William B. Stickle

Metabolic Adaptations of Several Species of Crustaceans and Molluscs to Hypoxia: Tolerance and Microcalorimetric Studies

Although some species of fish, crustaceans, and molluscs may behaviorally avoid hypoxic masses of small size and limited duration, others cannot. In a series of crustaceans, tolerance of hypoxia over 28 days at 30°C, decreases as follows: Eurypanopeus depressus (38 Torr = LC50)> Pa!aemonetespugio > Rhithropanopeus harrisii > Penaeus aztecus > Caiinectes sapidus (121 Torr = LC50).Caiinectes sapidus and E. depressus die during 12-hexposure to anoxia and their heat dissipation rates (quantified by microcalorimetry) are depressed in seawater at 25%air saturation (normoxia) to only 32 and 47% of their metabolic rate at normoxia. In contrast, starved Crassostrea virginica and Thais haemastoma are anoxia tolerant; their metabolic rates are depressed un der anoxia to 75%and 9%ofthe normoxic rate. Hypoxia tolerance is greater at 20°C than at 30°C for Penaeus az tecus and Crassostrea virginica, but no temperature effect on tolerance exists for Caiinectes sapidus. Hyp oxia tolerance varies inversely with salinity for Penaeus aztecus at 20° and 30°C and for Caiinectes sapidus at 30°C, but it varies directly with salinity at 20°C in Caii nectes sapidus. Greater depression of metabolic rate oc curs in molluscs during anoxia exposure (and is corre batedwith greater hypoxia tolerance) than occurs in Cal !inectes sapidus and Penaeus aztecus, which are not anoxia tolerant. Heavy mortality probably occurs in young Caiinectes sapidus and Penaeus aztecus and in

Effects of salinity gradients on the tolerance and bioenergetics of juvenile blue crabs (Callinectes sapidus) from waters of different environmental salinities

Juvenile Callinectes sapidus Rathbun were collected from brackish and hypersaline coastal environments in August 1986 and July 1987, respectively. The brackish collection site was a salt-marsh near Grand Isle, Louisiana (USA), and the hypersaline site was in the barrier island system on the north end of the Laguna Madre near Corpus Christi, Texas (USA). On the dates of collection, salinities fluctuated daily between 20 and 30‰ S and between 30 and 45‰ S at the brackish and hypersaline collection sites, respectively. The high-salinity 21 d LC50 (50% mortality) was 56.0 for brackish-water individuals and 66.5‰ S for hypersaline individuals. The brackish-water individuals survived 0‰ S. The lowsalinity 21 d LC50 was 0.5‰ S for the hypersaline individuals. Respiration and excretion comprised a small portion of the energy budget and did not vary with salinity for individuals from brackish water. However, both respiration and excretion increased with decreasing salinity in individuals from the hypersaline environment. Respiration accounted for more energy than excretion. As energetic expenditure (due to respiration and excretion) was relatively small, scope for growth usually paralleled energy absorption. Scope for growth responses to salinity differed significantly between crabs from the two environments. Peaks in scope for growth for both the brackish-water and hypersaline individuals corresponded to salinities normally encountered by these crabs in their natural habitats. Individuals from the brackish-water population had maximal energy absorption and scope for growth at 10 and 25‰ S. Individuals from the hypersaline population displayed maximal energy absorption at 35‰ S and maximal scope for growth at 35 and 50‰ S.

Effects of temperature and salinity acclimation of adults on larval survival, physiology, and early development of Lytechinus variegatus (Echinodermata: Echinoidea)

Larval survival and developmental rates of Lytechinus variegatus (Lamarck) were determined as a function of temperature and salinity in two experiments by: (1) directly transferring fertilized eggs to 35, 30, 27.5, 25, 20, 15, and 10‰S seawater at 18 and 23°C, and (2) acclimation of adult sea urchins to the conditions described above for 1 to 4 wk prior to spawning. Developmental rates and percent survival of larvae prior to metamorphosis decreased at salinities below 35‰ (Q10 values for metamorphosis=0.380 to 0.384). Temperature and salinity significantly (P<0.05) affected metabolic rates of L. variegatus plutei. These results show that L. variegatus larvae are stenohaline when compared to larvae of other echinoderm species. LC50 values (‰S), developmental rates, and survival to metamorphosis indicate that acclimation of adult sea urchins to lower salinity prior to spawing and fertilization does not enhance development or survival of embryos exposed to low salinity.

Effects of in situ tidal salinity fluctuations on osmotic and lonic composition of body fluid in Southeastern Alaska Rocky intertidal fauna

Tidal fluctuations in salinity and temperature were monitored at a location on Lynn Canal, north of Juneau, Alaska. Organisms were collected from 4 tidal levels during each slack water over a period of 24 h. Body-fluid milliosmolality as well as sodium, potassium, calcium, magnesium and chloride levels were determined. Mytilus edulis were collected at the +1.0 m tidal level, where ambient salinity ranged from 7.9 to 25.1% and body fluids from 356±62 to 730±17 mOsm/kg water. Cucumaria vegea and Katherina tunicata were collected at the +0.6 m level, where ambient salinity ranged from 13.5 to 24.9‰ and body fluids from 461±27 to 662±50 and 443±31 to 616±38 mOsm/kg water, respectively. Eupentacta quinquesemita and Evasterias troschelii were collected at the -0.9 m level, where ambient salinity ranged from 11.0 to 28.2‰ and body fluids from 504±32 to 632±51 and 316±31 to 664±37 mOsm/kg water, respectively. Strongylocentrotus droebachiensis were collected subtidally at the -3.7 m level, where ambient salinity ranged from 14.1 to 28.0‰ and perivisceral fluids from 448±35 to 661±51 mOsm/kg water. Ion levels of the perivisceral fluid of c. vegae were not determined. Potassium appeared to be regulated by all animals except Evasterias troschelii. Little regulation occurred for calcium, magnesium, sodium and chloride by the organisms. Eupentacta quinquesemita appeared to be regulating all ions determined, but this may have been due to its microhabitat. Water temperature cycled inversely to salinity at all tidal levels. Ambient-water sodium, chloride and calcium levels deviated from levels that would be expected upon dilution of seawater with deionized water. There was not indication that body-fluid osmoconcentration of the species collected intertidally increased on exposure to air.

The effects of tidal fluctuation of salinity on the perivisceral fluid composition of several echinoderms

Abstract 1. 1. Tidal fluctuations of salinity were simulated so that ambient salinity decreased from 30 to 10%. and returned to 30%. over a 12-hr period. 2. 2. Perivisceral fluid osmotic and ionic composition of all three echinoderm species declined to a lesser extent than ambient salinity and returned to control values in Pisaster ochraceus and Cucumaria miniata but did not do so in Strongylocentrotus drobachiensis . 3. 3. Perivisceral fluid osmotic shifts were due predominately to ion flux. 4. 4. The calcium concentration of C. miniata perivisceral fluid was regulated.

Population genetics and systematics of the Leptasterias hexactis (Echinodermata: Asteroidea) species complex

Morphological characters and 14 enzyme loci were examined for 1 040 sea stars, currently recognized as forms ofLeptasterias hexactis, from Lynn Canal, Alaska, and Puget Sound, Washington, USA, between March 1988 and April 1989. Three morphologically and two genetically distinctLeptasterias forms were identified. The most common form found at both localities wasL. epichlora (Brandt)sensu Verrill.L. hexactis (Stimpson)sensu Verrill co-occurred withL. epichlora at all study sites and apparently hybridizes extensively withL. epichlora in the Puget Sound region, but rarely, if at all, in Alaska. The presumptive product of this hybridization morphologically resembledL. aequalis (Stimpson)sensu Fisher, and was conspicuously absent from Alaskan samples. Considerable genetic distance existed betweenL. epichlora andL. hexactis (NeisD=0.19±0.01) and moderate genetic differentiation occurred between populations of each species from Alaska and Washington (Weir and CockerhamsFRT=0.29±0.04 forL. epichlora and 0.21±0.15 forL. hexactis). A significant (p<0.05) deficiency in the proportion of heterozygous individuals was found compared to Hardy-Weinberg expectations (Wrights fixation index,FID=0.12±0.04 and 0.31±0.08 forL. epichlora andL. hexactis, respectively). However, mean observed heterozygosity for each species (0.09±0.03, 0.14±0.04 and 0.14±0.04 forL. epichlora, L. hexactis andL. aequalis, respectively) fell within the range of reported values for other asteroid species (ca. 0.04 to 0.37). The results of this study indicate that considerable genetic integrity is maintained betweenL. epichlora andL. hexactis, which warrants their recognition as distinct species despite their apparent hybridization in the Puget Sound region.

Occurrence of tri-n-butyltin-caused imposex in the North Pacific marine snail Nucella lima in Auke Bay, Alaska

Like female dog whelks (Nucella lapillus) in the Atlantic Ocean, females of the Pacific gastropod N. lima respond to low concentrations of tri-n-butyltin (TBT) by growing a penis and vas deferens. This condition, termed imposex, was found to occur in N. lima collected from August 1987 to May 1988 along a TBT pollution gradient associated with a marina in Auke Bay, Alaska. The suite of symptoms characteristic of imposex in N. lima was slightly different than in N. lapillus. Imposex, as measured by relative penis size (RPS) of females to males, increased from 0.0 to 34.27 along this gradient and as measured by vas deferens sequenceindex (VDS) increased similarly from 0.0 to 4.29. Concentrations of TBT in N. lima increased from below detection limits (about 0.010 μg Sn g-1 dry tissue wt) to 0.065 μg Sn g-1 dry tissue wt along the gradient. The gradient was determined by measuring TBT in whole-body tissues of bay mussels (Mytilus edulis). Concentrations of TBT in mussels increased from below detection limits to 0.833 μg Sn g-1 dry tissue wt in mussels from within the marina that was the major local source of TBT. Imposex, tissue TBT burden, and position along a TBT pollution gradient are significantly correlated (P<0.01) in N. lima. TBT was tested as a causative agent for imposex by exposing snails at a distant control site to TBT paint. After 1 mo exposure, 33% of the females grew a penis ranging in size from 0.2 to 0.8 mm. Our results generally corroborate those found for N. lapillus and indicate that imposex in N. lima is caused by environmental TBT exposure. We suggest that the RPS in the genus Nucella may be useful in monitoring TBT in coastal waters worldwide.

Effects of salinity on respiration and nitrogen excretion in two species of echinoderms

The 30-d survival limit of Eupentacta quinquesemita and Strongylocentrotus droebachiensis is 12–13‰ S. The activity coefficient (1 000/righting time in seconds) of stepwise acclimated sea urchins declined from 16.3 at 30‰ S to 3.5 at 15‰ S. Oxygen consumption rates (QO2) of both species held at 30‰ S and 13°C were highest in June and lowest in December. During the summer, when environmental salinity is most variable in southeastern Alaska, the QO2 of both species held at 30, 20 and 15‰ S varied directly with salinity. Perivisceral fluid PO2 varied directly with acclimation salinity in sea urchins, but not in sea cucumbers. Perivisceral fluid oxygen content of acclimated sea urchins was significantly lower at 15 and 20‰ S than at 30‰ S due to reduced PO2 and extracellular fluid volume at the lower salinities. The QO2 of both species varied directly with ambient salinity during a 30-10-30‰. semidiurnal pattern of fluctuating salinity. No change occurred in the average QO2 of either species over a 15-30-15‰. semidiurnal pattern of fluctuating salinity. Sea urchin perivisceral fluid PO2 declined as ambient salinity fluctuated away from the acclimation salinity in both cycles and increased as ambient salinity returned to the acclimation salinity. Total nitrogen excretion of stepwise acclimated sea cucumbers declined significantly from 30 to 15‰ S, but there was no salinity effect on total nitrogen excretion in sea urchins. Ammonia excretion varied directly with salinity in stepwise acclimated sea cucumbers (67–96% of total nitrogen excreted), but there was no salinity effect on ammonia excretion (89–95% of total nitrogen excreted) of sea urchins. Urea excretion did not vary with salinity in sea cucumbers (2–4% of total nitrogen excreted) or sea urchins (2–9% of total nitrogen excreted). Primary amines varied inversely with salinity in sea cucumbers (2–30% of total nitrogen excreted), but did not vary with salinity in sea urchins (2–4% of total nitrogen excreted). The oxygen: nitrogen ratio of both species indicated that carbohydrate and/or lipid form the primary catabolic substrate. The O:N ratio did not vary as a function of salinity. Both species are more tolerant to reduced salinity than previously reported, however, rates of oxygen consumption and/or nitrogen excretion are modified by salinity as well as season.

Effects of salinity on the respiration and heart rate of the common mussel, Mytilus edulis L., and the black chiton, Katherina tunicata (Wood)

Abstract The rate of oxygen consumption of stepwise acclimated Mytilus edulis L. increased linearly from 30 to 10‰ salinity ( S ) while that of Katherina tunicata (Wood) was not significantly different between 10 and 30‰ S . Heart rate was 21–22 and 17–18 beats m −1 in Mytilus edulis and Katherina tunicata , respectively, and no difference was found in the heart rate of either species acclimated stepwise to 10, 20 or 30‰ S . The average oxygen consumption rate of Mytilus edulis exposed to 12 h, 30-10-30 and 10-30-10‰ S cycles of fluctuating salinity was significantly lower than the respective control rate: there was a similar response during the 30-10-30‰ S cycle in Katherina tunicata . The respiration rate of Mytilus edulis and Katherina tunicata declined as salinity deviated from the control salinity and increased as salinity returned to the control salinity. The rate of oxygen consumption by K. tunicata varied directly with the ambient salinity during the 10-30-10‰ S cycle. The average heart rate of Mytilus edulis was significantly lower during cyclic changes in salinity than at the respective control salinities; a similar relationship existed for Katherina tunicata during the 10-30-10‰ S cycle. Heart rate of Mytilus edulis varied in a parallel manner with oxygen consumption during both cycles. Katherina tunicata heart rate was relatively constant and could not be fitted to a regression line during the 10-30-10‰ S cycle. The normalized heart rate increased to 113% of control at 10‰ S of the 30-10-30‰ S cycle and returned to the control rate by 12 h. The oxygen consumption and heart rate of these two species are not directly coupled to regulation of water volume because different responses are observed with respect to salinity although there is poor water volume regulation in both species.

Effects of tidal fluctuations of salinity on pericardial fluid composition of the American oyster Crassostrea virginica

Crassostrea virginica Gmelin were subjected to simulated tidal fluctuations of salinity, and the subsequent effects on osmotic and ionic composition of the pericardial fluid, body water and valve movements were investigated. Ambient salinity fluctuation patterns of 20-10-20‰, 15-10-15‰ and 10-5-10‰ were simulated during 24.8-h periods. An additional 10-5-10‰ S experiment was performed using a dilution water approximating the ionic composition of Mississippi River water with regard to Mg++, Ca++ and SO4=, instead of deionized water. Finally the effects of a 2-week diurnal fluctuation pattern between 20 and 10‰ S were investigated with respect to pericardial fluid composition. Pericardial fluid osmolality, concentrations of Cl-, Na+, Mg++, K+, Ca++ and ninhydrin-positive substances (NPS) were analyzed periodically throughout all experiments. Pericardial fluid osmolality was slightly hyperosmotic as ambient water salinity decreased during a cycle, and then became slightly hyposmotic as ambient salinity increased. In the 2-week experiment, pericardial fluid osmolality tracked ambient seawater closely through Day 5, but became more intermediate between high and low seawater values as the experiment progressed. Similar patterns during fluctuations of salinity were observed for Na+, Cl-, Mg++ and Ca++. Pericardial fluid K+ levels did not track ambient seawater as closely as did other ions. The ionic composition of dilution water had little effect on the osmotic or ionic response of the oysters pericardial fluid. Pericardial fluid NPS level varied inversely with salinity during the 20-10-20‰ cycle. During the longterm fluctuation experiment, NPS values gradually decreased over the 2-week period compared to constant salinity control values. Percent body water also varied inversely with ambient salinity. Solute movement accounted for most of the change in pericardial fluid osmolality during the simulated cycles with water movement responsible for 1 to 11%. Water movement contributed more to the change of pericardial fluid osmolality during the decreasing salinity phase than the increasing phase of a given cycle. During 20-10-20‰ S cycles, oyster valves remained open 56% of the time (n=23). In contrast, when salinity was abruptly changed from 20 to 10‰ within 5 min, valve closure occurred in 4.8±0.3 min (n=20). Valves did not reopen for 19.3±1.2 h (n=15).