Relationship of population density of oceanic sea skaters collected from tropical and subtropical zones in the Pacific Ocean was examined to chlorophyll concentration/Dissolved Oxygen concentration and biomass in surface sea water. The four parameters shown above were measured at the site of 12 oN 135 oN during the cruise, MR13-03 cruise, and at the site of 25 oN 160 oE during another cruise KH-14-02. Significant and positive correlation between all biomass (especially invertebrates) and population density of oceanic sea skaters collected with a Neuston-Net trailing during 15 min was shown in overall analysis on the data of the both samplings ( p < 0.001). Moreover, dissolved oxygen was much lower at 25 oN 160 oE than that at 12 oN 135 oN with similar value of chlorophyll value ( p < 0.001). These results would suggest that more food resource would be available at 25 oN 160 oE than that at 12 oN 135 oN for keeping high density population of oceanic sea skaters.
Oceanic sea skaters inhabiting tropical and temperature Pacific Ocean
Marine insects have been thought to consist of a few thousand species, and most of them belong to the Coleoptera, Hemiptera and Diptera orders inhabiting various marine environments [
The combined data of chlorophyll concentration and dissolved oxygen concentration (DO) as an indicator of population density of the oceanic sea skaters.
A clear positive correlation was shown between the population density of H. micans and the combination of “higher chlorophyll concentration” plus “lower dissolved oxygen concentration” in the tropical Indian Ocean suggesting the higher biomass as food resources for the oceanic sea skaters [
This study aims, first, to clarify whether this combined data of higher chlorophyll and lower DO mean an indicator of higher population density of the oceanic sea skaters also in the Pacific Ocean population, and second, to investigate the direct relationship between the population density of the oceanic sea skaters and the biomass in the surface water as the food resources for the sea skaters.
During the two cruises: Cruises No.: MR13-03 by R/V MIRAI [8687t] and cruise No.: KH-14-02 by R/V HAKUHOMARU [3991t], both owned by JAMSTEC [Japan Agency of Marine-earth Science and Technology], samplings were performed in the dark with a Neuston net (an open box-typed frame and inner net with a 1.3 m wide opening and 6 m length of the net), between 1900 h and 0100 h. The net was towed for 15 min each time at the starboard side. Towing was repeated 2 times at each station with the ship cruising at a speed of 2 knots. During the MR13-03 cruise, three toes of Neuston net at one night were performed at a station located at 24˚N 138˚E, and 15 stations located at 12˚N 135˚E. The Neuston net was trailed for the 3 consecutive samplings (each 15 mm × 3 times) on the sea surface to allow us to rescue living sea skaters from the bottom of the net for use in cool coma experiments [
During the cruise, MR13-03, surface water sensor system was put at the bottom of the research vessel (R/V) MIRAI and consists of sensors to measure water temperatures, conductivity (salinity concentration), chlorophyll contents (can be measured by a fluorescence spectrometer) and dissolved oxygen continuously during the cruise. During the cruise, KH14-02, CTD casting was performed at all the sampling points. The cast was performed to use the Amado-cable more than 500 m long and to measure the conductivity, water temperature, depth, dissolved oxygen and chlorophyll contents continuously through water surface to 500 m in the depth. Data of dissolved oxygen and chlorophyll at 5 m depth were used for the analysis.
As shown in
Analysis of the relationship between the population density of oceanic sea skaters and all biomass collected by the Neuston net trailing (Pearson’s test: r = 0.605, p < 0.001) showed significant and positive correlation (
The relationship between the dissolved oxygen concentration and chlorophyll concentration in the surface water was shown in
A. 24˚00'N 138˚10'E (Station 1) | (a) MR-13-03: Western Subtropical and Tropical Pacific Ocean | ||||||
---|---|---|---|---|---|---|---|
Total | Hm | Hg | Hs | Hp or sp | AS# | ||
Females | Males | ||||||
Number | 179 | 126 | 6 | 0 | 299 | 0 | 0031594 |
Density | 56656.5 | 39881.1 | 1899.1 | 0 | 94638.5 | 0 | - |
B. 12˚00'N 135˚00'E (Stations 2 - 10) | Total | H.m | H.g | H.s | H.p or sp | AS# | |
Females | Males | ||||||
Number | 484 | 119 | 276 | 327 | 0 | 0 | 0.02802519 |
Density | 17270.2 | 4246.2 | 9848.3 | 11688.1 | 0 | 0 | - |
A. Northern Station at 47˚00'N 160˚00'N | (b) KH-14-02 (This cruise; Stations A and B): Western Subtropical and Tropical Pacific Ocean | |||||||
---|---|---|---|---|---|---|---|---|
Total | H.m. | Hg | Hs | Hp or sp | AS# | |||
Females | Males | |||||||
Number | 0 | 0 | 0 | 0 | 0 | 0 | 0 | |
Density | 0 | 0 | 0 | 0 | 0 | 0 | 0 | |
B: Southern Station at 25˚00'N 160˚00'E | Total | Hm | Hg | Hs | Hp or sp | AS# | ||
Female | Males | |||||||
Number | 593 | 254 | 0 | 0 | 847 | 0 | 0.0162708 | |
Density | 36445.7 | 15610.8 | 0 | 0 | 52056.4 | 0 | - | |
those at 12˚N 135˚E, although the range of the chlorophyll concentration in the areas at 24˚N 160˚E was greatly overlapped with that in the areas at 12˚N 135˚E. In the common chlorophyll value range of 0.05 - 0.70 microgram/L, the population density of sea skaters collected at “lower” oxygen dissolved area (24˚N 160˚E) was significantly higher than that collected at “higher” oxygen area (12˚N 135˚E) (
Andersen and Cheng [
A clear positive correlation was seen between the abundance of individuals and the whole biomass or biomass excluding fishes collected by the Neuston net in this study. This would mean that the main foods for the oceanic sea skaters could be speculated to be not the dead bodies of fishes but zooplanktons. Cheng [
The sampling areas at 25˚N 160˚E and at 12˚N 135˚E had common areas showing the surface water chlorophyll
value of 0.05 - 0.07 microgram/L. In the common areas, the area of 25˚N 160˚E showed higher sea skater population and lower dissolved oxygen value than the area of 12˚N 135˚E. This relationship would mean that the area of 25˚N 160˚E could be speculated to have more zooplanktons as foods of oceanic sea skaters than the area of 12˚N 135˚E. The clear positive correlation was shown between the population density of H. micans and the combination of “higher chlorophyll concentration” plus “lower dissolved oxygen concentration” in the tropical Indian Ocean suggesting the higher biomass as food resources for the oceanic sea skaters [
We would like to thank Prof. K. KOGURE (Chief Scientist of the cruise: KH-14-02, Professor, The University of Tokyo) and Dr. M. KATSUMATA (Head Scientist of the cruise: MR-13-03) for their permissions of doing this study during the cruises on the R/V HAKUHOMARU and R/V MIRAI, for their warm suggestions on this study, and encouragements and helps throughout these cruises. The samplings and the experimental study were also possible due to supports from all of the crew (Captain of KH-14-02: Mr. T. SEINO and Captain of MR13-03: Mr. Y. TSUTSUMI) and all the scientists and the engineers from GODI and MWJ in these cruises. We would like to give special thanks to them.
Takahiro Furuki,Takero Sekimoto,Noritomo Umamoto,Mitsuru Nakajo,Chihiro Katagiri,Tetsuo Harada, (2016) Relationship of Abundance of Oceanic Sea Skaters, Halobates in the Tropical Pacific Ocean to Surface Biomass and Chlorophyll/Oxygen Concentrations. Natural Science,08,264-270. doi: 10.4236/ns.2016.86031