Theresa F. Dabruzzi

Thermal Tolerance and Metabolic Responses of Two Damselfish Species from a Hyperthermic Rockpool Nursery in Dry Tortugas National Park, USA

Abstract Beachrock formations on Loggerhead Key in Dry Tortugas National Park, USA are an important nursery for many juvenile reef fishes. Wide variations in temperature are common in these areas and can markedly influence fish metabolism and thermal tolerance. We determined routine resting metabolic rate and temperature quotient (Q10) at 24 and 32°C. Thermal tolerance (measured as critical thermal maximum, CTmax) was also measured for sergeant major (Abudefduf saxitilis) and cocoa damselfish (Stegastes variabilis) acclimatized to beachrock nursery temperatures. Sergeant majors occupied shallow rockpool margins that experience rapid, extreme temperature changes. These fish exhibited relatively low metabolic rates, reduced Q10 values (2.40), and relatively high levels of temperature tolerance (CTmax = 40.0°C). Cocoa damselfish selected deeper, more thermally stable rockpool areas. These fish had higher metabolic rates, were more sensitive to temperature increase (Q10 = 2.84), and were less tolerant of high temperatures (CTmax = 38.6°C) than sergeant majors. Metabolic and temperature tolerance adaptations of juvenile sergeant majors and cocoa damselfish allow these fishes to exploit a variety of microhabitats found in beachrock areas on Loggerhead Key.

Metabolic Thermal Sensitivity Optimizes Sea Krait Amphibious Physiology

Abstract Yellow-lipped Sea Kraits (Laticauda colubrina) are tropical amphibious snakes that divide their time between land and sea. When moving between habitats, the kraits experience rapid and sometimes extreme shifts in body temperature that can have profound metabolic effects. We quantified cutaneous and pulmonary oxygen uptake in sea kraits from Hoga Island, southeast Sulawesi, Indonesia, at temperatures commonly encountered in aquatic (27.6°C) and aerial (35.2°C) habitats. Total oxygen uptake rate was 49.14 mL Kg−1 h−1 at 27.6°C and 115.27 mL Kg−1 h−1 at 35.2°C. Pulmonary and cutaneous uptake rates were 44.58 and 104.70, and 4.56 and 10.57 mL Kg−1 h−1, at 27.6 and 35.2°C, respectively. Sea kraits had a temperature coefficient (Q10) of approximately 3, suggesting that metabolic rates triple with every 10°C temperature increase. High Q10 values may minimize time on land by increasing digestion and nutrient absorption rates as well as promoting faster healing and injury recovery times. Cooler reef temperatures would decrease metabolic demand, thus increasing submergence and foraging times.

Juvenile Ribbontail Stingray, Taeniura lymma (Forsskål, 1775) (Chondrichthyes, Dasyatidae), demonstrate a unique suite of physiological adaptations to survive hyperthermic nursery conditions

Juvenile ribbontail stingrays, Taeniura lymma (Forsskål, 1775) of the tropical West Pacific inhabit mangal and seagrass nurseries that often experience rapid and extreme increases in water temperature. We hypothesized that juvenile rays possess a thermal strategy similar to other hyperthermic specialists, in which fish prefer high temperatures, are always prepared for thermal extremes regardless of previous thermal history, and exhibit low metabolic thermal sensitivity. Critical thermal methodology was used to determine the thermal niche, and a thermal gradient used to estimate stingray final preferendum. Temperature quotients (Q10) were calculated from metabolic rates determined at three temperatures using flow-through respirometry. As predicted, juvenile rays showed a relatively small thermal niche dominated by intrinsic tolerance with limited capacity for acclimation. Thermal preference values were higher than those reported for other elasmobranch species. Interestingly, the temperature quotient for juvenile rays was higher than expected, suggesting that these fish may have the ability to exploit the thermal heterogeneity in their environment. Temperature likely acts as a directing factor in this species, separating warm tolerant juveniles from adults living in deeper, cooler waters.

Cutaneous Resistance to Evaporative Water Loss in the Crab-eating Frog (Fejervarya cancrivora)

Abstract Resistance to cutaneous evaporative water loss has been examined in anuran amphibians that occupy a variety of habitats, except for the ocean. We measured evaporative water loss rate and cutaneous resistance to evaporation in the Crab-eating Frog, Fejervarya cancrivora, a euryhaline species that enters the sea. Studies were conducted on Hoga Island, southeastern Sulawesi, Indonesia. Area-specific evaporative water loss rate was significantly lower in living F. cancrivora than in agar replicas of the frogs and total water loss rate was dependent on body mass. Cutaneous resistance to evaporative water loss was 0.27 sec cm−1, which is the lowest significant resistance known for frogs. Cutaneous resistance may have evolved as a way for F. cancrivora to reduce water loss while on land, thereby offsetting high osmotic losses to seawater before frogs have fully acclimated to higher salinities.

Evidence for Control of Cutaneous Oxygen Uptake in the Yellow-Lipped Sea Krait Laticauda colubrina (Schneider, 1799)

Abstract Some sea snakes and sea kraits (family Elapidae) can dive for upward of two hours while foraging or feeding, largely because they are able to absorb a significant percentage of their oxygen demand across their skin surfaces. Although cutaneous oxygen uptake is a common adaptation in marine elapids, whether its uptake can be manipulated in response to conditions that might alter metabolic rate is unclear. Our data strongly suggest that Yellow-Lipped Sea Kraits, Laticauda colubrina (Schneider, 1799), can modify cutaneous uptake in response to changing pulmonary oxygen saturation levels. When exposed to stepwise 20% decreases in aerial oxygen saturation from 100% to 40%, Yellow-Lipped Sea Kraits spent more time emerged but breathed less frequently. A significant graded increase in cutaneous uptake was seen between 100% and 60% saturation, likely attributable to subcutaneous capillary recruitment. The additional increase in oxygen uptake between 60% and 40% was not significant, indicating capillary recruitment is likely complete at pulmonary saturations of 60%. During a pilot trial, a single Yellow-Lipped Sea Krait exposed to an aerial saturation of 25% became severely stressed after 20 min, suggesting a lower saturation tolerance level between 40% and 25% for the species. Reducing subcutaneous perfusion could optimize swimming performance during foraging, whereas redirecting blood to skin surfaces would maximize dive times when subduing prey or avoiding aerial predators.

Asymmetric thermal acclimation responses allow sheepshead minnow Cyprinodon variegatus to cope with rapidly changing temperatures.

Thermal acclimation responses in sheepshead minnow Cyprinodon variegatus were quantified by transfer and reciprocal transfer of fish between 11.1° and 18.2°C, between 18.2° and 25.7°C, or between 25.7° and 32.8°C. Changes in thermal acclimation status were assessed by posttransfer time series determinations of thermal tolerance (i.e., critical thermal minima and maxima). In general, heat tolerance gain and loss were complete in 20 and 25 d, respectively. Cold tolerance gain was achieved ca. 24 d posttransfer, but attrition was complete after only 12–13 d. Heat tolerance was gained asymmetrically, with fish acquiring approximately one-half of their accruable tolerance at the lowest transfer temperature. Likewise, the majority of cold tolerance accruement occurred during the warmest temperature transfer. Relatively uniform losses of heat and cold tolerance were seen in reciprocal transfers. Acclimation patterns were related to initial acclimation temperature, final acclimation temperature, and acclimation time and could be accurately modeled by multiple linear regression. The results suggest that sheepshead minnow accrue a majority of their high- or low-temperature tolerance early in the acclimation process well before potential damaging temperatures are likely to occur. This novel pattern of asymmetric heat and cold tolerance acquisition in sheepshead minnow may be a key adaptation for surviving rapid and unpredictable water temperature changes commonly encountered in their natural environment.

Density of Diadema antillarum (Echinodermata: Echinoidea) on Live Coral Patch Reefs and Dead Acropora cervicornis Rubble Patches Near Loggerhead Key, Dry Tortugas National Park, Florida, USA

Abstract Density of adult Diadema antillarum was assessed on live coral patch reefs and dead Acropora cervicornis rubble patches next to Loggerhead Key, Dry Tortugas National Park, Florida, USA in June 2009. Mean density on live coral patch reefs (0.49 individuals m-2) was not statistically different from mean density on dead A. cervicornis rubble patches (0.30 individuals m-2), while the highest density on live coral patch reefs (1.39 individuals m-2) was twice that of dead A. cervicornis rubble patches (0.63 individuals m-2). A significant negative correlation was found between two-dimensional area and density of adult D. antillarum on live coral patch reefs, while no significant correlation was found between two-dimensional area and density of D. antillarum on dead A. cervicornis rubble patches. No significant correlation was found between rugosity and density of D. antillarum on dead A. cervicornis rubble patches. While adult densities are higher than after the mass mortality event of the 1980s, they have not recovered to pre-mass mortality levels. The ability of D. antillarum to occupy completely dead rubble may help in the long-term reestablishment of the species on live reefs by allowing it to utilize additional areas for possible spawning and juvenile recruitment.