Table 3. Ivlev’s electivity index for seahorse holdfast preference in the Rio Formoso Estuary, Brazil.

The index is presented for the entire estuary (general) and its principal rivers. Values between 0-1 indicate a preference, and negative values indicate avoidance or a random selection. Values in bold indicate a preference.

Holdfast	General	Rio dos Passos	Rio Ariquindá	Rio Formoso
Algae	−0.88	−0.91	nr	−0.75
Leafy algae, articulated calcareous algae, red algae, filamentous green algae
Artificial	−0.91	nr	nr	−0.80
Discarded tire, nylon rope
Crustacean	−0.79	−0.56	nr	nr
Specimen of Paguroidea (shell)
Fallen mangrove branches	0.43	0.52	0.14	0.26
Fallen mangrove leaves	−0.52	−0.21	nr	−0.55
Mangrove roots	−0.15	−0.11	−0.07	−0.19
From the species Rhizophora mangle and Laguncularia racemosa
Muddy bottom	−0.75	−0.83	−0.64	−0.71
Octocoral	−0.71	−0.59	−0.39	nr
Carijoa riisei
Oyster	−0.20	−0.08	0.63	nr
Crassostrea sp.
Rock	−0.98	nr	nr	−0.95
Sponge	−0.81	−0.74	nr	−0.78
Unidentified species

Notes.

nr

not registered