Population size structure, growth, arm number and damage in the sea star Archaster angulatus Müller and Troschel, 1842 (Echinodermata: Asteroidea)

Rate of natural mortality in the sea starArchaster angulatus(Echinodermata: Asteroidea)

“…Asterias spp., Galstoff & Loosanoff, 1939; Sloan & Aldridge, 1981), quantification of the key population parameters of growth and mortality remain poorly studied. Growth parameters are established for a modest number of species (see summary of this literature in Keesing, 2017) but estimates of natural mortality are especially scant. Indeed, there have been few other estimates of the rate of population decline in adult sea stars, with most studies having focussed on measuring the mortality rates among juveniles (e.g.…”

“…Lawrence et al . (2010) and Keesing (2017) measured arm damage rates attributed to sub-lethal predation of between 5.4 and 13.7% in two populations of A. angulatus . The higher of these rates was measured at the same location as in this study.…”

“…The sampling carried out for this project was done as part of studies which have been previously published (Yeo et al ., 2015; Keesing, 2017) and the collection details are only summarized briefly here. Samples of A. angulatus were collected approximately monthly between February 2009 and June 2011 from Jervois Bank (32°09′13″S 115°45′03″E, water depth 8 m) in Cockburn Sound (Figure 1) using a 85 cm wide by 45 cm high epibenthic sled with a 5 cm cutting depth and 10 mm mesh which was towed along the sea bed at a speed of about 1 knot from 100–200 m behind a 17 m power vessel.…”

“…Natural mortality rates were calculated by constructing a length converted catch curve (King, 1995) whereby the natural log of the abundance of each size class is plotted against the mean age of sea stars of that size class and the slope of the resulting line (best linear fit by least squares) is the estimated rate of natural mortality. The predicted age for each size class (at the midpoint of each 5 mm size class) was calculated using the growth parameters of the von Bertalanffy growth model for A. angulatus of 2 years and over from Keesing (2017), equation (1). where age in years is T + 2.…”

“…It occurs from Cape Naturaliste in the west north to the Northern Territory and south to the Whitsunday Islands in Queensland (Edgar, 2012) as well as occurring throughout the Indian Ocean, north to Japan and eastwards to parts of the western Pacific Ocean (Clark & Rowe, 1971). Aspects of its population biology including reproductive periodicity, and reproductive physiology and growth have been studied (Lawrence et al ., 2010; Keesing et al ., 2011; Keesing, 2017). Along with its congener Archaster typicus , which has been studied extensively in Indonesia, Hong Kong, Taiwan, the Philippines and the Ryukyu Islands (Japan) (Boschma, 1924; Ohshima & Ikeda, 1934a, b; Clemente & Anicete, 1949; Komatsu, 1983; Mukai et al ., 1986; Run et al ., 1988; Bos et al ., 2011, 2013), A. angulatus is one of just three species of asteroids where males and females are known to pair up in a pseudocopulatory ‘mating’ posture when spawning (Keesing et al ., 2011).…”