Interpopulational differences in the nutritional condition of Aequiyoldia eightsii (Protobranchia: Nuculanidae) from the Western Antarctic Peninsula during austral summer

Abstract

The Western Antarctic Peninsula (WAP) is a hotspot for environmental change and has a strong environmental gradient from North to South. Here, for the first time we used adult individuals of the bivalve Aequiyoldia eightsii to evaluate large-scale spatial variation in the biochemical composition (measured as lipid, protein and fatty acids) and energy content, as a proxy for nutritional condition, of three populations along the WAP: O'Higgins Research Station in the north (63.3°S), Yelcho Research Station in mid-WAP (64.9°S) and Rothera Research Station further south (67.6°S). The results reveal significantly higher quantities of lipids (L), proteins (P), energy (E) and total fatty acids (FA) in the northern population (O'Higgins) (L: 8.33 ± 1.32%; P: 22.34 ± 3.16%; E: 171.53 ± 17.70 Joules; FA: 16.33 ± 0.98 mg g) than in the mid-WAP population (Yelcho) (L: 6.23 ± 0.84%; P: 18.63 ± 1.17%; E: 136.67 ± 7.08 Joules; FA: 10.93 ± 0.63 mg g) and southern population (Rothera) (L: 4.60 ± 0.51%; P: 13.11 ± 0.98%; E: 98.37 ± 5.67 Joules; FA: 7.58 ± 0.48 mg g). We hypothesize these differences in the nutritional condition could be related to a number of biological and environmental characteristics. Our results can be interpreted as a consequence of differences in phenology at each location; differences in somatic and gametogenic growth rhythms. Contrasting environmental conditions throughout the WAP such as seawater temperature, quantity and quality of food from both planktonic and sediment sources, likely have an effect on the metabolism and nutritional intake of this species.

Keywords: Bivalve; Fatty acid; Infaunal; Invertebrate; Physiology.

Figure 1. Map of the A. eightsii sampling along the Western Antarctic Peninsula (WAP). Filled circles indicate the northern, middle, and southern WAP sampling localities: O’Higgins Base (OB), Yelcho (Ye) and Rothera (Ro), respectively.

Dashed arrows represent Southern Ocean currents, modified from Moffat & Meredith (2018): Antarctic Circumpolar Current (ACC), Antarctic Peninsula Coastal Current (APCC), Coastal Current (CC).

Figure 2. Jitter boxplot of (A) shell length (mm ind.⁻¹) and (B) tissue dry mass (mg ind.⁻¹) of adult individuals of A. eightsii collected from three different localities of the Western Antarctic Peninsula.

Different letters on box indicate significant differences among sites after a multiple range test with a Bonferroni correction. In the boxplot, the horizontal end of the box nearer to zero represents the 25th percentile and the horizontal end of the box more distant from zero represents the 75th percentile. The horizontal black line within the box indicates the median and the red line within the box indicates the mean. Whiskers above and below the box represent 1.5 times the interquartile range from the box, respectively. Black circles above and below the whiskers are outliers (n = 58).

Figure 3. Jitter boxplot of (A) lipid content (mg 20 mg⁻¹), (B) lipid content (% DM), (C) protein content (mg 20 mg⁻¹), (D) protein content (% DM) of adult individuals of A. eightsii collected from three different localities of the Western Antarctic Peninsula.

Different letters on box indicate significant differences among sites after a multiple range test with a Bonferroni correction. In the boxplot, the horizontal end of the box nearer to zero represents the 25th percentile and the horizontal end of the box more distant from zero represents the 75th percentile. The horizontal black line within the box indicates the median and the red line within the box indicates the mean. Whiskers above and below the box represent 1.5 times the interquartile range from the box, respectively. Black circles above and below the whiskers are outliers (n = 58).

Figure 4. Jitter boxplot of the energy content (J 20 mg⁻¹) of adult individuals of A. eightsii collected from three different localities of the Western Antarctic Peninsula.

Different letters on box indicate significant differences among sites after a multiple range test with a Bonferroni correction. In the boxplot, the horizontal end of the box nearer to zero represents the 25th percentile and the horizontal end of the box more distant from zero represents the 75th percentile. The horizontal black line within the box indicates the median and the red line within the box indicates the mean. Whiskers above and below the box represent 1.5 times the interquartile range from the box, respectively. Black circles above and below the whiskers are outliers (n = 58).

Figure 5. Principal component analysis (PCA) plot based on Bray–Curtis similarity of fatty acid data of adult individuals of A. eightsii collected from three different localities of the Western Antarctic Peninsula.

Variables (fatty acids) are indicated in the vector plot according to Pearson correlation (>0.9). PC1 axis explained 62.4% and PC2 explained 19.2% of the fatty acid profile between individuals from different localities.