Systemic Respiratory Adaptations to Air Exposure in Intertidal Decapod Crustaceans

SYNOPSIS: The responses of intertidal decapods to emersion areclosely related to the particular conditions of emersion, yetall members of this group of animals face the problems of watershortage and internal hypoxia during air exposure. Several speciesexhibit modification of normal ventilatory activity and thisresponse seems to enable these crabs to take up seawater fromthe substrate. Other crabs have specific morphological adaptationspermitting recirculation of water from the exhalent aperturesback into the gill chamber. The hemocyanin of some species hasa higher affinity for oxygen, and this difference may be moreprevalent in tropical animals. The higher oxygen affinity undoubtedlycompensates in part for the lower internal oxygen tensions duringair exposure. Structural specialization of the branchial apparatusmay prevent the gill lamellae from adhering together, a processwhich reduces the surface available for gas exchange. Thereis a wide range of responses to emersion and yet relativelyfew specific adaptations. Some species are able to merely tolerateair exposure, while others are able to more fully exploit thehabitat.     

A Suite of Adaptations for Intertidal Spawning

Salt marshes and similar tide-dominated habitats present anunusual challenge for reproduction of resident aquatic organisms.Strong currents, siltation and hypoxia can potentially contributeto reproductive failure through mortality of the eggs or flushingof the eggs and larvae from the habitat. Fundulus heteroclitus,a small brackish water killifish, is a common resident of tidalmarshes along the east coast of North America from Newfoundlandto Florida. The reproductive strategy of this and related speciesis based on aerial incubation of eggs in the high intertidalzone. The eggs are resistant to desiccation and, when fullydeveloped, hatch on immersion. Copulatory behavior and anatomyof accessory reproductive structures are adapted to placementof eggs in protected incubation sites. The gonads of both malesand females mature rhythmically with an endogenous circasemilunarperiod, which is synchronized with the "spring" tides of newand full moons. Spawning occurs on high tides. Embryos developin 9–15 days, and usually hatch on the succeeding springtide series. Reproductive cyclicity in F. heteroclitus and relatedfishes ensures that spawning fish will have access to the highintertidal zone, thereby permitting aerial incubation of eggs.     

Respiratory Adaptations in Marine Mammals

This paper is a discussion of some of the possible structuraland functional modifications of the lung which represent adaptationsin mammals living in the sea. Lung capacities of marine mammalsseem to be larger than terrestrial mammals especially if theyare compared on a lean weight basis. It is proposed that atleast in some this represents an important increase in buoyancywhich enables these mammals to rest at sea. The importance ofthe lung as an O₂ store during dives is considered, and it seemsthat it would be important only to those species that have alow breath-hold tolerance. In their case the O₂ present in thefully inflated lung is from four times to equal that in theblood. In those species with a large breath-hold tolerance thelung O₂ store is a small fraction of blood stores. Several experimentsare discussed which indicate that during dives to depth gasexchange between the blood and lungs is low. One of the reasonssuggested is compression collapse of the alveoli. This occursbecause of the apparent rigidity of the airways which even inthe terminal segments possess an unusual amount of muscularor cartilaginous support. The reinforcement insures that duringcompression the airways will not occlude and trap gas in thealveoli. In fact, in some species, especially otariids and cetaceans,the airways seem overly strong and an additional function issuggested. Studies of mechanical properties of sea lion andwhale lungs show that they may be capable of high expiratoryflow rates at low volumes. This feature of the lung would makepossible an exchange of a large gas volume in very short periods.Such an ability is consistent with the ventilatory behaviorof many marine mammals.     

Adaptations of Host and Symbionts in the Intertidal Zone

SYNOPSIS. Different species of larval trematodes that utilizethe same intermediate host characteristically exhibit distinctivepatterns of response to environmental fluctuations. Not onlyare the responses distinctive for each species, but also theycannot be correlated with that of the host. The physiologicalresponses of the molluscan host to physical changes in the environment,however, are modified significantly by the presence of a larvaltrematode infection. The thermal metabolic acclimation patternsof infected Nassarius obsoleta are quite distinct from thoseof non-infected N. obsoleta. Thex activity patterns during thermalacclimation of cytochrome c oxidase from digestive glands ofsnails infected with different species of larval trematodesindicate that each species of larval trematodes differentiallyinfluences the hosttissue, so that the cytochrome oxidase systemdoes not respond to temperature in the same way as does uninfectedhost tissue.     

Respiratory Response to Periodic Emergence in Intertidal Molluscs

SYNOPSIS: The ratio of aerial: aquatic was computed for species of intertidal molluscs.This ratio was <1 for sub- and lower littoral species suggestingpartial anaerobiosis in air and >1 for high littoral archeogastropodssuggesting high metabolic demands in air. ratios were near unity for meso- and neogastropodspecies regardless of zonation. Littoral fringe mesogastropodshad ratios <1 reflecting reduced activity on emergence. Amajor gastropod adaptation to increasing emergence is reductionof ctenidium surface area and formation of a mantle cavity lung.Mid- and high littoral pulmonates with both a mantle cavitylung and secondary gills have ratios near unity. In contrast, littoral fringe pulmonates withoutsecondary gills are partially anaerobic in water. Emerged lowand mid-littoral bivalves close the valves, are almost entirelyanaerobic, have ratios 0.14:1and conserve energy by greatly reducing metabolic demand inair. In contrast, emerged high littoral bivalves remain aerobicby periodic gaping and mantle cavity ventilation. Such behaviorssupport an aerobic metabolism while minimizing evaporative waterloss. Aerial gas exchange prevents anaerobic end-product accumulationand, with a reduction in energy demand, allows efficient energystore utilization during prolonged emergence.     

Adaptations to Physical Stresses in the Intertidal Zone: The Egg Capsules of Neogastropod Molluscs

The encapsulation of eggs within benthic egg capsules or gelatinousegg masses is a common phenomenon among many marine invertebrategroups, yet the functional significance of many aspects of theseegg coverings remains unexplored. In this paper I review whatis known about the effectiveness of neogastropod egg capsulesin protecting embryos from physical stresses associated withthe marine intertidal environment. Egg capsules spawned by intertidalneogastropod molluscs can provide embryos with significant protectionfrom desiccation, osmotic stress, and ultraviolet (UV) radiation,relative to embryos devoid of such coverings. Despite this,capsules desiccate rapidly in air, are highly permeable to smallsolute molecules, and are not impervious to incident UV radiation.Egg capsules of intertidal gastropods are also substantiallymore permeable to water molecules than the well studied eggcases and egg shells of insects and terrestrial vertebratesand may be no more effective in protecting embryos from suchphysical stresses than the capsules of exclusively subtidalgastropods. Hence, capsular cases appear to be poorly adaptedto protecting embryos from environmental stresses associatedwith periodic exposure to air. The degree to which the encapsulatedembryos of intertidal neogastropods are protected from environmentalstresses thus may be more reflective of adult spawning siteselection and tolerances of encapsulated embryos to these stresses,than properties of the capsular case, per se. Clearly, however,there is much still to be learned about the protective natureof capsule walls and the tremendous diversity of egg coveringsthat exists within the Gastropoda.     

Adaptations of the Ribbed Mussel, Modiolus demissus (Dillvvyn), to the Intertidal Habitat

SYNOPSIS. This is a review of the behavioral, biochemical-physiological,and morphological adaptations of Modiolus demissus (Dillwyn)to the high intertidal habitat. The ribbed mussel, Modiolus,has fully exploited the behavioral adaptations within the limitsimposed by the bivalve body plan. Air-gaping is undoubtedlya significant behavioral adaptation which permits aerial respirationand penetration of the high intertidal zone. Modiolus fullyutilizes physiological-biochemical adaptations also. The musselis both eurythermal and euryhaline: the thermal range is atleast 56 °C and the salinity range is at least 70%, bothimpressive ranges for an organism which conforms to these environmentalparameters. The two primary adaptations made by Modiolus arean extensive tolerance to dehydration and a very high enzymethermostability. These two adaptations are resjxmsible for Modiolus'tolerance toward desiccation, variation in salinity, thermalstress, and possibly anaerobic conditions. There is no obviousmorphological adaptation. Thus, the physiological adaptations,coupled with air-gaping, are responsible for the vertical penetrationof Modiolus into the intertidal zone and its horizontal migrationover an extensive geographic range.     

Compound Eye Adaptations for Diurnal and Nocturnal Lifestyle in the Intertidal Ant,Polyrhachis sokolova

The Australian intertidal ant, Polyrhachis sokolova lives in mudflat habitats and nests at the base of mangroves. They are solitary foraging ants that rely on visual cues. The ants are active during low tides at both day and night and thus experience a wide range of light intensities. We here ask the extent to which the compound eyes of P. sokolova reflect the fact that they operate during both day and night. The ants have typical apposition compound eyes with 596 ommatidia per eye and an interommatidial angle of 6.0°. We find the ants have developed large lenses (33 µm in diameter) and wide rhabdoms (5 µm in diameter) to make their eyes highly sensitive to low light conditions. To be active at bright light conditions, the ants have developed an extreme pupillary mechanism during which the primary pigment cells constrict the crystalline cone to form a narrow tract of 0.5 µm wide and 16 µm long. This pupillary mechanism protects the photoreceptors from bright light, making the eyes less sensitive during the day. The dorsal rim area of their compound eye has specialised photoreceptors that could aid in detecting the orientation of the pattern of polarised skylight, which would assist the animals to determine compass directions required while navigating between nest and food sources.     

Physiological Adaptations (By the Example of the Exotrophy Process in Fish)

By the example of a complex process of exotrophy in fish, which includes not only search for and consumption, but also digestion of the victim, as well as transfer of products of its depolymerization into the internal organism medium, different types of physiological adaptations are described: adaptations of elementary functions, the local or subsystem adaptations, the organismal or supersystem ones, as well as the superorganism adaptations including victim-symbiotic, populational, and biocenotic ones.     

The Impact of Artisanal Fishery on a Tropical Intertidal Benthic Fish Community

We examined the benthic fishes and artisanal fishery in the intertidal flats of Inhaca Island, Mozambique. Results of a questionnaire indicated that catches had decreased, and that piscivorous fish have disappeared. Results of a catch sampling study indicated that current catch rates are low, < 2 kg person^–1 fishing trip^–1. Use of fishing gear was significantly related to season, diel and lunar tidal phase, and habitat. Forty-eight fish species were observed in the catches with eight species comprising 80% of the catch of 1814 specimens. The annual catch was estimated at 26.2t for the whole bay. Highest fishing pressure was observed in the central section of the bay. A demersal fish survey was carried out with a 2-m beam trawl to sample the fish community. Two different areas were sampled, one area with a low, and one with a high fishing pressure. A total of 19889 fishes were caught comprising 93 species. Gobies dominated the catches and accounted for 56% of all specimens. Fishes were small with a mean standard length of 29mm. The Saco area exhibited the highest catch rates and biomass (maximum of 1040 fish 1000 m^–2 and 1490g 1000 m^–2), and the highest species richness and evenness values. Catch composition was different between the two sampling areas, and was strongly affected by season, but less by habitat. Total fish biomass was estimated at 5.6t for the whole area. Stomach content varied with habitat, and season, and was dominated by benthic invertebrates. The largest estimates of consumption were obtained in the tidal channel and the Zostera beds. Mean consumption of benthic organisms was 1.3g AFDW m^–2 yr^–1. The area seemed to be overfished. The heavily fished areas exhibited lower catch rates, lower proportion of piscivorous fish, increased proportion of small fish, and a decrease in species diversity.     

Environmental Control on Fish and Macrocrustacean Spring Community-Structure,on an Intertidal Sandy Beach

The inter-annual variability of the fish and macrocrustacean spring community on an intertidal sandy beach near the Canche estuary (North of France) was studied from 2000 to 2013 based on weekly spring sampling over an 11-year period. Twenty-eight species representing 21 families were collected during the course of the study. The community was dominated by a few abundant species accounting for > 99% of the total species densities. Most individuals caught were young-of-the-year indicating the importance of this ecosystem for juvenile fishes and macrocrustaceans. Although standard qualitative community ecology metrics (species composition, richness, diversity, evenness and similarity) indicated notable stability over the study period, community structure showed a clear change since 2009. Densities of P. platessa, P. microps and A. tobianus decreased significantly since 2009, whereas over the period 2010-2013, the contribution of S. sprattus to total species density increased 4-fold. Co-inertia and generalised linear model analyses identified winter NAO index, water temperature, salinity and suspended particular matter as the major environmental factors explaining these changes. Although the recurrent and dense spring blooms of the Prymnesiophyte Phaeocystis globosa is one of the main potential threats in shallow waters of the eastern English Channel, no negative impact of its temporal change was detected on the fish and macrocrustacean spring community structure.     

High Country Adaptations

Abstract

A general model of high country adaptations by hunters and gatherers is proposed. It is derived from a consi eration of the specific nature of high country resources and the social structure that seems to exploit them most efficiently. The general model is then illustrated by two test cases, one from northwestern Wyoming and one from southwestern Asia. The paper concludes with a comparative perspective. and discusses the problem of why Native Amen cans 1n the central Rockies failed to domesticate wild sheep while hunters and gatherers in southwestern Asia did.     

Adaptations and history

The historical definition of adaptations has come into wide use as comparative biologists have applied methods of phylogenetic analysis to a variety of evolutionary problems. Here we point out a number of difficulties in applying historical methods to the study of adaptation, especially in cases where a trait has arisen but once. In particular, the potential complexity of the genetic correlations among phenotypic traits, performance variables and fitness makes inferring past patterns of selection from comparative data difficult. A given pattern of character distribution may support many alternative hypotheses of mechanism. While phylogenetic data are limited in their ability to reveal evolutionary mechanisms, they have always been an important source of adaptive hypotheses and will continue to be so.     

Salinity--stress and Desiccation in Intertidal Worms

SYNOPSIS. Intertidal worms (oligochaetes, polychaetes, sipunculids)inhabiting beaches and tidal fiats both on the open sea coastand in estuaries may be exposed to significant tidal as wellas seasonal variations in salinity. However, there are veryfew measurements of the actual variations in salinity encounteredby worms in nature. Behavior (irrigation of burrow, verticalmovements in burrows, migration in gradients of salinity)maybe important in determining to which of the available salinitiesin a tidal cycle the worms may be exposed. In response to rapidlowering of salinity, worms gain water and lose salts, theseprocesses combining in diluting the internal fluids. Internalilution occurs more slowly in euryhaline species than in stenohalinespecies. Worms fully adapted to salinities lower than 30 % seawater may be hyperosmotic (demonstrated for six species of Nereidae).Mechanisms involved in hyperosmotic regulation include activetransport of salts(demonstrated in Nereis diversicolor), reductionofthe permeability of the body surface to salts and perhapsto water, and perhaps production of hypo—osmotic urine.Sipunculids can tolerate considerable loss of water rom dehydrationand concomitant increases in osmotic concentration of the bodyfluids. It is suggested that worms exposed to significant tidalvariations in salinity may seldom be in osmotic equilibriumwith their external medium.