Historical Records, 1900-2018
Some of the first comprehensive surveys of natural environments occurred on Lambay and Clare Island in the early 1900s, and these multidisciplinary reports provide a comparison of intertidal algal communities between 1910 to the 1990s (Cotton, 1909; 1912), but more recent surveys have collected subtidally, expanding the flora record for these locations (Rindi & Guiry, 2004). Subtidal observations became easier for phycologists with the advent of diving bells and, later, the self-contained underwater breathing apparatus (SCUBA). Jack Kitching first described methods for studying sublittoral ecology in the UK using a diving helmet in the 1930s, which subsequently led to the first observation of the species associations in Laminaria spp. forests, including the dominance of L. hyperborea (formerlyL. cloustoni ; Kitching et al., 1934). He later brought that equipment to Ireland where he intensively studied the ecology of Lough Hyne (or Ine) with generations of students, providing the basis for kelp forest ecology in this region of the world which would later be proliferated by Joanna Kain (Jones) using SCUBA from 1960 – late 1980. The seaweeds of Lough Hyne were first described by Rees (1931), later followed up by Maggs et al. (1983) who also contributed to many reports on the biotope ‘kelp forests’ in Ireland and the UK (Birkett et al., 1998; Maggs et al., personal communication). Kain’s work definedL. hyperborea’ s population dynamics (Kain, 1963), reproduction (Kain & Jones, 1964), competition and growth (Creed et al., 1998; Kain, 1969; 1962; 1976a; 1977), and description of succession and subcanopy/understory seaweeds (Kain, 1976b; 1982; 1989). This research, alongside that of Norwegian and French phycologists, forms the basis of our understanding of kelp forest ecology in Ireland (summarised in Kelly, 2005), though more recent research projects in the UK and Ireland aim to supplement this knowledge base with modern data (e.g. Burrows et al., 2014; K. Schoenrock et al., personal communication).
The first distribution record with multiple georeferenced data points of large seaweeds in the UK and Ireland was published by Crisp and Southward in 1958, as a side note to their record of intertidal invertebrates (Crisp & Southward, 1958). From 1950 to 1990 multiple studies referenced seaweeds in specific regions (see Table 3), for instance Morton (1994) noted the abundance of marine algae in Northern Ireland by county. The BIOMAR survey (Picton & Morrow, 2006) of marine habitats across Ireland summarised species associated with subtidal kelp forest habitats in the 1990s using SACFOR abundance scales for taxa (super abundant, abundant, common, frequent, occasional, and rare) that could be repeated over time in the same locations. This was followed by a repeat survey of regions in Crisp & Southward (1958) by Simkanin et al. (2005) which highlighted increases or declines of species abundance over the 45 years between studies. Declines in northerly species in these intertidal habitats occurred in five of 12 species (includingL. hyperborea and S. latissima ) while increases occurred in one of 12 species (invasive barnacle Australminius modestus ; Simkanin et al., 2005). In contrast, one of nine southerly species declined in abundance, despite the trend in Europe for southerly species to expand their northern ranges (e.g., L. ochroleuca : Schoenrock et al., 2019; Smale et al., 2015). Merder et al. (2018) later showed that community similarity indices in Simkanin et al. (2005)’s data were more influenced by the environmental variables wave energy and Chla concentration than sea or air temperature, which resulted in differences in communities from east to west coasts. The formation of Seasearch Ireland in 2009 has boosted records of subtidal habitats, to the scale that most recent L. hyperborea records in Ireland are supplied by citizen scientists (2010-2018, Figure 1). The remaining data is from research agencies like the Environmental Protection Agency or National Parks and Wildlife Services.
BIOMAR data are unique in the fact that they can be analysed to highlight the impact that kelp species and region have on faunal assemblages within kelp ecosystems (Table 4 & 5). Species SACFOR scales were given a numerical value (0 = absent, 1 = rare, 2 = occasional, 4 = frequent, 5 = common, 6 = abundant, and 7 = super abundant) for each site record and a Bray-Curtis similarity matrix was created with species data across sites, finally similarity of species compositions within kelp forests a) within the same geographical region (Table 4) and b) within forests dominated by different kelp species (Table 5) were evaluated using an analysis of similarity (ANOSIM; Clarke & Gorley, 2006). Regional differences were apparent in kelp communities, for example more species contribute to community similarity in kelp forests in west Ireland than in other regions (Table 4). Dominant kelp species also affected community assemblages, but too few replicates exist in mixed and A. esculenta forests to define species driving differences (Table 5). When compared with a recent study in the west of Ireland (Table 1), species associated with L. hyperborea forests are notably different (Table 5), potentially due to the quantitative vs. qualitative data collection methodology, and survey focus. For instance, kelp blades where many hydroids reside (e.g., Electra pilosa , Table 4 & 5) were not included in the swath surveys used for community analysis in K. Schoenrock et al. (personal communication). Moving forward, creating a standard monitoring methodology would benefit analysis of data and highlight [changing] patterns in species distribution and habitat usage over time.
In summary, distribution records for kelp have fluctuated over time in terms of recording effort and regions visited. The focus of study has progressed from basic species description and use as a resource from the 1700s - 1910s, expanding to disciplines like ecology, evolution and natural product chemistry which are facilitated by technology (Young et al., 2015). Present-day investigations utilise species distribution models to project future distributions of seaweeds based on the habitat suitability or environmental forcing associated with records of species presence. Yesson et al. (2015a) modelled the distribution of kelp and fucoid species in the UK and Ireland using data from herbaria and online databases and found (i) most distribution data comes from studies after 1970 (in contrast to the present review where the majority were post-1990) and (ii) different environmental requirements for each species. Non-natives, like U. pinnatifida, are found in areas with high average temperatures (but also restricted to man-made or modified structures, e.g. harbours), while the native A. esculenta is found in regions with colder average temperatures (Yesson et al., 2015a) and is thought to be more susceptible to temperature than the Laminaria spp. of the region (Müller et al., 2009).Laminaria spp. are influenced more by substrate type than temperature or light in current distributions, and L. hyperboreais thought to cover 48, 654 km2 of coastline in the UK and Ireland, specifically on rocky substrate with moderate wave exposure (Yesson et al., 2015a). Species distribution models indicate thatL. hyperborea blankets all coastlines in Ireland that are not adjacent to major freshwater sources (see Figure 5 in Yesson et al., 2015a), though this potentially overestimates its distribution along the east coast because the coastline has more sand/mud/marsh habitats than rocky coastline (Neilson & Costello, 1999). More interestingly, the study also indicates regions suitable for species range expansions including Bellmullet County Mayo, where the first record of L. ochroleuca in Ireland was noted in 2018 (Schoenrock et al., 2019). Models that factor in climate change predictions show kelps retracting northward (Assis et al., 2016), and this has already been noted in species found in Ireland (Simkanin et al., 2005; Yesson et al., 2015b). These findings indicate the need for better habitat mapping tools, which are superior to point records, but also difficult to achieve with species in the sublittoral where remote sensing and monitoring require significant investment of resources.