Taxonomic, Spatial and Temporal Patterns of Bleaching in Anemones Inhabited by Anemonefishes

Abstract

BackgroundRising sea temperatures are causing significant destruction to coral reef ecosystems due to coral mortality from thermally-induced bleaching (loss of symbiotic algae and/or their photosynthetic pigments). Although bleaching has been intensively studied in corals, little is known about the causes and consequences of bleaching in other tropical symbiotic organisms.Methodology/Principal FindingsThis study used underwater visual surveys to investigate bleaching in the 10 species of anemones that host anemonefishes. Bleaching was confirmed in seven anemone species (with anecdotal reports of bleaching in the other three species) at 10 of 19 survey locations spanning the Indo-Pacific and Red Sea, indicating that anemone bleaching is taxonomically and geographically widespread. In total, bleaching was observed in 490 of the 13,896 surveyed anemones (3.5%); however, this percentage was much higher (19–100%) during five major bleaching events that were associated with periods of elevated water temperatures and coral bleaching. There was considerable spatial variation in anemone bleaching during most of these events, suggesting that certain sites and deeper waters might act as refuges. Susceptibility to bleaching varied between species, and in some species, bleaching caused reductions in size and abundance.Conclusions/SignificanceAnemones are long-lived with low natural mortality, which makes them particularly vulnerable to predicted increases in severity and frequency of bleaching events. Population viability will be severely compromised if anemones and their symbionts cannot acclimate or adapt to rising sea temperatures. Anemone bleaching also has negative effects to other species, particularly those that have an obligate relationship with anemones. These effects include reductions in abundance and reproductive output of anemonefishes. Therefore, the future of these iconic and commercially valuable coral reef fishes is inextricably linked to the ability of host anemones to cope with rising sea temperatures associated with climate change.

RETRACTED: Reef fishes can recognize bleached habitat during settlement: sea anemone bleaching alters anemonefish host selection

“…Amphiprion clarkii was the only species that spent equal time in cues from unbleached or bleached hosts versus seawater. Because host anemones are typically rare on reefs [20,[46][47][48][49], anemonefishes have relatively short pelagic larval durations of 7-22 days [50][51][52], and predation pressure is likely to be high during this time; settling on the first host encountered, even if bleached, may be beneficial as rejecting bleached habitat may mean that settlement does not occur. Our study provides laboratory-based comparative observations and insights into how anemonefishes may respond to bleaching, which are further supported by field observations, as Saenz-Agudelo et al [19] found no evidence of A. polymnus larvae avoiding bleached anemones in the field.…”

Cohabitation promotes high diversity of clownfishes in the Coral Triangle

“…Subordinate individuals tend to occupy the peripheral areas of the anemone [42], as occurs in intraspecific groups where competition forces subordinates to occupy suboptimal and less favourable environments [38][39][40]. Dominant species from interspecific social groups generally did not alter their spatial distribution within the host anemone, although the common dominant species A. clarkii increased the time it spent outside of the host anemone.…”

Experimental bleaching of a tropical sea anemone in situ

“…It is susceptible to bleaching over large geographical scales, although the percentage of naturally bleached anemones is usually in the range of 1–4% (Frisch & Hobbs ; Hobbs et al . ). Adult H. crispa are typically 20–25 cm in size (oral disc diameter) and light tan to brown in colour, with sinuous tapered tentacles (Fig.…”

“…1 of Hobbs et al . ), so by putting a black plastic sheet over the relevant part of each crevice, we were able to block direct sunlight to each anemone whilst still allowing for horizontal movement of water. Some physical contact between the plastic sheets and anemone tentacles was inevitable, but this was minimized in the sense that we tried to block sunlight from above rather than encapsulate the anemones within the plastic sheets.…”

“…Bleaching not only reduces size and survival of anemones (Hattori ; Hobbs et al . ) but also reduces reproduction and survival of resident anemonefish (Saenz‐Agudelo et al . ; Lönnstedt & Frisch ), because the latter are reliant on the former for protection from predators and access to resources (Fautin & Allen ).…”