Growth and utilization of internal nitrogen reserves by the giant kelp Macrocystis pyrifera in a low-nitrogen environment

An adult giant kelp plant (Macrocystis pyrifera), moved from an inshore kelp forest to an offshore, low-nitrogen environment near Santa Catalina Island, California (USA), maintained growth for 2 wk on internal nitrogen reserves. Frond elongation rates decreased significantly during the third week, and plant growth rate (wet wt) dropped from an initial inshore rate of 3.6 to 0.9% d^-1. During this 3 wk period, nitrogen contents and free amino acid concentrations decreased, while mannitol and dry contents increased in frond tissues. After depletion of internal nitrogen reserves, the nitrogen content of lamina and stipe tissues averaged 1.1 and 0.7% dry wt, respectively. The experimental plant was exposed to higher ambient nitrogen concentrations during the last 2 wk. Rates of frond elongation and plant growth increased, but nitrogen content and amino acids in frond tissues remained low. Of the total nitrogen contained in frond tissue of the plant before transplantation, 58% was used to support growth in the absence of significant external nitrogen supply. Amino acids constituted a small proportion of these internal nitrogen reserves. Net movement of nitrogen occurred within large fronds, but not between different frond size classes. The nitrogen content of holdfast tissue remained relatively constant at 2.4% dry wt and accounted for 18 to 29% of the total nitrogen. Holdfast nitrogen was not used to support growth of nitrogen-depleted fronds. In comparison to Laminaria longicruris, which is adapted to long seasonal periods of low nitrogen availability, M. pyrifera has small nitrogen-storage capacity. However, internal reserves of M. pyrifera appear adequate to make nitrogen starvation uncommon in southern California kelp forests.     

Growth of amputated and dark-exposed individuals of the brown alga Laminaria hyperborea

The seasonal growth of the brown alga Laminaria hyperborea (Gunn.) Foslie, which forms dense forests in the sublittoral zone of Helgoland, a rocky island in the Southern North Sea, was investigated by transplanting specimens of medium size onto PVC or wooden plates fixed to sub-tidal grwoth stations. The 2-year study revealed that, during the season of fast growth (January to June), young plants produce each year a new frond, larger in size than in the preceding year. This observation can be interpreted, in part, by assuming that the growth of the young frond is accomplished not only by its own assimilatory surplus, but also by reserve materials of the old frond assimilated during the preceding season of slow growth. This assumption is supported by experimental evidence: (1) Even in complete darkness Laminaria hyperborea is capable of producing a small new frond during the season of fast growth; (2) New fronds with stipe, but without old frond, grow (during the same period) considerably faster than isolated new fronds separated from the possible sources of reserve materials. Maximum growth occurs in normal plants which possess their old frond until April or May.An abbreviated version of this paper has been presented at the Sixth International Seaweed Symposium, held at Santiago de Compostela, Spain, September 9 to 13, 1968.     

Distribution patterns of meiofauna associated with a sublittoral<Emphasis Type="Italic"> Laminaria</Emphasis> bed in the Cantabrian Sea (north-eastern Atlantic)

This study deals with meiofauna associated with a sublittoral population of the kelp Laminaria ochroleuca located on the northern coast of Spain. By sampling once a year over a 4-year period, we examined patterns of faunal distribution as a function of some environmental factors at the meso-scale level (depth, and exposure to waves and surge). We also examined the relationship between L. ochroleuca abundance (as dry weight biomass and number of plants per sampling quadrat) and abundance and diversity of meiofauna. Finally, we investigated patterns of within-plant distribution (algal frond vs. algal holdfast), using also the meiofauna of the adjacent bottom as a referent to estimate the level of "phytal dependence" of the meiofauna collected on L. ochroleuca. We found that the bulk of permanent meiofauna consisted of nematodes, copepods, mites, polychaetes, tanaids and ostracods, with copepods being predominant on the fronds of the alga and nematodes in the holdfasts. The temporary meiofauna consisted of juvenile amphipods, bivalves and gastropods, together with barnacle nauplii and cyprids. Abundance and major composition of meiofaunal taxa were unrelated to both depth and hydrodynamic exposure of the sampling quadrats. However, we detected significant qualitative and quantitative faunal differences as a function of microhabitat. All meiofaunal groups were more abundant in holdfast samples than in frond and bottom samples. The gross taxonomic composition of meiofauna in bottom samples was similar to that in holdfast samples, but substantially different from that of meiofauna associated with the fronds. The L. ochroleuca holdfasts, in which dense aggregations of meiofauna can occur, appear to function as ecotone between phytal and rocky-bottom microhabitats. All together, our results suggest that the distribution of meiofauna within the Laminaria bed is mostly affected by factors operating at the microhabitat level rather than the meso-scale level.Communicated by L. Hagerman, Helsingør     

A survey of translocation in laminariales (Phaeophyceae)

A survey of translocation of photoassimilates in 13 genera of Laminariales is presented. All showed long-distance transport of ¹⁴C-labeled products from mature source tissue to meristematic sinks (haptera and intercalary growing regions). In plants with several laminae forming one frond, older laminae may provide assimilates for the growth of younger ones, and in Macrocystis spp., where fronds of different ages and developmental stage arise from a common holdfast, mature fronds initiate and support new fronds. Translocation velocities vary from species to species but are in the range of 55 to 570 mm/h. The results strongly support the hypothesis that Laminariales in general have an effective translocation system, on which their thallus growth depends.     

Morphological variation and phenotypic plasticity of buoyancy in the macroalga Turbinaria ornata across a barrier reef

Many aspects of morphology of benthic algae (length, surface area-to-volume ratio, and blade undulation) are plastic traits that vary in response to physical factors (such as light or water flow environment). This study examines whether frond buoyancy is a plastic trait, and whether differences in morphology including buoyancy affect the potential persistence of macroalgae in habitats characterized by different water flow regimes. Fronds of the tropical alga Turbinaria ornata in protected backreef environments in Moorea, French Polynesia possess pneumatocysts (gas-filled floats) and experience positive buoyant forces, whereas fronds in wave-exposed forereef sites either lack pneumatocysts entirely or have very small, rudimentary pneumatocysts and experience negative buoyant forces. Forereef fronds transplanted to the backreef developed pneumatocysts and experienced increased buoyant force indicating that buoyancy is a phenotypically plastic trait in T. ornata. In comparing the potential for dislodgement by drag, drag was greater on forereef fronds at low flow speeds as these fronds were stiffer and did not bend over at low flow speeds and therefore were less streamlined in the flow than backreef algae, which bent easily. The environmental stress factor (ESF) (a measure of the likelihood of detachment for a frond in its habitat) was higher for forereef than backreef fronds at all flow speeds. When examined with respect to the flow velocities likely in their respective habitats however, the chance of detachment for backreef and forereef was similar. Neither backreef nor forereef fronds were predicted to break under normal, non-storm conditions, but both were predicted to break in storms. Strong forereef morphologies are well suited to habitats characterized by rapid flow, whereas the weaker, buoyant, tall backreef fronds are well suited to habitats where crowding and shading is common but hydrodynamic forces are low.     

An annual carbon budget for the kelp Laminaria longicruris

Oxygen evolution and uptake by whole thalli of the large marine alga Laminaria longicruris de la Pylaie were measured for 24 h, once every 2 weeks for a year, using large chambers to incubate the plants on the sea bed. Diel rates of photosynthesis and respiration were calculated from these measurements and continuous light measurements were used to extrapolate the data between observation dates. The resulting estimates were combined with measurements of growth and carbon content to give an annual carbon budget for a typical mature plant. Annual net assimilation was 6.8 mgC per cm² of frond surface (71 cal cm^-2). Approximately 45% of this appeared in the production of new frond tissue, and a further 12% was accounted for by storage of carbon in mature frond tissue. About 8% was needed for stipe growth, and the remaining 35% was assumed to be lost as dissolved organic carbon. Diel net photosynthetic rates reached a maximum in June and July and were negative only in November, indicating an ability to produce a photosynthetic surplus throughout winter. In early winter the plants drew on stored reserves to supplement photosynthesis in providing carbon for growth, but from January onwards photosynthesis provided more than enough carbon for growth.     

Nitrogen supply,tissue composition and frond growth rates for Macrocystis pyrifera off the coast of southern California

Seasonal changes in ambient NO ₃ ^– and NH ₄ ⁺ , tissue composition (N, C, and C/N ratio), and frond growth rates for Macrocystis pyrifera (L.) Agardh were examined. Ambient NO ₃ ^– showed distinct seasonal variations. Frond growth rates were variable, but showed no clear correlation to ambient NO ₃ ^– . The average N content of plant tissue did, however, show the same seasonal variations as ambient NO ₃ ^– . The longitudinal distribution of total tissue N and various components of tissue N along fronds were also analyzed. Several distinct patterns were found: high levels of protein N at growing tips and elevated levels of soluble N in lower parts of the frond. Free amino acids accounted for a major portion of the soluble N, but neither NO ₃ ^– nor NH ₄ ⁺ accumulated in the plant tissue. The longitudinal distribution of N along the fronds is compared to reported variations in C metabolism, and it is concluded that C and N sourcesink relations do not always coincide and bidirectional translocation may occur.     

CO2 fixation and translocation in benthic marine algae. III. Rates and ecological significance of translocation in Laminaria hyperborea and L. saccharina

Translocation of ¹⁴C-labelled assimilates in Laminaria hyperborea and L. saccharina is strictly basipetal within the thallus. The lowermost 20 cm of the frond accumulates 71% (L. hyperborea) or 63% (L. saccharina) of the basipetallymoving translocate after a period of 96 h from initial feeding with NaH¹⁴CO₃. Whereas translocation was found to occur at all seasons in L. saccharina, which grows throughout the year, no translocation of newly synthesized photosynthate occurred in L. hyperborea in October, when no frond enlargement takes place, nor in January, when the new fond occurs as a tiny outgrowth. In L. hyperborea, organic material, assimilated by the old frond during the period of rapid growth, is exported at the rate of 0.5 mg C · dm^-2 · h^-1. In L. saccharina, 14 to 18 cm frond length are necessary for an elongation rate of the growing zone, situated in lowermost 10 cm of the frond, of 1 cm per week. The significance of translocation in the two Laminaria species is demonstrated by comparison of export rates with growth rates measured in situ and in the laboratory.Dedicated to Professor Dr. Otto Stocker on his 85th birthday.     

The ecology of temperate salt-marsh fucoids. II. In situ growth of transplanted Ascophyllum nodosum ecads

Growth, in terms of length, weight, and number of branches and/or dichotomies, in transplanted specimens of Ascophyllum nodosum ecad scorpioides in a temperate salt marsh is described. The ecad scorpioides, when transplanted from its characteristic habitat on the mid-intertidal, Spartina alterniflora-dominated, marsh flats to a location near mean low-water developed characteristics normally associated with A. nodosum ecad mackaii. The growth of these plants was more rapid than those in the mid-intertidal region and was not affected by the shading of algal fronds by S. alterniflora. Unusually high temperatures and light intensities during the winter and spring months were major factors affecting growth in plants that were subjected to relatively long periods of tidal exposure. The presence of S. alterniflora during the summer months may act in a protective capacity for mid-intertidal ecad populations.This research was supported by research grants AG-375 and BO 38018 from the National Science Foundation and, in part, by the State University of New York Research Foundation and the Energy Research and Development Administration (ERDA).     

Feeding and nutritional ecology of the sea urchin strongylocentrotus drobachiensis in Maine,USA

The sea urchin strongylocentrotus drobachiensis exhibited a high degree of food selectivity, whether foods were presented singly or in combination. Foods ranked from most to least preferred were, in summer, Laminaria longicruris, Chondrus crispus, Corallina officinalis, Ascophyllum nodosum, and Agarum cribrosum, whereas in winter A. nodosum and A. cribrosum exchanged ranks. Food preference was not correlated with caloric content but, because of higher feeding rates on preferred foods, caloric intake was positively correlated with preference. Similarly, food absorption rankings were not correlated with food preference, with the exception of gravimetric efficiencies in winter. However, the absorption of L. longicruris, the most preferred alga, was highest in all measurements. Growth and reproductive development of S. drobachiensis on single species diets were positively correlated with food preference. Highest values occurred with animals fed L. longicruris. Urchins transferred from non-preferred to preferred diets showed increased somatic and reproductive growth compared to control animals on the original, non-preferred diets. Conversely, when transferred from preferred to non-preferred diets, urchins showed reduced growth compared to controls. No combination diet tested supported significantly better gonadal growth than L. longicruris: 25% C. crispus supported slightly better somatic growth than L. longicruris alone. These data support the view that S. drobachiensis has evolved a feeding strategy resulting in the maximization of growth and reproduction.     

Optimal growth and maximal survival temperatures of Atlantic Laminaria species (Phaeophyta) in culture

The effects of temperature on growth rate of rapidly-growing cultured macrosporophytes of 9 isolates of Atlantic Laminaria comprising 4 species have been investigated. No significant population variation was observed within species despite wide variations in temperature between the original collecting sites. L. saccharina showed a broad temperature optimum in the 10°–15°C range, whereas L. longicruris had a sharp optimum at 10°C. L. digitata and L. hyperborea grew more slowly, with only slightly sub-optimal growth over a wide temperature range, but with peaks at 10°C (L. digitata) and 15°C (L. hyperborea). The maximum survival temperatures of individual male and female vegetatively-growing gametophytes were ascertained for these species plus the Arctic L. solidungula, and were as follows: L. saccharina and L. longicruris, 23°C; L. digitata (male), 23°C; L. digitata (female), 22°C; L. hyperborea, 21°C; L. solidungula, 18°C. The lack of within-species differences demonstrates that the success of the genus in areas with different temperature regimes is brought about by phenotypic plasticity of individuals rather than the selection of temperature races or ecotypes.     

Growth and production of the red alga Gelidium sesquipedale off the Basque coast (northern Spain)

Several aspects of the growth of the agarophyte Gelidium sesquipedale Clemente (Thuret) were studied in sublittoral populations of the Basque coast (northern Spain) from 1981 to 1986. The standing stock of the populations varied greatly with season. During two consecutive years, 60 to 70% of summer biomass had been lost by the end of the unfavourable period of year to growth (autumn and winter). The decline in biomass was mainly due to partial losses of branches, with more branches being lost from larger fronds. Yearly variations in the standing stock were also recorded. Production estimates obtained by a destructive sampling method were not satisfactory because of the spatial heterogeneity of the populations at the three locations studied. Indirect estimation of production by measuring the growth of marked fronds in a control quadrat gave more reliable estimates. Production values of 622±124, 735±147 and 615±123 g dry wt m^-2 yr^-1 were obtained at the three locations, respectively. Frond elongation rates of 7.5, 6.1, 7.5 and 7.9 cm yr^-1, respectively, were recorded during four consecutive years. In winter elongation rates of fronds were rather low. Elongation did not seem to be affected by frond length, the self-shading effect of the canopy, or changes in depth. Cuts resulting from grazing were frequent on fronds through the year, decreasing significantly with increasing depth. Sheared fronds regenerated promptly, independent of season or height at which the cut was made. For commercial purposes the best season for harvesting is summer, which is the period of maximum standing stock, infertility, and calm warm waters that provide easier working conditions for divers.     

Seasonal growth of the giant kelp Macrocystis pyrifera in New Zealand

The seasonal growth pattern of Macrocystis pyrifera (L.) C. Agardh in New Zealand was determined from measurements of blade-elongation rates between March 1986 and December 1987. Growth rates remained relatively constant throughout most of the year, but declined significantly during the summer months. Seawater nitrate levels had a marked seasonal cycle, with concentrations of 0.3 μM detected in summer. The timing of the decline in internal nitrogen concentrations varied for different-aged blades, but occurred ∼1 mo after the decrease in seawater nitrate concentrations. Sufficiently high irradiance levels and seawater nutrient concentrations support active growth for most of the year, but growth is nutrient-limited during summer. No carbon accumulation during summer was observed. Between March and August 1988, growth estimates were also derived from node-initiation rates and stipe-elongation rates to permit comparisons with previous studies from the northern and southern hemispheres. Direct comparisons of the three growth parameters determined for non-terminated canopy and sub-surface fronds were used to assess possible differential resource allocation in the two frond classes. Received: 16 May 1997 / Accepted: 28 May 1997     

Relationship between seasonal growth,photosynthetic production and apex mortality of Caulerpa paspaloides (Chlorophyceae)

Seasonal changes in rates of rhizome elongation, frond initiation, photosynthesis, respiration, starch content and mortality of rhizome apices were measured for a population of Caulerpa paspaloides (Bory) Greville located off Key Largo, Florida, USA. Maximal growth rates occur during spring and coincide with high photosynthetic production and low mortality of rhizome apices. A secondary period of rapid growth occurs during fall; however, rates are less than during spring. Minimal growth rates occur during winter and summer. Reduced growth during winter coincides with (1) low photosynthetic rates, (2) low photosynthesis: respiration ratios, and (3) reduced frond biomass, indicating that photosynthetic production is limiting. Reserve carbohydrate (starch) is apparently utilized to maintain vegetative growth during the winter. Increased mortality of rhizome apices is responsible for most of the reduction in growth during summer and fall.     

Temporal and spatial variation in the density of mobile epifauna and grazing damage on the seaweed<Emphasis Type="Italic"> Ascophyllum nodosum</Emphasis>

The temporal and multiple-scale spatial variation in the density of mobile epifauna and grazing damage was investigated in populations of the brown seaweed Ascophyllum nodosum (Fucales: Phaeophyta). The relationship between density of grazers and grazing marks was also analyzed. The study was carried out in two locations of the northeastern Atlantic: one at the Isle of Man, in the Irish Sea, and the other at Tjärnö, on the Swedish west coast. Furthermore, the effect of grazing marks on the probability of frond breakage was evaluated in a 1-year experiment carried out on the Isle of Man. High temporal and small-scale spatial variability was recorded in the density of mobile epifauna. A high percentage of species were herbivores, i.e. mesograzers. Adult plants of A. nodosum have several primary vegetative fronds with apical growth. Grazing marks were commonly found along the fronds. Similar levels of grazing damage were detected at the two locations, despite the observed qualitative differences in the grazing assemblages. Small-scale spatial variability in grazing marks was important, with differences in the density of grazing wounds among plants, fronds, and even within fronds. A significant correlation between the proportion of grazed apices and the density of the isopod Idotea spp. and grazing amphipods considered together was detected. This probably reflects the simultaneous feeding activity of these two groups of grazers and suggests the presence of feeding facilitation mechanisms between them. Grazing marks were concentrated in the apical part of the shoots. The results of this study also showed that grazing damage increased the probability of breakage, especially of shorter fronds. This suggests that grazing damage affects the demography of shoots and plants, increasing the transition probabilities to smaller sizes. The presence of interactive effects between grazing and plant density in these A. nodosum populations of northeastern Atlantic shores was also discussed on the basis of the results of this and a previous study.     

Ecological energetics of the seaweed zone in a marine bay on the Atlantic coast of Canada. I. Zonation and biomass of seaweeds

An intertidal and underwater survey of the zonation of seaweed in St. Margaret's Bay, NovaScotia, Canada showed 8 major zones as one proceeded away from shore: (1) Fucus and Ascophyllum; (2) Chorda with filamentous browns; (3) Chondrus crispus; (4) Zostera marina; (5) Laminaria digitata with L. longicrusis; (6) Laminaria longicruris; (7) L. longicruris with Agarum cribrosum; (8) Agarum cribrosum with Ptilota serrata. Zostera occurred at the same level as O. crispus but replaced it in sheltered water. Ascophyllum was more abundant in sheltered water. L. digitata was confined to the more exposed, steeper shore. The average horizontal extent of the seaweed zone was 369 m, and the greatest depth of significant amounts of seaweed 20 to 30 m. Laminaria longicruris contributed 36% of the total biomass, and Laminaria spp. and Agarum together constituted 83%, while intertidal seaweeds contributed less than 10% of the biomass. The estimated average total biomass per m of shore line was 1,481 kg fresh weight, 326 kg dry weight, 98 kg carbon, or 980x10³ kcal. When averaged over the whole area of the bay, the corresponding figures were 1.38 kg/m² fresh weight, 0.30 kg/m² dry weight, 91 g/m² carbon or 912 kcal/m². Dry matter of Laminaria was 15 to 27% of fresh weight in blades, 10 to 12% in stipes. The dry matter content of blades was least in spring and highest in autumn, but carbon content and calorific value of dry matter showed little difference with species or season.Contribution to the International Biological Programme CCIBP 108.Bedford Institute Contribution BI 249.     

Morphological variations of Macrocystis pyrifera in the Falkland Islands in relation to environment and season

Some morphological characteristics of the giant kelp Macrocystis pyrifera in the Falkland Islands were studied from December 1985 until March 1987 in a shallow and relatively sheltered coastal zone and from December 1985 until January 1987 in a deeper offshore field exposed to swells. Seasonal fluctuations in lamina wet weight, density and form as well as pneumatocyst wet weight form and stipe density (i.e., wet weight per unit length) paralleled fluctuations in frond wet weight. Morphological differences between canopies of the giant kelp in the coastal zone and the offshore bed were probably mainly due to differences in water movement and depth between the two sites. Laminae and pneumatocysts of submersed-frond sites had different shapes than those of canopy-forming portions of fronds at the same sites, and their internodes were longer.     

Isolation of cellulolytic microbes from the intestinal tract of the pinfish,Lagodon rhomboides: size-related changes in diet and microbial abundance

Pinfish, Lagodon rhomboides (Linneaus), undergo a gradual ontogenetic dietary shift during their first year of life, marked by an increase in the consumption of plant material. To determine if this shift in diet was associated with a change in the microbial flora of the intestinal tract that may assist in degradation of plant material, stomach contents were analyzed and microbes in the intestinal tract were isolated from fish ranging from 20 to 139 mm standard length. These fish were collected from Core Sound, North Carolina, USA between March and September 1991. Plant material increased from 16% of dry weight of stomach contents in pinfish under 40 mm standard length (SL) to 65% in pinfish above 120 mm SL, confirming previous observations of a diet-related ontogenetic change in L. rhomboides. Comparison of the total cultivatable facultative and anaerobic microbial flora isolated from the intestinal tract contents of pinfish ranging in size from 26 to 139 mm SL showed a 10-fold increase between fish <40 and fish >40 mm SL, with maximum population densities of approximately 2x10⁷ colony forming units (CFU) g^-1 of intestine including contents. The percentage of microbial isolates examined capable of hydrolyzing carboxymethylcellulose (CMC) increased from 12% in fish <40 mm SL to 13 to 50% in fish >40 mm SL, although there was no strict increase with increasing fish size classes. Although the percentage of CMC-hydrolytic microbial isolates varied with respect to fish SL, the percentage of skim-milk hydrolytic (proteolytic) isolates remained relatively constant (4% of total isolates) irrespective of fish SL and dietary composition. Results presented in this study document the first isolation of carboxymethylcellulase producing microbes from the intestinal tract of any fish and demonstrate that the ontogenetic dietary shift in L. rhomboides is paralleled by qualitative and quantitative changes in the intestinal microbial community. The use of strict anaerobic sampling methods in the preparation of intestinal contents from wild-captured fresh specimens was essential in obtaining these isolates.     

Bacterial flora from echinoderm guts and associated sediment in the abyssal Vema Fault

Individuals of the asteroid Solaster sp. and the holothurian Pseudostichopus villosus (Theel) were collected from deep-sea bottom of the Vema fault in the mid-Atlantic ridge during the BIOVEMA cruise (November, 1977) of the R.V. Jean Charcot. Heterotrophic aerobic bacteria of the guts were isolated, identified and compared with bacterial isolates from surface sediment of the same area. Bacterial population structures displayed a predominance of Gram-negative rods in the echinoderm guts and a predominance of Gram-positive bacteria (particularly cocci) in the surface sediment. Investigation of the metabolic potentialities of the isolates suggested that the microflora of echinoderms, and in particular of the Asteroidea, have more specialized orientations in the catabolism of organic compounds. Single-linkage cluster analysis of all the isolates (130 strains) based on 139 phenotypic features revealed that out of 15 identified clusters, only one included both enteric and sediment isolates. The bacteria in this cluster were similar to the genus Micrococcus.     

Two different proteases produced by a deep-sea psychrotrophic bacterial strain,<Emphasis Type="Italic"> Pseudoaltermonas</Emphasis> sp. SM9913

A psychrotrophic bacterial strain, Pseudoaltermonas sp. SM9913, was isolated from deep-sea sediment collected at 1,855 m depth. Two proteases produced by Pseudoaltermonas sp. SM9913 were purified, MPC-01 and MCP-02. MCP-01 is a serine protease with a molecular weight of 60.7 kDa. It is cold-adapted with an optimum temperature of 30–35°C. Its K_m and E_a for the hydrolysis of casein were 0.18% and 39.1 kJ mol^–1, respectively. It had low thermostability, and its activity was reduced by 73% after incubation at 40°C for 10 min. MCP-02 is a mesophilic metalloprotease with a molecular weight of 36 kDa. Its optimum temperature for the hydrolysis of casein was 50–55°C. The K_m and E_a of MCP-02 for the hydrolysis of casein were 0.36% and 59.3 kJ mol^–1, respectively. MCP-02 had high thermostability, and its activity was reduced by only 30.5% after incubation at 60°C for 10 min. At low temperatures, Pseudoaltermonas sp. SM9913 mainly produced the psychrophilic protease MCP-01.Communicated by O. Kinne, Oldendorf/Luhe