Population dynamics of corkscrew sea anemones Bartholomea annulata in the Florida Keys

Abstract

Corkscrew sea anemones Bartholomea annulata are important ecologically as hubs of a mutualistic network involving cleaner shrimps and client fishes on Caribbean reefs. They also are collected for the ornamental aquarium trade, but little is known about their population dynamics to support conservation management. We quantified variation in population structure among regions of the Florida Keys and levels of human impact within region. The Upper Keys and lowimpact sites supported higher population abundance and proportions of small anemones than the Lower Keys and high-impact sites. At 2 sites where we monitored anemone dynamics every 2 mo for 1 yr, individuals recruited frequently and grew rapidly to maximum body size and then remained static or shrank. Fewer than half the individuals survived all year, indicating rapid population turnover, with mortality occurring mostly among small individuals or large ones that appeared to senesce beforehand. Stasis of large individuals (or lack thereof) exerted the most influence on population size. We conclude that in Florida, corkscrew anemones experience relatively high recruitment and survival at sites with low human impact and in the Upper Keys, where summer water temperatures are cooler than in the Lower Keys. Populations are highly dynamic and appear to rely on frequent recruitment, potentially linked to the presence of resident adults at high enough abundances for fertilization of broadcast propagules. The ephemeral nature of these anemones has important implications for the dynamics of their anemoneshrimp symbionts, for reef fishes that utilize them as parasite cleaning stations, and for the conservation management of their populations.

Contrasting abundance and contribution of clonal proliferation to the population structure of the corkscrew sea anemone Bartholomea annulata in the tropical Western Atlantic

“…The average number of anemones within the radial transects was 20.4 AE 6.5 anemones. To our knowledge, the abundances of B. annulata recorded here are orders of magnitude greater than those reported byBriones- Fourzan et al (2012) andO'Reilly &Chadwick (2017), with anemone abundance at GKQ being the highest recorded density in the primary literature.…”

“…As mentioned above, a genet may be long lived even when a ramet has a short life span. Bartholomea annulata appears to fit this description: individual polyps exhibit short life spans under field conditions at St. Thomas, USVI (Nelsen 2008), and in the Florida Keys (O'Reilly & Chadwick 2017), and in laboratory aquaria (Titus 2011;O'Reilly & Chadwick 2017). Thus, genets at GKQ could undergo asexual reproduction, spread short distances in all directions (Titus 2011;O'Reilly 2015), grow, and then die.…”

“…Asexual reproduction occurs year round (Cary 1911), whereas sexual reproduction may occur twice each year (Jennison 1981). Populations of B. annulata are highly dynamic, appear to express phenotypically plastic life history strategies, and vary in abundance by reef zone; given this, their population genetic structure may vary widely, both spatially and temporally (Nelsen 2008;Titus 2011;Briones-Fourzan et al 2012;O'Reilly & Chadwick 2017).…”

Habitat segregation and population structure of Caribbean sea anemones and associated crustaceans on coral reefs at Akumal Bay, Mexico

“…Our field experiment demonstrates that both the hermit crabs and their gastropod shells appear to possess surface coverings that prevent them from being stung by the anemones, but only for individuals that are facultative associates of this host. Sea Anemones.-The abundance of rosetip anemones, C. gigantea, at Akumal is similar to that observed at Puerto Morelos approximately 70 km north along the Yucatán Peninsula (Briones-Fourzán et al 2012), and is within the range of abundances documented for other large sea anemones on coral reefs (Chadwick and Arvedlund 2005, Dixon et al 2014, O'Reilly and Chadwick 2017. The local abundance of rosetip anemones suggests that this population may not currently be exhibiting signs of stress, and their size class distribution indicates many small individuals, which potentially are recent recruits.…”

“…For each sea anemone observed inside the belt transects, the following information was collected: species (identified using Humann and DeLoach 2006), type of substrate (categorized as sand, seagrass, or reef), distance to nearest neighboring conspecific (for individuals <1 m away), and linear dimensions [tentacle crown length (L) and width (W) for calculation of tentacle crown surface area (TCSA) = (L/2*W/2)*π; following Hirose 1985, Roopin and Chadwick 2009, O'Reilly and Chadwick 2017. Each sea anemone also was examined carefully for the presence of crustacean symbionts, and the following information was collected for all crustaceans <10 cm distant from the anemone (maximum distance of regular associates from Caribbean sea anemones, Briones-Fourzán et al 2012): crustacean species (identified using Colin 1978, Humann andDeloach 2006), number of individuals per species, body size of each individual [shrimps: total length including carapace and abdomen, which correlates with carapace length (Chakravarty and Ganesh 2014); crabs: width of carapace, except for hermit crabs, see below], and microhabitat zone occupied on the anemone (1: under tentacle crown along the anemone column, 2: inner half of tentacle crown, 3: outer half of tentacle crown; Fig.…”