Dataset: Coralline algae experiment - algal growth data

Methodology:

Sampling and analytical procedures:

To test the response of the coralline algae Crusticorallina spp. and Bossiella orbigniana to future OA scenarios, we used an 18-aquaria indoor experimental system with flow-through seawater at the Sitka Sound Science Center to simulate three static pHT levels (current summer = 8.0, future summer/current winter = 7.7, future winter = 7.4) under two seasonal light regimes simulated with full-spectrum aquarium lights (AI Prime HD) (summer = PPFD 55μmol m-2 s-1, 13h d-1, winter = PPFD 40μmol m-2 s-1, 6h d-1). We had a total of 3 aquaria for each of the 6 treatment combinations. A full description of the pH control for this system can be found in Kroeker et al. 2021, but in short: pH was regulated using a relay system that controlled mixing of pre-equilibrated low-pH seawater (formed by bubbling pure CO2 gas into seawater: pH6.0) and ambient pH seawater into 9 header buckets (n=3 headers per pH treatment) that then flowed into the experimental aquaria. Each header bucket was equipped with a pH sensor (DuraFET, Honeywell) communicating with a controller (UDA 2152, Honeywell) to regulate flow of the low pH water through solenoid valves to maintain pre-programmed pH setpoints. Experimental pH levels were chosen to reflect current seasonal minimums of coastal pH measured at Harris Is. (57.032N, 135.277W) from 2016-2017, as well as end-of-century projections for Gulf of Alaska pH levels based on RCP 8.5 (-0.3 pHT from current levels). Experimental light regimes were defined using seasonal averages for day length and measured irradiance level at 10m depth at Harris Is.

Within each pH level and light treatment combination, half of the individual Crusticorallina spp. and B. orbigniana were randomly assigned to be paired in close proximity with the fleshy red alga Cryptopleura ruprechtiana (n=6 species treatment-1). All algal individuals were collected on Aug 5, 2017 at Harris Is. Total experimental duration was 45d (Aug 7-Sept 21, 2017).

The effects of each experimental pH and light treatment combination and fleshy red algal association on coralline net calcification rate were assessed using the buoyant weight technique (Jokiel et al. 1978), as well as the alkalinity anomaly technique. To determine total relative change in calcified mass over the experimental period, each coralline algae’s buoyant weight was measured to the nearest 0.0001g at the beginning and end of the experiment on a balanced platform suspended below a microbalance in a temperature-monitored seawater bath. To ensure precision, buoyant weights were repeated for each individual until measurements differed by less than ±0.005g, and then an average was taken of the measurements falling in this range of precision. Initial and final buoyant weights (BW; g) were used to calculate relative net calcification rate (RCRnet; g g-1 d-1) of each individual alga using the equation: RCRnet = (log(BWfinal/BWinitial)*100)/Δt where Δt (d) is the total days elapsed between the beginning and end of the experiment.

Growth rates of C. ruprechtiana reared in association with coralline algae in the different treatment conditions were quantified by measuring tissue wet weights (WW; g) at the beginning and end of the experiment. Thalli were removed from seawater, patted uniformly dry, and immediately weighed on a standard microbalance to the nearest 0.0001g. Relative growth rate (RGRnet; g g-1 d-1) of each individual alga was calculated using the equation: RGRnet = (log(WWfinal/WWinitial)*100)/Δt

where Δt (d) is the total days elapsed between the beginning and end of the experiment.

Problem report:

When processing these data for analysis and publication, we filtered out any individual with a weighing flag (weighing_flag = “y”), and any individuals in Poor condition at the end of the experiment (quality_code = “P”)