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Habitat Selection by the Burrowing Brittlestar Ophiophragmus filograneus: Grain Size, Vegetation & Structure Lee Ann J. Clements, Ph.D. & Indira Brown; Dept. Biology and Marine Science, Jacksonville University O. filograneus prefers to burrow in fine grain sand with the sea grass Halodule wrightii The attractiveness of sea grass micro- habitat is due to the presence of physical structure. Hypotheses Collection Banana River, near Melbourne, FL (28 o 12’ N, 80 o 37’ W) Salinity 24 ppt. Natural Sediment 0.15 cm sieve Lab holding conditions Ten-gallon aquaria 2- inch deep natural sediment Seawater at 24 ppt 24 hours Ophiophragmus filograneus Family Amphiuridae: the burrowing brittlestars Burrows in sediment 5 - 7 cm deep Patchy distribution Seagrass communities Collected from Banana River, FL (28 o 12’ N, 80 o 37’ W) Central Disc diameter ~ 1 cm Arm length ~ 10 cm Four grain sizes (Standard Sand Company, Jacksonville, FL) Very fine (50/140) Fine (45/60) Medium (30/65) Coarse (20/30) Individual choice arenas 12 animals per experiment Repeated 4 times, N= 48 Experimental Design Fine Very Fine Medium Coarse VF V M C 0.00% 5.00% 10.00% 15.00% 20.00% 25.00% 30.00% 35.00% 40.00% 45.00% 50.00% Percentage F Figure 1. Results of first grain size choice experiment. Lines connect treatments that were not significantly different (Freidman’s Rank Sums test, = 0.05). VF V 0.00% 10.00% 20.00% 30.00% 40.00% 50.00% 60.00% 70.00% 80.00% Percentage F Figure 2. Results of grain size choice experiment to determine differences in preference of finest grain sizes. The very fine (VF) sediment was significantly preferred over the fine (F) sediment. (Freidman’s Rank Sums test, = 0.05). SG VF B 0.00% 10.00% 20.00% 30.00% 40.00% 50.00% 60.00% 70.00% Percentage Figure 3. Results of experiment to determine preference for sea grass vs. bare sand. B indicates that animals chose to burrow at the border between the two treatment. The sea grass (SG) was significantly preferred over the VF sediment. (Freidman’s Rank Sums test, = 0.05). Artificial sea grass rhizomes made from ribbon and string. Natural sea grass rhizomes (Halodule wrightii). A VF B 0.00% 10.00% 20.00% 30.00% 40.00% 50.00% 60.00% 70.00% Percentage Figure 4. Results of experiment to determine preference for structure vs. bare sand. B indicates that animals chose to burrow at the border between the two treatment. The artificial sea grass (A) was significantly preferred over the VF sediment. (Freidman’s Rank Sums test, = 0.05). Patchiness is the result of habitat selection in a heterogeneous environment Grain size is an important determinant of burrowing site for this brittlestar Structure, represented by the sea-grass Halodule wrightii is also important for this organism Other submerged vegetative structures (the macro alga Caulerpa) may also be attractive as a structural component of Conclusions
