The Historical & Current Characteristics of Western Ireland Coastlines & Galway Bay

Introduction

An understanding of the historical and current characteristics of western Ireland coastlines and Galway Bay is necessary to interpret the results of our scientific study. Particularly an understanding of geology, physical and chemical oceanography, climate, ecology, and marine pollution. The purpose of this review is to give a broad overview of the characteristics of these subcategories in relation to Galway Bay.

Galway Bay Geology

One of the west coast of Ireland’s main distinguishing geological features is the transition from the limestone of the Aran Islands to the granite of Galway. The Galway Bay Fault line runs northwest to southeast and notes the transition of limestone to granite (“Celtic Voyager Survey”). The Islands create a barrier-like formation partially separating the bay waters from that of the Atlantic Ocean (Pybus). The islands were formed during a glaciation dated around 3.5 million years ago (“Island History”). The Killard Point Stadial marked the last glacial age of Ireland where the Irish Ice Sheet advanced from the lowlands of the central north to the northern Irish Sea Basin around 15.2 thousand years ago.

During this, the Irish Ice Sheet underwent the Heinrich Event 1 (icebergs broke off into the North Atlantic) creating moraine landscape cutouts. Simultaneously, a deglaciation of the Irish Ice Sheet occurred about 15 thousand years ago at the end of the KPS. In glaciation time scale, this is a very rapid response to climate change by the Irish Ice Sheet. During the deglaciation, moraines were deposited until about 15.6 thousand years ago (J. Clark et al.). The pattern of moraine extends from south-west Ireland to the Shetland Isles. The small Irish Ice Sheet contributed to the global sea level rising 2.5m during the last glaciation (C.D. Clark).

Physical and Chemical Oceanography

The two sections of Galway Bay are defined by the bathymetry of the ocean. The inner bay’s depths are defined as more shallow than 30m and the outer bay depths range from 30-60m. The length of Galway Bay travels from west of the Aran Islands to Oranmore for 62km. The widest section of the bay is 33km at the mouth and the narrowest is 10km at Black Head/Leac na Gibeoige (Fallon and Nash, 1). The bay’s circulation is affected by the Irish Coastal Current which contributes to fresh water mixing with saline rich Atlantic waters. The current less likely correlated with the pressure gradient force balanced by the Coriolis effect as it is with the wind speeds around Ireland. The wind contributes massively to the circulation of coastal waters on the west coast of Ireland (Fernand et al.).

A study by W.G. Huang proposed that wind regulates the River Shannon’s northward plume of buoyancy flow in Galway Bay (Huang et al.). Despite this fact, the wind does not play a role in the maintenance of the microlayer nutrient composition of Galway Bay. The layer is produced by biological activity of phytoplankton and is primarily compromised of phosphate, silicate, and nitrate (Lyons et al.). The oxygen concentrations of Galway Bay are at healthy levels with no data suggesting the bay has supersaturation, deficiency, hypoxia, or anoxia (O’Boyle et al.). Shellfish aquaculture sites, which remove phytoplankton, are common among western Ireland bays and help prevent the eutrophic condition growth (Smith and Cave).

Climate

Ireland’s past climate of the Holocene (past 11,500 years) was analyzed in a study by Barber et al. His study of plant macrofossil remains in bogs (specifically the Abbeyknockmoy and Mongan Bog in western and mid-Ireland) indicated that the Holocene had three distinct climates. First, the early Holocene showed a Monocot-rich faction which indicated dry conditions. Second, the mid-Holocene showed factions that thrived in predominantly wet conditions and that Ireland experienced a sequence of expeditious sea level rises.

Finally, the late Holocene showed a variety of factions that indicate a fluctuation or oscillation of wet and dry conditions (Barber et al.). After extreme storms in 2014, Prof Michael Williams of the University of Massachusetts discovered that Galway Bay used to be covered in forests and lagoons some 7,500 years ago. The storms exposed the north coastline of Galway (west of Spiddal) resulting in spots of “drowned” forests (Siggins, “Storms Reveal ‘Drowned Forest’ in Galway”). Ireland’s current climate is described as a Temperate Oceanic Climate consisting of abundant rainfall, moist and humid air, and temperatures without extremes. According to the Climatological Note No.14 of 2011, the mean temperatures and rainfall for season and annum were determined over a 30-year period from 1981-2010. The seasonal summer temperatures revealed that the highest maxima ranged between 18°C and 20°C located in the inland areas.

The annual mean temperatures ranged between 9°C and 10°C and revealed that the higher values were in the coastal regions rather than the inland regions suggesting a stronger coastal effect than mean maxima. The seasonal rainfall in spring and summer averaged 260mm while autumn and winter averaged 350mm. According to the annum data, the highest rainfall occurred along the west side decreasing toward the north east of the island averaging 1230mm for all of Ireland (Walsh, 1). With Galway Bay being on the west coast of Ireland, it experiences more rain and moderate temperatures than that of the inland lands and east/north side of Ireland.

Ecology

Galway Bay hosts a diverse set of organisms including fish, plankton, diatoms, and more. A study of plankton conducted by J. Fives revealed that over 67 species of fish larvae were present in Galway Bay in 1972-1973. Of the fish larvae for both 1972 & 1973, 32.80% were Clupeids, 23.80% were Gadidae, and 10.8% were Gobiidae. All other families were recorded in percentages less than 7%. The Clupeids consist of foraging marine fish with small teeth. The Gadidae consist of Gadiformes including cod, pollock, haddock, and more. The Gobiidae family is extremely large with over 2,000 species. These fish are bony benthic bottom dwellers. These three main families of fish make up the majority of Galway Bay’s fish species and their populations give insight to Galway Bays benthic health (Fives and O’Brien).

In addition to fish species, phytoplankton play an important role in the ecology of Galway Bay. Galway Bay’s phytoplankton population varies from coastal waters to estuarine waters. The variance of phytoplankton species in coastal waters is due to the tidal and thermohaline fronts, ocean currents, coastal upwelling, wind, and transmittal of heat. The variance of species in estuarine waters is due to changes in river flow, tides, and other local factors. Overall, the phytoplankton growth is determined by the circulation of water (coastal upwelling) and the vertical stability of the water column. The stability of coastal waters is determined by sunshine and net primary production. The coastal waters the phytoplankton’s bloom is most abundant in summer and is limited by sunlight in winter. The estuarine phytoplankton will only bloom if the rate of growth is greater than the rate of flush. The rate of flush is highly variable because it considers factors created by wind, tidal state, and river discharge (O’Boyle at al.).

Specifically, planktonic diatoms play an important role in the ecology of Galway Bay. Galway Bay has a pronounced seasonal cycle of diatoms. At the beginning of the year, small rapid growing diatoms are most prevalent. As the water column stabilizes into summer, the larger slower growing diatoms start to dominate. As temperatures cool into autumn, wind mixes the waters and reduces the stability of the water column once again creating a waxing and waning diatom population (Pybus). The major pigments of these diatoms are chlorophylls. Chlorophyll A was studied by C.M. Roden in Connemara (just north west of Galway Bay). This study revealed that chlorophyll a was highest in the spring during neap tides and early summer spring tides while the transient chlorophyll bloomed during the neap tides of late summer. Roden postulated that this was ascribed to stable conditions yielding a confined assembly of flagellates. The stable conditions were suggested to be because of horizontal mixing (Roden).

Marine Pollution

Marine pollution has become a forefront of scientific studies in the last 30 years, especially microplastic pollution. Microplastics are boundless in the marine environment concentrating along ocean gyres and coasts. Little is known about the future of microplastic pollution and especially their effects on the marine food web. Four ways microplastics can be assessed in the marine environment are sediment sampling, trawls, observational surveys, and biological sampling. Sediment sampling measures microplastics of benthic material from the seafloor, estuaries, and beaches. Trawling allows scientists to measure the presence of microplastics suspended in the water column. Observational surveys allow scientists to observe the location, size, and type of plastic fragments within our oceans. Biological sampling allows scientists to examine plastic consumed by marine creatures (Cole et al.).

The effects of microplastics consumed by marine biota is little understood because it is extremely hard to measure. In the Atlantic Ocean, microplastics gathers in the coastal pelagic zones. Determining how much microplastic is within the water column was the starting point for a study conducted by A. Lusher in 2015. She found that over 60% of the trawls she studied in the Atlantic and Caribbean Sea has the presence of microplastics in densities over 580,000 particles/km. Lusher proposes that a better understanding of ocean mixing, sinking rates, and re-suspension of sediments, is necessary to begin to understand the fate of microplastics in the ocean (Lusher et al.). Not only are they a consumption threat to marine biota, they are a threat to the gas exchange ecology of the ocean as well.

Over the past 20 years, the rate of microplastic deposition has superseded the rate of production. Because of this accumulation of debris, gas exchange has been inhibited between pore waters of sediments and overlying waters (Moore). Along the Irish Continental Shelf, microplastics have been discovered in sizes ranging from 5mm-250μm and classified as secondary microplastics (fragments of larger plastics). Two areas (remote and proximal) were specifically studied in 2017. The remote area looked at Blacksod Bay in County Mayo and stations located 70km northwest of the Inishkea Islands. The proximal area sites included areas around the Aran Grounds fishery and a location in Galway Bay. Sixty-two microplastics were discovered throughout the stations in depth locations down to 3.5cm. The remote locations did not yield a statistically significant gathering of microplastics, but the proximal locations in and around Galway Bay did. As the core samples were analyzed a correlation of increased depth and decreased concentration of microplastics was observed. Along with Lusher’s conclusions in her 2015 study, this study also revealed need for a better and wider understanding of the accretion development of microplastics (Martin et al.).

In addition to microplastic debris polluting coastal regions of the ocean, primary production also poses a threat to the marine environment. Coastal eutrophication is fed by fossil fuel burning and river runoff of fertilizers. Estuaries are particularly at risk of becoming hypoxic due to agriculture runoff. The bottom waters are the most threatened waters by eutrophication due to a decrease in dissolved oxygen. When dissolved oxygens concentration decreases below 2ml, benthic fauna displays abnormal behavior due to hypoxic conditions. The hypoxic environment is formed when planktonic algae die and microbial respiration increases. There were over 400 sites reported in 2008 with hypoxic conditions in the world with 20 of them being around the Irish coast (Diaz and Rosenberg). Galway Bay has not displayed any oxygen deficiency or hypoxia (O’Boyle et al.).

Conclusion

Western Ireland and Galway Bay were affected by the last glacial period dramatically due to the Irish Ice Sheet responding rapidly to climate change. Moraine deposits show a pattern of progression and cessation of the glacier and provide insight into the sediment composition of Galway Bay. The mixing of estuarine waters and Atlantic waters of western Ireland is due to several factors, particularly wind and the Irish Coastal Current. The nutrient composition of Galway Bay is primarily compromised of phosphate, nitrate, and silicate. Ireland’s climate plays an important role in the make-up of the ecology of Galway Bay.

The humid temperate climate lacks extremes and provides a stable environment for fish, plankton, diatoms, and more. These marine biotas are at risk for pollution from microplastics and nutrient runoff creating hypoxic conditions. Thus far, microplastics were found in statistically significant accumulations in Galway Bay as recently as a study conducted in 2017. Although Galway Bay has not been reported as hypoxic, it is well reported that fertilizer runoff from agriculture aids in creating hypoxic conditions. Since Ireland is an agricultural hub, Galway Bay is at risk of succumbing to overt primary production.