Epibiotic Fauna on Cetaceans Worldwide: A Systematic Review of Records and Indicator Potential

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.

Epibiotic fauna of the Antarctic minke whale as a reliable indicator of seasonal movements

“…The former is an obligate skin-feeding ectoparasite associated to Balaenoptera spp. worldwide 27 , 72 , 73 . In most surveys, its prevalence is surprisingly low (< 10%) 27 and higher values have only been reported in Antarctic minke whales: 20% in South Africa 33 , and 22% and 36% in the Southern Ocean [ 36 , this study].…”

“…Four additional epibionts appear to be more generalist dwellers. The commensal barnacle Xenobalanus globicipitis is known to settle on over 41 cetacean species 27 , with no clear evidence of preferential attachment to particular host species. Nevertheless, this species rarifies in cold regions (see below) and, indeed, records in the Southern Ocean are scanty regardless of cetacean species.…”

“…In the case of X. globicipitis , our results also reveal an area of higher probability of cetacean colonization within 50°N-40°S, especially in regions where minimum SST is 15-20 °C. Indeed, all cetacean species harboring this barnacle exploit, at least partially, waters within the 30°N-30°S belt [see 27 ]. In this context, Kasamatsu et al 11 inferred that breeding areas of Antarctic minke whales might be located between 5° and 30°S, and neonates and calves have been spotted within 2-34°S 18 , 19 , 33 , 130 – 132 .…”

“…worldwide 27 , 72 , 73 . In most surveys, its prevalence is surprisingly low (< 10%) 27 and higher values have only been reported in Antarctic minke whales: 20% in South Africa 33 , and 22% and 36% in the Southern Ocean [ 36 , this study]. Reasons behind these figures are difficult to decipher, but the role of hosts’ population density should be considered since whale lice are transmitted by contact 74 .…”

“…Firstly, we investigated the geographical limits and thermal tolerance of this species. To this end, we adopted the systematic approach described in Ten et al 27 to obtain all the available records of the presence/absence of X. globicipitis worldwide based on publications that reported the examination of the external surface of cetaceans. For each selected survey, we also compiled the sampling coordinates (to the nearest 0.1°) and sampling period.…”