Microhabitat preference, body size, and egg allocation in the gill parasite Naobranchia lizae (Copepoda)

The relationships between microhabitat preference, body size, and egg allocation were examined in the copepod Naobranchia lizae, which establishes on the gills of striped mullet Mugil cephalus. A total of 297 individual N. lizae (mean intensity = 5.0 ± 4.8 SD) were recovered from 60 infected hosts collected from the Charleston Harbor Estuarine System, South Carolina USA. For each mullet, we identified 16 microhabitats per gill arch, which yielded 128 microhabitats per host that could potentially be occupied. On average, only 5% of these microhabitats were occupied per host. The distribution pattern of the copepods on the gills revealed that microhabitat preferences occurred both among and within gill arches. For the microhabitats occupied, there was no effect of preference on body size, egg number, or egg size. Similarly, microhabitat sharing, which was more likely to occur at higher infection intensities, was not costly in terms of the copepod body size and egg allocation and there was no detectable trade-off between egg number and egg size. However, results also revealed that about half (48%) of the available microhabitats were never occupied by the copepods. We suggest that the occupancy of these potentially poor quality sites could carry fitness costs not realized in nature since numerous high quality sites are available per host. The findings are consistent with the interpretation that female N. lizae occupy a resource-rich habitat on the gill arches of striped mullet that provides conditions for optimal growth and reproduction.