Multiple-Mark Multiple-Recapture Population Size Estimates of Stygobromus tenuis potomacus from a Hypotelminorheic Habitat William Farmer and Daniel Fong American University, Department of Biology Abstract Population Size Estimates Weekly interval multiple-mark multiple-recapture estimates of the Population sizes were estimated using the Schnabel (S) and the Schumacher-Eshmeyer (S-E) population sizes of the troglomorphic amphipod crustacean, Stygobromus estimates. Lower and upper 95% Confidence intervals were generated. Population sizes were tenuis potomacus, at two adjacent seepage springs (sites B and C) associated estimated weekly until the estimates stabilized and the confidence interval decreased. with hypotelminorheic habitats were conducted during the winter through early summer months in 2014, 2015 and 2017 using both Schnabel (S) and Schumacher- Confidence Ct = number of individuals captured at Schumacher-Eschmeyer (S-E) methods. Estimates based on S and S-E methods Schnabel Eschmeyer Interval were similar, but the estimates fluctuated over the years and differed between time t Mt = total number of the two seepage springs although they were only 5.8m apart. Estimated values C M 2 1 marked individuals in Ct M t t t 95% 퐶퐼 = and 95% CI in parentheses for Schnabel estimates were: for 2014, ~ 440 (320 – Nˆ Nˆ 1 the population at time t R 1 R M ± 푡 ∗ 푆퐸 t t t 푁෡ Rt = recaptures in 660) in B and ~ 670 (450 – 790) in C; for 2015, ~ 1,240 (990 – 1940) in B and ~ sample at time t 5,270 (1,300 – 15,000) in C; and for 2017, ~ 3,150 (2,270 – 9,570) for C with B having dried up. The proportion ovigerous females also differed between B and C each year and fluctuated over time at each site. Our results indicate that long-term monitoring is necessary to reveal the population dynamics over time Results and the extensive variation in population dynamics between sites in proximity Date CB R M 10000 as well as the ephemeral nature of such habitats. 02/20/14 25 0 Seep B-Schn 02/27/14 21 0 23 Seep B-SEsc 03/05/14 18 0 44 03/11/14 20 0 62 Seep C-Schn Introduction 03/19/14 18 0 82 Seep C-SEsc 03/29/14 25 1 99 04/04/14 14 2 122 C.I. 95% 1000 04/11/14 22 1 135 ± 04/18/14 12 1 156 04/25/14 24 6 162 05/02/14 20 10 176 05/09/14 20 15 181 N Estimated 05/16/14 9 4 197 05/23/14 13 6 200 100 05/30/14 18 14 199 05/16 05/26 05/30 06/06 06/13 06/20 06/27 07/11 06/06/14 20 17 200 06/13/14 36 24 196 Estimate Dates in 2014 (mm/dd) 06/20/14 39 18 213 Figure 1: The figure above shows the Schnabel (Scnh) and Schumacher-Eschmeyer 06/27/14 70 22 247 (SEsc) population size estimates for 2014 on a log scale with 95% confidence intervals 07/11/14 72 21 296 for both seeps B and C. Population sizes were evaluated weekly until the estimates Table 1: The collection data for seep B in stabilized and confidence intervals decreased. 2014 is shown. CB represents the number of organisms captured that week and R is the number of recaptures for that week. M 8000 is the cumulative number of organisms Seep B Hypotelminorheic habitats are unique freshwater habitats that are perched marked and released. 7000 2014 Seep B Seep C Seep C above the local ground water table by an aquiclude, usually an impermeable Estimated Population 6000 442 673 5265 clay layer. The source of water for these habitats comes from rainwater or Size (S) Estimated Population 432 610 5000 snowmelt or both percolating vertically through the soil. The accumulated Size (S-E) 95% C.I. Total Number ± water then flows laterally until emerging as a seepage spring. Seepage springs 296 391 4000 Marked 3156 serve as access points to the organisms living in the hypotelminorheic. These Total Number of 36 187 seepage springs are temporal and can be curtailed or even cease to flow in dry Ovigerous Females 3000 Estimated Number of 432 2244 N Estimated conditions or drought periods, especially during the summer periods with high Babies 2000 rates of evapotranspiration. Organisms living in these habitats are assumed to Table 2: Estimated population 1244 sizes, total number of ovigerous 1000 673 retreat to the hypotelminorheic. 442 females and individuals marked, and estimated number of babies 0 Common organisms that live in the seepage springs and hypotelminorheic is listed above for 2014. 2014 2015 2017 habitats are crustacean amphipods and crustacean isopods. In the Washington Figure 2: The population size estimates for the entire sampling period, 19 weeks in 2015 Seep B Seep C 2014, 22 weeks in 2015, and 31 weeks from late 2016 to 2017, are shown above with D.C. area Stygobromus (Crustacean: Crangonyctidae) are the most widespread Estimated 1244 5265 the population size ± 95% confidence interval on the Y-axis. Only the Schnabel species of amphipod found in seepage springs. These amphipods are all Population Size (S) Estimated estimates are shown here. It is seen that the population sizes are highly variable 1308 5592 present with troglomorphic adaptations, characterized by the lack of pigment, Population Size (S-E) between seeps and over time. Total Number absence of eyes, and elongated appendages. Within the Stygobromus genus is 1082 595 Marked the only endangered species in Washington D.C., Stygobromus hayi, which is Total number of 0.6 185 93 Ovigerous Females found only on federal land. Seep B Estimated Number 2220 1116 0.5 0.48 of Babies Seep C Despite these habitats containing the only endangered species in D.C., little Table 3: Estimated population Females is known about the basic biology, including life history, food and nutrient sizes, total number of ovigerous 0.4 females and individuals marked, requirements, and population sizes. This study aims to estimate the population and estimated number of babies 0.3 sizes of Stygobromus tenuis potomacus from two proximate seepage springs in is listed above for 2015. Ovigerous Pimmit Run, VA using the Schnabel estimate (E) and the Schumacher- 2016-2017 Seep B Seep C 0.2 0.17 Eschmeyer estimate (S-E) during the winter to summer months of 2014, 2015, Estimated 0.16 - 3156 Population Size (S) 0.12 and 2017. 0.10 Estimated 0.1 - 3673 of Proportion Population Size (S-E) Total Number - 441 Marked 0 Total number of 2014 2015 2016-2017 Materials and Methods - 42 Ovigerous Females Estimated Number of Figure 3: The proportion of ovigerous (egg-bearing) females to the proportion of Study Sites - 504 Two seepage springs, seep B and C, located in Pimmit Run, VA, five minutes Babies Stygobromus tenuis potomacus that were marked and released for each seep and Table 4: Shown above is the same each year is shown above with the proportion on the Y-axis. It is observed that the from AU’s campus, were sampled weekly for population size estimates. descriptive data shown in tables 2 proportion of ovigerous females captured is also highly variable between seeps and and 3, for 2016-2017. Only seep C over time. Sampling was performed over the same seasons, so it was expected that data is shown as seep B had dried. the proportions would be similar. American Study University Site Campus Conclusions • Through sampling the same sites in the same seasons for 3 separate years it was observed that the population sizes of Stygobromus tenuis potomacus can easily be in the multiple thousands. • Despite the sites being so close together, 5.8m, it is believed that these two seepage Sampling springs are two separate habitats resulting from two discharge points. This is Two persons collected Stygobromus specimens from two different reaches of assumed as the population sizes and proportion of ovigerous females varied the site for 15 minutes at weekly intervals. Specimens were transported back between the two sites each year. Seep B experienced a change in the estimated to American University campus where the number of organisms collected were counted. The night before sampling the next week, previous weeks’ population from 442 to 1244 while seep C experienced a change from 672 to 5265 specimens were stained with 200mg/L neutral red solution. After the next to 3156 individuals. The proportion of ovigerous females captured changed from collection period, stained specimens were released into the study site. 0.12 to 0.17 for seep B, and 0.48 to 0.16 to 0.10 for seep C. It is possible that there is Samples were collected for 19 weeks in 2014 for sites B and C, 22 weeks in a meta-population in the hypotelminorheic that separates into subpopulations that 2015 for sites B and C, and 31 weeks in 2017 for site C only, as B had dried up. are unique to each seepage spring. • We found that the Stygobromus organisms are actively moving between the seepage spring and the hypotelminorheic habitat. If they were being passively flushed out of the hypotelminorheic through rain discharge, we would expect to find few recaptures. It is also clear that we are not capturing the same specimens each week, otherwise the number of recaptures would be larger. We assume that they are moving in and out of the hypotelminorheic to forage for food..