Orientation of Tigriopus californicus (Copepoda, Harpacticoida) to natural and artificial substrata

The harpacticoid copepod Tigriopus californicus was introduced into culture dishes containing either mimics. extract, or fragments of two macroalgae commonly found in the copepod's supralittoral habitat: the tubular Enteromorpha compressa and the encrusting, Ralfsia-like alternate phase of Scytosiphon lomentaria in equal abundance. Natural and artificial food sources were offered equivalently with control substrata and the copepod's position relative to each surface was recorded on videotape over a 12-hour period. The copepods preferred experimental treatments to controls immediately after introduction (within 1 hour) but favored the controls after 12 hours. This suggests either (1) a more random orientation after an initial feeding to relieve starvation; or (2) over time, dissolved organic material more fully permeated the water in each dish. The copepods also preferred the extract of S. lomentaria crust to that of E. compressa, perhaps due to a higher content of dissolved organic matter in the former treatments. Extracts of both algae were preferred over their respective mimics, suggesting a chemical (non-visual) response to dissolved organic matter.