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DATA SET IDENTIFIER:Neritina snails upstream migrations

PROJECT TITLE: Physical habitat, disturbances, and the population ecology of the migratory snail Neritina virginea (Gastropoda: Neritidae) in streams of Puerto Rico (Community Ecology of Streams Snails)

PROJECT DESCRIPTION: Diadromous fauna, migrating between marine and coastal streams is dominant in the neotropics. However, the factors controlling their population distribution and size are poorly understood. The migratory snail Neritina virginea (Gastropoda: Neritidae), abundant in estuaries and coastal rivers in the Caribbean, was studied to understand those factors. The objectives of the study were three-fold: 1) to identify the factors controlling the distribution of diadromous fauna at different spatial scales, 2) to determine patterns and causes of massive upstream migrations and their importance for population persistence, and 3) to integrate this knowledge into conservation strategies for migratory species and stream management plans.

After a survey of 32 coastal streams around Puerto Rico (Greater Antilles), it was evidenced that physical variables operating at different levels of the spatial hierarchy controlled longitudinal distribution of N. virginea. The hierarchically organized variables were river-ocean connectivity (regional scale), instream barriers and water chemistry (stream-network scale), habitat hydraulics (reach scale) and nearbed-flow roughness and depth (habitat scale). However, michohabitat scale distribution depended upon habitat and reach scale context. At habitat scale, water depth in pools, and nearbed flow roughness in riffles were the most important controls. At the reach scale, spatial heterogeneity among and within streambed patches was related to flow refugia, therefore controlling sensitivity of N. virginea density to flooding disturbances.

In addition, the role of structures (bridges) and maintenance activities (downstream channel realignment) associated to road crossings over streams was assessed. By splitting the stream channel and deflecting the flow, bridge pilings altered upstream migration routes. In particular, migratory individuals used more frequently boulder-and-cobble riffle reaches and avoided gravel-bed run reaches. Impact assessment of channel realignment over a 70 m reach in lower Rio Mameyes (NE Puerto Rico) showed that increase in frequency of fine sediment patches contributed to local population depletion and high mortality of juvenile individuals migrating upstream. As a consequence a population located 100 m upstream became isolated and did not recover from a crash caused by a major storm flood occurred after the channel realignment. In conclusion, distribution and size of populations of diadromous fauna such as N. virginea in coastal streams is influenced by hierarchically organized variables. By affecting variables at microhabitat to reach scales, road crossings over streams contribute to reduce longitudinal connectivity, and isolate upstream populations of N. virginea.

LTER CORE AREAS: Annotate all that apply (See online list)

LEF LTER 1 RESEARCH  TOPIC:  (Annotate all that apply) (See online list)

We define adata file as a component of a data set. A data set can have only one data file or more. Basically, different data files have different data structures or format.
DATA SET FILES (SUBSETS):

RESEARCH LOCATION: Río Mameyes at intersection with PR Route 3 (Municipality boundary between Luquillo and Río Grande)

INVESTIGATORS:

SOURCE OF FUNDING (SPONSOR): IITF-USDA Forest Service

DATA SET ABSTRACT: This data set includes N. virginea densities and sizes from two channels in lower Río Mameyes under PR Route 3 bridge during the upstream migration season Aug-Dec 2000. Microhabitat use (near-bed water velocities and depth) within both channels is also included. Massive migrations in long trails occurring on the sloped concrete embankment of the main channel were also documented during 99 weeks. Individual size from migratory aggregations was measured during selected dates. 

DATA SET METHODS: Snails on and under rocks were counted within 0.5 x 0.5 m quadrats (n=10) placed on the streambed on a weekly basis.  Sampling quadrats were placed ˜1 m apart across the main channel (MC), and in five pairs along the side channel (SC). At SC, one quadrat of each pair was placed on the thalweg and another on the shallow part.  In addition, a random sample of individuals was collected from each quadrat to measure shell size. Shell size was measured as aperture width (straight line running along the columnella from the base of the operculum to the shell shoulder on body whorl). Total length (TL, perpendicular to AW) is related to aperture width (AW) but cannot be measured in individuals with broken outer lips (TL=1.24AW+0.04, r²=0.98).

Individuals were divided into the following size groups: <4.00 mm (spats), 4.00-6.00 mm (early juveniles), 6.00-8.00 mm (late juveniles), and >8.00 mm (adults). This grouping was based on preliminary field observations indicating distinctive behavior relative to individual size (cf., Pyron and Covich 2003). Spats had small and smooth, dark-brown shells, and were usually found underneath rocks. Juveniles exhibited greenish coloration with a variable pattern of axial lines or small yellow “tongues.” These juveniles were very mobile and were commonly found on the sides of rocks. Adults exhibited the same coloration as juveniles, but moved randomly and were more common on the top of rocks. Sexual maturation was not considered for the grouping because it may be variable in tropical neritids, and it is not easy to determine in small sized individuals.

Each sampling date was classified as either a migration or non-migration event.  Migratory events were readily identified becausetdsmall individuals were abundant and aggregated into dense clusters or long trails that persistently moved upstream.  All massive migrations appeared a few of days after spates (>2 m³td/s) and increased snail density 2 to 10 times (200 - 800 ind.m^-2td) over values observed during non-migration periods (20 - 100 ind.m^td-2).  Near-bed water velocity was measured at 2 cm above the streambed using a Marsh-McBirney flowmeter.  Each velocity measurement was averaged over 30 s and 3 to 5 measurements were made at each point.  Ten points every 1 m were sampled across MC.  Paired sampling points (thalweg vs. shallow) were measured in five cross sections along SC.

Snail density, size, cohort percent and occurrence of massive migrations were correlated to discharge regime descriptors calculated using data from USGS gage 50066000 located 50 m upstream of Route 3 bridge.

REFERENCES : Pyron, M., and A. P. Covich. 2003. Migration patterns, densities and growth ofNeritina punctulatasnails in Río Espíritu Santo and Río Mameyes, Northeastern Puerto Rico.Carib. J. Sci. 39:338-347.

CROSS-REFERENCES (other data sets related to this one): LTERDBAS #141: Neritina snails hierarchical distribution; LTERDBAS #140: Neritina snails upstream migrations; LTERDBAS # 151: Neritina snailsrsponses to channel realignment

SAMPLE LOCATION:NA

STORAGE SITES (of data files): ITES

INVESTIGATOR'S ASSIGNED KEYWORDS: Neritid snails, diadromy, physical habitat, disturbances, Neotropical streams

PUBLICATIONS :

Blanco, J. F. 2005. Physical habitat, disturbances, and the population ecology of the migratory snail Neritina virginea (Gastropoda: Neritidae) in streams of Puerto Rico. Ph. D. Dissertation, University of Puerto Rico, Rio Piedras Campus, Department of Biology. 250 p.

Blanco, J. F. and F. N. Scatena.2005. Floods, Habitat Hydraulics and Upstream Migration of Neritina virginea (Gastropoda: Neritidae) in Northeastern Puerto Rico.td Caribbean Journal of Science,tdVol. 41, No. 1, 55-74

Blanco, J.F. & F. N. Scatena. 2007. The spatial arrangement of Neritina virginea (Gastropoda: Neritidae) during upstream migration. River Research and Applications 23: 235-245.

DISSEMINATION :

RESTRICTED UNRESTRICTED X

REASONS TO RESTRICT DATA IN THIS DATA SET BEYOND ITS TWO YEAR POLICY PERIOD*:

*WILL HAVE TO BE APPROVED BY  AT LEAST ONE LUQ LTER PRINCIPAL INVESTIGATORS: N. Brokaw, J. ZIMMERMAN, A. LUGO

FILING

_X_ "File" copy only : Data Management will only file an electronic copy of the data file and its documentation 
___ "Enter" data on-line : Data Management will be in charge of entering the data on computer files  (ContactEda C. Meléndez)

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COMPUTATIONAL METHODS:

FOR DATA MANAGER USE ONLY

DATE OF LAST REVIEW: April 15, 2009

DATE OF LAST ENTRY : June 30, 2002

STAGE OF DATA SET MANAGEMENT (dates) :
RECEIVED: December 28, 2005
ENTERED: December 28, 2005
FILED ON-LINE: February 6, 2006
REVIEWED BY RESEARCHER

FILING MEDIA :
NAME OF DOCUMENTATION FILE : lterdb140.htm
NAME OF ON - LINE CATALOG : LTERDBAS
RECORD # :   140
DOCUMENT TYPE : binary data only
PRIORITY TO BE ENTERED :  N/A