No abstract

Each individual cetacean is an ecosystem itself, potentially harboring a great variety of animals that travel with it. Despite being often despised or overlooked, many of these epizoites have been proven to be suitable bio-indicators of their cetacean hosts, informing on health status, social interactions, migration patterns, population structure or phylogeography. Moreover, epizoites are advantageous over internal parasites in that many of them can be detected by direct observation (e.g., boat surveys), thus no capture or dissection of cetaceans are necessary. Previous reviews of epizoites of cetaceans have focused on specific geographical areas, cetacean species or epibiotic taxa, but fall short to include the increasing number of records and scientific findings about these animals. Here we present an updated review of all records of associations between cetaceans and their epibiotic fauna (i.e., commensals, ecto- or mesoparasites, and mutualists). We gathered nearly 500 publications and found a total of 58 facultative or obligate epibiotic taxa from 11 orders of arthropods, vertebrates, cnidarians, and a nematode that are associated to the external surface of 66 cetacean species around the globe. We also provide information on the use as an indicator species in the literature, if any, and about other relevant traits, such as geographic range, host specificity, genetic data, and life-cycle. We encourage researchers, not only to provide quantitative data (i.e., prevalence, abundance) on the epizoites they find on cetaceans, but also to inform on their absence. The inferences drawn from epizoites can greatly benefit conservation plans of both cetaceans and their epizoites.

We analyzed patterns of aggregation and spatial distribution of the epizoic barnacle Xenobalanus globicipitis on the flukes of Mediterranean striped dolphins, Stenella coeruleoalba, assessing its potential use as an indicator of the host's hydrodynamics based on data from 55 dolphins. Barnacles occurred along the trailing edge with the cirri oriented towards the oncoming flow. Nearest neighbor analyses suggested that new recruits actively seek placement next to already settled barnacles, forming aggregations possibly to facilitate copulation. The probability of spanwise settlement strongly increased with fluke width (presumably enabling prolonged leading‐edge vorticity), and with chordwise length where pressure is predicted to be positive. Consequently, clustering tended to increase nonlinearly towards the fluke notch. Furthermore, it was three times more likely for barnacles to occur on the dorsal vs. ventral side of flukes, at an average abundance ca. 12 times higher. This difference could result from a host's asymmetric oscillation of the tail, which would alter leading‐edge vorticity, and/or an interaction between the wake produced by the dorsal fin and the flow associated with flukes. Both processes could primarily enhance cyprid contact and/or attachment on the dorsal side. This study offers a starting point for future comparison with other cetaceans.

Antarctic minke whales, Balaenoptera bonaerensis, breed in tropical and temperate waters of the Southern Hemisphere in winter and feed in Antarctic grounds in the austral summer. These seasonal migrations could be less defined than those of other whale species, but the evidence is scanty. We quantitatively describe the epibiotic fauna of Antarctic minke whales and explore its potential to trace migrations. Seven species were found on 125 out of 333 examined Antarctic minke whales captured during the last Antarctic NEWREP-A expedition in the Southern Ocean: the amphipod Balaenocyamus balaenopterae (prevalence = 22.2%), the copepod Pennella balaenoptera (0.6%); three coronulid, obligate barnacles, Xenobalanus globicipitis (11.1%), Coronula reginae (8.7%), C. diadema (0.9%); and two lepadid, facultative barnacles, Conchoderma auritum (9.0%) and C. virgatum (0.3%). Species with prevalence > 8% exhibited a modest increase in their probability of occurrence with whale body length. Data indicated positive associations between coronulid barnacles and no apparent recruitment in Antarctic waters. All specimens of X. globicipitis were dead, showing progressive degradation throughout the sampling period, and a geographic analysis indicated a marked drop of occurrence where the minimum sea surface temperature is < 12 °C. Thus, field detection -with non-lethal methodologies, such as drones- of coronulid barnacles, especially X. globicipitis, on whales in the Southern Ocean could evince seasonal migration. Future investigations on geographical distribution, growth rate, and degradation (for X. globicipitis) could also assist in timing whales’ migration.