The seasonal biology of the brachiopod Liothyrella neozelanica (Thomson, 1918) from Doubtful Sound, New Zealand.

Abstract

Liothyrella neozelanica (Thomson 1918) (Subphylum: Rhynchonelliformea) is a temperate brachiopod that makes up ecologically important habitat in Doubtful Sound, New Zealand. From December 2010 to December 2011, the seasonal metabolism, seasonal biochemistry, reproductive cycle and annual growth of L. neozelanica were investigated. Findings enabled direct biological knowledge of a temperate New Zealand brachiopod, providing insight into how the genus Liothyrella has adapted to both temperate and polar environments. Furthermore, the findings enabled insight into how increasing sea temperatures at mid and high latitudes may affect brachiopods belonging to the genus Liothyrella over the next century, as a result of climate change. Seasonal ambient respiration rates of L. neozelanica ranged between 243.5 and 560 µg(O2) g-¹(AFDM) hr-¹ suggesting L. neozelanica actively adjusts its metabolism to changing surrounding environmental conditions. L. neozelanica showed evidence of thermal compensation to seasonal changes in ambient sea temperature and displayed a broad thermal tolerance; aerobically respiring at temperatures 5°C above the maximum ambient sea temperature in Doubtful Sound (18°C). Soluble protein was the major energy substrate utilised within the internal tissues of L. neozelanica; however lipid was found to occur in high levels within the gonads (46% gonad AFDM) suggesting it is stored during reproductive development. Gametogenic observations suggest that L. neozelanica spawns between July and September, although the occurrence of mature oocytes within female gonads throughout an annual period suggests L. neozelanica may undergo multiple spawning events annually. Spawning is likely cued to photoperiod and primary productivity. Growth by L. neozelanica was found to be highest in juveniles (8.4 - 8.9 mm yr-1). The absence of high numbers of juvenile L. neozelanica (< 10 mm length) in a population size-frequency distribution, suggests juvenile L. neozelanica may require a size-refuge to avoid early mortality. Annual growth cohorts suggest recruitment takes place annually. Biological comparisons between L. neozelanica and the Antarctic brachiopod Liothyrella uva (Broderip 1833) revealed L. neozelanica to have metabolic rates (89 – 110 µg(O2) g-¹(AFDM) hr-¹) 1.9 to 2.9 times higher than those exhibited by L. uva (38 – 46 µg(O2) g-¹(AFDM) hr-¹) after a Q10 correction was applied. Biochemical comparisons revealed both species utilise protein, carbohydrate and lipid in similar ways suggesting this may be a historic link between the two brachiopods. Both species showed evidence of spawning in spring which may occur to coincide with increasing sea temperatures and primary productivity. Growth comparisons revealed L. neozelanica to grow 3 to 5 times faster than L. uva despite reaching similar maximal sizes (S∞(mm length) = 52.5 (L. neozelanica); 47.2 – 54.1 (L. uva)). L. uva was found to have a greater life-span compared to L. neozelanica (30 + years (L. neozelanica); 46 – 71 years (L. uva)). Based on the findings in this study it is suggested that L. neozelanica will be largely unaffected by warming sea temperatures resulting from climate change over the next century. In contrast, evidence suggests L. neozelanica’s polar sister species Liothyrella uva may face physiological (metabolism) and biological (growth and energetics) difficulties as sea temperatures increase.