ABSTRACT
The effects of temperature and pH on haemocyanin oxygen-binding were compared for three species of diurnally vertically migrating and two species of non-migrating, pelagic oplophorid shrimps from the deep sea off the Hawaiian island of Oahu. The effects of L-lactate were also measured for three of these species. Haemocyanin concentrations were higher in the haemolymphs of oplophorids that migrate vertically (39.4, 46.8 and 57.6 mg ml−1) than in those of non-migrators (26.0 and 36.4 mg ml−1). Moderately high Bohr effects were found for vertically migrating and non-migrating oplophorids at all temperatures examined (5−25°C, ϕ= −0.46 to −0.80, and −0.55 to −0.88, respectively). The vertically migrating species had temperature-sensitive haemocyanins (ΔH=−23.1 to −41.2 kJ mol−1) across the normal temperature range (5–25 °C) encountered during diurnal vertical migration. This results in haemocyanins that have relatively high affinities (P50=0.80–1.06 kPa at pH 7.8,5 °C) at the low temperatures and low O2 partial pressures (approximately 2.66kPa O2 at 5°C) found at depth, and low affinities (P50=4.00–4.66kPa at pH 7.5, 25°C) at the higher temperatures and higher O2 partial pressures (approximately 13.33–17.50 kPa at 25°C) found in the near-surface waters. In contrast, the non-migrating species, which live within a narrower temperature range (3–6°C) and at a constant, low partial pressure of O2 (2.66–4.00 kPa), have haemocyanins with a high affinity for oxygen (P50=0.67–0.93 kPa at pH 7.8, 5°C) and lower sensitivity to temperature (ΔH−4.2 to −21.6kJ mol−1). The effects of temperature on the haemocyanin oxygen-affinities of the vertical migrators appear to be highly adaptive, enabling these haemocyanins to be functional across the entire depth (and thus, temperature and oxygen partial pressure) range encountered.
