Type: Critical Essays
Sample donated: Daisy Jensen
Last updated: September 20, 2019
Carter (2014) also reported in herstudy that mud clams in the northwestern Santa Isabel, Solomon Islands of theSouth Pacific can be found in the seaward mangrove fringe where it experiencesits longest aerial exposures during the spring tides. Morton (1975), on theother hand noted the opposite in the mud clams of Southeast Asia. They arefound in the landward fringe and are only covered by waters during the springtides. Mud clams in the Southeast Asia are adapted in a semi-terrestrial way ofliving (Nagelkerken et al., 2008). In addition, Hiong et al. (2004) said that Polymesoda spp.
spends portions of theirlives exposed aerially during the low tides. They usually inhabit the highshores where high tides only occasionally reach the area. This suggests thatthey can be found in the landward area of mangrove forests, specifically in thehigh intertidal areas (Clemente and Ingole, 2011). Due to this, they are buriedin mud and are usually hidden in between mangrove roots when the tides are low.They may also be seen in small water pools, which form at the bases of mangrovetrees (Cremades, 2014). Since the mud clams are only seldom submerged orexposed to water as they are only occasionally being reached by high tides,this therefore suggests that these mud clams are highly tolerant to aerialdesiccation during aerial exposure when the tides are low. Clemente et al.(2013) said that this ability of the mangrove clams to withstand prolongedperiods of aerial exposure is an extreme adaptation to a semi terrestrial modeof life.
This may imply that mud clams must have the ability to retain watersomehow within their tissues in order to live. This is where their large sizeand their characteristic hard shells come into action. This does not onlyprovide protection for the clams against erosion but is also responsible inallowing the bivalves to keep a large volume of water within their shellsspecifically at times when the tides are low and they are exposed. This willkeep the mud clams’ tissues able to survive as they are being maintained in anenvironment where there is enough and adequate water (Carter, 2014). Thisexplains why the Polymesoda clams,specifically the shells are large. Growth is focused more on the growth of theshell rather on the growth of the tissues. Nevertheless, tissue growth at lowrates is very vital for the mangrove clam’s survival under extended exposure(Gimin et al., 2004).
The need and the ability to contain water in relation tothe habitat of the mangrove clam are very critical for their survival. It wouldbe detrimental for the mangrove clam to have a continuous growth of the softtissue inside the shell and occupy a large space within it. This would lead tolessened capacity to hold water inside the shell leading to insufficient waterto support the necessary metabolic needs in case the clam’s tissues continue togrow (Gimin et al., 2004).
Sincemud clams remain more exposed to air than being submerged in water, they arealso able to undergo aerial respiration. Aerial respiration in the mud clam isaccomplished in the mantle cavity and happens during emersion (Clemente andIngole, 2011) or aerial exposure. In most bivalves, emersion could restrain anumber of metabolic function (Hiong et al.
, 2004). Some of these includerespiration, feeding and even excretion. This suggests that oxygen consumptionin many bivalves is greatly reduced when they get exposed to air.
As a responseto this increasing demand for oxygen due to the ongoing shortage, most of theenergy requirements for these bivalves are met through anaerobic strategies.The lower intertidal and subtidal bivalves utilize this strategy. In order toshift to anaerobic metabolic pathways, these organisms usually close theirshells. In contrast to the lower intertidal and subtidal bivalves, Polymesoda spp. open up their shellsposteriorly to expose their mantle margins at times of aerial exposure.
Theadduction of the shells of the valves that immediately follows the emersion andat periodic intervals ventilates the mantle cavity and on the mantle, gasexchange occurs (Hiong et al., 2004). This is how Polymesoda spp. maintains aerobic respiration to survive the longperiods of exposure to air. In the study conducted by Hiong et al. (2004), theywere able to show that species of the mud clam that is the P. expansa, does not encounter lack or even shortage in oxygenduring aerial exposure.
They were able to observe that after 17 days ofexposing the clams to air, there was no significant increase in the alaninecontents of within its tissues. Alanine is one of the major end-products ofanaerobic glucose catabolism, which is the anaerobic metabolic pathway thatmost bivalves shift into as they close their shells when they get exposed toair. They also mentioned that the absence of increase in the alanine contentsmay be related to the capability of the P.
expansa to maintain normal oxygen utilization rate during emersion. Theirresults therefore show that mud clams do not readily shift to anaerobicrespiration but utilize the aerobic respiration instead when they are exposedto air. Marinebivalves as mentioned earlier are often the dominant inhabitants of mangroveecosystems characterized by the muddy environment. In relation to theirhabitat, most of these marine bivalves are either deposit feeders or suspensionfeeders (Lopez, 1988) which may also be called as a filter feeder. According toArgente et al. (2014), the mud clam P.erosa is a filter feeder, which is also termed by others as a suspensivore.In the study of Lopez (1988), it was reported that the P.
erosa filters particles of subterranean or underground watersspecially those that remains in the burrows of burrowing animals includingcrabs at low tides. It has its bio-filter mechanism that is carried out bytheir gills. It therefore has the ability to remove suspended particles fromthe water column in which the outcome is the formation of biodeposits. These biodepositsare mucus-coated particles that become the source of nutrients needed by themangrove clam. Assimilation or the processing of these biodeposits areaccomplished within the mantle cavity and after which, ejected in the siphon oralong the ventral mantle margin. Feeding of the mud clam only takes placeduring the spring tide (Clemente et al., 2013). This is in relation to itshabit of living towards the landward area in the highest high tide level regioncausing the mud clam to be left sometimes without food.
Mudclams, also, are economically important species. According to Carter (2014),the genus Polymesoda is one of themain sources in the Indo-Pacific region that contributes to marine resourceeconomies. This therefore means that a large fraction of marine resources isgreatly attributed to the mangrove clams. They are highly exploited byfishermen in Indonesia (Nuryanto and Susanto, 2010), in India (Clemente andIngole, 2011) and even in the Philippines (Dolorosa and Dangan-Galon, 2014a)and is commonly sold in local market stalls as they are being utilized as afood resource especially by communities near coastal areas. Moreover, the mudclams have considerably large size which implies a more fleshy body (Nuryantoand Susanto, 2010) making them more suitable for consumption.
Moreover, mudclams are also reported to contain high amounts of protein (Nasution andZulkifli, 2014). According to Cremades (2014), seafood that mainly includesfishes, shrimps and a variety of many other invertebrate species such asshells, serve as one of the major food sources for the native population on themangrove coastal zones of Southeast Asia. This is made possible by mangroveconditions that are highly advantageous that favor the recruitment of a widearray of edible species. Mangrove inhabitants such as the mangrove clamstherefore grow well under favorable environmental circumstances, which on theother hand become more beneficial to fishermen and other consumers. Moreover,the P.
erosa has a high potential foraquaculture and mariculture (Dolorosa and Dangan-Galon, 2014b) which couldgreatly help in better production.