Intertidal Biodiversity and Their Response to Climatic Variables, Temperature and pH—What We Know

P. M. Mohan^*, V. Swathi

Department of Ocean Studies and Marine Biology, Pondicherry University of Campus, Port Blair, Andaman and Nicobar Islands, India.

DOI: 10.4236/ojms.2020.104016                

Abstract

As per the Essential Climate Variables (ESV) of World Meterological Organisation (WMO), the physical, chemical and biological variables critically contribute to the earth’s climate. Among them, the variables such as temperature and pH in the marine environment may affect seriously and in turn it has an impact on the biota, especially in the intertidal environment, where it has brunt force. According to United Nations Framework Convention on Climate Change (UNFCCC), the datasets should provide the empirical evidence needed to predict the climate change and evoluate the mitigation and adaptation measures. Under this context, a review was carried out to know what extent marine scientists understand this factor and what level the biodiversity was evoluated and its impact was analysed in this article. Based on the existing literature review, it was understood that only a few groups that also only few species from these groups were studied in this aspect. The remaining groups and their species and their basic trophic were not evolved in this aspect. So, the marine scientific community, environmentalist and policy makers should take stock on this aspect and give thrust on this study.

Keywords

Climatic Variables, Temperature, pH, Salinity, Marine, Biodiversity

1. Introduction

Climatic change is one of the important factors to consider for the futuristic research activities, especially with biodiversity concern. According to Global Climate Observing System (GCOS), it should be ensured that observations and information needed to address the climate issues are obtained and made available to all potential users. The World Meterological Organisation (WMO) also suggested that under the Essential Climate Variables (ECV) the datasets on EVS should provide the empirical evidence, which needed to understand and predict the climatic change to evoluate the mitigation and adaptation measures to underpin the climatic services [1]. Under this programme, it was suggested generating and archiving data on the variables, wherever possible, using historical dataset. The predication of the future climate states that the temperature is the important factor for the terrestrial and temperature and pH are the two major components to be altered in the marine environment concern. As predicted by IPCC [2], a rise of temperature around 1˚C to 2.5˚C was suggested based on the year 2000 data. The expected outcome of this 20% - 30% of plants and animals may extinct and Island States undergo the sea due to increase of sea level rise. The climate change affected drastically and the ecosystem shifts and numerous extinctions will be resultant [3] - [8].

The effect of climate change is rapid and highly influence in marine ecosystem, especially in the intertidal zone where the upper temperature differences have their impact [9] [10] [11] [12]. If the species cannot acclimatize physiologically or change genetically to cope with temperature increment to move cooler habitats, i.e. high latitude [5] [7] [13] [14] [15] [16] [17]. It was proposed that the shift of marine species in an average 19 km/year [11] than the terrestrial shift, i.e. 0.6 km/year [5]. Since, the shift range can be predicated well in marine species because of its thermal tolerance limit [18], so as the web interactions changes within ecological community [19].

2. Methodology

Understanding the importance of impact of temperature and pH variables on the intertidal life forms, the existing literature was scanned. The available information was shared here to understand the level of our knowledge on this aspect and discussed the views for the future need on this aspect. Even though good amount of literature is available on the distribution and taxonomy, the impact of the individual group is species were scanty. The available studies were discussed in this article.

3. Intertidal Region

The seashore which covered during the high tide and exposed during the low tide is defined as intertidal zone or littoral zone. This eco zone covers a unique biome with variety of plant and animal [20] [21]. This zone is characterised by unique temperature, ecological factors and micro climates. This zone is divided into four distinct regions:

Lower Littoral Zone - Low Tide Zone

This area is closest to the sea and submerged majority time with seawater. The waves in this region protect the harmful radiation and severe temperature fluctuation. The species lives in this region are larger in size, greater in number, more diverse than the other areas of intertidal zone. The organisms in the low tide zone do not have to be well adapted to drying out and temperature extremes. The common fauna and flora observed in this region are sea anemone, brown sea weed, green algae, chiton, crabs, hydroids, isopods, limpets, mussels, sometimes small fishes.

Mid-Littoral Zone - Mid Tide Zone

The region is submerged half of the time of tidal fluctuations. The plant and animal species are living in this region but not as diver as Low Tide Zone. The organisms in the mid tidal zone are snails, sponges, sea stars, barnacles, mussels, sea palms and crabs.

Upper Mid-Littoral Zone - High Tide Zone

The zone is submerged during the high tide only. Very few plants and animals survived in this region. The most of the animals in this region are mobile (Crab) or attached to the substrate (Barnacles). The organisms in the high tidal zone are seaweeds, marine algae, sea anemone, starfish, chiton, crabs, mussels, nudibranchs and hermitcrabs.

Splash Zone

The splash zone is located above the upper mid-littoral zone. The water splash during the high tide by the wavers and never submerged with water.

4. Results and Discussion

4.1. Temperature

All organisms have an influence on climatic variables in the range of molecular to ecosystem scales because the temperature dependent process is imminent [22] [23] [24]. Comparative to terrestrial species marine ectotherms act faster because of its sedentary nature and short life spans prevent escape from the change of environmental regimes [25] [26]. The flora and fauna existed in the intertidal regime responding quicker than the higher trophic level [27] [28] [29], because this quicker response leads to surge of deficiency of food chain [30]. Even though, semidiurnal and diurnal tidal effect along with seasonal variable may affect the intertidal organism to the tune of 2.5˚C over a single tidal cycle [31], the temperature increment of air may affect further on this fact leads to some kind of thermal extremes for the intertidal flora and fauna.

The temperature increment affected the Boreal Barnacle Semibalanus balanoides larval development [32] [33]. The blue mussel Mytilus edulis exhibited impaired respiration and metabolism change [34] [35] [36]. The pink coralline algae show impaired growth in the intertidal environment [37]. The Pacific Oyster Crassostrea gigas (Figure 1) located in the intertidal zone adapted to massive temperature fluctuations around 2˚C in a tidal cycle. Additionally, the exposure to high thermal variability can cause shifts in gene expression patterns which set limits for physiological function [38]. The sea star Crossaster papposus (Figure 2) has lecithotrophic larvae which have less susceptible to environmental change than the planktotrophic larvae of asteroid species.

Figure 1. Crassostrea gigas [75].

Figure 2. Crossaster papposus [76].

The enhanced respiration rates of faunal community through temperature raise affect the carbon balance of macroalgae assemblages which declines net productivity of seaweed and due course of time species richness [39]. The crab has good sustainability for temperature and pH variation in the intertidal regions. However, the effect of these combined two factors leads to decline its resistivity and its population. This in turn exhibited a potential long term adverse effect on the ectotherm. The sea anemone Actinia equina (Figure 3) in the rocky Mediterranean coast exhibited the growth of polyp will shunted along with reduced biomass during the raise of temperature [40]. The brown dinoflagellates (Symbiodinium californium, A. T. Banaszak, R.Iglesias-Prieto & R. K. Trench

Figure 3. Actina equina [77].

and S. muscatinei, La Jeunesse & R. K. Trench) called zooxanthellae translocate during the high temperature to the host [41] [42].

4.2. pH

The studies on the pH of marine water suggested that during the end of 21^st Century, the CO₂ level may be increased to three to four fold than the pre-industrial levels [43] [44] [45]. This increment may effect on the surface of the water and increase the dissolved CO₂ and in turn alter the seawater pH which was not seen in the last 300 million years by the change the carbonate chemistry [46]. The year 2016, carbon dioxide parts in the atmosphere surpassed 400 ppm (parts per million), the highest since the Pliocene epoch, a geological period known for its warm temperatures. Morris and Taylor [47], Truchot [48] and Wootton et al., [49] reported that in the tide pool studies the pH changed from 9.5 to 6.5 which was higher than the proposed value of next century predication on the surface water. Feely et al., [45] and Hofmann et al., [50] reported that the intensity of upwelling increased and in turn the deep hypercarbanic waters mixing in the surface water also lowering the pH towards acidic side.

The change of pH was termed as Ocean Acidification (OA) as mentioned by Caldeira and Wickett [51] and Meehl et al., [44]. This large variation of pH may affect the biota’s metabolism, growth and reproduction [52] [53] [54] through the intracellular pH homeostasis [55]. This may lead to ecological implications by the way disappearance of the particular species or genetical modification of the same and in turn affect the local biodiversity with the result of disturbed community composition [55] [56] [57] [58]. Further, the change of pH may be affected the intertidal regions of the ocean than the deeper habitats [32] [50] [59]. This fact is very much significant for the crustaceans and snails [32] [60] [61]. However, it was not affected the teleost fish and brachyuran crabs but increased its availability more [52] [62] [63]. Another interesting findings also observed that the early life history of organisms (embroyonic, larval or juvenile stages) show more response on the OA factor than the latter stages of their life history [54] [64] [65]. This factor was very much significant for mollusks, echinoderm and crustaceans [32] [60] [66] [67]. The studies on the porcelain crab Petrolishthes cinctipes stated (Figure 4) that the survival rate of juvenile reduced to the tune of 30% in hepercapnic waters influence [68]. The above studies were clearly mentioned that the whole life history of a fauna or flora should be studied [69] to understand the impact of OA in the marine environment. The California mussel—Mylitis californiansis (Figure 5) precipitated smaller shells with less thickness due to pH level towards acidic [70]. The coralline algae recruitment and deficient growth were observed under acidic conditions [71].

As reported by Alenius and Munguia [72] the species Paradella dianae (Figure 6) from the Isopod living in the intertidal regions showed its variation among the consumption of oxygen, swimming speed, food response varied when the pH conditions varies. As reported by Orr et al., [43] and Bednaršek et al., [73], the OA may also reduce calcification in planktonic organisms. The pH fluctuate daily ≥ 0.5 pH units and up to ≥1 pH level on temperate rocky shores [49]. The coral reef environment suggested that the pH varies ≥ 0.5 pH units day and night cycles Birkeland et al., [74].

5. Conclusion

The existing literature was stated that the studies on intertidal fauna and flora for the impact on climatic variables executed only for few groups of organisms. The number of other intertidal fauna like polycheate, sponges, hydroids, bryozoans, etc., (Table 1) is not known for its effect on the temperature and pH changes in the intertidal mechanism, which is highly essential for the food web of marine trophic as a total. If scientific community does not understand its effect, which in turn estimation of the range extension of faunal distribution will become more cumbersome and effect on the climatic variable will not be understood fully

Figure 4. Porcelein crab [78].

Figure 5. Mylitis californiansis [79].

Figure 6. Parandella dianae [80].

Table 1. Intertidal faunal and floral distribution.

for the intertidal biodiversity. Not only that, the need to understand the impact of climatic variable to the fauna and flola of the intertidal regions as needed for Globla Climatic Observation System and if the scientist, not able to provide a clear cut information, the mitigation efforts was also not successful for future developmental aspects.

Acknowledgements

I thank the Authorities of Pondicherry University for providing the facilities to execute this work in their Port Blair Centre. I also acknowledge the Indian Institute of Tropical Meteorology (IITM), Pune, under the Ministry of Earth Sciences for providing fund through Metflux Project.

Conflicts of Interest

The authors declare no conflicts of interest regarding the publication of this paper.

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