Structure is to introduce lagoons and the Sussex resource status, describe monitoring results at two lagoons, and then review current issues and challenges for conservation.
Partial barrier or connection to the seaSalinity is the range at which most lagoonal species seem to exist in Sussex. Sea water is about 33-35ppt.
Barriers that reduce storm surges, act as ‘natural’ sea defences, stabilize shorelinesHigh primary and secondary production – shallow depth, high light penetration, high residence times = amongst most productive systems in world. Important nurseries for fish and for aquaculture. Biodiversity includes rare specialists and also waders and waterfowlAny coastal water body seems to have the potential to be lagoonal and support specialist species.Natural lagoons are formed by sedimentary barriers blocking rivers or bays. Only five sites in Sussex considered of natural origin.Geologically ephemeral, typically lasting tens to hundreds of years.
First survey using a standardised approach. The aim was to find out how many coastal water bodies in Sussex are lagoons.The 28 included gravel pits, borrow pits, field ponds, scrapes, mill pools, marinas as well as 5 ‘natural’ sites.Fauna = inverts in benthic substrate, water column, vegetationEnv variables were distilled from previous studies of lagoons, e.g. salinity, area, shape, substrate types, depth.Some of the team are here today – gone on to bigger and better things!
Note: this classification is of FAUNA only; flora showed much the same.1st division is Little Spit at Pagham harbour, which had a strong marine fauna.Next division separates fresh/brackish sites (mean 3ppt) indicated by the Common Pond snail from saline sites (mean 28ppt) in end groups E-H indicated by Lagoon Cockle and the Spire (or Mud) snail (ulvae is NOT specialist).
Ordination shows the distribution of the end groups E-H highlighted. Axes scores could be significantly related to these variables where saline lagoons = saline, more complex shape, more isolated, coarser substrate, steep or shallow banks (not intermediate) and a functional connection to the sea.
Six of the 13 sites have no statutory protection. The area may be only a third as much as previous estimates (184ha).Salinity is all important (but note summer survey).80% of Sussex saline lagoons have a sluiced connection to the sea.
Probably a natural lagoon with specialist species, recharged through the shingle barrier but insufficient to maintain water levels. So pipe put through the barrier during coastal defence works to allowed controlled sea water ingress from June 2003.NOTE: must be careful as cannot prove cause and effect.
Pipe working from June 2003, hence colour change.Salinity levels apparently increased following the opening of the pipe, but probably no more than the long-term average.Specialists: Ruppia is a plant and has a consistent presence, but Cerastoderma and perhaps Hydrobia may be declining.Dynamic fauna: annelids Hediste and Perinereis absent but crustacean Microdeutopus flourishing, which is a common coastal generalist species.Are lagoonal specialists being replaced by marine generalists?
Probably a natural lagoon, possibly affected by organic pollution in early 2000’s. Any recovery?
Post-pollution sampling is shown darker from 2005.Salinity increased but is still low for a typical lagoon.Ruppia has re-appeared, but algae have not.Species that indicate enrichment (Polychates, tubificoides, nemertodes) spiked but now mostly absent.Hydrobia showing encouraging signs but Cerastoderma not, and molluscs generally decimated since the 2001 survey.Lekanosphaera is a specialist and seems to be OK.Overall, partial recovery since 2005 but molluscs and algae still impoverished = changed.
Invasion – not yet as apparent as freshwater systems, but non-natives are found in lagoons (e.g. Zebra mussel, shrimps)Poor relation – coastal transitional waters lag behind in terms of knowledge, management prescriptions, policies such as EU directivesClassifying – challenging as lagoons are dynamic, but a consistent approach would help managers. Estimates of lagoon resource are likeley to be exaggerated.Management is often based upon assumptions from estuarine studies. Need to recognise lagoons are transitional and closely linked to adjacent terrestrial, freshwater and marine environments. Lagoons function as ecocomplexes, with heterogeneous habitat networks and multiple linked ecosystems (e.g. wetland, intertidal, pelagic) exchanging hydrological, energy, material and species flows.
Lagoon research would benefit from a co-ordinated facilitation, not just in Sussex but generallyBiomonitoring – use of in situ probes for salinity, turbidity, temperature etc, specialised surveys for cryptic, rare speciesBioindicators – which fish are resident or transient? Fish community diversity and structure (used in Med lagoons)Ecocomplex – dispersal and colonisation are important factors, genetic linkages, connectivity between coastal habitats
Sussex Wetland Conference: Chris Joyce
Sussex saline lagoonsStatus, changes and challengesDr Chris Joyce, School of Environment and Technology
Key features Partial barrier: micro-tidal of saline lagoonsSaline: 15-40ppt? Shallow: <1m deep
Lagoon ecology• Ecosystem services, e.g. buffers, productive, recreation• Rare: 5% of European coasts - priority for EU Habitats Directive• Specialist lagoonal species, e.g. invertebrates, many legally protected• Variable resource with diverse origins• ‘Natural’ lagoons are very rare and may be short- lived• Artificial lagoons include mill ponds, marinas, and gravel pits
Status survey of Sussex lagoons• Estimated resource of 35 lagoons comprising 184ha• 28 surveyed in summer 2001• Flora (n=10 per site)• Fauna (invertebrates, n=15 per site)• Environmental variables: 13 hydrological and biogeographical characteristics
Survey results: invertebratefauna marine Cerastoderma glaucum Lymnaea peregra Hydrobia ulvae A B C D E F G H IPett 3 Pett 1 Camber 2 Rye Hbr Ch. Norton Quarry, Rye Widewater Bton Mar Little SpitPett 4 Pett 2 Hooe N’pt Pit Birdham Wader, RyeCam1 Long Pool N’pt Small Slipper Newhaven Sidlesham Camber 3 Peter Oxbow, Cu Tidal, Cu Scrape, Cu Pagham Thorney Source: after Joyce et al. (2005)
Survey results: invertebratefauna Salinity, shape, isolation, substrate, bank slope, D E connection to sea A 2 F I B C G H 2 4 Axis 1 (SD)
Survey conclusions• 13 of 28 sites supported a lagoonalcommunity, comprising 64ha• saline (usually >28ppt)• ‘reliable’ connection to sea, e.g. sluice• partial tidal exchange
Conservation challenges• Climate change, e.g. storms, sea level rise• Invasion ‘hot spots’?• ‘Poor relation’ to freshwater and marine systems• Classifying and quantifying the lagoonal resource base• Managing lagoons specifically but within the coastal ecocomplex• Lack of scientific understanding
Research challenges• Co-ordinated research and monitoring to establish the lagoon resource and baseline ecology• Longer-term, specialised methods that assimilate lagoon dynamics• Developing biological indicators, e.g. fish, invertebrates• An ecocomplex approach that acknowledges the transitional and networked nature of lagoonal patches within the coastal landscape Source: Beer and Joyce (in review)
AcknowledgementsNatural EnglandWest Sussex CountyCouncilEarthwatch InstituteDr Cristina Vina-Herbon, JNCCDr Cath Waller, HullUniversityDr Nicola BeerAll the field and labteams