Influence of phytoplankton concentration and wave exposure on the ecophysiology of Mytilus californianus

Abstract

ABSTRACT:The relationship between nearshore food availability and physiological state of the suspension-feeding mussel Mytilus californianus was examined along a wave-exposure gradient at 2 rocky intert~dal sites on the Oregon coast, USA. differing in nearshore concentrations of phytoplankton. The RNA:DNA ratio (an indirect measure of protein synthetic capacity) of adductor muscle was used as an indicator of dietary status and growth. The activities of 2 metabolic enzymes, citrate synthase (CS) and malate dehydrogenase (MDH), were measured for gill (CS) and adductor (MDH) as indicators of metabolic activity. Mussels were sampled at wave-exposed and wave-protected areas at Strawberry Hill (SH), a site with relatively high phytoplankton concentrations, and Boiler Bay (BB), a site with relatively low phytoplankton concentrations. Individuals at wave-exposed areas at both SH and BB had higher RNA:DNA ratios in spring and summer than those at wave-protected areas. RNA:DNA ratios in spring and summer were higher at SH than at BB, and these differences were especially pronounced following coastal upwelling events Increases in RNA:DNA ratio dunng phytoplankton blooms after upwelling suggest that mussels respond rapldly to short-term changes in nearshore oceanographic conditions. Both CS and MDH activities were higher at SH than at BB many times throughout the year. suggesting metabolic activity was higher overall for SH mussels. Reciprocal transplant experiments were performed to evaluate the degree of physiological plasticity in relation to site-and exposurerelated factors (e.g. phytoplankton concentration, heat and/or desiccation stress, wave forces). Between-site transplants were done between wave-exposed areas at SH and BB; within-site transplants were done between areas of different wave-exposure at each of the 2 sites. RNA:DNA ratios of transplanted mussels converged on those of the site or area to which they were transplanted, suggesting that mussel physiology is h~ghly plastic in response to site and area-related variations in environmental factors. The strong apparent response of mussels to variations in phytoplankton concentration suggests that physiological indices may b e useful tools in assessing the magnitude of 'bottom-up' effects in rocky intertidal communities.

Local‐ and regional‐scale effects of wave exposure, thermal stress, and absolute versus effective shore level on patterns of intertidal zonation

“…At the upper limits of these two species, average ESL was the least spatially variable environmental correlate that we measured. Emersion time may set upper limits of invertebrates via a complex interaction with temperature and/or desiccation (see, e.g., Dahlhoff and Menge 1996;Dahlhoff et al 2001). Desiccation stress, however, is modified by patterns and timing of thermal conditions, and there is little evidence that degree hours above a physiologically relevant threshold temperature exhibit any relationship with the position of the upper limit of mussels or barnacles on Tatoosh.…”

“…The upper limits of barnacles have been attributed to a variety of abiotic factors, including temperature and desiccation (Foster 1971a,b;Raimondi 1988). Additional factors related to the duration of emersion, including food availability (Dahlhoff and Menge 1996;Roberts et al 1997;Dahlhoff et al 2001) and hypoxia (Shick et al 1986) may also operate to set the upper limits of intertidal invertebrates at any given site.…”

“…Thus, although ESL explains most of the local-scale variation in zonation at a cool site, other factors (temperature, desiccation) likely become important as spatial scale increases to incorporate warmer sites. Our results emphasize that an understanding of where and when specific ecological factors are limiting is crucial for our ability to explain and predict large-scale biological patterns in space and time.Recent advances in physiology, ecology, and biological oceanography have considerably improved our understanding of the environmental factors that generate and maintain biological pattern in the marine environment (Bertness et al 2001;Dahlhoff et al 2001; Helmuth and Hofmann 2001). Emerging from this recent work is the realization that the importance of any given environmental driver may vary tremendously through space and time (e.g., Bertness and Ewanchuk 2002).…”

“…Recent advances in physiology, ecology, and biological oceanography have considerably improved our understanding of the environmental factors that generate and maintain biological pattern in the marine environment (Bertness et al 2001;Dahlhoff et al 2001;Helmuth and Hofmann 2001). Emerging from this recent work is the realization that the importance of any given environmental driver may vary tremendously through space and time (e.g., Bertness and Ewanchuk 2002).…”

Relating nucleic acid and protein indices to growth in Mysis relicta: ration, cycling temperature, and metabolism

“…Physiological correlates of growth, such as enzyme activity, lipid level and nucleic acid concentration or ratios (Clarke & Walsh 1993, Houlihan et al 1993, Bergeron 1997) may provide an alternate means of detecting changes. We chose to study nucleic acids because they are closely linked to the production of body mass and appear to change at a time frame of interest for studying species interactions (Foster 1990, Schlechtriem et al 2008 Growth rate and protein synthesis rates are often correlated with RNA content, or ratios of RNA:DNA and RNA:protein in both vertebrates and invertebrates (Buckley 1979, Houlihan et al 1993, Dahlhoff & Menge 1996, Bergeron 1997, Saiz et al 1998, Wagner et al 2001. While ribosomes, which are composed largely of ribosomal RNA (rRNA), set the upper capacity for protein synthesis, the actual rate will vary with translational efficiency depending on short-term needs (Millward et al 1973, Preedy et al 1988.…”