Kelvin–Helmholtz (KH) billows can facilitate microscale turbulent mixing around seamounts in the Kuroshio. This study sought to describe the influence of billow intensity (i.e., “intermittent and small” and “steady and large” billows) on vertical nitrate fluxes. KH billows led to turbulent kinetic energy dissipation rates [ε = O (10–7 to 10–6) W kg–1] and eddy diffusivities [Kρ = O (10–4 to 10–3) m2 s–1] that were significantly stronger than those outside the billow depths. The mean nitrate flux estimated using Kρ in the billow depths had a maximal value of 10.0 mmol m–2 day–1, which was much higher than estimates for the open ocean. The nitrate flux associated with the shallow KH billows at two vertical levels contributed to enrich the subsurface phytoplankton maximum, while the deeper billows closer to the summit were found to induce a large amount of nitrate flux from the deeper to the subsurface water. This study showed that KH billows make important contributions to seamount ecosystems, particularly in the cycling and vertical mixing of nutrients to make them available for potential downstream transport.
The Lubang and Looc Islands in Occidental Mindoro are located west and form part of the Verde Island Passage (VIP), an ecologically important corridor linking the South China Sea and the Philippine internal waters. The VIP has also been labelled as a regional hotspot for tropical marine biodiversity, highlighting the need for management and conservation efforts that are science-based. Thus, this assessment was done to provide baseline data on the seagrass beds of the Lubang and Looc Islands. Thirteen sites were surveyed around the Lubang and Looc Islands, Occidental Mindoro on April 13-17, 2009. The seagrass beds are generally multispecific meadows that are characterized by both continuous and patchy meadows, with cover ranging from 0.62% to 59.49%. Eight seagrass species were observed, with Thalassia hemprichii and Cymodocea rotundata the most ubiquitous. Shoot densities observed in the area are generally high (mean = 961 shoots m-2), and composite leaf biomass (mean = 212.70 gDW m-2) is comparable to other seagrass beds surveyed in other sites in the country. The observed "kaingin" practices in the uplands pose the greatest threat to the seagrass ecosystems of the area because of the long-term domino effect of erosion and sedimentation on the seagrass beds. However, fisheries practices also need to be quantified to determine hierarchy of anthropogenic disturbance that causes habitat fragmentation of the seagrass beds of Lubang and Looc Islands.
This study examined the abundance and diver sity of fish larvae passing through the Taklong Island National Marine Reserve, Southern Guimaras in relation to moon phase (full vs. new) and time of day. The reserve is dominated by mangrove, seagrass and coral reef hab itats. These were monitored during the full and new moon phases in August and September 2007, respectively, us ing nearbottom and the subsurface 335 µm mesh nets moored in the two major channels that open to waters adjacent to the reserve. The direction of the current in the northern channel (Nabinbinan) reverses with change in tides, while water current in the central channel (TaklongTandog Pass) constantly flows outside of the reserve. A total of 16,387 larval fish from 69 families was caught during the two sampling periods with the highest contribution com ing from Gobiidae, Pomacentridae, Engraulidae and Blen niidae. Fewer larvae were collected during the full moon compared to the new moon. For both moon phases, highest larval catches were observed at night coinciding with the incoming tide. Larval concentrations decreased towards dawn and no significant changes were observed during the day. Lower flux rates were observed in the bottom compared to the surface. The influx of larval fish and eggs in the area reflects the importance of the reserve as a nursing ground for young stages of fish. Higher abundances observed in the Nabinbinan channel may be attributed to the coral reefs located further north. Densities were expressed as individuals per hour and plotted with tidal cycles to examine the periodicity of the influx of eggs and larval fish.
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