ignored, sea urchin herbivory on coral resilience. Reef managers should consider monitoring locally remnant herbivores and incorporating them into management strategies.

Proteomic responses to ocean acidification in the brain of juvenile coral reef fish

Elevated CO2 levels predicted to occur by the end of the century can affect the physiology and behaviour of marine fishes. For one important survival mechanism, the response to chemical alarm cues from conspecifics, substantial among-individual variation in the extent of behavioural impairment when exposed to elevated CO2 has been observed in previous studies. Whole brain transcriptomic data has further emphasized the importance of parental phenotypic variation in the response of juvenile fish to elevated CO2. In this study, we investigate the genome-wide proteomic responses of this variation in the brain of 5-week old spiny damselfish, Acanthochromis polyacanthus. We compared the expression of proteins in the brains of juvenile A. polyacanthus from two different parental behavioural phenotypes (sensitive and tolerant) that had been experimentally exposed to short-term, long-term and inter-generational elevated CO2. Our results show differential expression of key proteins related to stress response and epigenetic markers with elevated CO2 exposure. Proteins related to neurological development were also differentially expressed particularly in the long-term developmental treatment, which might be critical for juvenile development. By contrast, exposure to elevated CO2 in the parental generation resulted in only three differentially expressed proteins in the offspring, revealing potential for inter-generational acclimation. Lastly, we found a distinct proteomic pattern in juveniles due to the behavioural sensitivity of parents to elevated CO2, even though the behaviour of the juvenile fish was impaired regardless of parental phenotype. Our data shows that developing juveniles are affected in their brain protein expression by elevated CO2, but the effect varies with the length of exposure as well as due to variation of parental phenotypes in the population.

APLIKASI ASTAXANTHIN DARI HAEMATOCOCCUS PADA BENIH KERAPU SUNU (Plectropomus leopardus) TERHADAP TOTAL KAROTENOID DAN PROFIL DARAH

Haematococcus merupakan alga yang kaya karotenoid dari jenis astaxanthin yang tidak hanya berpotensi sebagai sumber pigmen merah tetapi juga sebagai antioksidan. Aplikasi haematococcus telah dilakukan pada larva kerapu sunu dan menunjukkan adanya perbaikan peformansi warna merah yang cukup signifikan. Tujuan dari penelitian ini adalah mengetahui pengaruh haematococcus sebagai sumber astaxanthin terhadap pertumbuhan, total karotenoid, dan profil darah (hematokrit dan haemoglobin) pada juvenil ikan kerapu sunu. Benih kerapu sunu ukuran panjang rata-rata 14,07 ± 0,07 cm dan bobot rata-rata 45,92 ± 6,35 g dipelihara dalam jarring berukuran 0,5 m x 0,5 m x 1 m yang diletakkan dalam bak beton ukuran 3 m x 1,2 m x 1,2 m. Kepadatan ikan tiap jaring adalah lima ekor. Perlakuan yang diujicobakan adalah penambahan haematococcus ke dalam pakan buatan dengan dosis dan kompisisi sebagai berikut: A) 1% dari berat pakan, B) 1% dari berat pakan + 10% minyak ikan, dan C) 0% (kontrol). Hasil penelitian menunjukkan bahwa penambahan haematococcus ke dalam pakan tidak memberikan perbedaan nyata terhadap pertumbuhan mutlak panjang dan bobot, serta laju pertambahan panjang dan bobot (P value > 0,05). Penambahan haematococcus memberikan perbedaan nyata (P value < 0,05) terhadap konversi pakan di mana perlakuan A (1,99 ± 0,09); B (2,12 ± 0,14); dan C (2,28 ± 0,09). Penambahan haematococcus memberikan peningkatan terhadap akumulasi kandungan total karoten, hematocrit, dan haemoglobin darah.Haematococcus, an alga rich in carotenoids of the astaxanthin type, not only has the potential as a source of red pigment but also as an antioxidant. The purpose of this study was to determine the effects of hematococcus as astaxanthin source on the growth, total carotenoids, and blood profile (hematocrit and hemoglobin) of coral trout grouper juvenile. Coral trout grouper seed with an average length of 14.07± 0.07 cm and an average weight of 45.92 ± 6.35 g were maintained in a net cage measuring 0.5 m x 0.5 m x 1 m placed in a 3 m x 1.2 m x 1.2 m concrete tank. Fish density per net was five fish. The treatment tested was the addition of haematococcus into the artificial feed with the following dosages and compositions: A) 1% of the weight feed, B) 1% of the weight feed + 10% fish oil, C) 0% (control). The results showed that the addition of haematococcus to the feed did not give a significant difference to the absolute growth of length and weight and also specific growth and length rate (P-value > 0.05). The addition of haematococcus gave a significant difference (P-value < 0.05) to feed conversion ratio between treatment A, B and C with the values of 1.99 ± 0.09, 2.12 ± 0.14, and 2.28 ± 0.09, respectively. The addition of haematococcus also increased the levels of total carotene content, hematocrit, and hemoglobin. This study suggests that the application of haematococcus could significantly improve the red color performance of trout grouper larvae.

Habitat degradation and predators have independent trait-mediated effects on prey

Coral reefs are degrading globally leading to a catastrophic loss of biodiversity. While shifts in the species composition of communities have been well documented associated with habitat change, the mechanisms that underlie change are often poorly understood. Our study experimentally examines the effects of coral degradation on the trait-mediated effects of predators on the morphology, behaviour and performance of a juvenile coral reef fish. Juvenile damselfish were exposed to predators or controls (omnivore or nothing) in seawater that had flowed over either live or dead-degraded coral over a 45d period. No interaction between water source and predator exposure was found. However, fish exposed to degraded water had larger false eyespots relative to the size of their true eyes, and were more active, both of which may lead to a survival advantage. Non-consumptive effects of predators on prey occurred regardless of water source and included longer and deeper bodies, large false eyespots that may distract predator strikes away from the vulnerable head region, and shorter latencies in their response to a simulated predator strike. Research underscores that phenotypic plasticity may assist fishes in coping with habitat degradation and promote greater resilience to habitat change than may otherwise be predicted.