The influence of environmental parameters on the spawning aggregation of Euphausia sibogae was investigated along the southwest coast of India during the peak phase of summer monsoon 2005. The prevailing ecological conditions between the aggregation period (peak phase) and non-aggregation period (early phase) were also compared. The aggregation was observed at station 1 ( ; , 480？ind·m？3) and 6 ( ; , 839？ind.m？3) during the peak phase of the summer monsoon. Eggs (14769？eggs？m？3) and different developmental stages were observed in higher abundance at station 6. The physicochemical conditions indicated that the aggregation coincided with the upwelling. The nutrient enrichment due to the upwelling triggered phytoplankton blooms, and this appeared to provide a conducive environment for spawning and development of E. sibogae. 1. Introduction The euphausiids (Class: Crustacea; Order: Euphausiacea) are keystone members of planktonic food webs in the coastal and oceanic waters. They act as a link between primary and tertiary producers in the pelagic food web. Being omnivores, their diet includes a broad spectrum of food items, ranging from phytoplankton to small zooplankton to detritus, and even some higher trophic level consumers. Euphausiids are considered as one of the potential prey items for many fish species especially tunnies. According to Roger [1], they contribute to about 15.5% of the total crustacean prey items of Thunnus albacares and Katsuwonus pelamis from the Western Indian Ocean. The young ones (100–119？mm) of Selar crumenophthalmus prefer 59.9% euphausiid as their main food item. Thus, studies on euphausiids, especially their survival and reproductive strategies are attaining greater importance among researchers. Early studies on euphausiids of the Indian Ocean were carried out by many researchers [2–8]. Spatial and temporal variations of euphausiid population along the southwest coast of India have been described by Mathew et al. [9]. Spawning and rapid development of euphausiid characterize the high potential of growth to supply energy and matter to higher trophic levels. Along the southwest coast of India, the breeding of euphausiid species usually coincides with the coastal upwelling during the summer monsoon [10]. The present study aimed to understand (a) the ecological conditions prevailing during the breeding period of E. sibogae, (b) the relationship between phytoplankton standing crop and breeding behaviour of E. sibogae, and (c) the variations in the ecological conditions between the breeding and nonbreeding periods. Coastal upwelling
References
[1]
C. Roger, “The plankton of the tropical western Indian ocean as a biomass indirectly supporting surface tunas (yellowfin, Thunnus albacares, skipjack, Katsuwonus pelamis),” Environmental Biology of Fishes, vol. 39, no. 2, pp. 161–172, 1994.
[2]
A. de C. Baker, “The latitudinal distribution of Euphausia species in the surface waters of the Indian Ocean,” Discovery Report, vol. 33, pp. 309–334, 1965.
[3]
K. Gopalakrishnan and E. Brinton, “Preliminary observations on the distribution of Eupahusiacea from the International Indian Ocean Expedition,” Bulletin of National Institute of Science India, vol. 38, no. 2, pp. 594–611, 1969.
[4]
E. Brinton and K. Gopalakrishnan, “The distribution of Indian Ocean euphausiids,” in Ecological Studies-3, The Biology of the Indian Ocean, B. Zeitschel, Ed., pp. 357–380, Springer, New York, NY, USA, 1973.
[5]
L. A. Ponomareva, The Euphausiids of the Indian Ocean and the Red Sea, Academy Nauk, Moscow, Russia, 1975.
[6]
E. G. Silas and K. J. Mathew, “Spatial distribution of euphausiacea (Crustacea) in the southeastern Arabian Sea,” Journal of Marine Biological Association, India, vol. 28, no. 1&2, pp. 1–20, 1986.
[7]
K. J. Mathew, T. S. Naomi, G. Antony, and K. S. Scariah, “Distribution of euphausicea in space and time in the Indian EEZ and contiguous sea,” in Proceedings of the 1st Workshop on Scientific Results of FORV Sagar Sampada, K. J. Mathew, Ed., pp. 121–127, 1990.
[8]
K. J. Mathew, “A review of the studies on Euphausiacea (Crustacea) of the Indian Ocean with special reference to the EEZ of India,” CMFRI Bulletin, no. 49, 2000.
[9]
K. J. Mathew, G. Sivan, P. K. Krishnakumar, and S. Kuriakose, Euphausiids of the West Coast of India, CMFRI Special Publication, 2003.
[10]
K. J. Mathew, “Studies on larval euphausiids of the southwest coast of India with notes on the developmental pathways and breeding seasons,” Journal of Marine Biological Association, India, vol. 25, no. 1&2, pp. 51–70, 1983.
[11]
S. L. Smith, “The northwestern Indian Ocean during the monsoons of 1979: distribution, abundance, and feeding of zooplankton,” Deep Sea Research Part A, Oceanographic Research Papers, vol. 29, no. 11, pp. 1331–1353, 1982.
[12]
K. Banse, “Issues related to the vertical flux in the Arabian Sea,” US JGOFS: Arabian Sea process study, US JOGOFS Planning Report 13, Woods Hole Oceanographic Institution, 1991.
[13]
S. Smith, M. Roman, I. Prusova et al., “Seasonal response of zooplankton to monsoonal reversals in the Arabian Sea,” Deep-Sea Research Part II, vol. 45, no. 10-11, pp. 2369–2403, 1998.
[14]
M. Madhupratap, S. R. S. Nair, P. Haridas, and G. Padmavati, “Response of zooplankton to physical changes in the environment: coastal upwelling along the central west coast of India,” Journal of Coastal Research, vol. 6, no. 2, pp. 413–426, 1990.
[15]
K. K. C. Nair, M. Madhupratap, T. C. Gopalakrishnan, P. Haridas, and M. Gauns, “The Arabian Sea: Physical environment, zooplankton and myctophid abundance,” Indian Journal of Marine Sciences, vol. 28, no. 2, pp. 138–145, 1999.
[16]
R. Subrahmanyan, “A systematic account of the marine plankton diatoms of the Madras coast,” Proceedings of the Indian Academy of Sciences—Section B, vol. 24, no. 4, pp. 85–197, 1946.
[17]
C. R. Thomas, Identifying Marine Phytoplankton, Academic Press, New York, NY, USA, 1997.
[18]
L. Postel, H. Fock, and W. Hagen, “Biomass and abundance,” in ICES Zooplankton Methodology Manual, R. P. Harris, P. H. Wiebe, J. Lenz, H. R. Skjoldal, and M. Huntley, Eds., p. 684, Academic Press, San Diego, Calif, USA, 2000.
[19]
UNESCO, Zooplankton Sampling. Monograph of Oceanographic Methodology: No 2, UNESCO Publication, 1968.
[20]
G. E. Newell and R. C. Newell, Marine Plankton, a Practical Guide, Hutchinson Biological Monograph, London, UK, 2nd edition, 1973.
[21]
C. D. Todd and M. S. Laverack, Coastal Marine Plankton: A Practical Manual for the Students, Cambridge University Press, Cambridge, UK, 1991.
[22]
H. Habeebrehman, M. P. Prabhakaran, J. Jacob et al., “Variability in biological responses influenced by upwelling events in the Eastern Arabian Sea,” Journal of Marine Systems, vol. 74, no. 1-2, pp. 545–560, 2008.
[23]
M. Madhupratap and P. Haridas, “Zooplankton, especially calanoid copepods, in the upper 1000 m of the south-east Arabian Sea,” Journal of Plankton Research, vol. 12, no. 2, pp. 305–321, 1990.
[24]
R. D. Brodeur and W. G. Pearcy, “Effects of environmental variability on trophic interactions and food web structure in a pelagic upwelling ecosystem,” Marine Ecology Progress Series, vol. 84, no. 2, pp. 101–119, 1992.
[25]
J. Gómez-Gutiérrez, W. T. Peterson, and C. B. Miller, “Cross-shelf life-stage segregation and community structure of the euphausiids off central Oregon (1970-1972),” Deep-Sea Research Part II, vol. 52, no. 1-2, pp. 289–315, 2005.
[26]
K. J. Mathew, “Studies on quantitative abundance of Euphausiacea with special reference to distribution in space and time along the southwest coast of India,” Journal of Marine Biological Association, India, vol. 22, no. 1&2, pp. 123–148, 1980.
[27]
K. J. Mathew, “The ecology of Euphausiacea along the southwest coast of India,” Journal of Marine Biological Association, India, vol. 27, no. 1&2, pp. 130–135, 1985.
[28]
A. Thiriot , “Zooplankton communities in the West African upwelling area,” in Upwelling Ecosystems, R. Boje and M. Tomczac, Eds., pp. 32–61, Springer, Berlin, Germany, 1978.
[29]
C. E. Stelfox, P. H. Burkill, E. S. Edwards, R. P. Harris, and M. A. Sleigh, “The structure of zooplankton communities, in the 2 to 2000 μm size range, in the Arabian Sea during and after the SW monsoon, 1994,” Deep-Sea Research Part II, vol. 46, no. 3-4, pp. 815–842, 1999.
[30]
R. R. Makarov, “Larval distribution and reproductive ecology of Thysanoessa macrura (Crustacea: Euphausiacea) in the Scotia Sea,” Marine Biology, vol. 52, no. 4, pp. 377–386, 1979.
[31]
M. Barange and S. C. Pillar, “Cross-shelf circulation, zonation and maintenance mechanisms of Nyctiphanes capensis and Euphausia hanseni (Euphausiacea) in the northern Benguela upwelling system,” Continental Shelf Research, vol. 12, no. 9, pp. 1027–1042, 1992.
[32]
G. A. Tarling, J. Cuzin-Roudy, and F. Buchholz, “Vertical migration behavior in the northern krill Meganyctiphanes norvegica is influenced by moult and reproductive processes,” Marine Ecology Progress Series, vol. 190, pp. 253–262, 1999.
[33]
K. J. Mathew, “Net avoidance behaviour among larval juvenile and adult euphausiids,” Journal of Marine Biological Association of India, vol. 30, no. 1&2, pp. 93–98, 1988.
[34]
J. Mauchline and L. R. Fisher, “The biology of euphausiids,” Advances in Marine Biology, vol. 7, pp. 1–454, 1969.
[35]
K. F. Wiborg, Investigations on Euphausiids in Some Fjords on the West Coast of Norway in 1966–1969, Serie Havundersokelser, Fiskeridirektoratets skrifter, 1971.
[36]
J. Mauchline, “The Biology of euphausiids,” in Advances in Marine Biology, J. H. S. Blaxter, F. S. Russel, and M. Yonge, Eds., vol. 18, pp. 373–554, Academic Press, London, UK, 1980.
[37]
A. I. Pinchuk and R. R. Hopcroft, “Egg production and early development of Thysanoessa inermis and Euphausia pacifica (Crustacea: Euphausiacea) in the northern Gulf of Alaska,” Journal of Experimental Marine Biology and Ecology, vol. 332, no. 2, pp. 206–215, 2006.
[38]
L. R. Feinberg and W. T. Peterson, “Variability in duration and intensity of euphausiiid spawning off central Oregon, 1996–2001,” Progress in Oceanography, vol. 57, pp. 363–379, 2003.
[39]
J. F. Gillooly, E. L. Charnov, G. B. West, V. M. Savage, and J. H. Brown, “Effects of size and temperature on developmental time,” Nature, vol. 417, no. 6884, pp. 70–73, 2002.
