In 2010 BirdWatch Ireland engaged Claire Moore to carry out a baseline study of the intertidal shore at Cuskinny Bay at the southern end of the reserve. A summary of the results of that study are presented here.
Cuskinny Nature Reserve is set on the lower reaches of the Ballyleary Stream and consists of twelve hectors of mixed habitat. Given its proximity to the coastline, there are a number of marine influences on the Nature Reserve, including salt-water incursions and influxes of marine species. Therefore, a deeper understanding of the health and functioning of Cuskinny Bay would lead to a more complete view of the Nature Reserve as an ecosystem.
The main objectives of this survey were to determine the habitat types within the intertidal zone of Cuskinny Bay, their community compositions, health, and relative importance both locally and nationally. This survey was also used to establish a baseline dataset for continued long-term monitoring within Cuskinny Bay.
Cuskinny Bay is situated on the southern shore of Great Island, along the south coast of Ireland. The bay itself is approximately 98 km2 in size and consists predominantly of soft sediment substrates. Intertidally, the shore is dominated by course mixed substrata, which is exposed by a strong inshore current that is forced across the bay and along the shore. The ecology of this site is also influenced by freshwater outflow from the Ballyleary Stream and Cuskinny Marsh, which enter the sea at this site.
Cuskinny Bay is set within the Special Protection Area of Cork Harbour,
site number 004030 (NPWS 2004). Under the European Habitats Directive
(79/409/EEC) this designation protects the annual influx of approximately
20,000 wintering waterfowl that rely on this internationally important
site every year (NPWS 2004). Cuskinny Bay itself is noted specifically
for its importance to salmonid populations (Halcrow 2007) and is boarded
by Cuskinny Marsh Nature Reserve, which is a designated a proposed Natural
Heritage Area (site number 001987).
Variation in species richness across the site
The intertidal zone of Cuskinny Bay consists of areas of rock face, shingle, course sediments and fine mud. As the substrate composition changed along the shore, so to did the species richness (n). Across the site high species richness was associated with stable surfaces such as rock face and fine-grained substrates, and a low species richness, with medium sized substrates. This trend was more obvious along the mid to upper section of Cuskinny Bays’ intertidal zone. Evidence of this trend can be seen in both the biotope map (fig 1), and the community composition survey (table 2 and 3).
During the mapping of the biotopes the highest species richness recorded was of 31, and this was found along a rock face in a community dominated by the algae Fucus vesiculosus on full salinity (LR.LLR.F.Fves.FS). The two lowest species richness were found along sections of unstable medium sized substrates of shingle with species barren littoral shingle (LS.LCS.Sh.Barsh) and a Talitridae dominated community with a species richness of 1 (LS.LSaSt.Tal). This trend was also mirrored within the community composition survey where the occurrence of multiple groups was associated with the high abundance of rock or sand and mud (table 2 and 3), and the low number of groups was associated with the occurrence of shingle (table 2 and 3). When rock was recorded as superabundant (S) it was associated with the occurrence of up to 7 other groups of organisms (table 2 and 3). Whereas the when shingle was recorded as superabundant it was associated with no other groups of organisms along some stations (table 2 and 3).
The low species richness associated with medium sized intertidal substrates is influenced by two major factors. Firstly, medium sized substrate is highly mobile and prone to disturbance, with stones being constantly overturned by wave action, thus crushing both sessile and mobile organisms that live on or under them (Sousa 1980). Secondly, shingle and cobble substrates are small objects and are not buffered from the sun as large outcrops of rock face would be therefore cobbles can heat up dramatically in sunlight during low tide exposure, thus creating thermal instability (Bertness 1989).
The variation biotopes and species richness across the site was further influenced by the presence of the freshwater outflow form Cuskinny Marsh and the Ballyleary Stream. While all intertidal species are, to varying degrees, tolerant to changes in salinity, few can tolerate persistent low salinity levels created by a year round freshwater influence such as this. For this reason the species richness of the two biotopes surrounding the outflow area are low. The mid to upper shore around the outflow area is dominated by a community of ephemeral green and red seaweeds (LR.FLR.Eph.Ephx) that have a species diversity of 5 (fig. 1). Along the lower shore this community shifts into a biotope dominated by the annelid Hediste diversicolor Müller 1776 (LS.LMx.GvMu.HedMx) with a species richness of only 2 (fig1).
Aside from the freshwater influenced zone, the lower shore of Cuskinny Bay has a high biodiversity. This high biodiversity is due to the presence of two bioengineering species, Lancie conchilega Pallas 1766 and Sabella pavonina Savigny 1822, that both define their respective biotopes. The bristle worm Lancie conchilega defines a biotope in littoral mud (LS.LSSa.MuSaLan)(fig. 1) with a species richness of 22. Sabella pavonina defines a biotope of sponges and on mixed littoral sediment (SS.SMx.IMx.SpavSpAn)(fig. 1) with a species richness of 10. Both of these species have local, national and international importance.
Species of importance
Lancie conchilega Pallas 1766 is designated as an Annex V species under Ospar as it is both threatened and declining species (Tyler-Walters and Hiscock 2005). The presence of extensive bed of L. conchilega, such as those along lower sections of the shore, are an indication of the health of the site as they are considered to prefer clean sediments (Agar 2008). This is an important fact as Cuskinny Bays’ waters have been noted as important waters for local populations of salmonids that require clean water (Halcrow 2007).
L. conchilega acts as a bioengineer by consolidating the sediment around it, and obstructing the activities of predatory burrowers and enabling other sedentary animals to establish themselves (Wood, 1987). As stable habitat is a limiting resource within the marine environment (Little and Kitching 1996), L. conchilega are functionally very important for increasing biodiversity locally (Godet et al. 2008), even expanding the niche of several species (Rabaut et al. 2007). This increase of biodiversity does not only have a localized impact but also has an important impact within the wider ecosystem. Additionally, L. conchilega is an important food source for wading birds. As Cork Harbour is a Special Protection area, of internationally importance due to the 20,000 wading birds which winter there every year (NPWS 2004), such as the curlew which are one of the main predators of (Goss-Custard et al. 1977) L. conchilega numbers have an international importance.
Another important species found along the shore of Cuskinny Bay is Sabella pavonina Savigny 1822. S. pavonina, commonly known as the peacock fan worm, has been recorded as widespread around the coasts of Britain and Ireland (Avant 2008). However, high densities this species are rare and hugely important as they form biodiversity hot spots (Dyryndam 2005). Though the population of S. pavonina found at the site could only be described as a community of moderate density, it appears to be associated with an increased species richness (n=10). Although the importance of S. pavonina is noted by organisations such as the NPWS (2006) and MarLIN, information on the intertidal impact and biology of this species is limited.
Internationally, the importance of habitat engineers such as L. conchilega and S. pavonina are widely agreed upon. However, despite the importance of these species being recognised by organisations such as MarLIN (Marine Life Information Network), intertidal communities of these two species are not currently protected under the EU Habitats Directive (79/409/EEC). Under the Habitats Directive a species must have a certain longevity and persistence in order to be defined and protected as a biogenic species. Unfortunately, there are conflicting records as to the longevity and persistence of communities of both L. conchilega and S. pavonina. But there is currently a push to change the definition of a biogenic reef within the Habitats directive, so that intertidal populations of these important species can be protected (Raubaut et al. 2007, 2008, Callaway et al. 2010).
This conservation status is also mirrored within Irish legislation where the importance of these species is only noted but not defined. In particular reference to the large shallow bay of Cork Harbour SPA (site code 004030), the NPWS have classed subtidal communities of L. conchilega and S. pavonina as ecologically significant and infrequent to rare (NPWS 2006). Along with the importance of these communities their weaknesses have also been noted. In 2006 the NPWS stated the importance of ensuring the availability of large areas of habitat for the long-term survival of the species subtidally. It is becoming increasingly more obvious that the health and functioning of protected areas such as Cork Harbour, and the species that they contain, depends more heavily on the import and export of larvae from the area then the size of it (Jessop and MacAllen 2008). Therefore, given that species such as L. conchilega are noted to have a dispersal potential of more then 10km (Agar 2008), healthy sites such as Cuskinny Bay may have a role in maintaining the flow of larvae within the SPA. Given that the outlook for Large Shallow Bays such as Cork Harbour was noted as poor from a conservation perspective, in the most recent survey by the NPWS in 2007, the importance of sites such as Cuskinny Bay may increase over time.
Current and Potential Disturbance
Cuskinny Bay is located within an area of high human activity. Therefore it was not surprising that a number of indicators of disturbance were recorded during this survey. One of these indicators can be clearly seen on arrival to the shoreline, where a thin mat of ephemeral green algae can clearly been across the mid to upper sections of the shore (see cover photo). This group of primary producers play an important role in the food web of every shore and typically define biotopes that have are effected by a strong environmental factors such as low salinity. A biotope defined by this group of algae was noted along the banks of the freshwater outflow that runs across a section of the site (LR.FLR.Eph.Ephx). Normally, ephemeral green algae like this are limited in their development by the physical, chemical and biological characteristics of the intertidal environment. Yet a thin but noteworthy band of algal mat stretches across the mid to upper shore of much of the site with Ulva spp. (previously known as Entramorpha spp.) being recorded in 10 of the 15 biotopes along the shore. The three major anthropogenic factors that may lead to an increase of algal mats like those at Cuskinny Bay are eutrophication, global warming and food web alteration (Lotze and Worm 2002). As the growth of these mats can disrupt local ecology (Worm et al. 1999) it would be advisable to monitor their development and impact at this site. Algal mats are not an issue isolated to east Cork, in fact, large-scale blooms of these ephemeral green algal have been reported in shallow coastal waters worldwide (Fletcher 1996, Raffaelli 1999).
As Cuskinny Bay is a popular local recreational beach, it is important to consider the impact this may have on the community present. The current disturbance create by recreational activity at the site include bait digging and trampling of habitat. Bait digging is a traditional activity along the shore of Cuskinny Bay, with three of the eleven species of annelids recorded during the survey being commonly used as fishing bait (Hayward and Ryland 2004); Marphysa sanguinea Montagu 1815, Arenicola marina Lamarck 1801, Hediste diversicolor Müller 1776. For intertidal communities trampling is a major issue, whether they are composed of a hard or soft substrate the impacts are similar, resulting in a shift in community composition. Along rocky sections of the intertidal zone, studies show no small scale spatial variation, but a significant shift in community composition, with a typical increase in herbivores such as limpets and decreases in fragile organisms such as coralline algae (Addessi 1994, Keough and Quinn 1998). Along soft substrate section, such as mud, trampling has been shown to have negative impacts on population structures, including a reduction in numbers of bivalves such as clams and cockles (Rossi et al. 2007). In the United Kingdom there is substantial qualitative evidence that many rocky shores that are extensively walked by tourists and school/university educational visitors have lower levels of biodiversity than they did in the 19th Century when such usage was negligible (Davenport and Switalski 2006).
There have also been large-scale disturbances to the substrate along the intertidal zone of Cuskinny Bay. In the winter of 2009, an ESB line running from Aghada Power Station in the south across Cork Harbour to Cows Cross, was brought on shore via Cuskinny Bay and buried at the site. This construction involved the disturbance of a large area of sand and mud at the shore and has resulted in an obvious beach scar at the site. Although this beach scar is not permanent physical feature, these activities may have had implications for the species along the shore, in particular the two bioengineers found along the soft sections of this shoreline. Lancie conchilega and Sabella pavonina are both species are sensitive substrate disturbances of this nature, which if prolonged can result in population decline (Tyler-Walters and Hiscock 2005, Ager 2008). As both these species are associated with biodiversity hot spots this sensitivity should be considered in further activity along the shore.
Cuskinny Bay like all marine environments is under constant threat of invasion (e.g. Streftaris et al. 2005, Chapmen et al. 2006), however due to the sites proximity to the busy international ports of Ringaskiddy and Cobh this threat is intensified. The invasive barnacle Austrominius modestus (Darwin 1854) was recorded across the site during this survey. A. modestus was found to have a higher frequency of occurrence then the three native species present, being recorded in seven of the fifteen biotopes along the shore. Whereas the native species of barnacle Semibalanus balanoides Pilsbry 1916 in just 6 biotopes, and Chthalamus montagui Southward 1976 and Chthalamus stellatus Poli 1791 in 4 and 3 biotopes respectively.
This trend was further explored within the barnacle survey. The invasive A. modestus was only found to have marginal dominance within the barnacle community along the upper mid shore. However, as can be seen in the kite diagram in figure 2, A. modestus, unlike the three native species, has a continuous presence from high to low shore. It is clear from the results in both the biotope and the barnacle survey that A. modestus has a foothold within the intertidal community of Cuskinny Bay. Although there is no way of knowing from a single survey whether or not A. modestus is having an impact on the community at Cuskinny Bay, it is important to note the potential impacts of this invasive. Worldwide the invasive potential of this A. modestus has been well documented (e.g. Crisp & Southward, 1959; Simkanin et al., 2005; Allen et al., 2006) and once established it has the potential to out compete native species (Lawson et al., 2004). A. modestus has number of adaptations which have allowed it to achieve this, including a tolerance of reduced salinity (Fish & Fish, 1996), and both higher and lower temperatures then native Irish species, allowing it to survive at all shore levels (Hui & Moyse, 1987). Invasive species typically initially settle within vacant niches where disturbance regime or resource availability have recently changed (e.g. Davis et al. 2000, Facon et al. 2006). For this reason disturbance events, which may effect native populations are worth discussing as they may create an opportunity for an invasive such as A. modestus to become dominant (e.g. Dawes 1998, Stachowicz et al. 1999). Worldwide the distribution of species is being effected by the major disturbance event of global warming (Chapmen et al. 2006). In the United Kingdom long-term studies show the shift in community structure of the barnacle community and an increase in the invasive A. modestus, associated with increase water temperature due to climate change (Southward and Crisp 1954, Southward et al. 1995, Hawkins et al. 2003). In Ireland historical data has been used to detect temporal changes in the abundance of intertidal species. Although the increase in A. modestus cannot be directly linked to climate change, it does show the need for continued monitoring (Simkanin et al. 2005)
This survey described the intertidal section of Cuskinny Bay using three simple methodologies. The results showed that although this typical, semi sheltered, intertidal community contains healthy populations of two nationally important, there is evidence of disturbance at the site. To gain a better understanding of the true impact of this disturbance a repeated monitoring over a long period would be essential. As all the methodology used in this survey is easily and cheaply replicated, it could be used as a structure for a long-term monitoring program at the site. Each section of the methodology has its strengths and weaknesses, and allows for varying levels of resolution in the detection of disturbances. The mapping of biotopes is essential yet the borders of the biotopes themselves are subjective. Therefore any shifts in community structure, unless major, may not be detected. While the community composition survey would detect more detailed community shifts in the groups of organisms present. Additionally, continued monitoring of the barnacle community as a bioindictor species, would allow for a more detailed view of the healthy and functioning of the shore.
Finally, it should be considered, that further studies include a nutrient
and chemical analysis of the substrates and water present. Cuskinny
Bay is set within the highly disturbed area of Cork Harbour, where human
activity is a constant. This activity can result in a number of types
of pollution, including industrial and agricultural waste, all of which
can have a major impact on the communities present. Previous studies
in the area show the necessity for this addition, with three authors
noting that high levels of TBT had led to the development of imposex
in the population of periwinkles along the shore (Minchin et al. 1996,
Casey et al. 1998, Harding et al. 1998). This may explain why periwinkles
only occur as abundant at one station along one transect of the community
composition survey at Cuskinny Bay despite the high levels of grazing
available at the shore (table 2 and 3). However without the addition
of nutrient and chemical analysis it would be impossible to confirm.
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Download the full report here: Intertidal
Survey of Cuskinny Bay, Co. Cork. May 2010, Prepared by: Claire Moore