Threats and knowledge gaps for ecosystem services provided by kelp forests: a northeast Atlantic perspective

Abstract

Kelp forests along temperate and polar coastlines represent some of most diverse and productive habitats on the Earth. Here, we synthesize information from >60 years of research on the structure and functioning of kelp forest habitats in European waters, with particular emphasis on the coasts of UK and Ireland, which represents an important biogeographic transition zone that is subjected to multiple threats and stressors. We collated existing data on kelp distribution and abundance and reanalyzed these data to describe the structure of kelp forests along a spatial gradient spanning more than 10° of latitude. We then examined ecological goods and services provided by kelp forests, including elevated secondary production, nutrient cycling, energy capture and flow, coastal defense, direct applications, and biodiversity repositories, before discussing current and future threats posed to kelp forests and identifying key knowledge gaps. Recent evidence unequivocally demonstrates that the structure of kelp forests in the NE Atlantic is changing in response to climate- and non-climate-related stressors, which will have major implications for the structure and functioning of coastal ecosystems. However, kelp-dominated habitats along much of the NE Atlantic coastline have been chronically understudied over recent decades in comparison with other regions such as Australasia and North America. The paucity of field-based research currently impedes our ability to conserve and manage these important ecosystems. Targeted observational and experimental research conducted over large spatial and temporal scales is urgently needed to address these knowledge gaps.

Keywords: Laminariales; kelp forests; marine biodiversity; subtidal benthic habitats; temperate reefs..

Figure 1

(A) Number of kelp ecology papers by nation (ISI Web of Science search on “kelp,” 2002–2011, n = 402 ecology papers). (B) Number of ecology papers focussed on each major benthic marine habitat type in the UK (2002–2011, n = 187 papers); I-R = intertidal rocky, S-S = subtidal soft, I-S = intertidal soft, S-R = subtidal rocky.

Figure 2

Dark gray hatching indicates the recorded distributions of kelp species in the UK and Ireland (data reproduced from MarLIN, with permission).

Figure 3

Habitat-specific probability of occurrence for dominant kelp species in UK waters, for both western regions (A) and eastern regions (B), along a latitudinal gradient (∼49–59°N). Probabilities derived from subtidal habitat surveys conducted at 0–10 m depth (data from Marine Nature Conservation Review, 1977–2000, see Burrows for more methodological details and geographic limits of regions), which used ACFOR values (a semiquantitative abundance scale) to quantify benthic organisms. The number of independent surveys per region (i.e., n) ranged from 300 to 734.

Figure 4

The kelp Laminaria hyperborea is a dominant canopy former on both subtidal (A) and intertidal (B) rocky reefs around the UK and the wider NE Atlantic. Kelp forests provide habitat for a wide range of flora and fauna, including the hydroid Obelia geniculata (C) and the commercially important European Lobster Homarus gammarus (D). Although kelps and their epiphytes are grazed directly, by the blue-rayed limpet Patella pellucida for example (E), the majority of kelp production is consumed as detritus (F).

Figure 5

Kelp species abundance and local species richness. Box plots show 10th, 25th, 50th, 75th, and 90th percentiles of species richness data for each modified SACFOR category of kelp species abundance. For each SACFOR category, n, which is the number of independent surveys conducted during the Marine Nature Conservation Review (1977–2000), is given.