How do coral barnacles start their life in their hosts?

Abstract

Coral-associated invertebrates are the most significant contributors to the diversity of reef ecosystems, but no studies have examined how larvae manage to settle and grow in their coral hosts. Video recordings were used to document this process in the coral barnacle Darwiniella angularis associated with the coral Cyphastrea chalcidicum . Settlement and metamorphosis in feeding juveniles lasted 8–11 days and comprised six phases. The settling cyprid starts by poking its antennules into the tissue of the prospective host (I: probing stage). The coral releases digestive filaments for defence, but tolerating such attack the cyprid penetrates further (II: battling stage). Ecdysis is completed 2 days after settlement (III: carapace detachment). The barnacle becomes embedded deep in the coral tissue while completing metamorphosis between 4 and 6 days (IV: embedding stage), but reappears as a feeding juvenile 8–11 days after settlement (V: emerging stage; VI: feeding stage). Cyprids preferably settle in areas between the coral polyps, where they have a much higher survival rate than on the polyp surfaces.

Parasites and coral‐associated invertebrates that impact coral health

“…They typically settle between coral polyps as cyrpid larvae, then metamorphose and become encapsulated by the coral host (Liu et al 2016). The nature of their symbiotic association with host corals is unclear and often contested (Ross & Newman 1969, 1995; Cook et al, 1991; Achituv & Mizrahi 1996; Ross 2000; Liu et al 2016). Pyrgomatids feed in different ways; the majority are suspension feeders, but some directly feed from their host corals (Ross & Newman 1969, 1995, 2000; Ross 2000).…”

“…Hoekia barnacles represent ‘energy sinks’ to their host corals (Ross & Newman 1969, 1995; Pearse & Muscatine 1971; Oren et al 1997, 1998; Ross 2000) by slowly consuming tissue and forcing their hosts to constantly expend energy for tissue regeneration (Ross 2000). Although to a lesser degree than Hoekia spp., suspension‐feeding pyrgomatids also impose physiological consequences for their coral hosts (Benzoni et al 2010; Liu et al 2016). Liu et al .…”

“…Liu et al . (2016) investigated the settlement process of the barnacle Darwiniella angularis Chan, Chen & Lin, 2012, on Cyphastrea chalcidicum (Forskål, 1775) coral hosts, describing a six‐step process between first interaction with the host and the commencement of suspension feeding as metamorphosed adults. Most notably, in phases one (probing stage) and two (battling stage), the cyprid juveniles penetrate the host coral tissue with their antennules and attempt to move deeper into the host, eliciting a physiological response from the host, including the protrusion of mesenteries as a defensive mechanism (Liu et al 2016).…”

“…Despite the evidence of negative consequences to the coral host (Ross & Newman 1969, 1995, 2000; Ross 2000; Benzoni et al 2010; Liu et al 2016), some studies suggest that pyrgomatid barnacles may benefit the coral holobiont via nutrient provision (Cook et al, 1991; Achituv & Mizrahi 1996). Cook et al (1991) suggested that carbon and phosphorus ingested by Neotrevathana elongata Hiro, 1931, were terminally excreted and taken up by Symbiodiniaceae within the Millepora dichotoma Forskål, 1775, host, while nitrogen in the form of ammonium (NH 4+ ) was also provided to the coral holobiont by N. elongatum (see Achituv & Mizrahi 1996).…”

Collecting and processing thoracican, acrothoracican, and rhizocephalan cirripedes

“…For sampling mangrove barnacles, a knife is useful to cut off a piece of bark together with the barnacles. The numerous species of barnacles associated with corals and sponges are best collected live by snorkeling or scuba (see Liu et al, 2016), but they are very hard to detect as they reveal themselves only by the outline of the opercular aperture in the coral tissue (Fig. 1D).…”