Salinity dependence of recruitment success of the sea star Asterias rubens in the brackish western Baltic Sea

Abstract

Salinity strongly influences development and distribution of the sea star Asterias rubens. In Kiel Fjord, located in the western Baltic Sea, A. rubens is the only echinoderm species and one of the main benthic predators controlling blue mussel (Mytilus edulis) abundance. However, Kiel Fjord with an average salinity of about 15 is located close to the eastern distribution boundary of A. rubens in the Baltic Sea. In this study, we combined field and laboratory investigations to test whether the salinity of Kiel Fjord is high enough to enable successful development of A. rubens. Sea star eggs were fertilized in vitro, and development was monitored in the laboratory at four salinities (9, 12, 15 and 18) for 10 weeks. At a salinity of 9, development ceased prior to the blastula stage. At a salinity of 12, no larvae reached metamorphosis. At higher salinities, larvae developed normally and metamorphosed into juvenile sea stars. Abundances of A. rubens larvae and settled juveniles were also observed in Kiel Fjord and correlated to salinity values measured from March until June during 6 years (2005)(2006)(2007)(2008)(2009)(2010). Results revealed high A. rubens settlement rates only in 2009, the year when salinity was the highest and least variable during the period of spawning and larval development. It appears that only years with high and stable salinities permit recruitment of A. rubens in Kiel Fjord. Projected desalination of the Baltic Sea could shift the distribution of A. rubens in the western Baltic Sea north-westwards and may lead to local extinction of a keystone species of the benthic ecosystem.

Capacity for Cellular Osmoregulation Defines Critical Salinity of Marine Invertebrates at Low Salinity

“…However, a closer look at the main organic osmolyte glycine demonstrated stabilizing concentrations at salinities ≤13 (Figure 6). We can, hence, corroborate a low-salinity threshold between salinities of 12 and 13, which was published before (Casties et al, 2015;Schmittmann, 2017).…”

“…Persistent salinity changes can lead to geographic range shifts, vertical distribution shifts and, if relocation is not possible, (local) extinction (Tomanek, 2012). Benthic marine invertebrates are especially affected by environmental salinity changes as they often have limited mobility and larval stages with reduced tolerance to low-salinity (Casties et al, 2015;Nasi et al, 2018).…”

Calcification in a marginal sea – influence of seawater [Ca<sup>2+</sup>] and carbonate chemistry on bivalve shell formation

“…[Ca 2+ ] was calculated for salinity values measured in Kiel Fjord (N = 4250, weekly measurements 2005-2009, 0-18 m; 54 • 19.8 N, 10 • 9.0 E; Clemmesen et al, unpublished data;Casties et al, 2015) and at the Oder Bank (N = 260 000, hourly measurements, 2000-2015, 3 + 12 m water depths; 54 • 4.6 N, 14 • 9.6 E; ∼ 8 km off the M. trossulus-like collection site at Usedom(BSH, 2000(BSH, -2015 …”

The Effects of Salinity and pH on Fertilization, Early Development, and Hatching in the Crown-of-Thorns Seastar

“…An extreme example of salinity tolerance among asteroids is found in populations of the seastar Asteria rubens in brackish waters of the Baltic Sea, where it occurs at salinities from 15 to 35 ppt [65]. In some populations of this species, survival of fertilized eggs to embryos is actually highest at 24 ppt [65] and development to metamorphosis can be completed at salinities as low as 15 ppt [66].…”