Persistence of Daphnia in the epilimnion of Lake Mead, Arizona–Nevada, during extreme drought and expansion of invasive quagga mussels (2000–2009)

Figures & data

Figure 1 Location of Lake Mead zooplankton sampling stations (CR = Colorado River, LVB = Las Vegas Bay, VR = Virgin River). ▴ = Colorado River Stations; • = Overton Arm Stations; • ▪ Boulder Basin Stations.

Figure 2 Chl-a (μg/L) and Daphnia abundance (#/L; n = 1872) for (a) Boulder Basin (n = 981); (b) Overton Arm (n = 323); and (c) Colorado River (n = 568) from Jan 2000–Dec 2009.

= Chl-a (μg/L);

= Daphnia abundance (#/L).

Figure 3 Daphnia biomass (μg d.w./L) for (a) Boulder Basin (n = 515); (b) Overton Arm (n = 183); and (c) Colorado River (n = 369) during Oct 2006–Dec 2009. ▪ = Daphnia biomass (μg d.w./L); □ = total zooplankton biomass (μg d.w./L).

Figure 4 Daphnia biomass (μg d.w./L; a = Boulder Basin, b = Overton Arm, c = Colorado River) and abundance (#/L; d = Boulder Basin, e = Overton Arm, f = Colorado River) for the sampling stations within Boulder Basin (n = 255), Overton Arm (n = 80) and Colorado River (n = 148) during the period Jan–May for 2007, 2008, and 2009. □ = 2007;

= 2008; ▪ = 2009.

Figure 5 Quagga veliger abundance (#/L) for (a) Boulder Basin (n = 515); (b) Overton Arm (n = 183); and (c) Colorado River (n = 369) during Oct 2006–Dec 2009.

= quagga veliger abundance (#/L).

Figure 6 Abundance of quagga veligers (organisms/L) at the sampling locations on (a) October 2007, (b) October 2008, and (c) October 2009. Sampling station CR343.2 was not sampled in October 2009. Sampling station VR12.9 was not sampled on the selected dates.

Table 1 Characteristics of zooplankton sampling stations. For each station, values represent means for chlorophyll a (n = 1506) and Secchi depth (n = 1148).

	Station ID	Depth (m) Apr 2009	Chl-a (μg/L)	Secchi Depth (m)
Boulder Basin	LVB 3.5	∼14	7.3	3.5
	LVB 4.95	∼41	2.1	7.3
	LVB 6.7	∼75	1.2	10.0
	LVB 7.3	∼87	1.1	10.3
	Intake	∼49	1.1	10.5
	CR 346.4	∼116	1.0	11.5
	CR 343.2	∼118	1.0	11.5
	CR 342.5	∼118	0.9	12.1
Overton Arm	VR 25.1	∼5	3.2	2.2
	VR 18.0	∼33	1.3	5.1
	VR 13.0	∼50	0.9	8.0
	VR 12.9	∼51	1.2	7.9
	VR 9.4	∼66	0.9	9.3
	VR 6.0	∼86	1.1	9.3
Colorado River	CR 394.0	∼47	2.3	4.3
	CR 390.0	∼63	1.7	5.0
	CR 380.0	∼79	1.1	8.3
	VR 2.0	∼94	1.2	10.1
	CR 360.7	∼105	1.1	11.7
	CR 355.75	∼107	1.0	12.1
	CR 351.7	∼112	0.9	11.6
	CR 348.4 NW0.8	∼93	1.0	11.6
LVB: Las Vegas Bay, CR: Colorado River, VR: Virgin River.