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.