Fucus distichus L. and related species in the British Isles in relation to sea temperature change

Abstract

Seawater temperature rise may have adverse effects on Fucus species in the British Isles with changes in distribution, abundance or loss of northern species. The use of the F. distichus complex as an indicator of sea temperature rise is investigated. Plants were cultured at 5, 10 and 15ºC to investigate the temperature tolerances in both juvenile and adult life stages of various Fucus species and taxa from different geographic locations. Head, rhizoid and total length of germlings were measured. Surface area, wet (fresh) weight, photosynthesis and respiration measurements were taken for apical tips of adult plants. Extra growth, regeneration and formation of receptacles was noted. Phenotypic variations between populations of the subspecies anceps from Scotland and Ireland were examined. Germlings of Orkney species F. distichus subsp. anceps, F. serratus, F. spiralis and F. vesiculosus grew best at 15ºC; F. vesiculosus var. linearis initially best at 15ºC, changing thereafter to 10ºC; F. spiralis f. nanus grew best at 5ºC. F. distichus subsp. anceps from Ireland grew best at 10ºC. In Orkney adult plants optimum temperature for growth was 15ºC for anceps and serratus, 10ºC and 15ºC for spiralis, vesiculosus, nanus and linearis. In Ireland populations, adult plants of anceps and linearis showed a similar response to temperature with no optimum temperature preference for growth. F. distichus subsp. edentatus from Moray Firth grew best at 5ºC. No temperature preference was noted for edentatus from Shetland. In serratus, spiralis and vesiculosus from South Queensferry, Firth of Forth, only spiralis showed a temperature preference, at 10ºC. Formation of receptacles, new growth and regeneration was present on apical tips of Orkney anceps cultivated at 5ºC. Reproductive tips were noted at temperatures of 5, 10, 15ºC in Ireland anceps. Key findings were: The effects of different temperatures on growth rates of head, rhizoid or both and total length varied between Fucus species and within species. Ecophysiological preferences may be different between the geographically different populations of anceps and linearis from Orkney and Ireland. Populations of anceps from Scotland and Ireland showed no evidence of two discrete phenotypic entities. However differences were seen with respect to size and form and aspects of reproduction with smaller oogonia in anceps from Ireland. The use of the subsp. anceps from Ireland as an indicator of climate change and sea temperature rise in the British Isles seems appropriate. In Britain, increased sea temperatures may not directly determine the distribution of the subsp. edentatus, distribution possibly determined by nutrient enrichment in seawater and/or daylength. There is little evidence to suggest that sea temperature rise and climate change will have any immediate effect on the distribution of the other Fucus species investigated.