Temperature and salinity shape the distribution and genetic structure of marine communities. Future warming and freshening will exert an additional stress to coastal marine systems. The extent to which organisms respond to these shifts will, however, be mediated by the tolerances of all life-stages and populations of species and their potential to adapt. We investigated nauplius and cypris larvae of the barnacle Balanus (Amphibalanus) improvisus from the Swedish west coast with respect to temperature (12, 20, and 28 °C) and salinity (5, 15, and 30) tolerances. Warming accelerated larval development and increased overall survival and subsequent settlement success. Nauplii developed and metamorphosed best at intermediate salinity. This was also observed in cypris larvae when the preceding nauplii stages had been reared at a salinity of 30. Direct comparisons of the present findings with those on a population from the more brackish Baltic Sea demonstrate contrasting patterns. We conclude that i) B. improvisus larvae within the Baltic region will be favoured by near-future seawater warming and freshening, that ii) salinity tolerances of larvae from the two different populations reflect salinities in their native habitats, but are nonetheless suboptimal and that iii) this species is generally highly plastic with regard to salinity.

Experiments were conducted at the Sven Lovén Centre for Marine Sciences - Tjärnö, Sweden (58°52.5'N, 11°08.1'E), in October 2009. Field temperature and salinity were obtained from measurements at 1 m depth monthly from 2009 to 2013 and daily from August to October 2011. Newly hatched barnacle nauplii were obtained from routine cultures of broodstock barnacles. Broodstock (several hundred adult B. improvisus) were collected in the late August 2009, held in filtered seawater at ~ 25 °C and salinities of ~ 30 (salinity was measured using the Practical Salinity Scale) in flow-through seawater, and fed ad libitum with freshly hatched Artemia salina occasionally supplemented with diatom algae (Chaetoceros calcitrans, Skeletonema marinoi and Thalassiosira pseudonana). Lab conditions were aimed to be a continuation of the field conditions at the time of collection, thus, prolonging summer conditions when barnacles reproduce best. This is done to obtain all year-round availability of nauplii and cyprids, feeding research for well over a decade. Barnacle nauplii were collected on sieves (60 µm mesh) from the seawater outflows of the broodstock tanks. Newly released nauplii were at stage I but developed to stage II within a few hours. Batches of stage-II larvae from different subsets of multiple parents were used for each of two experiments. Our experimental design followed that of Nasrolahi et al. 2012 33. Briefly, three different temperature (12, 20, 28 °C) and salinity (5, 15, 30; salinity is presented using the Practical Salinity Scale) treatments were applied to barnacle larvae in a fully crossed experimental design using replicate six-well plates (CELL STAR #657160). Temperatures were controlled using thermostatted water baths. Different salinities were obtained by diluting filtered (0.2 µm) seawater (salinity of ~ 30) with de-ionized water. Target temperatures were maintained at ± 0.5 °C (YSI30 Multimeter, Brannum Lane, USA). Each treatment combination was replicated six (Experiment I) or eight (Experiment II) times. To control for "room effects", the positions of the six-well plates in the water baths were randomly re-distributed every day.

Supplement to: Nasrolahi, Ali; Havenhand, Jonathan N; Wrange, Anna-Lisa; Pansch, Christian (2016): Population and life-stage specific sensitivities to temperature and salinity stress in barnacles. Scientific Reports, 6, 32263